[time-nuts] Don't use cheap cables -- a cautionary tale

John Ackermann jra at febo.com
Sun Mar 3 09:59:38 EST 2013

I was measuring two OCXO and was getting some quite unusual results -- a 
symmetrical frequency cycling of several more than 1e11 p-p, with a 
period of around 15 seconds.

I removed an RG-58 3 foot jumper cable that fed 5 MHz from the rear 
panel of another OCXO to a patch panel (where it was terminated in 50 
ohms), and the noise quieted right down.  See the attached frequency plot.

The other OXCO had a similar jumper cable in the path, and although the 
two cables were not parallel to each other for any significant distance, 
there was still enough signal radiation and pickup to cause a nasty problem.

Lesson learned -- use only double-shielded cable in the oscillator rack 
(and in any RF measurement path) from now on.

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