[time-nuts] 3048A Expert Needed

Richard (Rick) Karlquist richard at karlquist.com
Tue Jan 20 13:47:57 EST 2015

On 1/20/2015 7:59 AM, Martyn Smith wrote:
> Hello,
> 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.

> 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?

> Martyn

I believe this is not specifically related to anything going
on in the 3048, but rather that you can't lock together the
two 100 MHz oscillators you have in general.  Whenever I have
run into that, the fix is to simply divide down both of the
100 MHz outputs by the same number N.  Now feed those into an
external phase detector and make a phase locked loop independent
of the 3048.  Then measure the noise using the 3048 in residual
mode.  The purpose of dividing down is to reduce the phase
fluctuations to a level that is within the linear range of the
phase detector.

Rick Karlquist N6RK

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