[Test-Equipment] HP 8656A question

[Carl Walker]

Hello to the list.

I'm the proud owner of an HP 8656A signal generator, but it seems to be 
suffering from a bit more residual FM than I would like - but only below 
100MHz.

Above 100 MHz, the tone produced in a SSB/CW receiver is pure and 
un-wavering. Below 100 MHz, there's several Hz of "warble" - and it gets 
worse as you go down in frequency - becoming perhaps 20 to 40 Hz as one 
approaches the lowest operating range of 100 KHz. It's a fairly fast loop 
instability that's really quite difficult to judge frequency deviation from 
by ear alone, and far too random in nature to get a feeling for with a 
counter.

As you've probably guessed, I don't have the service and maintenance manual 
for this beast - nor do I have the operators manual to confirm what the 
residual FM specifications are for the unit (I'd hope they would be better 
than what I'm witnessing).

This is an Option 1 unit - but the generator suffers from this ailment 
whether on the internal oscillator or being driven externally from a rubidium.

Is there with anyone that can confirm what the specification is? Is there an 
alignment section for PLL operation that can be copied from the service 
manual that wouldn't require copying the entire manual? I'd also not mind 
purchasing a photocopy of the service manual if someone has one they would 
like to sell (I've only seen copies on the expensive manual vendors web sites 
that are going for 25% of what the generator cost).

Thanks for any pointers,

-Carl, WA1RAJ