[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Ed, Thanks for the many good advice. I've tried to incorporate as much as possible, updated schematic can be found here: http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG For audio into the PC I'm using a professional balanced microphone to USB input with a noise level of -130dBc/Hz and no spurs. Using a 7805 and 1500uF capacitors I tried to create a solid reference instead of the buffer op amp output and that did make a difference. Further the input of the first opamp has been change to have identical resistors at both the + and - input to reduce common mode signals. None of the capacitors (5.6pF) I tried to reduce high frequency gain improved the results. Most of the time it got worse. Removal of a ceramic capacitors eliminated the microphony. I've added a switch to select between 0dB and 20dB gain so I can calibrate the level by offsetting the DUT frequency while keeping the drive to the mixer. To calibrate the effective noise BW of the FFT I create a test signal combining a -70dBm 10.001MHz signal with a -90dBm/Hz noise signal. The 20dB power ratio was confirmed using a calibrated spectrum analyzer. The FFT length and sample rate at the PC where then changed till the PC FFT showed the same power ratio. Noise level at 1kHz is now -150dBc/Hz and -155dBc/Hz at 10kHz which is the spec of the DOCXO used so no need to go any lower. Also the 50Hz spurs and its harmonics are greatly reduced. I'll have to invest in better coax cables as the current cable seem to leak RF. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Am 2022-07-13 4:10, schrieb glenlist via time-nuts: Oh and now LED lights overhead your bench which are driven at 5-50kHz are are next new coupling of noise into your open bench circuits !!! The LED ringlight on my microscope creates 57KHz noise peaks when I have an unshielded low noise amplifier under it. Immediately visible on the scope, let alone the FFT-analyzer. Gerhard ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Super advice Ed, this is really really good advice. Erik this is sage advice. especially CMR at high frequencies... Oh and now LED lights overhead your bench which are driven at 5-50kHz are are next new coupling of noise into your open bench circuits !!! Glen. (RF engineer) On 13/07/2022 7:09 am, ed breya via time-nuts wrote: Erik, I'd really recommend that you use a real, "solid" ground reference on the instrumentation side, with +/- large (12-20 V) supplies, as others have suggested. Your most recent setup diagram indicates that you're relying on the "differential" input of the audio PC card etc analyzer to allow for the "floating" common of the analysis circuit. Do you know what the common-mode rejection characteristics are? A true differential input would have two coax lines entering a symmetric differential to single-ended conversion stage at the front end. I doubt that the PC card actually has this, but maybe some form of DC/LF isolation from the local input common to chassis ground. The PC likely has lots of SMPS noise in common-mode form, which probably can be ignored for audio (the SMPS frequencies are almost always quite far above audio). As long as the interference signals aren't too big to upset the LNA operation by say, rectification in various junctions (especially the front end), it should be OK. You will also have in-band line frequency and harmonics present in the common-mode signal, but these should be easier to deal with by virtue of whatever LF CMRR the sound card does have at lower frequencies. Now consider the analysis circuit environment, where you have apparently zero intentional bypassing capacitance from the floating measurement common to chassis/earth ground. Here, the only bypass caps effectively are C1 at the REF buffer's input (which will only aggravate the situation), and the small capacitance between the ports of the mixers. I believe you have some bypassing at points in the other portion of the circuit - the PLL for the reference - but I don't know what that looks like now. So, just looking at this section, I'd say you need some serious bypassing to ground, for the RF signals from the mixers, and the common-mode signals in and out of the audio analyzer, DUT, and REF. I recall there were some recent discussions about rail-splitting and such, but I didn't look closely. I thought surely someone would have mentioned the simple way to rail-split with an opamp, into a large capacitive load, but maybe not. Without resorting to a more desirable ground-referenced, +/- supply scenario, you can add significant bypass capacitance from the signal common to ground, with slight change to the buffer circuit. 1. Add a resistor between the opamp's output and the load, which is signal common. The current demand appears small, so maybe around a couple to few hundred ohms should do. 2. Add a resistor in series with the (sense line) inverting input. This can be in the many k ohms range, depending the opamp's bias current. 3. Add a small capacitor between the opamp's output and inverting input to stabilize it. 4. Add the bypass cap. This setup just isolates the opamp from the capacitive load, with the LF/DC regulated by the opamp, and the HF shunted by the bypass cap. I'm guessing that once you get good bypassing here, the LNA will work much better, and you should see the difference with the lower noise opamp. The reason is that any opamp has limited CMRR, so improving the bypassing makes the "CM" part smaller. This is also another reason to operate opamp inputs at or near ground. Actually, the best CM improvement can be provided by running in inverting mode, so both inputs are always at ground. Non-inverting modes require the inputs to move, depending on the signal. In your LNA, the CM input signal range is not too bad, due to the high gain. The trick is to keep the overall CM - the operating common level wrt ground and the power supplies - constant and noise-free. Regarding microphonics, since you mentioned tapping the housing, it sounds like you have "canned it up," which is a good thing. Assuming the REF and DUT are external, so not involved, the audible is coming from the analysis circuit only, right? That's not too surprising since it's a high gain system. It could be related to individual component microphonics, but I'd guess it's an RF effect. The whole thing is awash in the 2f signal and harmonics from the mixer, and to a lesser extent the DUT frequency signal that leaks through, so mechanical dimension changes or movements in the can, board, wiring etc, can change the EM pattern inside, giving tiny, noticeable phase shifts - after all, that's what it's for. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
HI We’re not building a synthesizer here. We are putting together a simple piece of test gear. The purpose of the test gear is to measure phase noise down into the -170 dbc / Hz range ….. Bob > On Jul 12, 2022, at 4:05 PM, Mike Monett via time-nuts > wrote: > > To Bob kb8tq: > > Unfortunately, most of your post made very little sense. D-flops are noisy, > and the higher you go in frequency, the noisier they are. This is clear > from the schematic. Here is the schematic for a MC1670 D-flop: MC1670SC.PDF. > > Most of the noise is generated in the input SR latch. When the clock signal > arrives, the input latch state is transferred to the output SR latch. > Obviously, the sheer number of transistors involved is going to generate > noise. > > Unfortunately, the D-flop is needed in every known synthesizer. Keeping > this noise out of the signal is the goal of every designer. Stanford > Research Systems is one company that has mastered the art. See > > https://www.thinksrs.com/products/siggen.html > > But you need to know how much noise is involved. That is where my new > method can help. I am busy collecting parts - the HMC984LP4E's will arrive > tomorrow, and I am looking for a pair of low noise VCXO's. > > I will have to regenerate test equipment that I haven't used in 5 decades > to measure deadband, loop bandwidth, damping, crosstalk, jitter response, > etc. I will also get a DBM to compare the results. > > I will also need ripple filters for the electronics. I have described this > before in 2N3906G.PNG > > All this will take time - maybe months. But I have intended on making my > own phase noise analyzer for a long time, and this will be an excellent way > to get started. > > Along the way, there are plenty of other projects to attend to: a 4GHz to > 8GHz low noise signal generator using YIG oscillators, a GPSDO to supply an > accurate 10MHz reference, a new method of eliminating the sampling jitter > in the 1PPS signal from the GPDSO, a low noise VCXO to supply a 10MHz > reference from the 1PPS signal, an ultra stable signal generator to allow > sampling of signals up to 150GHz, and so on. > > As there is little else to talk about, I will go silent while I am working > on these projects. > > Bye > > Mike > <2N3906G.PNG>___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
On 7/12/22 3:51 PM, ed breya via time-nuts wrote: I forgot to mention that you should also consider possible effects from the RF present, on the LNA. This can be more significant than SMPS frequencies getting where they don't belong, especially since the RF is intentionally right at the opamp's input. Your LPF only reduces, and does not eliminate, the 2F and harmonics, so there can be significant RF present on the LNA circuit. A simplistic view is that the RF is far beyond the opamp's GBW or closed loop gain and should have no response, but it's not at all beyond upsetting or altering the operation. This can result in extra DC offsets and noise due to RF rectification in the input circuits, which only remain "linear" at frequencies where the output and feedback can keep up with the input. This can be fixed if necessary, by adding extra RF filtering, particularly some built to low-pass at a higher cutoff frequency well above the analysis frequency, and well below the expected f and 2f. For instance, in your circuit it looks like L1 is 1 mH, with 100 nF caps, which ideally cuts off quite low. However, 1 mH is a pretty big choke, and will tend to have a lot of inter-winding capacitance (and high resistance - don't forget to include it in noise), making it less effective at the higher frequencies. Adding an LC section in front of it, but set up for something in the MHz region, will give much greater rejection of the f and 2f, due to having more appropriate smaller L and C. Anyway, if it works fine as is, then no problem, but it's something to be aware of if you get strange effects down the road. Ed and a single LC is only a single pole, so the roll off isn't all that great in a dB/decade sense. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Erik, I'd really recommend that you use a real, "solid" ground reference on the instrumentation side, with +/- large (12-20 V) supplies, as others have suggested. Your most recent setup diagram indicates that you're relying on the "differential" input of the audio PC card etc analyzer to allow for the "floating" common of the analysis circuit. Do you know what the common-mode rejection characteristics are? A true differential input would have two coax lines entering a symmetric differential to single-ended conversion stage at the front end. I doubt that the PC card actually has this, but maybe some form of DC/LF isolation from the local input common to chassis ground. The PC likely has lots of SMPS noise in common-mode form, which probably can be ignored for audio (the SMPS frequencies are almost always quite far above audio). As long as the interference signals aren't too big to upset the LNA operation by say, rectification in various junctions (especially the front end), it should be OK. You will also have in-band line frequency and harmonics present in the common-mode signal, but these should be easier to deal with by virtue of whatever LF CMRR the sound card does have at lower frequencies. Now consider the analysis circuit environment, where you have apparently zero intentional bypassing capacitance from the floating measurement common to chassis/earth ground. Here, the only bypass caps effectively are C1 at the REF buffer's input (which will only aggravate the situation), and the small capacitance between the ports of the mixers. I believe you have some bypassing at points in the other portion of the circuit - the PLL for the reference - but I don't know what that looks like now. So, just looking at this section, I'd say you need some serious bypassing to ground, for the RF signals from the mixers, and the common-mode signals in and out of the audio analyzer, DUT, and REF. I recall there were some recent discussions about rail-splitting and such, but I didn't look closely. I thought surely someone would have mentioned the simple way to rail-split with an opamp, into a large capacitive load, but maybe not. Without resorting to a more desirable ground-referenced, +/- supply scenario, you can add significant bypass capacitance from the signal common to ground, with slight change to the buffer circuit. 1. Add a resistor between the opamp's output and the load, which is signal common. The current demand appears small, so maybe around a couple to few hundred ohms should do. 2. Add a resistor in series with the (sense line) inverting input. This can be in the many k ohms range, depending the opamp's bias current. 3. Add a small capacitor between the opamp's output and inverting input to stabilize it. 4. Add the bypass cap. This setup just isolates the opamp from the capacitive load, with the LF/DC regulated by the opamp, and the HF shunted by the bypass cap. I'm guessing that once you get good bypassing here, the LNA will work much better, and you should see the difference with the lower noise opamp. The reason is that any opamp has limited CMRR, so improving the bypassing makes the "CM" part smaller. This is also another reason to operate opamp inputs at or near ground. Actually, the best CM improvement can be provided by running in inverting mode, so both inputs are always at ground. Non-inverting modes require the inputs to move, depending on the signal. In your LNA, the CM input signal range is not too bad, due to the high gain. The trick is to keep the overall CM - the operating common level wrt ground and the power supplies - constant and noise-free. Regarding microphonics, since you mentioned tapping the housing, it sounds like you have "canned it up," which is a good thing. Assuming the REF and DUT are external, so not involved, the audible is coming from the analysis circuit only, right? That's not too surprising since it's a high gain system. It could be related to individual component microphonics, but I'd guess it's an RF effect. The whole thing is awash in the 2f signal and harmonics from the mixer, and to a lesser extent the DUT frequency signal that leaks through, so mechanical dimension changes or movements in the can, board, wiring etc, can change the EM pattern inside, giving tiny, noticeable phase shifts - after all, that's what it's for. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
I forgot to mention that you should also consider possible effects from the RF present, on the LNA. This can be more significant than SMPS frequencies getting where they don't belong, especially since the RF is intentionally right at the opamp's input. Your LPF only reduces, and does not eliminate, the 2F and harmonics, so there can be significant RF present on the LNA circuit. A simplistic view is that the RF is far beyond the opamp's GBW or closed loop gain and should have no response, but it's not at all beyond upsetting or altering the operation. This can result in extra DC offsets and noise due to RF rectification in the input circuits, which only remain "linear" at frequencies where the output and feedback can keep up with the input. This can be fixed if necessary, by adding extra RF filtering, particularly some built to low-pass at a higher cutoff frequency well above the analysis frequency, and well below the expected f and 2f. For instance, in your circuit it looks like L1 is 1 mH, with 100 nF caps, which ideally cuts off quite low. However, 1 mH is a pretty big choke, and will tend to have a lot of inter-winding capacitance (and high resistance - don't forget to include it in noise), making it less effective at the higher frequencies. Adding an LC section in front of it, but set up for something in the MHz region, will give much greater rejection of the f and 2f, due to having more appropriate smaller L and C. Anyway, if it works fine as is, then no problem, but it's something to be aware of if you get strange effects down the road. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
On Tue, 12 Jul 2022 08:17:33 -0800 Bob kb8tq via time-nuts wrote: > Hi > > If you have any ceramic capacitors in the mix, they are often > microphonic. The X7R versions are typically the best “high C” types. > NPO’s normally are completely non-microphonic. Other non-ceramic caps > should be ok, but who knows. > _ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com Actually X7Rs are quite bad. Z5Us, also. Both are piezoelectric. I don't use them any more except for power supply bypass in non-critical supplies. As a part of a precision temperature controller project (microKelvin), I needed to select capacitors for low microphonics. The ceramic types mentioned above are the worst offenders; but several other types (certain film types included) show some microphonic activity. Best to evaluate every capacitor type by charging to 10 Volts, or so, AC coupling to an audio amplifier/sensitive oscilloscope/or other and tapping to see if noise is produced. Stephen Menasian ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
On 7/12/22 8:53 AM, Erik Kaashoek via time-nuts wrote: I'm struggling with the noise floor. First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, but that made no difference, noise floor at 10kHz was still -140dBc/Hz The setup was simplified to this schematic: http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG What's the noise contribution of the resistors? V = sqrt(4*k*T*R*B) 51 ohms is sqrt (4 * 1.38E-23 * 300 * 51) = 0.9 nV/sqrt(Hz) 100 ohms is ~1.4 nV/sqrt(Hz) What kind of op amp? what's the current noise vs the voltage noise? - you might low voltage noise, but high current noise, and that current noise across the input impedance can turn into surprisingly high voltage noise at the output. The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the differential audio output . Why did the lower noise opamp not make a difference? Also the setup is acting like a nice microphone. Tapping the housing is clearly audible. Which component may be causing the microphony? My guess would be a parasitic capacitance between circuit and housing. changing the distance changes the C. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Hi If you have any ceramic capacitors in the mix, they are often microphonic. The X7R versions are typically the best “high C” types. NPO’s normally are completely non-microphonic. Other non-ceramic caps should be ok, but who knows. Roughly speaking, 1 nV / Hz should be low enough to not matter. Since all these specs are “typical” one never knows quite what this or that part may be doing. You *should* see a drop putting in a 1 nV in place of a 5 nV. Bob > On Jul 12, 2022, at 7:53 AM, Erik Kaashoek wrote: > > I'm struggling with the noise floor. > First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted > mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, > but that made no difference, noise floor at 10kHz was still -140dBc/Hz > The setup was simplified to this schematic: > http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG > The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the > differential audio output . > Why did the lower noise opamp not make a difference? > Also the setup is acting like a nice microphone. Tapping the housing is > clearly audible. Which component may be causing the microphony? > > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
I'm struggling with the noise floor. First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, but that made no difference, noise floor at 10kHz was still -140dBc/Hz The setup was simplified to this schematic: http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the differential audio output . Why did the lower noise opamp not make a difference? Also the setup is acting like a nice microphone. Tapping the housing is clearly audible. Which component may be causing the microphony? ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
Hi There are a very small number of signal generators that *might* help when measuring phase noise on a good source. The “rest of them” are very much in the “don’t bother” category. Just which one is in the “maybe” category depends a lot on your frequency of interest. None of them seem to be very affordable …. wonder why :) :) :) Do useful ones pop up from time to time? Sure they do. They might require a bit of work to get going. Thanks very much to those who make them available. Bob > On Jul 11, 2022, at 6:41 PM, Alex Pummer via time-nuts > wrote: > > yes there are much better signal generators out there, that frequency doubler > tuning circuit is for religious people only -- you need to be able to > believe, that it could work > 73 > KJ6UHN > Alex > > On 7/11/2022 12:24 PM, Dave B via time-nuts wrote: >> On 11/07/2022 08:30, time-nuts-requ...@lists.febo.com wrote: >>> I also measured a Marconi 2022 signal generator and it was possible to >>> lock but the phase noise was terrible with strong factional PLL spurs. >> >> Indeed, those signal generators are renown for having "some rather >> interesting" spectral content... >> Around, above and often well below the "desired" signal! >> >> Not entirely surprising though, if you look at the block diagram of one such. >> >> Regards to All. >> >> Dave G0WBX(G8KBV) >> >> >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
yes there are much better signal generators out there, that frequency doubler tuning circuit is for religious people only -- you need to be able to believe, that it could work 73 KJ6UHN Alex On 7/11/2022 12:24 PM, Dave B via time-nuts wrote: On 11/07/2022 08:30, time-nuts-requ...@lists.febo.com wrote: I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. Indeed, those signal generators are renown for having "some rather interesting" spectral content... Around, above and often well below the "desired" signal! Not entirely surprising though, if you look at the block diagram of one such. Regards to All. Dave G0WBX(G8KBV) ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Regardless of what you call the “ 1 Hz normalized noise “ of a digital phase detector, it does predict what the noise floor does on it as the reference frequency is changed over some reasonable range. This has been demonstrated a lot of times and on a lot of different parts. Based on a number of RF designs using them ( and using gates for RF purposes ) the basic gate is what is at fault here. They are noisy and that noise changes with frequency. Frequency goes up / noise goes up. There are very good reasons for this. Getting a gate with a noise figure below 6 db is highly unlikely …. That is what you would have to do in order to make a gate based circuit measure a lower noise floor than the DBM based approach. Folks have spent a lot of time searching for the magic “zero noise gate”. The sine wave component present at the DBM output at 2X the input frequency ( in the case of the phase noise test setup) are *way* higher than the highest noise you are after. You put in 10 MHz or 100 MHz and you go up to *maybe* 100 KHz on the noise. With a sound card, even getting to 100 KHz is going to be a challenge. 20 KHz may be the max. Knocking down the 2 x Fin component with a low pass filter is pretty easy. Indeed the sound card or audio spectrum analyzer likely has some filtering already. The design and implementation of an adequate LPF is far from the biggest challenge that the person building the circuit will face. Indeed 1/F noise and noise corners do matter. All of the above has been simply talking about noise floor. Gates have significant 1/F issues along with their other “features”. This carries over to the detectors based on them. As the gate speed goes up ( and the floor typically comes down), the 1/F corner normally moves up …. Bob > On Jul 11, 2022, at 8:05 AM, Mike Monett via time-nuts > wrote: > > To Bob kb8tq > > Figure Of Merit sounds like a useless number. I have a different > approach that yields immediate and useful results. Before I explain > my method, let me introduce myself. > > In 1970, I invented, and Memorex patented, the original > zero-deadband phase-frequency detector. You can see it in page 3 of > my '234 patent at https://patents.google.com/patent/US3810234A/ > > This invention soon led to another invention of tremendous > significance to today's world. > > In 2014, researchers published a study in the journal Supercomputing > Frontiers and Innovations estimating the storage capacity of the > Internet at 1e24 bytes, or 1 million exabytes. > > When I started working for Memorex, an IBM 2314 disk pack could > store 29.2 million bytes. At that rate, today's internet would > require 1e24/29e6=3.44e16, or 34,400,000,000,000,000 IBM 2314 disk > drives. This is an impossible number. Other estimates give equally > outrageous numbers. > > The problem in those days was improvements in disk drive capacity > were basically trial and error. This is a slow and very expensive > business. > > My new invention allowed peering into the hard disk and separating > out all the variables that affect performance. With this > information, researchers could see the effect of changes and quickly > optimize the performance. This allowed the tremendous improvement in > tape and disk drive capacity that now allows the internet to store > all the needed data. > > You can see how this invention works in the Katz paper at > https://tinyurl.com/2bmuz3n2 > > Now for my new method. > > The schematic for a phase-frequency detector is shown in > DBAND2S.PNG. In operation, a pulse arrives at the DATA pin and pin > U1Q goes high. Then a pulse arrives at the VCO pin and pin U2Q goes > high. > > This allows the NAND gate to bring the CLR signal low, which > immediately resets both d-flops. > > The result is shown in ZERODB.PNG. It is a very narrow pulse with > both d-flops superimposed. > > This is the basis for my new approach. Simply tie both inputs of the > PFD together and measure the noise spectrum of the output. (Of > course, you have to ensure that both outputs match at zero error.) > > Once you have the PFD noise, you can enable the loop and measure the > total noise spectrum. Then simply subtract the PFD spectrum to get > the OCXO noise. If you have two identical VCXO's, each one > contributes half the noise. > > I don't know if this method would work with a double-balanced mixer. > The problem is a DBM requires quadrature signals, so the noise is a > function of the OCXO noise as well as the mixer diodes. But the OCXO > noise is what you are trying to measure. > > This method works with the PFD since only a single pulse is needed > to activate both d-flops, so you are measuring only the PFD noise. > > Et Voila. > > Now that you can measure the OCXO noise, you might want to try your > hand at desig
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)
On 11/07/2022 08:30, time-nuts-requ...@lists.febo.com wrote: I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. Indeed, those signal generators are renown for having "some rather interesting" spectral content... Around, above and often well below the "desired" signal! Not entirely surprising though, if you look at the block diagram of one such. Regards to All. Dave G0WBX(G8KBV) -- Created on and sent from a Unix like PC running and using free and open source software: ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Erik, On 7/10/22 17:52, Erik Kaashoek via time-nuts wrote: I've updated the schematic to include the latest additions and added some new measurements Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf The resistor values (many 18k) are a bit weird but I happen to have a big box of 18k resistors. The value of the low pas filter after the mixer (C2,C3,L1) are probably wrong. Calculate yourself for the corner frequency you want. I get 22,5 kHz which isn't completely off the charts. Sure helps to eat the 20 MHz and higher, as well as stray 10 MHz. For the 20 MHz it will in ideal have -180 dB damping, but in practice it will leak over but probably not too bad. The elco's in the PI_controller and the input of the Audio_LNA are probably going to explode due to reverse polarity. You want the resistor and capacitor to be in series and not in parallel in that negative feedback. As you put a resistor in parallel you will drain the state of the capacitor and loose performance. You can choose to either locate a 1 uF non-polar cap, or shift the values a bit to get into plastic caps such as polypropylene. 100 nF and 220 nF should be easy enough to get hold off. You could even put a pair of 470 nF in parallel. A generic note: Most if not all op-amps tends to operate better in terms of offset behavior as they see about the same resistance DC on both + and - inputs. The output of the REF_Buffer acts as the virtual ground so care was taken (almost) not to draw any current, except for the input of the Audio_LNA. The supply of the opamps is not drawn but its from Ground and Vcc (+12V) I've tested symmetric supply but the combination of the REF output voltage from the DOCXO and the REF_Buffer provided the least noise. The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and above The R/C values around the PI_Controller have not been optimized but they work. As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to 0-5V for the Vtune of the DOCXO You could do away with the Summer and Inverter op-amps if you fed the TUNING into the + input of the inverter. By skewing the PI-controller balance the output will be suitably offset. The benefit will be that you avoid noise contribution from two op-amps and their resistors. The LED's provide visual feedback on the tuning. IF both are just on the PLL is in lock. It may be better to have two LED's in series at each side to increase the dimming. I would advice moving those LEDs off-board. Let that run on separate "dirty" power. I love the direct observation aspect, but I fear it just add noise to the measurement. Keep up the good work! Cheers, Magnus Some measurements.: All indicated levels are 40dBc/Hz higher compared to actual. The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG This is measured without DUT input. Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it should be at -88dBc, so there must still be a big mistake somewhere. AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG All seems OK, a bit of 50Hz and harmonics. OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG very weird spurs between 40 and 50 Hz The famous cheap Chines TCXO: http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB worse. A home designed/build arduino GPSDO: http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG The GPSDO has a good ADEV but is clearly very noisy! I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. I also tried to measure the phase noise of an old Philips analog 10Hz to 12MHz signal generator but it was impossible to get a lock because the generator output is jumping around several Hz at 10MHz output. The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to be able to do a first assessment of some not too good oscillator performance. Feedback welcome as these are my first baby steps on phase noise nuttery. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi There’s really no need to use the Vref out of the OCXO at all. Since many devices don’t have one, you will need a “replacement” at some point. Simply pulling the “set reference” off of a cleaned up output of your main supply(s) is typically how it is done. The most basic reason to not hard wire a specific device into the circuit is to allow a A to B / B to C / C to A swap process to be done. That is about the only way to get close to working out the numbers on this or that reference. Without that data, you are flying blind as you get close to the limits of the reference. Given the characteristics of the mixer and the other stuff involved, with a roughly +7 dbm input, anything past -174 dbc / Hz is suspect. -180 dbc / Hz is significantly better than what you likely can do with this approach. Indeed, it also is quite a bit better than what you will find your signal sources doing so that’s not a major constraint. Yes there is a wonderful “bet a beer” / after work conversation to be had about the ultimate phase noise of a +7 dbm signal. More or less, the bet is won by postulating a 1 ohm source impedance. For real world sources …. not so much …. Bob > On Jul 10, 2022, at 7:52 AM, Erik Kaashoek via time-nuts > wrote: > > I've updated the schematic to include the latest additions and added some new > measurements > > Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf > > The resistor values (many 18k) are a bit weird but I happen to have a big box > of 18k resistors. > The value of the low pas filter after the mixer (C2,C3,L1) are probably > wrong. Calculate yourself for the corner frequency you want. > The elco's in the PI_controller and the input of the Audio_LNA are probably > going to explode due to reverse polarity. > The output of the REF_Buffer acts as the virtual ground so care was taken > (almost) not to draw any current, except for the input of the Audio_LNA. > The supply of the opamps is not drawn but its from Ground and Vcc (+12V) > I've tested symmetric supply but the combination of the REF output voltage > from the DOCXO and the REF_Buffer provided the least noise. > The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and > above > The R/C values around the PI_Controller have not been optimized but they work. > As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to > 0-5V for the Vtune of the DOCXO > The LED's provide visual feedback on the tuning. IF both are just on the PLL > is in lock. It may be better to have two LED's in series at each side to > increase the dimming. > > Some measurements.: > All indicated levels are 40dBc/Hz higher compared to actual. > The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG > This is measured without DUT input. > > Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise > at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ > > Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at > 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG > The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it > should be at -88dBc, so there must still be a big mistake somewhere. > > AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG > All seems OK, a bit of 50Hz and harmonics. > > OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG > very weird spurs between 40 and 50 Hz > > The famous cheap Chines TCXO: > http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG > Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB > worse. > > A home designed/build arduino GPSDO: > http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG > The GPSDO has a good ADEV but is clearly very noisy! > > I also measured a Marconi 2022 signal generator and it was possible to lock > but the phase noise was terrible with strong factional PLL spurs. > I also tried to measure the phase noise of an old Philips analog 10Hz to > 12MHz signal generator but it was impossible to get a lock because the > generator output is jumping around several Hz at 10MHz output. > > The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at > 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to > be able to do a first assessment of some not too good oscillator performance. > > Feedback welcome as these are my first baby steps on phase noise nuttery. > Erik. > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Pretty much the best mixer to use for this in a basement / DIY basis is a Mini Circuits RPD-1 or one of it’s siblings. It has a 500 ohm output on the mix port instead of 50 ohms. Yes, you open circuit terminate it ( so 5K ) but as noted, it’s the Zout of the mixer that likely sets what the op amp sees. With it’s higher output impedance, you are even less driven to nutty low noise op amps and 4 ohm feedback resistors. The good old OP-27 / OP-37 sitting in the dusty back of your parts drawer from back in 1993 will do just fine. Yes, this all gets back to being nutty as you get close to carrier. If you are after -150 dbc / Hz at 1 Hz offset, you will need go a bit crazy. If you head this way, there are a lot of posts back in the archives leading you down various paths to get it done. While others have indeed fried expensive setups while loosing a supply leg, I’ve never run into that problem. It most certainly can happen. I’ve never taken any special precautions and have yet to “get bit” by the issue. As a rough guess, I’d say I’ve powered up various implementations these setups a couple thousand times over the years. Bob > On Jul 10, 2022, at 6:32 AM, Gerhard Hoffmann via time-nuts > wrote: > > Am 2022-07-09 22:06, schrieb Erik Kaashoek via time-nuts: > >> Ultra low noise opamps have been ordered to hopefully reduce the internal >> noise of the PNA but the reference OCXO may already be the limiting factor. >> The REF voltage output of the OCXO turned out to be rather clean. Much >> cleaner than a 7805 voltage regulator > > The existence of my own ultra-low noise amplifiers was originally triggered > by this problem but has turned into a sport of it's own. Don't yield to the > temptation of driving this too far. A single AD797, LT1028, or ADA4898-2 > all deliver an input noise density of abt. 1nV/rtHz which is the thermal > noise of a 60 Ohm resistor. ADA4898 has goof price/performnce. > > The diodes in the mixer can easily feature RS = 20 Ohms, and the 2 conducting > diodes then show 40 Ohms, which is not much less than the 60 Ohm equiv of the > opamps. > RS is ohmic resistance of silicon and contacts, not the differential > slope resistance of the diode which is only half-thermal IIRC. > > High level mixers often have additional resistors in series to the diodes. > It's no wonder then that high level mixers are usually not the winners in > dynamic range. Maybe an array of low-level mixers that are Wilkinsoned > together on RF and LO, with the IF ports in series would give good results. > > 1. Stephan R. Kurtz, Watkins-Johnson: Mixers as Phase Detectors > 2. Bert C. Henderson, W-J: Mixers: Part 2 Theory and Technology > Copyright © 1981 Watkins-Johnson Company > Vol. 8 No. 3 May/June 1981 > Revised and reprinted © 2001 WJ Communications, Inc. > > cheers, Gerhard > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Yes it is a pain to implement dual supplies. I ponder that issue every time I build one of these setups. I’ve built a lot of them …. If you are going to do a single supply, setting up a “virtual ground” is probably the best way to go. Do it with a drive circuit to provide very clean 15V off of a 30V supply then tack everything ( including *all* the mixer grounds to that 15V supply. Keeping the signal undistorted before you check the beat note and use it to drive the EFC does keep you out of various issues. You do not want to deal with possible clipping / saturation artifacts getting into either process. With devices having positive side EFC, negative side EFC, and “both sides” EFC, it’s hard to get around a dual supply in any sort of general purpose device. A 15V center point is not going to fit any EFC that I’ve seen :). Struggling with the ground loop problem is always the big deal in any setup. Trying to rule out / take out line noise is usually the final straw in any series of tests. Doing that with everything at “real ground” is just a bit easier. Part of the calibration is measuring the beat note as it goes past zero. The ’scope gets cranked up and you look at a bit of the crossing right at ground. Keeping the device happy while doing this is much easier if the chassis does not need to float at 15V. Whatever is used as a supply turns out to be a dedicated device. The same ground loop / isolation stuff get in here. An old style non-switching design is just about mandatory. Keeping switching artifacts out of things is almost impossible. All of this makes a “build from scratch” approach less and less crazy. Old style three terminal regulators ( so 78x18 / 79x18 ) are not as easy to find these days. They do fine if you happen to have a pair …. There’s really not much power used by any of this. The need for anything massive. 100 ma out of each side is overkill …. As you build things up, you eventually come to the realization that a big sheet of brass is a good idea for the ground. Tie this and that to the sheet. Keep everything non-essential away and likely keep it turned off. Tying a dedicated supply to that sheet along with the amp and EFC stuff is not at all unusual. Bob > On Jul 9, 2022, at 11:11 PM, Erik Kaashoek wrote: > > Hi Magnus, > Yes, and it works very well, locking is easier as once locked it nicely > stay's in lock, , even with a slow drift of either the DUT or the reference. > As I could not find a bipolar capacitor the tuning potmeter has to be kept at > the low side to avoid blowing the integration capacitor. Maybe a back to back > series capacitor with pull down resistor is safer to use. > Will need to update the schematic to show the small improvements. > > @Bob, > You mentioned "dual supplies with high voltage" for the first gain opamp. How > much impact would dual voltage bring as its a pain to implement. > I understand everything gets ground reference and you loose the noise of the > buffer opamp but as the first gain opamp is in differential mode for its > input it does not see the noise of the buffer opamp. Or am I making a mistake? > > On 10-7-2022 2:02, Magnus Danielson via time-nuts wrote: >> Have you attempted doing a PI-loop as I've suggested? > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
I've updated the schematic to include the latest additions and added some new measurements Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf The resistor values (many 18k) are a bit weird but I happen to have a big box of 18k resistors. The value of the low pas filter after the mixer (C2,C3,L1) are probably wrong. Calculate yourself for the corner frequency you want. The elco's in the PI_controller and the input of the Audio_LNA are probably going to explode due to reverse polarity. The output of the REF_Buffer acts as the virtual ground so care was taken (almost) not to draw any current, except for the input of the Audio_LNA. The supply of the opamps is not drawn but its from Ground and Vcc (+12V) I've tested symmetric supply but the combination of the REF output voltage from the DOCXO and the REF_Buffer provided the least noise. The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and above The R/C values around the PI_Controller have not been optimized but they work. As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to 0-5V for the Vtune of the DOCXO The LED's provide visual feedback on the tuning. IF both are just on the PLL is in lock. It may be better to have two LED's in series at each side to increase the dimming. Some measurements.: All indicated levels are 40dBc/Hz higher compared to actual. The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG This is measured without DUT input. Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it should be at -88dBc, so there must still be a big mistake somewhere. AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG All seems OK, a bit of 50Hz and harmonics. OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG very weird spurs between 40 and 50 Hz The famous cheap Chines TCXO: http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB worse. A home designed/build arduino GPSDO: http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG The GPSDO has a good ADEV but is clearly very noisy! I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. I also tried to measure the phase noise of an old Philips analog 10Hz to 12MHz signal generator but it was impossible to get a lock because the generator output is jumping around several Hz at 10MHz output. The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to be able to do a first assessment of some not too good oscillator performance. Feedback welcome as these are my first baby steps on phase noise nuttery. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Am 2022-07-10 9:11, schrieb Erik Kaashoek via time-nuts: @Bob, You mentioned "dual supplies with high voltage" for the first gain opamp. How much impact would dual voltage bring as its a pain to implement. I think is was Rubiola who wrote that he exploded a costly microwave mixer with a LT1028 that had lost one of its power rails. If you go AC coupling, don't forget that the input capacitor must not be selected for f-3dB but that it must be much bigger to short the thermal noise of the bias network to pV levels through the low impedance source. Otherwise you see a noise rise towards 0 Hz that is MUCH steeper than 1/f. Scott Wurzer (designer of ad797) saw that immediately on my 20 * ada4898 220pV/rtHz amplifier. Wish he was more explicit. It took me some time to get it. :-) I had 10K/100u foil, ended up with 10k/4700uF wet tantalum, which opens another can of worms. I have converted to FETs now. A few pVrtHz more, but much less noise current. In cross correlation setups, the noise current of both amplifiers produces a common voltage drop in the (common) source resistance, and that does not average away. (May apply only to voltage measurements from a single source.) Gerhard ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Magnus, Yes, and it works very well, locking is easier as once locked it nicely stay's in lock, , even with a slow drift of either the DUT or the reference. As I could not find a bipolar capacitor the tuning potmeter has to be kept at the low side to avoid blowing the integration capacitor. Maybe a back to back series capacitor with pull down resistor is safer to use. Will need to update the schematic to show the small improvements. @Bob, You mentioned "dual supplies with high voltage" for the first gain opamp. How much impact would dual voltage bring as its a pain to implement. I understand everything gets ground reference and you loose the noise of the buffer opamp but as the first gain opamp is in differential mode for its input it does not see the noise of the buffer opamp. Or am I making a mistake? On 10-7-2022 2:02, Magnus Danielson via time-nuts wrote: Have you attempted doing a PI-loop as I've suggested? ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Erik, On 7/9/22 22:06, Erik Kaashoek via time-nuts wrote: Getting the simple PNA to lock was a bit difficult due to the overly simplistic translation of the mixer output to the Vtune of the OCXO To get some more flexibility I added a summing opamp that summed the mixer output with the output of the coarse tuning potmeter. As the summing causes inversion one extra inverting opamp was added. This made the loop gain constant To ensure the mixer is in quadrature another opamp was added that amplified the mixer output into two LEDs. One LED on when below zero ouput from mixer, the other on when above zero and both dim when zero output. This made tuning the coarse frequency simple. Turn till the blinking stops and both LED's light up dim. The fine frequency potmeter was no longer needed and the frequency counter is also no longer needed to get into lock With the summing opamp it is also possible to add an integrator but this has not been done yet. So, this is where you should attempt the PI loop. In theory, you have one proportional path P and one integrating path I that sums to form the EFC. You can imagine this as two op-amps having inverted gain and then a summing amp to sum these two up. Thus, you have for the P path a resistor in the negative feedback path and for the I path a capacitor in the negative feedback path. Such a setup is nice for testing, but a bit excessive as one progresses. One can actually reduce this to a single op-amp with the resistor and capacitor of the negative feedback to be in series, having a common input resistor. The integrator part will hold the state that ends up being the DC part of EFC. The proportional path will provide the AC path and set the damping factor for the PLL, you want it well damped. This would replace your normal loop filter. You would still want a filter to reject the sum-frequency out of the mixer. The P gain is proportional to the PLL bandwidth time damping factor. The I gain is proportional to the PLL bandwidth squared. The capture range is for all practical purposes infiinte (it's wide enough). The capture time depends to the cube on the PLL bandwidth, so altering the PLL bandwidth between unlocked and locked conditions have proven very useful approach to speed things up if one has a need for larger lock-in frequencies. Rough-tuning with a trimmer can reduce it significantly. The lock-detection is very simple detection of the presence of beat-notes or not, that AC component dies away as it locks. Anyway, the benefit of the PI loop filter is that you can be rather brutal with parameters, it will lock. So, it can be worth experimenting with it. I've found that one can ball-park things fairly quickly knowing how to change the P and I for wished PLL bandwidth and damping. Very experimentally friendly. I should advice you that any PLL will provide a low-pass filter of the reference input, and a high-pass filter on the noise inside the loop, which includes that of the oscillator. This can help you identify likely sources of disturbances as per their frequency in relation to the PLL loop bandwidth. Cheers, Magnus Shielding is now the biggest problem as any nearby coax connected to a 10MHz source will cause a huge amount of spurs when not at exactly the same 10MHz Ultra low noise opamps have been ordered to hopefully reduce the internal noise of the PNA but the reference OCXO may already be the limiting factor. The REF voltage output of the OCXO turned out to be rather clean. Much cleaner than a 8705 voltage regulator Erik ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On Sonntag, 10. Juli 2022 01:24:49 CEST djl via time-nuts wrote: > I checked the Hittite/AD part at Mouser, $21 and change. Problem is, > they have a few, but it is marked obsolete/discontinued. Also, a > devilish package to work with. . . For a one-off project, lifetime doesn't really matter, does it? The package is QFN, even with center pad. That is inconvenient, but not too bad. It's just kind of small, 4mm edge length. You'd certainly need a microscope and hot air to solder it or a quite fine soldering tip if you would want to deadbug it. Were I to use it, and wanted to breadboard a prototype, I'd certainly make a suitable breakout board for easier handling. > On 2022-07-08 22:19, Mike Monett via time-nuts wrote: > > To Bob kb8tq. You wrote: > >> Hi > >> > >> The noise floor of the double balanced mixer (used as a phase > >> detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I've > >> used the parts you are talking about. Their floor is *way* higher. > >> > >> Bob > > > > I stated the MC100EP140 would not match the Hittite HMC984LP4E. It has > > -231 dBc/Hz noise. > > > > -231 dBc is *way* lower than -170 dbc. About 60 dB lower. > > > > You might be interested in trying it. Only $13.25 at Arrow: > > > > https://octopart.com/search?q=HMC984LP4E > > > > Thanks, > > > > Mike > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-le...@lists.febo.com > > > When in trouble, when in doubt, > Run in circles, scream and shout. > (Naval War College Football Team) > -- > Dr. Don Latham AJ7LL > PO Box 404, Frenchtown, MT, 59834 > VOX: 406-626-4304 > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Erik, On 7/8/22 17:12, Erik Kaashoek via time-nuts wrote: Not something I want to implement on short notice but maybe for the future. The biggest limitation in this DIY PNA is the phase noise of the reference OCXO and the noise of the opamp amplifying the output of the mixer. So I was wondering if it would make sense to do the following 1: Split the output of the DUT into two completely separate PNA's 2: Feed the output of the two PNA's into the PC left/right audio inputs where the noise of both ADC's gets added. 3: Do a cross correlation of the two inputs. This should (as far as I have understood the feedback) eliminate both the phase noise of the two independent OCXO's used as reference and eliminate the noise of the opamps in the two PNA's and the ADC's, given enough time to do the correlation. This makes perfect sense. You will not remove the noise of the two channels, but you will get a direct benefit and as you average the complex output of successive FFT-cross-correlations you will suppress the measurement noise even further. Have you attempted doing a PI-loop as I've suggested? However, you benefit greatly at optimizing the performance of a single channel first before going to the cross-correlation. Bob's many good suggestions should provide you directions enough. Cross-correlation is not a replacement for doing the homework well, it's to get the icing on the cake. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
I checked the Hittite/AD part at Mouser, $21 and change. Problem is, they have a few, but it is marked obsolete/discontinued. Also, a devilish package to work with. . . On 2022-07-08 22:19, Mike Monett via time-nuts wrote: To Bob kb8tq. You wrote: Hi The noise floor of the double balanced mixer (used as a phase detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I've used the parts you are talking about. Their floor is *way* higher. Bob I stated the MC100EP140 would not match the Hittite HMC984LP4E. It has -231 dBc/Hz noise. -231 dBc is *way* lower than -170 dbc. About 60 dB lower. You might be interested in trying it. Only $13.25 at Arrow: https://octopart.com/search?q=HMC984LP4E Thanks, Mike ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com When in trouble, when in doubt, Run in circles, scream and shout. (Naval War College Football Team) -- Dr. Don Latham AJ7LL PO Box 404, Frenchtown, MT, 59834 VOX: 406-626-4304 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi (see below) > On Jul 9, 2022, at 12:06 PM, Erik Kaashoek wrote: > > Getting the simple PNA to lock was a bit difficult due to the overly > simplistic translation of the mixer output to the Vtune of the OCXO > To get some more flexibility I added a summing opamp that summed the mixer > output with the output of the coarse tuning potmeter. As the summing causes > inversion one extra inverting opamp was added. This made the loop gain > constant Putting some sort of “gain switch” on the summing amp can help in getting the loop gain to the point it is usable. > To ensure the mixer is in quadrature another opamp was added that amplified > the mixer output into two LEDs. One LED on when below zero ouput from mixer, > the other on when above zero and both dim when zero output. This made tuning > the coarse frequency simple. Turn till the blinking stops and both LED's > light up dim. The fine frequency potmeter was no longer needed and the > frequency counter is also no longer needed to get into lock That sounds right. > With the summing opamp it is also possible to add an integrator but this has > not been done yet. Typically a simple roll off cap on the feedback R is about all that is done. > Shielding is now the biggest problem as any nearby coax connected to a 10MHz > source will cause a huge amount of spurs when not at exactly the same 10MHz Terminating unused devices “at the socket” is often the only way to keep things reasonable. > Ultra low noise opamps have been ordered to hopefully reduce the internal > noise of the PNA but the reference OCXO may already be the limiting factor. Even a “not so fancy” op amp should do pretty well. The big deal is to get to dual supplies with a fairly high voltage on the first stage. > The REF voltage output of the OCXO turned out to be rather clean. Much > cleaner than a 8705 voltage regulator The Ref voltage likely also supplies the oscillator. It can be 20 to 40 db “noisier” than the phase detector output and have little or no impact on the oscillator performance. Yes, there likely is some filtering between the regulator and the oscillator …. Bob > Erik ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Mike, On 7/8/22 15:34, Mike Monett via time-nuts wrote: You wrote: Mike, He was using an analog mixer, but your comment about XOR mixer does not apply to analog mixers. Your oversimplification that analog mixer and XOR gates being the same thing does not apply here, and thus the assigned missbehavior does not carry over to the analog mixer case. Cheers, Magnus Magnus, Thanks for your comment. Here are some attached files: 1. DBMS.PNG This shows the schematic of a double-balanced mixer. Note the mixer output is on pin U24. A low pass filter is at R1C1. 2. DBMWFM.PNG These are the waveforms in quadrature lock. The bottom waveform in red is the signal at pin U24. It is a square wave at twice the signal frequency. This signal is identical to an XOR, such as a 7486 logic ic, except the amplitude is much lower at only 900 mV p-p. The top waveform in green is the signal at the low pass filter. It is a triangle wave, the same as you would get from adding a low pass filter to any square wave. Thus my statement that a double-balanced mixer is an XOR is accurate. No, it's not. You addresses this from the wrong side of things, considering that the waveform and amplitude is the only critical part, it's not. The way that the digital gate behaves is not providing the dynamics for the noise as the DBM does. A DBM has far less noise, which is why it is beneficial to use, as Bob pointed out. So, while large-scale properties is similar between DBM and XOR, their noise behavior is quite different. Also their ability to handle signals of various amplitudes and the way they change behavior from it. Also, all digital gates degrade their performance in face of higher amount of noise. On their way there they compress the noise. Stateful PFD can step state before they should, and that also compresses noise (and make it larger). See Gardner to cover part of this, I've done similar work that also reflect the same understanding. As the goal here is to measure very low phase noise, DBM have proven to be the best technology until we started oversampling and digital radio style of processing, which is more expensive but state of art for wide frequency systems. More delicate systems with DBMs also achieves state of art, see the interferometric methods of Rubiola for instance and also the cross-correlator approach. I've contributed in that field myself by contributing the interferometric cross-correlation phase-noise setup, which combines the techniques to overcome a particular issue with cross-correlation at the thermal noise-floor. So I continue to disagree about your generalization that DBM and XOR achieve the same thing, for this purpose they do not. If we where not looking for as deep noise floor, but only had moderate S/N needs, I would agreed. I've used XOR gates just fine for such applications, and there is plenty of such cases, it's just that this is not one of those. 3. DUBLBA01.ASC This is the double-balanced mixer schematic input for the LTspice simulator. 4. DUBLBA01.PLT This is the output waveforms from LTspice. Ordinarily, the triangle ripple output from a double balanced mixer would add considerable jitter to any PLL. Eric's application avoids this problem since his loop bandwidth is so low, at much less than 1 Hz. This makes it extremely difficult for him to obtain lock, which is why I proposed using a phase/frequency detector. I suggested a PI loop instead. It avoids all the issues while maintaining the noise behavior from the DBM. The low capture range of Eric's PLL for sure indicate the lack of loop gain, which also gives low bandwidth, so the end to end range of phase only allows for small adjustment of EFC to steer the oscillator into lock. A PI loop consisting of two resistors, a capacitor and an op-amp is a fairly good way to orthogonalize out the capture range from the bandwidth issue. The first block diagram I posted earlier, PNA.PNG, contained two errors. I corrected them in PNA2.PNG, which I will post to Eric. At first, I did not realize the significance of Eric's low loop bandwidth, and I erroneously assumed the triangle wave ripple output would cause significant jitter to his loop. It is now obvious the low loop bandwidth will reduce the ripple amplitude to insignificance, and I now retract my claim. The ripple amplitude is also very limited to only cover a very narrow frequency range and those the beat note will be very low frequency. That take ages to lock unless one is very close at which is more the remaining lock-in. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Getting the simple PNA to lock was a bit difficult due to the overly simplistic translation of the mixer output to the Vtune of the OCXO To get some more flexibility I added a summing opamp that summed the mixer output with the output of the coarse tuning potmeter. As the summing causes inversion one extra inverting opamp was added. This made the loop gain constant To ensure the mixer is in quadrature another opamp was added that amplified the mixer output into two LEDs. One LED on when below zero ouput from mixer, the other on when above zero and both dim when zero output. This made tuning the coarse frequency simple. Turn till the blinking stops and both LED's light up dim. The fine frequency potmeter was no longer needed and the frequency counter is also no longer needed to get into lock With the summing opamp it is also possible to add an integrator but this has not been done yet. Shielding is now the biggest problem as any nearby coax connected to a 10MHz source will cause a huge amount of spurs when not at exactly the same 10MHz Ultra low noise opamps have been ordered to hopefully reduce the internal noise of the PNA but the reference OCXO may already be the limiting factor. The REF voltage output of the OCXO turned out to be rather clean. Much cleaner than a 8705 voltage regulator Erik ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi As noted in another post, the phase detector guys talk about a figure of merit that is not directly comparable to the floor of a DBM. If I translate the -170 dbc/ Hz at 100MHz on the DBM, to the PLL chip FOM, I would add 80 db. That would make it a -250 dbc FOM vs the -231. Since the FOM stuff does not really apply to a DBM approach, you would never see this done. One works one way, the other works in a very different fashion. Bob > On Jul 8, 2022, at 8:19 PM, Mike Monett via time-nuts > wrote: > > To Bob kb8tq. You wrote: > >> Hi > >> The noise floor of the double balanced mixer (used as a phase >> detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I've >> used the parts you are talking about. Their floor is *way* higher. > >> Bob > > I stated the MC100EP140 would not match the Hittite HMC984LP4E. It has > -231 dBc/Hz noise. > > -231 dBc is *way* lower than -170 dbc. About 60 dB lower. > > You might be interested in trying it. Only $13.25 at Arrow: > > https://octopart.com/search?q=HMC984LP4E > > Thanks, > > Mike > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
HI > On Jul 8, 2022, at 7:44 PM, Mike Monett via time-nuts > wrote: > > To Erik: > > ……. > Another item that might be of interest is the PFD. The Hittite > HMC984LP4E has -231 dBc/root(Hz) of noise, which is quite low. The > datasheet is at > https://www.analog.com/media/en/technical-documentation/data-sheets/hmc984.pdf > > …... > > If you would like to eliminate the problem of quadrature lock, the > Hittite HMC984LP4E PFD might be of interest. The -231 dBc/Hz of > noise is very low and might be hard to reach with a DBM. > > If you are interested in following up on phase-frequency detectors > to eliminate the narrow lock range of double-balanced mixers, I can > supply you with a wealth of information on the design, implementation, > and testing. Just let me know if this would help. > > Mike > <2N3906S.PNG><2N3906G.PNG><54E696BA.ASC><54E696BA.PLT>___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com Ok, since this keeps coming up …. The chip guys rate their phase detectors in a somewhat unique way. It works for their product so that’s fine. However you can’t just toss out their number and quickly compare it to another number from an entirely different approach. You need to do the math. The -231 dbc / Hz number quoted above is a “normalized to one hertz carrier” number. They call it a FOM or “Figure of Merit” due to the normalization. Other data sheets phrase things slightly differently when referring to the same number. The first hint you get that there’s something going on with the > 200 db noise number is in figures 11,12, and 13 where they show actual performance at a couple of frequencies. The noise at “phase noise test set” sort of offsets isn’t making it past 120 dbc / Hz on those plots. The quick and dirty explanation is that you translate the “FOM” number by 10 Log F to get the noise at the operating frequency. So, if you are at 100 MHz, you add 80 db to the magic 231 db. That gets you to -151. That still sounds ok …. but … this is the broadband FOM and not the close in number. It gets worse as you go closer to carrier …. So no, that’s not going to beat a typical RPD-1 based setup. Bob ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi > On Jul 8, 2022, at 10:35 AM, Mike Monett via time-nuts > wrote: > > Bob, you wrote: > >> Mike. One concern I have with active components as mixer is noise. >> For an SA I designed only a passive DB diode mixer had low enough >> output noise. Would a PF detector as being an active component, >> not create more noise as output? Erik > >> Yes, you are correct. The only thing with a low enough noise floor >> for good phase noise measurements (via the quadrature technique) >> is some sort of mixer. Normal digital phase detectors have way to >> high a noise floor. > >> Bob > > You are talking about old technology. Old tecnology PFD's were built with > discrete circuits and probably suffered from crosstalk, deadband, ground > bounce, VCC noise, and noisy input oscillator signals. > > Modern PFD's have very low noise. For example, the Hittite HMC984LP4E > digital phase-frequency detector has -231 dBc/Hz of noise and goes up to > 350MHz: > https://www.analog.com/media/en/technical-documentation/data-sheets/hmc984.pdf Hi The noise floor of the double balanced mixer (used as a phase detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I’ve used the parts you are talking about. Their floor is *way* higher. Bob > > Too bad the price jumped enormously when Analog bought Hittite. > > The MC100EP140 Phase-Frequency Detector has 200 femtoseconds of jitter and > goes up to 2GHz. That is not going to match the HMC984LP4E but will be > adequate in many applications: > https://www.onsemi.com/pdf/datasheet/mc100ep140-d.pdf > > Modern synthesizer IC's have PFD's as the frequency detector and offer very > low noise. > > You also forget that double-balanced mixers are also very noisy. For > example, most receivers need a good low noise preamp in front of the mixer > to get an acceptable noise figure. I am told that part of the reason for > the high DBM noise is multiple harmonics are generated by the internal > signals, which combine as part of the output signal. > > Mike > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Indeed you can switch the gain of the amp. You still need to provide a low gain output to feed the EFC input on your reference. The chain to feed the sound card will be crazy high gain for the typical TCXO or OCXO. Don’t even think of running that sort of gain into a VCO …. Bob > On Jul 8, 2022, at 9:16 AM, Erik Kaashoek wrote: > > Bob, > Clear, you have a lot more experience and knowledge. For me this is typical a > case of "If you don't know about something it must be simple" > So best would be to make it possible in the simple PNA to switch off the > opamp gain, without changing the impedance the mixer sees, so the offset > tuned signal can be used to calibrate the slope. > I found this picture very helpful to understand the relation between phase > modulation depth and the strength of the side bands > http://athome.kaashoek.com/time-nuts/PM_Sidebands.JPG > It shows that below 0.2 radian peak phase modulation you can simplify to > narrowband FM as only the 1st sideband has relevant power (certainly for the > accuracy I am after) > The whole presentation including the calculation can be found here: > http://athome.kaashoek.com/time-nuts/Measuring_phase_modulation.pdf > Written by Bob Nelson from Keysight. > Very helpful presentation for people (like me) that are new to all this. > Erik. > > On 8-7-2022 18:58, Bob kb8tq wrote: >> Hi >> >> Like it or not, the mixer is a non-linear load. It also has a frequency >> dependence. Even with “saturation” levels, the slope can and does >> change. That’s the short list, as you dive into it, things get even more >> complex in terms of “might be” sort of issues. >> >> How can you be in saturation and have the slope change ( it does sound >> unreasonable) ? The fundamental is not changing much (so you are >> in saturation). The harmonics of the fundamental are changing. Since >> the output is actually a triangle wave with rounded “corners” there are >> indeed harmonics very much present. >> >> The flat parts of the triangle wave are a “good thing” in this case. It >> makes the device linear over a bit wider range than a sine wave would >> provide. This gets you out of all sorts of nutty analysis concerning the >> noise being “to much” to measure with the device. It also relaxes the >> needed accuracy of the DC lock part of things. ( = slope of a sine wave >> changes quickly ….). >> >> You never really get away from the “to much noise” question. The >> common definition of phase noise is that it’s more than 60 db below >> carrier. That is really just the commonly used limit for “you may need >> to think about FM sidebands”. Yes, that’s another rabbit hole to wander >> down …. >> >> Bob >> >>> On Jul 8, 2022, at 8:32 AM, Erik Kaashoek wrote: >>> >>> Bob >>> This confuses me. The calibration of the system changes ( or can change ) each and every time you swap out signal sources. The levels are not going to be consistent setup to setup. Thus you calibrate each and every time you change out either device. >>> Assuming each source is saturating the mixer sufficiently (to be confirmed >>> by measuring the output level of the source into 50 ohm) I do not >>> understand how changing a source can change the calibration. Can you >>> explain what is happening? >>> Please keep in mind I'm not after 0.1dBc/Hz accuracy, +/- 5dBc/Hz would >>> already be great. >>> Erik. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Bob, Clear, you have a lot more experience and knowledge. For me this is typical a case of "If you don't know about something it must be simple" So best would be to make it possible in the simple PNA to switch off the opamp gain, without changing the impedance the mixer sees, so the offset tuned signal can be used to calibrate the slope. I found this picture very helpful to understand the relation between phase modulation depth and the strength of the side bands http://athome.kaashoek.com/time-nuts/PM_Sidebands.JPG It shows that below 0.2 radian peak phase modulation you can simplify to narrowband FM as only the 1st sideband has relevant power (certainly for the accuracy I am after) The whole presentation including the calculation can be found here: http://athome.kaashoek.com/time-nuts/Measuring_phase_modulation.pdf Written by Bob Nelson from Keysight. Very helpful presentation for people (like me) that are new to all this. Erik. On 8-7-2022 18:58, Bob kb8tq wrote: Hi Like it or not, the mixer is a non-linear load. It also has a frequency dependence. Even with “saturation” levels, the slope can and does change. That’s the short list, as you dive into it, things get even more complex in terms of “might be” sort of issues. How can you be in saturation and have the slope change ( it does sound unreasonable) ? The fundamental is not changing much (so you are in saturation). The harmonics of the fundamental are changing. Since the output is actually a triangle wave with rounded “corners” there are indeed harmonics very much present. The flat parts of the triangle wave are a “good thing” in this case. It makes the device linear over a bit wider range than a sine wave would provide. This gets you out of all sorts of nutty analysis concerning the noise being “to much” to measure with the device. It also relaxes the needed accuracy of the DC lock part of things. ( = slope of a sine wave changes quickly ….). You never really get away from the “to much noise” question. The common definition of phase noise is that it’s more than 60 db below carrier. That is really just the commonly used limit for “you may need to think about FM sidebands”. Yes, that’s another rabbit hole to wander down …. Bob On Jul 8, 2022, at 8:32 AM, Erik Kaashoek wrote: Bob This confuses me. The calibration of the system changes ( or can change ) each and every time you swap out signal sources. The levels are not going to be consistent setup to setup. Thus you calibrate each and every time you change out either device. Assuming each source is saturating the mixer sufficiently (to be confirmed by measuring the output level of the source into 50 ohm) I do not understand how changing a source can change the calibration. Can you explain what is happening? Please keep in mind I'm not after 0.1dBc/Hz accuracy, +/- 5dBc/Hz would already be great. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Like it or not, the mixer is a non-linear load. It also has a frequency dependence. Even with “saturation” levels, the slope can and does change. That’s the short list, as you dive into it, things get even more complex in terms of “might be” sort of issues. How can you be in saturation and have the slope change ( it does sound unreasonable) ? The fundamental is not changing much (so you are in saturation). The harmonics of the fundamental are changing. Since the output is actually a triangle wave with rounded “corners” there are indeed harmonics very much present. The flat parts of the triangle wave are a “good thing” in this case. It makes the device linear over a bit wider range than a sine wave would provide. This gets you out of all sorts of nutty analysis concerning the noise being “to much” to measure with the device. It also relaxes the needed accuracy of the DC lock part of things. ( = slope of a sine wave changes quickly ….). You never really get away from the “to much noise” question. The common definition of phase noise is that it’s more than 60 db below carrier. That is really just the commonly used limit for “you may need to think about FM sidebands”. Yes, that’s another rabbit hole to wander down …. Bob > On Jul 8, 2022, at 8:32 AM, Erik Kaashoek wrote: > > Bob > This confuses me. >> The calibration of the system changes ( or can change ) each and every time >> you swap >> out signal sources. The levels are not going to be consistent setup to >> setup. Thus you >> calibrate each and every time you change out either device. > Assuming each source is saturating the mixer sufficiently (to be confirmed by > measuring the output level of the source into 50 ohm) I do not understand how > changing a source can change the calibration. Can you explain what is > happening? > Please keep in mind I'm not after 0.1dBc/Hz accuracy, +/- 5dBc/Hz would > already be great. > Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Bob This confuses me. The calibration of the system changes ( or can change ) each and every time you swap out signal sources. The levels are not going to be consistent setup to setup. Thus you calibrate each and every time you change out either device. Assuming each source is saturating the mixer sufficiently (to be confirmed by measuring the output level of the source into 50 ohm) I do not understand how changing a source can change the calibration. Can you explain what is happening? Please keep in mind I'm not after 0.1dBc/Hz accuracy, +/- 5dBc/Hz would already be great. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi (see below) > On Jul 7, 2022, at 10:10 PM, Erik Kaashoek wrote: > > Bob, > You may have explained this before but I still do not understand. > Does the phase modulation slope at the detector depend on the depth of the > phase modulation? I think not. The “phase modulation” you are looking at when observing the slope with a beat note is a full 2-pi radians of modulation for every cycle of the beat note. Since that’s guaranteed with no further effort, it makes a nice standard to use. There *is* no modulation being done to either signal in this case. > With 57 degrees one should get an output voltage that is to be regarded as > the 0dBc level but this can not be measured due to the high gain in the audio > path. Which is why you want a two op amp approach. This also gets you a nice path to use for the DC feed for lock. > When you reduce the modulation depth with a factor 10 the measured output > voltage should decrease with 20dB. Except you didn’t start out modulating either signal. You simply unlocked them and got a result that happens to provide 2 pi radians of signal at the output of the mixer. > Modern digital signal generators are supposed to provide phase modulation > with at least 0.01 degree accuracy. > So it could be possible to measure the phase detector slope with 0.57 phase > modulation depth by measuring what should be -40dBc > Or, if the gain is very high, less accurate with 0.06 phase modulation. > Or am I making a mistake in my reasoning? The calibration of the system changes ( or can change ) each and every time you swap out signal sources. The levels are not going to be consistent setup to setup. Thus you calibrate each and every time you change out either device. Since signal generators are not likely to get you to the same sort of noise levels as a very good stand alone source, you very much do not typically want a signal generator involved in a real measurement. Yes, there are always exceptions to any blanket statement … Bob > Erik. > > > On 8-7-2022 3:57, Bob kb8tq via time-nuts wrote: >> Hi >> >> One consideration: >> >> If you do signal injection for calibration, you have the amplitude >> uncertainties on >> both the “carrier” and injected signals. The slope at zero on the beat note >> is likely >> to be *much* more accurate ( even if gain measurement at audio gets thrown >> in …) >> >> Bob >> > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Not something I want to implement on short notice but maybe for the future. The biggest limitation in this DIY PNA is the phase noise of the reference OCXO and the noise of the opamp amplifying the output of the mixer. So I was wondering if it would make sense to do the following 1: Split the output of the DUT into two completely separate PNA's 2: Feed the output of the two PNA's into the PC left/right audio inputs where the noise of both ADC's gets added. 3: Do a cross correlation of the two inputs. This should (as far as I have understood the feedback) eliminate both the phase noise of the two independent OCXO's used as reference and eliminate the noise of the opamps in the two PNA's and the ADC's, given enough time to do the correlation. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi, Well, both amplitudes can be measured. The method I refer to is one of several out of NIST, so it's not one of my own invention. See their AM and PM Calibration material. Using multiple methods you can evaluate how well the method functions. The side-tone method generates known PM with the uncertainty in relative amplitude. It can be easier to validate than a phase modulator approach, as it needs calibration. Cheers, Magnus On 2022-07-08 03:57, Bob kb8tq wrote: Hi One consideration: If you do signal injection for calibration, you have the amplitude uncertainties on both the “carrier” and injected signals. The slope at zero on the beat note is likely to be *much* more accurate ( even if gain measurement at audio gets thrown in …) Bob On Jul 7, 2022, at 5:19 PM, Magnus Danielson via time-nuts wrote: Hi, A well established method is to use a separate offset RF generator that you can steer frequency to form suitable offset and amplitude to form known level. You can now inject this ontop of a signal to measure. Consider that you steer your offset frequency to be +1 kHz of the carrier you measure, and you set the amplitude to be -57 dB from the carrier. This now becomes equivalent to having a -60 dBc phase modulation at 1 kHz. The RF generator does not have to be ultra-clean in phase noise just reasonably steerable in frequency and amplitude. Cheers, Magnus On 2022-07-07 12:47, Erik Kaashoek via time-nuts wrote: Bob, others. It has been explained that for the best phase noise level calibration on should use a signal with one radian phase modulation and measure the output voltage. The problem with this approach is the unknown gain of the path into the PC. And due to the gain one can not modulate with one radian as this saturates the whole path. An alternative method for phase noise level calibration could be to create an oscillator so bad its phase noise can be measured using a spectrum analyzer. To make such a bad oscillator a 10MHz signal was phase modulated with noise. The phase noise became visible on the spectrum analyzer just above 20 degrees of modulation. The phase noise level saturated between 55 and 60 degrees which is consistent with one radian (57 degrees). The spectrum analyzer could measure the phase noise at a flat -80dbc/Hz ( yes Bob, I better use the right dimensions) The simple phase noise analyzer also measured the phase noise at -80dBc providing evidence the level calibration was done correctly. I also tried to increase the DUT drive into the mixer further above saturation so see if this made any change in the measured level but once above 0dBm I did not observe any change up to +10dBm drive. Any higher levels felt too dangerous. There is still a lot of work to be done to further increase accuracy. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Bob, You may have explained this before but I still do not understand. Does the phase modulation slope at the detector depend on the depth of the phase modulation? I think not. With 57 degrees one should get an output voltage that is to be regarded as the 0dBc level but this can not be measured due to the high gain in the audio path. When you reduce the modulation depth with a factor 10 the measured output voltage should decrease with 20dB. Modern digital signal generators are supposed to provide phase modulation with at least 0.01 degree accuracy. So it could be possible to measure the phase detector slope with 0.57 phase modulation depth by measuring what should be -40dBc Or, if the gain is very high, less accurate with 0.06 phase modulation. Or am I making a mistake in my reasoning? Erik. On 8-7-2022 3:57, Bob kb8tq via time-nuts wrote: Hi One consideration: If you do signal injection for calibration, you have the amplitude uncertainties on both the “carrier” and injected signals. The slope at zero on the beat note is likely to be *much* more accurate ( even if gain measurement at audio gets thrown in …) Bob ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi One consideration: If you do signal injection for calibration, you have the amplitude uncertainties on both the “carrier” and injected signals. The slope at zero on the beat note is likely to be *much* more accurate ( even if gain measurement at audio gets thrown in …) Bob > On Jul 7, 2022, at 5:19 PM, Magnus Danielson via time-nuts > wrote: > > Hi, > > A well established method is to use a separate offset RF generator that you > can steer frequency to form suitable offset and amplitude to form known > level. You can now inject this ontop of a signal to measure. Consider that > you steer your offset frequency to be +1 kHz of the carrier you measure, and > you set the amplitude to be -57 dB from the carrier. This now becomes > equivalent to having a -60 dBc phase modulation at 1 kHz. > > The RF generator does not have to be ultra-clean in phase noise just > reasonably steerable in frequency and amplitude. > > Cheers, > Magnus > > On 2022-07-07 12:47, Erik Kaashoek via time-nuts wrote: >> Bob, others. >> It has been explained that for the best phase noise level calibration on >> should use a signal with one radian phase modulation and measure the output >> voltage. >> The problem with this approach is the unknown gain of the path into the PC. >> And due to the gain one can not modulate with one radian as this saturates >> the whole path. >> An alternative method for phase noise level calibration could be to create >> an oscillator so bad its phase noise can be measured using a spectrum >> analyzer. To make such a bad oscillator a 10MHz signal was phase modulated >> with noise. The phase noise became visible on the spectrum analyzer just >> above 20 degrees of modulation. The phase noise level saturated between 55 >> and 60 degrees which is consistent with one radian (57 degrees). The >> spectrum analyzer could measure the phase noise at a flat -80dbc/Hz ( yes >> Bob, I better use the right dimensions) >> The simple phase noise analyzer also measured the phase noise at -80dBc >> providing evidence the level calibration was done correctly. >> I also tried to increase the DUT drive into the mixer further above >> saturation so see if this made any change in the measured level but once >> above 0dBm I did not observe any change up to +10dBm drive. Any higher >> levels felt too dangerous. >> There is still a lot of work to be done to further increase accuracy. >> Erik. >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-le...@lists.febo.com > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi, A well established method is to use a separate offset RF generator that you can steer frequency to form suitable offset and amplitude to form known level. You can now inject this ontop of a signal to measure. Consider that you steer your offset frequency to be +1 kHz of the carrier you measure, and you set the amplitude to be -57 dB from the carrier. This now becomes equivalent to having a -60 dBc phase modulation at 1 kHz. The RF generator does not have to be ultra-clean in phase noise just reasonably steerable in frequency and amplitude. Cheers, Magnus On 2022-07-07 12:47, Erik Kaashoek via time-nuts wrote: Bob, others. It has been explained that for the best phase noise level calibration on should use a signal with one radian phase modulation and measure the output voltage. The problem with this approach is the unknown gain of the path into the PC. And due to the gain one can not modulate with one radian as this saturates the whole path. An alternative method for phase noise level calibration could be to create an oscillator so bad its phase noise can be measured using a spectrum analyzer. To make such a bad oscillator a 10MHz signal was phase modulated with noise. The phase noise became visible on the spectrum analyzer just above 20 degrees of modulation. The phase noise level saturated between 55 and 60 degrees which is consistent with one radian (57 degrees). The spectrum analyzer could measure the phase noise at a flat -80dbc/Hz ( yes Bob, I better use the right dimensions) The simple phase noise analyzer also measured the phase noise at -80dBc providing evidence the level calibration was done correctly. I also tried to increase the DUT drive into the mixer further above saturation so see if this made any change in the measured level but once above 0dBm I did not observe any change up to +10dBm drive. Any higher levels felt too dangerous. There is still a lot of work to be done to further increase accuracy. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi The idea is partly to lock the two devices. The bigger objective is to hold the mixer output at the correct zero volt operating point. Cabling things to a different device and then doing phase correction to keep things at zero would be a major pain. Bob > On Jul 7, 2022, at 5:52 AM, Mike Monett via time-nuts > wrote: > > You wrote: > >> Mike. >> One concern I have with active components as mixer is noise. For an SA I >> designed only a passive DB diode mixer had low enough output noise. Would a >> PF detector as being an active component, not create more noise as output? >> Erik > > Eric, you do not have to give up your double balanced mixer. You can use a > phase/frequency detector to lock the reference to the DUT, and still use > the DBM to do the phase noise analysis. > > Here is a block diagram of the circuit: pna.png > > I don't know if this is going to work, so I will send this email and wait > for it to show up in the lists. If it does, I have a lot more information > for you. > > > > > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On 7/7/22 8:55 AM, Bob kb8tq via time-nuts wrote: Hi Yes, you do need to know the system gain. Since we are talking about gain at audio, measuring the gain directly is not a crazy thing to do. One of the things that makes audio spectrum analyzers a nice tool for this that they eliminate the “variable gain to the sound card” issue. Some sound card setups are a lot easier to work with than others. If you are restricted to the sound input on your motherboard things can get a bit crazy. It is not unusual for folks to dig up a “pro” (whatever that means on a sound card ) card that has better drivers and more access to this and that. Given how fast the PC world changes, the board that was a wonderful thing last time somebody dove in, likely is long out of production by now. The drivers that made it work so well may have been “improved” and it no longer gives you the control it once did. This makes for a bit of trial and error to get it all going. Bob Rather than a sound card, it might be better to pick a small singleboard like a Teensy that has a decent ADC, and make a "sampling engine" with a USB interface. Or, in general, going to a USB interface sound interface might be good. You can get them with a lot of channels (at least 8) and they sample simultaneously, so the uncertainty in USB latency won't bite you. Google for things like the Focusrite Scarlett I've not tried it for this kind of application, but it is likely to have better noise properties than a "inside the PC" card. Typically 24 bit converters and 192kHz sample rates. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Yes, you do need to know the system gain. Since we are talking about gain at audio, measuring the gain directly is not a crazy thing to do. One of the things that makes audio spectrum analyzers a nice tool for this that they eliminate the “variable gain to the sound card” issue. Some sound card setups are a lot easier to work with than others. If you are restricted to the sound input on your motherboard things can get a bit crazy. It is not unusual for folks to dig up a “pro” (whatever that means on a sound card ) card that has better drivers and more access to this and that. Given how fast the PC world changes, the board that was a wonderful thing last time somebody dove in, likely is long out of production by now. The drivers that made it work so well may have been “improved” and it no longer gives you the control it once did. This makes for a bit of trial and error to get it all going. Bob > On Jul 7, 2022, at 2:47 AM, Erik Kaashoek wrote: > > Bob, others. > It has been explained that for the best phase noise level calibration on > should use a signal with one radian phase modulation and measure the output > voltage. > The problem with this approach is the unknown gain of the path into the PC. > And due to the gain one can not modulate with one radian as this saturates > the whole path. > An alternative method for phase noise level calibration could be to create an > oscillator so bad its phase noise can be measured using a spectrum analyzer. > To make such a bad oscillator a 10MHz signal was phase modulated with noise. > The phase noise became visible on the spectrum analyzer just above 20 degrees > of modulation. The phase noise level saturated between 55 and 60 degrees > which is consistent with one radian (57 degrees). The spectrum analyzer could > measure the phase noise at a flat -80dbc/Hz ( yes Bob, I better use the right > dimensions) > The simple phase noise analyzer also measured the phase noise at -80dBc > providing evidence the level calibration was done correctly. > I also tried to increase the DUT drive into the mixer further above > saturation so see if this made any change in the measured level but once > above 0dBm I did not observe any change up to +10dBm drive. Any higher levels > felt too dangerous. > There is still a lot of work to be done to further increase accuracy. > Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Bob, others. It has been explained that for the best phase noise level calibration on should use a signal with one radian phase modulation and measure the output voltage. The problem with this approach is the unknown gain of the path into the PC. And due to the gain one can not modulate with one radian as this saturates the whole path. An alternative method for phase noise level calibration could be to create an oscillator so bad its phase noise can be measured using a spectrum analyzer. To make such a bad oscillator a 10MHz signal was phase modulated with noise. The phase noise became visible on the spectrum analyzer just above 20 degrees of modulation. The phase noise level saturated between 55 and 60 degrees which is consistent with one radian (57 degrees). The spectrum analyzer could measure the phase noise at a flat -80dbc/Hz ( yes Bob, I better use the right dimensions) The simple phase noise analyzer also measured the phase noise at -80dBc providing evidence the level calibration was done correctly. I also tried to increase the DUT drive into the mixer further above saturation so see if this made any change in the measured level but once above 0dBm I did not observe any change up to +10dBm drive. Any higher levels felt too dangerous. There is still a lot of work to be done to further increase accuracy. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On Tue, July 5, 2022 5:27 am, Mike Monett via time-nuts wrote: > The phase-frequency detector has zero ripple at lock. The PF detector also locks at 0 degrees offset. How do you get the demodulated phase noise out of that? The point of the a diode mixer is that it locks at quadrature, and the output is 0V DC at that point, but any instantaneous phase offset (i.e. phase noise from reference and DUT) shows up as AC signal at the output. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Mike, He was using an analog mixer, but your comment about XOR mixer does not apply to analog mixers. Your oversimplification that analog mixer and XOR gates being the same thing does not apply here, and thus the assigned missbehavior does not carry over to the analog mixer case. Cheers, Magnus On 2022-07-05 12:27, Mike Monett via time-nuts wrote: Eric, Another problem I forgot to mention, the exclusive-or phase detector has a severe output ripple. This will cause frequency shift in the oscillator frequency which will show up in the measurements. The phase-frequency detector has zero ripple at lock. There is a small transient at the sample time, but this is easily filtered with a simple low pass filter. With zero ripple in the output, the PFD will not cause any shift in the oscillator frequency. This will not cause any error in the measurements. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi, On 2022-07-05 12:13, Mike Monett via time-nuts wrote: You stated: Mike, The phase detector is an ADE-1 mixer, the IF output of the mixer goes into a loop filter that has a corner frequency of about 0.2Hz to enable Phase noise measurements down to 1Hz offset That is your problem. A double balanced mixer is an exclusive-or phase detector. The lock range is determined by the loop bandwidth, as you have found. The phase-frequency detector is completely different. It will lock to any signal in the lock range, independent of loop bandwidth. You can have a bandwidth of 0.001 Hz, and it will still lock. Think of what this could do for your phase measurements. Actually, there is two schools here. There is the school of stateless phase-detectors (such as mixers) and the school of stateful phase-detectors (such as three-state mixers). Now, in the school of stateless phase-detectors, mixers, XOR-gates, samplers etc. the capture range becomes dependent on the loop gain. For passive lag filters, you will need a significant static phase-difference on the input to provide the state of the EFC to compensate on the frequency. It's very simply that the DC volt difference coming out of the detectors, through the DC gain of the filter is then what becomes the EFC. In active lag filters, you add additional gain, and this requires lower phase detector voltage to support the same EFC error. Both these actually have an implicit state in the phase detector to compensate the lack of state elsewhere. It is just not that the phase detector holds explicit state. In PI filters, the state of the frequency error is moved from the phase detector to the filter. The integrator has close to infinity in DC gain (naturally limited in practice, but for many purposes we can assume it being infinite) such that it drives the DC phase offset out of the phase detector to zero and builds up the needed EFC state in the integrator capacitor. This have the benefit that capture range is in theory unlimited, but even if the actual range is in practice limited, it is so wide that we can treat it as infinite for most cases. The PI loop those do not need any form of aiding to lock up. However, aiding it can increase lock-up time. You could either pre-trim the EFC or you could increase the PLL bandwidth to achieve quick lockup. The later is actually very simple and has very huge impact. The thing people do wrong with PI filters is to scale the bandwidth on the output side of the integrator. This is wrong, as one then needs to scale the output to maintain the acquired state to match the needed EFC. The right way to do it is to scale it on the input side. That way the scaling to EFC is maintained and no state-scaling is needed. As one scales the bandwidth through I one needs to scale P accordingly to maintain good damping properties. Fairly simple PI-loop setups allow for good lockup and stability properties. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi > On Jul 5, 2022, at 9:00 AM, Erik Kaashoek via time-nuts > wrote: > > Mike. > One concern I have with active components as mixer is noise. For an SA I > designed only a passive DB diode mixer had low enough output noise. Would a > PF detector as being an active component, not create more noise as output? > Erik Yes, you are correct. The only thing with a low enough noise floor for good phase noise measurements (via the quadrature technique) is some sort of mixer. Normal digital phase detectors have way to high a noise floor. Bob > > On Tue, Jul 5, 2022, 18:20 Mike Monett via time-nuts < > time-nuts@lists.febo.com> wrote: > >> You stated: >> >> Mike, >> The phase detector is an ADE-1 mixer, the IF output of the mixer goes >> into a loop filter that has a corner frequency of about 0.2Hz to enable >> Phase noise measurements down to 1Hz offset >> >> That is your problem. A double balanced mixer is an exclusive-or phase >> detector. The lock range is determined by the loop bandwidth, as you have >> found. >> >> The phase-frequency detector is completely different. It will lock to any >> signal in the lock range, independent of loop bandwidth. You can have a >> bandwidth of 0.001 Hz, and it will still lock. Think of what this could do >> for your phase measurements. >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-le...@lists.febo.com >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Mike. One concern I have with active components as mixer is noise. For an SA I designed only a passive DB diode mixer had low enough output noise. Would a PF detector as being an active component, not create more noise as output? Erik On Tue, Jul 5, 2022, 18:20 Mike Monett via time-nuts < time-nuts@lists.febo.com> wrote: > You stated: > > Mike, > The phase detector is an ADE-1 mixer, the IF output of the mixer goes > into a loop filter that has a corner frequency of about 0.2Hz to enable > Phase noise measurements down to 1Hz offset > > That is your problem. A double balanced mixer is an exclusive-or phase > detector. The lock range is determined by the loop bandwidth, as you have > found. > > The phase-frequency detector is completely different. It will lock to any > signal in the lock range, independent of loop bandwidth. You can have a > bandwidth of 0.001 Hz, and it will still lock. Think of what this could do > for your phase measurements. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Mike, The phase detector is an ADE-1 mixer, the IF output of the mixer goes into a loop filter that has a corner frequency of about 0.2Hz to enable Phase noise measurements down to 1Hz offset Thanks for the excellent references, a lot to study. Yes, one can do very advanced cross correlation things but I am doing this for a hobby and just needed something to check if the phase noise of some oscillators was good enough and could be build in a couple of hours using point to point wiring and a perforated board so I tried the least complex Phase Noise analyzer I could think of. Erik. On 4-7-2022 15:49, Mike Monett via time-nuts wrote: Thank you for your detailed description. I wonder what kind of phase detector you are using. I have never heard of one that required 0.01Hz phase offset to lock. Even the simplest Phase-Frequency Detector (PFD) would do orders of magnitude better. Here are some papers: 1. Motorola App. Note AN-535 Phase-Locked Loop Design Fundamentals - the original mother lode on phase-frequency detectors - does not discuss deadband - I corrected this problem in my patent US3810234A https://www.nxp.com/files-static/rf_if/doc/app_note/AN535.pdf 2. HCT4046A phase-locked loop (PLL) Appendix B on Page 42: Loop Parameters and Equations Appendix C on Page 45: Basic Program for VCO Frequency Calculations https://www.ti.com/lit/an/scha003b/scha003b.pdf 3. Motorola MCK12140 Phase-Frequency Detector description https://pdf.dzsc.com/MCH/MCH12140.pdf 4. I prefer the filter network shown at the bottom of Table 2 on Page 4: Integrator Lead/lag network https://www.minicircuits.com/app/VCO15-10.pdf 5. You mentioned the difficulty in getting a low enough noise floor to measure the noise floor of the DOCXO. Rubiola has a nice paper on cross-correlation techniques that can easily add 20 dB to your measurement range: https://arxiv.org/pdf/1003.0113.pdf He shows some circuits in Figure 14 on Page 25: Basics schemes for the measurement of phase noise. Hope this helps. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
