[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] Isolation amp transistors
Thanks Gerhard, for putting up the schematic. After a quick look, I'd recommend trying the following changes. Of course, I don't know the fine details, so this is just from a general circuit perspective - could be all wrong versus the actual situation. 1. Delete the Q7 circuitry including R10 and R11, and take +2.7 V bias from D2, bypassed by a good cap. Around 220 to 1k ohm (depending on Q2's gain and final emitter current needed) from there to the B2 node may be about right. This puts Q2's emitter around 2 V, and the R8, R1 and C9 combo can set the DC bias and AC gain somewhat separately. BTW, if Q7 and its circuitry are as shown, it appears that the DC base bias loop provides positive feedback rather than negative. Unless I'm missing something, I don't think this is what you want. It may be moot anyway, if a simpler scheme is used. 2. Change the base resistors R3, R4, and R16 to something around 2.7 to 10 ohms range, and optionally delete C3. 3. Consider deleting R14 or raising its value, and just let L1 terminate the DC. This can reduce the DC bias needed, or get you up to 3 dB more gain. You can make a matching network if needed, depending on the output cable driving situation. 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 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: Isolation amp transistors
Hi > On Jul 7, 2022, at 12:09 AM, Gerhard Hoffmann via time-nuts > wrote: > > Am 2022-07-07 7:22, schrieb Bob kb8tq via time-nuts: >> Hi >>> On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts >>> wrote: >>> The 2N5179 has high base spreading resistance (decreases isolation). >> As does sticking a resistor (even a small one) in series with the base >> …. Yes, inductance is even worse. > > and at frequencies where beads work, they also generate thermal noise, > like any other dissipative thingie. See the sim of a random ferrite bead > from the LTspice library. V1 is only there as a compiler pleaser to > enable the proper syntax. It really has no influence. A cascode buffer is a very common thing in an oscillator. Over the decades folks have made a *lot* of them. Having them turn into oscillators at UHF / microwave frequencies is not at all unusual. Having the loose isolation for various reasons ( somebody used the wrong bypass cap maybe …) is also not at all unusual. Coming up with a model for a spice analysis that will always catch these things is non-trivial. A transistor intended to be used to < 50 MHz rarely has a model that includes everything that’s relevant at 1.8 GHz. > >> For “best isolation” in a cascode you very much want the base of >> the common base stage nailed to ground. Typically “lower” Ft transistors >> with a decent base structure are the best choice for the common base stage. >> Both stages benefit from low 1/F noise > in the audio range if this is for >> a phase noise test set. This is why people use what would normally be >> considered “audio” transistors …. > > Cascodes do not add much noise when they have a decent beta. Zin at the > Emitter is a few Ohms and Zout of the driving stage is maybe KOhm. That > makes the driving stage DICTATE the collector current. Also, 1/f noise > is not THAT bad since the load resistance is near 0 in the 1/f region. > Thus, at least no gain at 1/f frequencies. In a linear amplifier, it > would not get mixed up anyway. Makes me like the Driscoll oscillator. > > I could not find a transformer (Macom, Pulse Eng.) that provided an > acceptable S22. In this case, the amplifier is driving into a double balanced mixer that has a *very* similar transformer. Whatever you are seeing with the part you buy off the shelf is already there in the next stage. If you are trying for S22 from DC to light then yes, transformers have issues. They also have issues if your “acceptable” number something past 40 db. Mixers (used as phase detectors) need to see termination at fairly specific frequencies. This helps quite a bit. Bob > The resistive 50 Ohm in par with (4.7u + bead) worked best. > At least the momentary collector voltage can exceed the supply. > Appreciated in the light of 12V operation. But without the transformer, > one pays with a lot of bias current, therefore sot-89. > The circuit is not exact, it was in the middle of what/if experiments. > Thus, some funny values. > The cascode is mostly harmless (TM). What hurts, that is Q2 stability. > > @Florian: 150 mA, not too much Vce required, 1-1.5 GHz ft. > > 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: Isolation amp transistors
Hi The tube cascode has it’s own issues. Setting up a tube circuit for the sort of isolation we are talking about here is very difficult. Bob > On Jul 6, 2022, at 9:46 PM, glenlist via time-nuts > wrote: > > how about grounded grid ? > > Bob can you get better isolation with a vaccuum tube cascode than a solid > state cascode ? > > -glen > > On 07/07/2022 15:22, Bob kb8tq via time-nuts wrote: >> Hi >> >>> On Jul 6, 2022, at 1:53 PM, Richard Karlquist via >>> time-nuts wrote: >>> >>> The 2N5179 has high base spreading resistance (decreases isolation). >> As does sticking a resistor (even a small one) in series with the base …. >> Yes, inductance >> is even worse. >> >> For “best isolation” in a cascode you very much want the base of the common >> base >> stage nailed to ground. Typically “lower” Ft transistors with a decent base >> structure >> are the best choice for the common base stage. Both stages benefit from low >> 1/F noise >> in the audio range if this is for a phase noise test se >> > ___ > 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: Isolation amp transistors
Hi, On 2022-07-07 07:22, Bob kb8tq via time-nuts wrote: Hi On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts wrote: The 2N5179 has high base spreading resistance (decreases isolation). As does sticking a resistor (even a small one) in series with the base …. Yes, inductance is even worse. For “best isolation” in a cascode you very much want the base of the common base stage nailed to ground. Typically “lower” Ft transistors with a decent base structure are the best choice for the common base stage. Both stages benefit from low 1/F noise in the audio range if this is for a phase noise test set. This is why people use what would normally be considered “audio” transistors …. The NIST isolation amplifiers does exactly this. Looking for Fred Walls in the NIST T&F archive usually makes me find the article quick. 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)
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] Isolation amp transistors
All good comments about the isolation issues, but remember we're talking about a desired 200 MHz amplifier system here, not a 10 MHz one, so RF transistors are appropriate. This is a little different from the original DIY PN test discussion, which is why I replied in a different thread title. 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: Isolation amp transistors
I assume with grounded grid, that you mean a vacuum tube with heated cathode. The cathode will have a noise P = kTB, where T is the red hot cathode, and B is your bandwidth. k is as usual Boltzmann constant. That said, if you could cancel the capacitances inside the tube, then you could get a decent isolation, but it's much easier with semiconductors. BR. Thomas. tor. 7. jul. 2022 kl. 07:57 skrev glenlist via time-nuts < time-nuts@lists.febo.com>: > how about grounded grid ? > > Bob can you get better isolation with a vaccuum tube cascode than a > solid state cascode ? > > -glen > > On 07/07/2022 15:22, Bob kb8tq via time-nuts wrote: > > Hi > > > >> On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts< > time-nuts@lists.febo.com> wrote: > >> > >> The 2N5179 has high base spreading resistance (decreases isolation). > > As does sticking a resistor (even a small one) in series with the base > …. Yes, inductance > > is even worse. > > > > For “best isolation” in a cascode you very much want the base of the > common base > > stage nailed to ground. Typically “lower” Ft transistors with a decent > base structure > > are the best choice for the common base stage. Both stages benefit from > low 1/F noise > > in the audio range if this is for a phase noise test se > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com -- With Best regards, Thomas S. Knutsen. Please avoid sending me Word or PowerPoint attachments. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
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
