[time-nuts] Brand new OCXO/TCXO reccomenations

[Bob kb8tq]

Hi



> On Sep 24, 2020, at 6:32 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
>> 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). 
> 
>> 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)).
> 
> How much can the temperature change in a few minutes?

In a normal building with “typical” HVAC, a 2C change over 45 to 90 minutes 
is a reasonable guess. It could be 2X that. It could be half that in terms of the
number of degrees. Faster than 30 minutes is rare.

Picking your gizmo up off the nice warm table and heading into a stiff winter 
breeze ( in the arctic …) can be > 40 C in < 5 minutes. This is an issue for 
things like portable radios ….

> 
>> 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
> 
> How much could you improve the holdover if you monitored the temperature?

How many months do you want to spend taking data? How complex an algorithm
do you want to implement. How well are you controlling air flow direction (and a 
bunch of other stuff?) 

2X is doing pretty well. Anything over 5X is going to be difficult to repeat the 
next time you look. 

Bob

> 
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