[time-nuts] Looking for good SR620 setup to compare GPS and rubidium

kd7ts kd7ts at ispwest.com
Mon Sep 25 16:24:41 EDT 2006

Hi , I have looked through the archives occasionally, and finally decided to subscribe... 

I compare 10 MHz frequencies using an SBL-1 mixer and a RS232 enabled DVM. Connect the two frequencies to be compared to the IF and RF ports, bypass the LO port for RF, and measure the DC at the LO port. The DVM can be used with software to either save, or graph the results. Tweak it and come back in a few hours to see how you did.

The LO port must be DC coupled. TUF-1, SBL and many others from MCL fit the bill.

If you don't see a very slow change, then you're not very close. A dual trace O'scope can be used to get close in a hurry. Just put each signal into its own channel, and trigger from one channel. Adjust to make the traces stand still. My scope is not very fast, so I go to the mixer from this point. If your scope is good enough to see one cycle at a time, or so, you might do better.

I find this method very easy to use. If the voltage is low, you might try an opamp to boost the DC a little. I have not found it necessary.

Recently I compared the "Pyro-Joe" offering against the Shera controller and 10811. Fun stuff !

I put this together from the "junk box" so expense was zero. Accuracy is limited by your patience.

Mike KD7TS

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