[time-nuts] Brand new OCXO/TCXO reccomenations

[Bob kb8tq]

Hi

> On Sep 23, 2020, at 8:20 PM, Forrest Christian (List Account) <lists at packetflux.com> wrote:
> 
> I'm hoping some of the list are familiar with the newer currently-available
> oscillators available from the distributors.
> 
> Some background:
> 
> I'm starting to play with a short-term 1PPS holdover application, mainly to
> cover up brief GPS signal loss events (a few minutes at most).

Is “a few minutes” < 10? I’m guessing it is.

> 
> Since I may at some point want to make numerous copies of this, I'd rather
> start with a new oscillator as opposed to digging through the junkbox or
> buying surplus.   Lower cost (<$100 ideal, lower is even better) and power
> consumption is good.   My short-term stability requirements indicate to me
> that I'm probably looking for an OCXO instead of a TCXO, although it looks
> like some of the best TCXO's out there are in the range which will work in
> most cases (50ppb over temperature (or better)).

What is your holdover requirement in ns ? 

If 10 minutes is the max number, that’s 600 seconds. 1 ppb average error
would be 600 ns. Is this to much?

> 
> I suspect I'm going to handle the holdover in a FPGA.  As such, I don't
> think I'm going to bother trying to voltage control the oscillator.  Seems
> like it will make the overall circuit simpler and I don't have to worry
> about a whole bunch of control circuit temperature compensation.

Without knowing the holdover requirement there’s no way to really guess if this
makes sense. A 2 ppm TCXO that costs < $1 can be steered with a $2 DAC. 
Steering it to < 0.1 ppb is not super crazy. To get 0.1 ppb out of a “static” device
you would need a Rb rather than an OCXO.


> 
> I've dug through enough datasheets at this point, my eyes are glazing
> over.   I also know that the spec sheets are only part of the story when it
> comes to oscillators.  I also have found over the years that often the part
> I'm looking for (that 20ppb Temperature-stable TCXO for a reasonable price)
> exists if you know the vendor to look at...
> 
> So any specific recommendations or pointers toward a brand/type would be
> appreciated.
> 

Steer a TCXO ….

Bob

> -- 
> - Forrest
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