[time-nuts] Close-in phase noise question...more info...

John Miles jmiles at pop.net
Wed Dec 17 00:53:06 UTC 2008


> More info on the LO chain:
>
> 1) 5MHz Wenzel OCXO <--Custom Osc for me.
> 2) MSA-1105 buffer MMIC and lumped LPF
> 3) 5MHz to 10MHz 1N5711 diode based doubler
> 4) MSA-1105 buffer and lumped LPF
> 5) 10MHz to 20MHz 1N5711 diode based doubler
> 6) 20MHz BPF

What kind of BPF?  A really narrow crystal filter would be nice here.  (You
have basically reproduced the 8568A/B's 20 MHz reference section.)

> 7) 20MHz drives sampling detector inside surplus Frequency
> West PLL block to lock 1320MHz cavity oscillator.

Sounds OK as long as the sampler loop's noise floor doesn't limit you.  I
haven't measured the in-band residual floor of any bricks but I'd be
surprised if an SRD multiplier wouldn't be quieter.

> 8) 1320MHz drives Frequency West SRD multiplier to 6.6GHz.

If I wanted to get to several GHz with what's in my junk box right now, I
would do what you did to get to 20 MHz, BPF it with a multipole crystal
filter, and then use a few more multiplier stages to get somewhere between
100 MHz and 1 GHz, a la the 8662A reference section, depending on the choice
of the next stage.

That VHF drive signal would go into either an HP 33002A or 33004A SRD
multiplier, or one of the Picosecond NLTL multipliers (e.g.,
http://www.picosecond.com/product/product.asp?prod_id=109 ) I picked up in
their fire sale when they shut down their fab.

> 9) 6.6GHz to 39.6GHz Milliwave diode multiplier/amp/filter
> 10) 39.6GHz to 79.2GHz in varactor doubler
> 11) 79.2GHz to 158.4GHz in varactor doubler
> 12) 158.4GHz into x4 sub-harmonic mixer

AFAIK the rest of the chain is fine.  I'd focus on getting rid of the brick
PLL, or at least taking pains to make sure that it's not the problem, before
worrying about the MMICs in your early stages.

Remember that there's no point in optimizing the PN of any one stage much
below the input-referred residual noise of the following stage.  MMICs, in
saturation or not, are pretty quiet.  Quieter than sampler loops anyway.

-- john, KE5FX




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