[time-nuts] 3048A Expert Needed

Martyn Smith martyn at ptsyst.com
Tue Jan 20 10:59:24 EST 2015


I have both the HP3048A and Timepod Phase Noise test Sets.

I have two low noise 100 MHz PLL's.  The 100 MHz output is locked to a 10 
MHz reference input.

I want to measure their phase noise.  Their spec is -100 @ 10 Hz with a -168 
noise floor.

I connect both 100 MHz outputs to the 3048A.  I then connect a 10 MHz 
reference to one of the 100 MHz PLL's.  This 10 MHz reference is tuned by 
the HP3048's DC output.

So the DC tunes the 10 MHz that then tunes the 100 MHz.

However, the 3048A won't achieve lock.  The 100 MHz PLL's loop bandwidth 
(about 0.2 Hz) is too slow for the 3048A to achieve lock.

Does anyone have any ideas?

On the timepod, I've used the technique whereby I have two oscillators @ 70 
MHz and two double balanced mixers.  So I actually measure the 30 MHz 
offset.  In theory the phase noise of the two 70 MHz references should be 
cancelled out.  But I just don't achieve lower enough floor levels.



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