[time-nuts] [qs1r] Looking for good, cheap, external reference

[jimlux]

Lester Veenstra wrote:
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> From: qs1r at yahoogroups.com [mailto:qs1r at yahoogroups.com] On Behalf Of David
> Sent: Tuesday, September 21, 2010 10:55 PM
> To: qs1r at yahoogroups.com
> Subject: [qs1r] Looking for good, cheap, external reference
> 
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> Hi,
> 
> I'm interested in doing some ionospheric research, but I don't want to break
> the bank with an $8,000 USD GPS disciplined Rubidium clock.
> 
> Anyone have some ideas on cheaper alternatives? The QS1R, and the Flex-3000,
> both use a TCXO and they have pretty good long-term stability, but there is
> a 1-2 Hz wander at 10 MHz imposed on the frequency over a duration of about
> 45 minutes to one hour. It looks like an exponential rise to one limit,
> followed by an exponential decay to the opposite limit. 

That sounds an awful lot like an airconditioner/heater/airflow changing 
during the day sort of variation.


> 
> For long term stability, it obviously requires a temperature stabilized
> environment, but I have observed a slow diurnal variation in the TCXO mean
> frequency of about 1-2 Hz at 10 MHz just sitting on my desk, exposed in the
> morning to some brief sunlight.
> 
> For comparison, my old Icom 756ProIII looks astonishingly stable, but with a
> fixed frequency offset of around 0.8 Hz (the best I could do by tweaking the
> pot on the PLL). At most I see a very slow diurnal wander of around 0.5 Hz
> at 10 MHz. Whatever Icom did, they did it very well.
> 


Measured against what?

---

but to practicalities..
Do you actually need to generate a signal stable to fractions of a Hz, 
or is being able to calibrate a recorded/digitized signal good enough?

If the latter, you could just record a 1 pps along with your data, and 
calibrate it out.

For what it's worth, a GPS disciplined ovenized quarts oscillator is 
"cobble together able" for a lot less than $8k  (and since you're 
considering QS1Rs and Flexradios, you're clearly in the "willing to 
cobble" category).

A SRS Rb is uner $2k, by the way, brand new.  http://www.thinksrs.com/
PRS10 is list $1495

A FS725 is about $2500