Re: [time-nuts] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Tom Van Baak said the following on 09/24/2007 08:57 PM: I would think this is especially true for non-local frequencies, such as one received over the air. I'll leave it to you FMT guys to comment on the magnitude of degradation due to transmission and reception noise. Absolutely. Probably the best real-world performance you can get with a skywave signal is on the order of 0.01 Hz. Propagation effects play havoc, but the longer the averaging period, the more short-term effects will average away. One of the reasons for the fairly long transmission periods is to both allow longer averaging, but also provide the opportunity to observe the atmospheric conditions at work. While were at it, in the case mentioned above I'm a curious about their FMT frequency standard -- if it's really accurate to parts in 10^12, as they imply, over 10 minutes. I could believe this if it were an Rb or Cs-based GPSDO. We're using an Austron 1250A OXCO that's been measured as better than 9x10e-13 for averaging times of 1 second out to 1000 seconds; over a broader range, it's better than 3x10e-12 from 0.1 seconds to 40,000 seconds. Now, an important point -- we're not trying to trim the Austron to be precisely on frequency. We're going to let it run at whatever offset it happens to be. That will help make sure that the signal doesn't have lots of zero's at the end, even though the resolution of the synthesizers driving the transmitters is limited to 0.1 Hz. We'll be comparing the Austron against a Z3801a (via my TSC-5120A analyzer) and logging the frequency difference for at least several hours prior to the test until several hours following. The TSC gives 16 digits over 1000 seconds; depending on how much jitter we see, we'll probably throw away the last two or three. Even though the Z3801A may be wandering around a bit, with successive 1000 second measurements we should have confidence in the actual frequency over 1000 second periods to at least parts in the 12s, ultimately limited by the Austron's stability. But since that's known to be in the 13s over the averaging period of interest, we think we're safe in claiming accuracy and stability of parts in the 12s. Tom, if I'm missing something in this analysis, I'm seriously open to education... By the way -- the synthesizers used to drive the transmitter amplifiers will be PTS 250 SX-51 low noise units, so hopefully the transmitted signals will have a better-than-the-average-ham-rig phase noise. The synthesizers will directly feed the driver and final amplifier stages of some vintage Kenwood TS-520 ham transceivers with no other mixing -- it'll purely be the synthesizer and a transistor buffer amp driving two vacuum tube stages to get up to about 75 watts (the rigs can run 100 watts, but we're derating -- and adding fans -- to support the long key-down times). John ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Didier Juges said the following on 09/24/2007 09:40 PM: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. I did some measurements on the frequency counter capability of my 5370B some time ago, and found that the performance wasn't as good as in time interval mode. But it's still not bad -- the internal noise floor was 4x10e-11 for 1 second (using the 1 second gate time). See http://www.febo.com/time-freq/hardware/5370B/index.html John ___ 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] 5370B frequency counter capability
I was looking at the wrong plot when I mentioned the noise floor of my 5370B in frequency counter mode; blame my temporary mono-vision after having had some eye surgery! If you look at http://www.febo.com/time-freq/hardware/5370B/index.html *properly*, you'll see that the actual noise floor is about 3.7x10e-10 in 1 second, roughly an order of magnitude worse than the time interval noise floor. I also noticed that I ran that test five years ago... I should try it again with some of my current equipment. Sorry about that... John ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY While were at it, in the case mentioned above I'm a curious about their FMT frequency standard -- if it's really accurate to parts in 10^12, as they imply, over 10 minutes. I could believe this if it were an Rb or Cs-based GPSDO. We're using an Austron 1250A OXCO that's been measured as better than 9x10e-13 for averaging times of 1 second out to 1000 seconds; over a broader range, it's better than 3x10e-12 from 0.1 seconds to 40,000 seconds. Ah, if they is you, then I have no more worries. Yes, using that free-running 1250A is the perfect solution; much better than using the output of a GPSDO. Now, an important point -- we're not trying to trim the Austron to be precisely on frequency. We're going to let it run at whatever offset it happens to be. That will help make sure that the signal doesn't have lots of zero's at the end, even though the resolution of the synthesizers driving the transmitters is limited to 0.1 Hz. Clever. We'll be comparing the Austron against a Z3801a (via my TSC-5120A analyzer) and logging the frequency difference for at least several hours prior to the test until several hours following. The TSC gives 16 digits over 1000 seconds; depending on how much jitter we see, we'll probably throw away the last two or three. Even though the Z3801A may be wandering around a bit, with successive 1000 second measurements we should have confidence in the actual frequency over 1000 second periods to at least parts in the 12s, ultimately limited by the Austron's stability. But since that's known to be in the 13s over the averaging period of interest, we think we're safe in claiming accuracy and stability of parts in the 12s. Yes, running the measurement for hours before and after is the right thing to do. All sounds good. Make sure not to get near any of the equipment. Free-running oscillators are sensitive to vibration or shock. You've probably heard the story of my best Sulzer oscillator making small phase or jumps which I eventually correlated to when the kids flushed the toilet down the hall. Tom, if I'm missing something in this analysis, I'm seriously open to education... Nothing missing; you nailed it. /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] Osc. Phase Noise Article
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY In the current (September) issue of the Microwave Journal there is a pretty comprehensive article Oscillator Phase Noise: Theory and Prediction. It may viewed on the Microwave Journal Web site at www.mwjournal.com. Page 178 for the print version. Best to all, Had ___ 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] Osc. Phase Noise Article
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY But watch out for the mistakes in some of the equations - e.g. the right hand side of eqn 2 is wrong, but eqn 3 is correct, and eqn 9 is wrong. Don't know if there are any other mistakes, but it's a good article so far - haven't finished reading it yet, I can only take so much trig. in one day. regards Grant Message: 3 Date: Tue, 25 Sep 2007 08:30:49 -0700 From: Had [EMAIL PROTECTED] Subject: [time-nuts] Osc. Phase Noise Article To: time-nuts-febo.com time-nuts@febo.com Message-ID: [EMAIL PROTECTED] Content-Type: text/plain; charset=us-ascii; format=flowed In the current (September) issue of the Microwave Journal there is a pretty comprehensive article Oscillator Phase Noise: Theory and Prediction. It may viewed on the Microwave Journal Web site at www.mwjournal.com. Page 178 for the print version. Best to all, Had ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Make sure not to get near any of the equipment. Free-running oscillators are sensitive to vibration or shock. You've probably heard the story of my best Sulzer oscillator making small phase or jumps which I eventually correlated to when the kids flushed the toilet down the hall. Did mounting it on a block of foam help? -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
