); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: [EMAIL PROTECTED] Subject: Re: [time-nuts] HP 5370B jitter Date: Fri, 13 Jul 2007 17:16:38 EDT Message-ID: <[EMAIL PROTECTED]>
Said, Returning to this message... > I sent spectrum plots of the 10MHz 5370B output to this list earlier, the > output is very sad. It's extremely dirty and jittery (well, compared to the > 4ps > noise you got, and compared to what the 10811 can deliver). Further investigations have now shown that the 10811 output is clean, just a little 3rd harmonic but nothing to worry about. The INT test point is also clean. I suspect the output drive part, as other outputs to various parts are also free of the 5 MHz. The 10 MHz present detector circuit is currently my main suspect. It consists of a "one-shot multi-vibrator triggered by the 10 MHz signal". Having a RC time-constant of 100 ns makes it a suspect indeed. Probing it (pin 11 on A8U1) clearly shows a waveform wich looks like a 25% 5 MHz with a short spike on it. This little culprit of a detector is infact a wideband comb-generator which contributes its 5 MHz as sidebands to the output 10 MHz. It's only purpose in life is to light a LED only visible to the servicing engineer (me in this case). Thus, making a small modification to disable it during normal operation would improve the quality of the 10 MHz output considerably if I am right. Since I don't do ECL design on a daily basis, I will have to ponder a bit in order to come up with a good method of acheiving this. > After calibration to 4ps, what does your 5370B unit read for it's internal > RMS noise now? Self-reference from 10 MHz output gives 29.9-34.0 ps. A 130 MHz +15 dBm sine results in readings in the 35-41 ps range. A 5 MHz +15 dBm sine from the Cesium does not acheive as deep levels, but reaches 39-43 ps but does not vary as much. A 10 MHz from anther 10811 source reaches 37-43 ps. All measures where taken in TI mode, +/- TI, StdDev for 1k samples. Optimum 1M/50 Ohm termination strategy selected for each signal. Flipping the input termination switches for both channels quickly creates different levels of input jitter. I have not trimmed anything but the multiplier stage. I have tested running frequency measurements and up to about 130 MHz seems safe. At 133 MHz it will start to false-trigger and at 134 MHz it is just starting to make obvious errors and at higher numbers it gives nonsense readings. I might add that I have only trimmed the 200 MHz multiplier chain so far. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
