[time-nuts] Freq cal to 1ppm without GPSDO

[Bob Camp]

Hi

There is another route to getting where you want to go.

Buy an atomic clock. If you spend some time shopping, telcom rubidium atomic
clocks are out there for sub $50 prices. For $100 you can get one quite
quickly. An Efratom LPRO is one example. There are many others.

They normally put out 10 MHz and some put out 1 pps. I'd avoid the 1 pps
only versions for what you are trying to do. 

To be absolutely perfect, you do need to calibrate an Rb. I have never seen
one that was off by more than 0.5 ppb (0.0005 ppm). Their tune range is
rarely more than a few ppb. More or less - if they fire up and lock, they
will do what you need to do.

Of course if you have both the GPS *and* the Rb then you can calibrate the
Rb against the GPS and get it real close. Welcome to time nuts ....

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Beale
Sent: Thursday, February 17, 2011 1:10 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Freq cal to 1ppm without GPSDO

Hi Murray,

Thanks to you and the others for your replies. After some more HF reception 
problems here, I have come to the same conclusion as you. I found an Oncore 
M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan.

best regards,
John Beale


 > 1. My best advice is to get hold of a cheap GPS module with a 1pps 
(seconds pulse) output. Connect it up, and when you have a fix, use the 
1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to 
start with, and ultimately 100ns, and observe the 10MHz output of your 
TCXO. You will see the waveform drifting slowly. Counting how long it takes 
to slip one cycle will tell you how far off the TCXO is. If you have a 
counter with Time Interval mode capability, you could use that, using the 
GPS to start and 10MHz to stop, again observing the drift.

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