[time-nuts] Re: Low Phase Noise 10 MHz bench signal source sought

[Joseph Gwinn]

On Sat, 02 Apr 2022 03:27:06 -0400, time-nuts-request at lists.febo.com 
wrote:
time-nuts Digest, Vol 216, Issue 3

>   11. Re: Low Phase Noise70 10 MHz bench signal source sought
>       (Richard (Rick) Karlquist)
>
> Date: Fri, 1 Apr 2022 19:12:07 -0700
> From: "Richard (Rick) Karlquist" <richard at karlquist.com>
> Subject: [time-nuts] Re: Low Phase Noise70 10 MHz bench signal source
> 	sought
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at lists.febo.com>,        Bob kb8tq <kb8tq at n1k.org>
> Message-ID: <0f524fb8-2220-635e-3f62-28f7f081665e at karlquist.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> 
> He [Joe] should be looking at Wenzel Associates and NEL.
> Wenzel specs -170 dBc at 100 Hz offset.  

I know of Wenzel, but they don't make bench-top lab instruments.  
Rack-mount is available, but as a custom part.

I did find NEL, and they do look very good.  The NEL 2030A and 2030B, 
which are rack-mount, are plausible.

Both are likely expensive, with long lead times.


>    Hope he has lots of money for 
> this one.  Some of the NEL OCXO's are $5,000 and 6 months to 1 year
> delivery.  Both vendors also sell noisier cheaper versions.
> He needs to trade off noise vs offset vs cost vs delivery time.

Yes.  I assume that it takes 6 to 12 months of screening the run of 
production to get these few golden units.  Or they make a special 
circuit version, but still screening is required, with low yield.

And so yes there is a tradeoff to be made.


> If he is going to measure phase noise of another source with it,
> he may need a VCOCXO to make a PLL.

Yes, voltage control is also needed, so a Rubidium can be used to 
stabilize the OCXO.  Or the OCXO already has that built in.

What is also needed is a very quiet source of DC power for the Rb, 
OCXO, et al.  None of the vendors seem to specify their PSRR (power 
supply rejection ratio), and I assume that all published curves are 
obtained using a battery-powered unit under test.


> Rick N6RK
> 
> On 4/1/2022 4:57 PM, Bob kb8tq wrote:
>> Hi
>> 
>> Rb and low phase noise ( at least far removed ) are sort of mutually
>> exclusive specs. You need to pick one …

Mutually-exclusive, yes.  Impossible, no - Wenzel OCXOs locked to a 
Rb already do this.


>> Assuming the decision is to go for the -170 dbc/Hz spec, Congratulations
>> you are buying on OCXO. Not quite clear which OCXO, but it’s pretty likely
>> to be an OCXO. (Yes, there are exceptions, but they are rare enough to be
>> in the “don’t bother” category),

Yes, an OCXO is the only plausible answer.


>> Next step would be to decide on the max offset that needs to cut in at.
>> 100 Hz is into the “crazy/ not gonna happen” region. 1KHz is unlikely.
>> 10 KHz is doable. 100 KHz relaxes things a bit.

Would be figured out using the measured performance of the Rb and 
OCXO.  The exact crossover frequency isn't all that critical, so long 
as it's reasonably close.  Wenzel OCXOs use 2nd order PLLs with a 
loop bandwidth around one Hertz.


>> While the “buy a bunch and test” approach works for things like ADEV,
>> it probably isn’t the best approach for this spec. If you buy a 
>> bunch of this
>> or that OCXO, their 10KHz phase noise *should* be pretty consistent.
>> Sorting to get 2 db … nope, not worth it.  It *is* a pretty good bet that
>> a commercial spec at 10K will be beat by 3 to 6 db.

Buy and select is out.  I'm trying to buy a self-contained instrument 
intended to live in the rough-and-tumble of a lab bench.

 
>> What to buy? Head off to the spec sheets on whatever you see on eBay
>> and make some guesses.

Yep. 


Joe Gwinn