[time-nuts] Low phase noise affordable GPSDO

Attila Kinali attila at kinali.ch
Wed Jun 20 17:26:46 EDT 2018

On Wed, 20 Jun 2018 14:27:35 +0000
Ethan Waldo <ewaldo at healthetechs.com> wrote:

> 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.  That being said, I am in the market for a GPSDO that has the least
> amount of phase noise.

Phase noise is usually not the strong traits of GPSDOs.
That said, I guess a Trimble Thunderbolt or Nick Sayer's GPSDO with
the OCXO option would probably fit your bill.

Alternatively, take any of those two GPSDO and replace the OCXO
by one that has as low phase noise as you need.

> 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.

You are looking a bit naively at this. The noise floor of modern,
low-noise OCXO is limited by the Johnson noise of the 50R impedance.
Ie the higher the output signal level, the lower the noise floor (in dBc).
Hence, just using some passive splitters will increase your noise
levels. The 1/f^a noise levels are unaffected by this, though. 

I would recommend going for a seperate distribution amplifier in order
to keep the noise at a minimum. If you are fine with DIY, go for the 
design by Anders Wallin.

			Attila Kinali
<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.

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