[time-nuts] Comparing 10 MHz Oscillators at 10 GHz

[Ulrich Bangert]

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: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Brucekareen at aol.com
> Gesendet: Mittwoch, 5. Januar 2011 00:09
> An: time-nuts at febo.com
> 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
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