[time-nuts] 10 MHz - 16 MHz clock multiplier
If you divide by 5 the phase noise sideband amplitude (voltage) will be divided by 5. That is a reduction of 14db for all phase noise sideband frequencies . Then when you multiply that by 8 you will add the phase noise sidebands will be multiplied by 8 or 3x6db or 18 db. So the end result will be a factor (if I did my math right in my head, which is getting more difficult these days) 4db increase. The crystal filter will reduce the phase noise sidebands to some degree. That is to say if you had a perfect filter you could pass only the carrier with out the sidebands and thus no phase noise. However, if your filter has 1kHz bandwidth you would only eliminate the sidebands beyond 500 Hz on either side of the carrier. So the answer is sort of yes. When I read the email about multiply by 16 and divide by 10 it occurred to me that it would be easier to divide and then multiply and then I began to brain storm, which is hard to do when you stay up too late. If you chose to use a crystal ladder you need to use 16 MHz parallel resonant crystals since the series resonance will be slightly less than 16 MHz. These crystals are rather cheap. If you want to use a simple high Q (narrow bandwidth) phasing type filter you need to use a crystal with a 16MHz series resonance and use a termination resistance greater than the crystals series resistance. You can adjust the crystal filters bandwidth by changing the termination resistance. This type of filter was mostly used in early vacuum tube receivers. They usually shot for a minimum bandwidth of 500 Hz or so. you need to adjust the phasing capacitor so it equals the crystals parallel capacitance to minimize feed thru. Experimenting with these filters is a lot of fun. I have made lots of crystal filters. I even have a digital crystal impedance meter so I can compare crystals. If reducing phase sidebands in not a goal all you need is a filter that will eliminate all the other 2 MHz harmonics. 73 Bill wa4lav At 05:37 PM 1/4/2013 +, time-nuts-requ...@febo.com wrote: THis is exactly what they are talking about the 74HC390 can do over 50MHz and costs abut 30 cents. You don't need ECL or anything so exotic the 30 cent part will work. Set it for divide by 5. I guess this is imperfect enough that there is some fourth harmonic content in the 2MHz square wave, then you select that with a narrow band filter and amplify it to whatever you need. A smart design might try and add fourth harmonics be using a slightly not-symetric 2MHz square wave My question is about the phase noise of the final 16MHz signal. Do crystal filters clean up the signal. It seems that after several 16MHz crystals in series the output should look a lot like an XO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 10 MHz - 16 MHz clock multiplier
At 07:51 PM 1/4/2013 +, you wrote: My question is about the phase noise of the final 16MHz signal. Do crystal filters clean up the signal. It seems that after several 16MHz crystals in series the output should look a lot like an XO. For offsets out to 100 Hz or so, using a crystal filter will cause the signal to have the same flicker noise that an oscillator built with that crystal would have. Thus don't try to use some junky clock crystals to make a crystal filter as described in numerous ham radio articles about receiver IF filters. If you have a residual phase noise measurement system like the Agilent E5505A and a very low flicker noise source, you can actually measure your filter crystals. Of course, the crystal time base in the source has to be better than the crystals you are measuring. You also have to avoid overdriving the crystal. This will require a low noise buffer amplifier to bring the signal back up to a high level. Now after considering all that, crystal clean up filters don't sound like such a great idea unless you have no alternative. Rick Karlquist N6RK Flicker noise (1/f ) noise would be introduced by an amplifier and not by the filter. I am only suggesting ways to multiply the frequency. You could use LC filters or a crystal filter. Using 3 doublers would do the job just as well. Naturally if you are concerned about flicker noise you could simply make the 2 MHz signal higher in amplitude before selecting the 8th harmonic. I was not saying your going to clean up a good crystal oscillator with a crystal filter. I though you were talking about generating 16MHz from 10MHz in a clean way. Using a microcontroller or even most synthesizers techniques would make it even worse. The PTS synthesizers have fairly good phase noise when they use frequency multiplication, division, mixing, comb generation and filtering on the most part to achieve low phase noise. The later models use a DDS at the lower frequency levels but do have greater phase noise close to the carrier. In fact in the SGA unit the reference input goes thru a transistor ( to distort it) and then into a series 10MHz crystal filter so that it can accept either a 5 or 10 MHz input. The crystal also helps filter out any birdies that may be on the reference signal. The filter should be fairly high Q since it has 47 Ohm drive impedance and 100 Ohm load impedance. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 10 MHz - 16 MHz clock multiplier
One way is to divide by 10 and then multiply by 16. Divide by 10 and then follow by 4 tuned frequency doublers. This should introduce little phase noise. Another way to do it is to divide by 10, then pass the output thru a narrow 16 MHz filter and amplify. Sounds difficult but the filter can be one or two 16 MHz crystals followed by a simple amplifier. Look at the reference input circuit for a PTS-160. The output of the divide by 10 needs to be asymmetrical so it produces even harmonics. If you are using a divide divide by 52 such as a 74HC90, divide by 2 first then by 5. Ideally the pulse width should be a half period of 16 MHz for the maximum harmonic content at 16 MHz. You can take the output of the frequency divider and send it to a NAND gate. One input of the gate is directly connected and the other is delayed. You can use an RC with a variable capacitor to ground to get it just right. Just adjust the capacitor to get the maximum output from your filter amplifier. 73 Bill wa4lav At 07:41 PM 1/2/2013 +, you wrote: What's the simplest way to generate 16 MHz from 10 MHz? This will be for clocking a microcontroller at 16 MHz given 10 MHz (Cs/Rb/GPSDO). Low price and low parts count is a goal; jitter is not a concern but absolute long-term phase coherence is a must. The ICS525 (as in TAPR Clock-Block) is a good candidate but I was wondering if there's something cheaper, less functional, and maybe not SSOP. Any suggestions? Thanks, /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 10 MHz - 16 MHz clock multiplier
At 12:58 AM 1/4/2013 +, time-nuts-requ...@febo.com wrote: Where can one get some of these mythical 74HC90 's and 74AC90 's that have been mentioned. None of the usual places have them, ie ebay, digi-key, farnell, or even the Chinese. Also data-sheets are not to be found. Thanks This is what happens when one stays up too late 74HC390. However, any discussion on the technical merits? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Very challenging phase noise measurement, does anyone have an idea??
If you want a low noise mixer use a varicap mixer. A varicap has no ohmic characteristics thus no Johnson noise. Secondly, You can create low noise harmonics using a vaicap multiplier or a nonlinear transmission line using inductors and nonlinear capacitors (varicaps). NIST has been doing this for some time and even has used nonlinear fiber optics to phase lock oscillators to lasers as atomic references. Guys got Nobel Prize for that one. Measuring the phase noise at a high order harmonic has the advantage that the phase is multiplied by the harmonic number thus bring the sidebands up further from the noise floor. Here is a reference, that could be scaled down for your frequency, on phase noise measurements using harmonics produced by a nonlinear transmission line. This example just a few sections in its nonlinear transmission line 73 Bill wa4lav http://ecee.colorado.edu/microwave/docs/publications/2008/Milos-Jason-TMTT-July08.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Best phase detector / mixer for 100MHz?
At 03:56 PM 11/29/2012 +, you wrote: By theory, yes... but we use a sound card with a lot of flicker noise on the lower end, also we have the 10...20Hz low freq. cutoff due the usage of a servo / single 5V power. Also the raising noise below 100Hz (ADC serve noise on the ADC power / input circuit) limits the performance. One way to avoid the problem in the 1/f noise region is to avoid it. Mix down to a few kHz and analyze you signal or if you must mix down to DC then chop it to bring it up to a kHz or so and analyze it using a program such as spectrum lab or in software to internally mix back down to DC using software digital mixer and then analyze. You can use a MOSFET analog switch to chop the signal. When you chop it you will have an carrier with upper and lower sidebands. You can simply take the FFT data and either shift the bins making the carrier (chopping frequency) the Zero or DC bin or even better yet add the upper and lower sidebands so that you get a 3db improvement in S/N. I will be db since the sidebands are identical mirror of each other, ie voltage doubles when they are added increasing the signal by 6db but noise introduced by electronics on upper and lower sidebands are not coherent and only increases by 3db. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 99, Issue 120
There are two ways to measure the carrier frequency using a Spectrum analyzer. 1) have bandwidth sufficient to capture all the sidebands produced by the FM signal. 2) Have your bandwidth set very narrow, 10Hz or so and tune it directly on the carrier frequency. The carrier frequency should stand out at the wide bandwidth and then zoom in on it when using the spectrum analyzer. There are situations with PSK signals where the carrier is always canceled out. As there are certain modulation indexes when a pure tone is being used where the carrier goes to zero. But with music or voice modulation this will not be a problem. I have notices that only one digital TV station here in Lexington KY is right on. Some are hundreds of Hz off. 73 Bill wa4lav At 12:00 PM 10/27/2012 +, you wrote: From: Peter Gottlieb n...@verizon.net I've used the HP 3586 for measuring AM carrier frequencies as well as my Tek 495P (both referenced to Rb) for higher frequencies such as air band. Some carriers are dead nuts on while others are quite far off (at least to my mind) although I've never found one outside of its required tolerance. It seems possible to measure pretty accurately with these instruments, at least on AM or CW signals, but not sure the best way for FM. I've played with the HP 53310A but haven't set it up for precise measurements yet, or really studied what all it is capable of. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] PTS synthesizer options
Does someone have a list of the options that are not listed in the PTS catalog? Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cables dor 10 mHz
Lets see. 10 mHz is .01Hz Do any of you remember when this mHz thing started? It happened about the same time DE9 connectors became DB9 and DA15 connectors became DB15 connectors. Also, during that time the RS232 spec did not specify a connector. Just signals, voltage levels and rise/fall times. But, long ago a pF was mmfd. OK that is milli-milli-femto-deci today oops, no units. And there was kilomegacycles for GHz. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Wow, I have not checked this list for some time. But there is a lot said about zero crossing detectors. Lots and lots of replies, so many that I have not looked at all of them. 1. Do not use CMOS inverters. Even though so much has been published on using these in linear mode by adding a feedback resistor, they can be a nightmare. The fast ones (74HC, 74AC, etc) have so much high frequency gain they are likely to take off into oscillation on their own. 2. The first thing you can do to get a good clean zero crossing is to reduce the noise. This means to pass it thru a narrow band pass filter such as a crystal filter. The narrower this filter is the closer to a pure sinewave it becomes and the less noise you have. 3. In research when we want a precise trigger we use what is called a constant fraction discriminator. This may not be needed if you have a very clean signal and its amplitude does not vary and you are wanting to trigger exactly at zero. But a constant fraction discriminator triggers on a point that is a constant fraction of the amplitude of the signal. They require a delay so that a fraction of the peak of the cycle can be compared with the rising edge of that cycle. This is mostly used with triggering on pulses of varying heights and when subnanosecond timing is required. My suggestion is to clean up your signal as much as possible and reduce noise bandwidth using a bandpass filter and then use a low noise amplifier for the front end of your zero-crossing detector. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Lock-in amplifier as wwvb receiver
Has anyone ever used an Lock-in Amplifier such as a PAR HR-8 or later models as part of a receiving system for WWVB? These are mostly used in detecting weak signals in noise in scientific experiments. Some have used the analog output to phase lock a voltage controlled oscillator to the input signal. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] WWVB phase plots
Yes---it's too bad that the proposed WWVB changes don't increase the number of transitions at all. Could they not do the low-modulation-index DCF77-like signal on top of the BPSK? That is, put some small, fast phase wiggles on top of the slow 180-degree transitions (or 120-degree transitions if NIST can be convinced to change to that)? The problem is that if you superimpose a wider bandwidth modulation over the narrow one you have distributed the available sideband power over the broader bandwidth. You have less power transmitted over the narrow bandwidth than before. This reduces the range of the station for narrow and wide bandwidth users. I changed the batteries in our cheap clock here at home and it took several days for it to finally get a signal strong enough to set the time. The signals are weak for many everyday users since their clocks have relative small antennas and they have lots of local interference from compact florescent bulbs and switching power supplies in computers and TV sets. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OP-Amps for 10MHz distribution...?
Low noise voltage at the cost of noise current which is around 1000 times that of low noise JFETs. The discussion suggest that opamps contribute to the sideband phase noise of the signal. I am interested in the mechanism that adds this phase noise. It would have to be a small shift in either gain (changing Miller capacitance) or an internal capacitance in the opamp. I am new to this group and have some catching up to do. I know of one op-amp that comes close to 1 nV/rtHz at 10 Hz and being capable of useful operation as a 10 MHz distribution amplifier -- the ADA4898 (1.2 nV/rtHz at 10 Hz, 4.3 nV/rtHz at 1 Hz). These are wonderful parts, but the large signal frequency response with a 100 ohm load is less than desired for a 10 MHz distribution amplifier. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] OP-Amps for 10MHz distribution...?
Discrete amplifiers are always less noisy than integrated amplifiers. If you want really low noise design a one with JFETs and Bipolar transistors. I am trying to understand the contribution to phase noise by the opamps. Perhaps the threshold is shifting and amplifier is being driven to saturation? I am new to this group but have had lots of RF experience and weak signal detection experience. 73 Bill wa4lav Date: Tue, 28 Feb 2012 07:34:09 -0500 From: Bob Camp li...@rtty.us Hi Very cool. How much power can you run through the device? Put another way, if you drive it with +13 dbm do all the numbers get 5 db better? I doubt very many of us will be worrying about weather it's below -153 at 10 Hz or not? Bob On Feb 28, 2012, at 5:42 AM, Bruce Griffiths wrote: The attached plot indicates the phase noise performance obtainable with a wideband FET (OPA653) input opamp. With a 10MHz +9dBm input, the phase noise floor is around -163dBc/Hz at 1kHz offset and around -154dBc/Hz at 10Hz offset. A quieter test source would be useful particularly for offsets below 10Hz. Bruce OPA653PN2.gif___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. William L. Fuqua III P.E. Sr. Electrical Engineer CP 177 Chemistry Physics Building Department of Physics and Astronomy University of Kentucky Lexington,KY 40506-0055 Phone: 1-859-257-4155 e-mail: wlfuq...@uky.edu ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 91, Issue 168
At what frequency do you have 1 nv per square root Hz with opamp and what opamp ? The 1/f region is the killer and if it is a low frequency shift in the input effectively changing the threshold then you have to be concerned about the 1/f region. Discrete embedded JFETs have the best 1/f of all such as the IF3601. Go to www.interfet.com 73 Bill wa4lav At 05:11 PM 2/28/2012 -0500, time-nuts-requ...@febo.com wrote: Date: Tue, 28 Feb 2012 11:51:54 -0800 From: gary li...@lazygranch.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] OP-Amps for 10MHz distribution...? Message-ID: 4f4d305a.5030...@lazygranch.com Content-Type: text/plain; charset=ISO-8859-1; format=flowed You need to look at the driving impedance before you declare one technology quieter than another. That is, you have voltage noise and current noise. For low driving impedance, bipolar will be quieter since current noise will not be significant, plus a bipolar will have lower thermal noise. For high impedance, JFET may be a better solution. Opamps are around 1nv/rootHz these days. That isn't all that easy to achieve discretely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] science projects
My experiments with CW laser diodes is that they don't take well to being switched on and off with out a soft start. They will only last a certain number of on off cycles before output begins to drop and they quit working. Perhaps something has changed in the last few years. I need to do some experiments with these myself. Maybe they have improved. Alignment of the mirror is not easy either. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] PTS synthesizers
I am new to the list and would like to know if anyone has a list of the suffixes (options) for PTS synthesizers. There seem to be a number of them that are not in their catalog. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
