[time-nuts] Low phase noise affordable GPSDO

[Bob kb8tq]

Hi



> On Jun 20, 2018, at 10:27 AM, Ethan Waldo <ewaldo at healthetechs.com> wrote:
> 
> Hello time afficionados.  I've tried my best to scan through the archives to see if this has already been answered, so apologies if I missed something relevant.  I am going to be experimenting with >10Ghz microwave frequency grounded coplanar waveguide phase combining/cancellation/detection across a number of generated signals.

If you are multiplying up, even a very low phase noise 10 MHz will get you in trouble outside a pretty narrow region around carrier. It’s far better / easier to use a 
100 MHz (or higher) cleanup VCXO ( or OCXO) than to try to find a -187 dbc/ Hz GPSDO. 


>  That being said, I am in the market for a GPSDO that has the least amount of phase noise.  A secondary factor in my choice is how many 10Mhz references the GPSDO can provide to sync all my signal generators; not as concerned about what amplitude is provided.

Signal generators / counters / test gear generally have pretty modest input requirements. They normally do an internal cleanup process on the reference input. 
Put another way, they expect a dirty reference. 

> 
> Most of the cheap GPSDOs on eBay seem to have only 1-2 sine outputs with no understanding of expected phase noise.  A solid option seems to be the TrueTime XL-AK but something tells me there might be options out there better than 1x10-12.  


Assuming you are talking now about ADEV, it is highly unlikely that you will find a 1x10^-12 at 1 second tau GPSDO. Yes it you go out far enough ( long tau )
they all will get there some day.  Good ADEV is not an indication of good phase noise in the sense of doing things at microwaves. 


> Price is the right ballpark though I could justify spending a little more for better phase noise specs.  I have no need to run without GPS lock so Rubidium source doesn't seems as necessary compared to something with a high quality (D)OXCO, but it would be nice to add that as an external source at a later time.  Build vs. buy is an option, but I would like to avoid making costly mistakes so would favor buy if specs are comperable.

Simple answer is to get a reasonable GPSDO. Do something simple to distribute the output to your test gear. There are lots of ideas in the archives. 
CMOS gate based buffers work perfectly well for a sub $20 sort of solution. Then take one output and run it through your cleanup chain to form 
the base of your microwave stuff.  That way each building block is easy to come by and none are ghastly expensive. 

Bob

> 
> I would really appreciate advice from folks around here who already have some hard-earned experience on what my best options are. Whatever I get I'm likely to be stuck with for a while so I would rather take the time and research than to do a knee-jerk buy.  Thank you ahead of time for any replies.
> 
> Sent from my Verizon Wireless 4G LTE Droid
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