[time-nuts] Phase noise vs warmup or time

[Brian Kirby]

If you have a spectrum analyzer, depending on its resolution, you can 
also measure the phase noise directly.

When I worked in the Satellite Communications industry, we needed up and 
down converters faster than our vendor could make them.  They use to go 
thru a long QA process and they were very reliable.  We waved the long 
QA test and tested the local oscillators in the field.  If they were 
bad, we sent them back and they replaced them.

If you analyzer does not have the resolution, you can notch the carrier 
and get more dynamic range or use the classic setup , which is the 
"loose" phase lock loop.

Brian KD4FM

John Ackermann N8UR wrote:
> Tom Van Baak said the following on 12/29/2009 04:24 PM:
>
>> But, depending on the equipment you use, a phase noise
>> measurement (e.g., script L of f) doesn't require the source
>> to be long-term stable; you get pretty much the same phase
>> noise results in the first minute as you would a day or week
>> later.
>
> As a practical matter, you need to allow an OCXO time to stabilize or 
> else the warm-up frequency drift may cause difficulties in the phase 
> noise measurement.  You need to keep the DUT and reference in the 
> proper phase relationship, and if the drift is too fast the PLL may 
> not be able to keep up.  From what I've seen using the TSC test set, 
> you'll get glitches in the flicker-noise region (say, around 1 Hz 
> offset); the floor isn't much affected.
>
> I fully agree with Tom on the main point -- I'm not talking days or 
> weeks, but an hour or so is probably a good idea.
>
> John
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>