Bruce, I had the same idea as you and my friend Frank and I performed the following experiment to check whether it is possible or not:
Two brick oscillators (I believe to remember in the 8 GHz region) were locked to the same source (HP8660) in the 100 MHz region which in turn was locked to my local 10 MHz reference (Z3805). The two signals were mixed down to DC with a M14A mixer. By means of a phase shifter in one of the cables we were able to change the phase between the signals and so to determine the mixer's sensivity as a phase detector. The mixer's output was sampled with a HP3457 at a one second sample rate. The voltage measurements were then re-computed into phase fluctuations and this data was fed into my PLOTTER utility to compute what must be considered the AD noise floor of this system. I have not documented the results but I remember that the noise floor indicated a clear improvement against a direct phase comparison at 10 MHz for a given TIC resolution. What you suggest will produce you a mixer output signal which (when looked at with a scope) will easily enable you to trim your LPRO within seconds. If you can lock the bricks directly to 10 MHz this is even better. I have been thinking to use this scheme as a general tool for oscillator stability measurements. Since we must consider that two odcillators may not always be THAT close to each other in terms of frequency it would be better not to mix to zero but to a beat freaquency of say some 1-100 kHz (depends of course on the brick's pull range). This would involve a offset generator for one of the signals. I have drawn a circuit but not actually built that uses a ADF4002 and a DDS block to lock a 100 MHz signal to a 10 MHz signal where the DDS will provide the possibility to offset the 100 MHz signal in small amounts. I plan to lock two low noise WENZEL 100 MHz OCXOs to the 10 MHz sources with one of them with a small offset. Then these two 100 MHz signals are compared after being multiplied by the brick oscillators (I have two bricks that translate 100 MHz to 10 GHz). Perhaps the group can comment on the feasibility of the plan. Best regards Ulrich Bangert > -----Ursprungliche Nachricht----- > Von: [email protected] > [mailto:[email protected]] Im Auftrag von [email protected] > Gesendet: Mittwoch, 5. Januar 2011 00:09 > An: [email protected] > Betreff: [time-nuts] Comparing 10 MHz Oscillators at 10 GHz > > > Luciano Paramithiotti's January 1 post about his 10-to-100 > MHz multiplier > project reminded me of past musings about using two 10GHz, > phase-locked > oscillators to compare the 10MHz outputs of my T-bolt and > LPRO so I could > quickly adjust the latter by observing the mixed 10 GHz > signals with a > microammeter. I am talking about the California Microwave, > Frequency West, etc., > modules that were used as local oscillators in commercial > microwave systems. > > I was about to ask Luciano for more information on his coil forms, > amplifiers, and RF chokes when it occurred to me that > loop-noise in the PLOs might > force a very narrow bandwidth and correspondingly long > observation time. > Have members of the list been successful with this technique? > > While most common PLO modules require an input signal in the 100 > MHz-range, I have heard of versions that lock directly to a > 10 MHz input. Is anyone > familiar with these and how difficult it would be to modify > conventional > oscillators to securely lock to 10 MHz? > > Bruce, KG6OJI > _______________________________________________ > 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. _______________________________________________ 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.
