[time-nuts] Unexpected problem found

Joseph Gray jgray at zianet.com
Fri Oct 28 20:43:53 EDT 2016

This really is Time Nuts related. Keep reading.

I recently bought some surplus Motorola UHF mobiles. They came with
the previous frequencies blanked and only channel one programmed with
460.000 MHz.

I put all of them on the bench to do a quick test to see if they
transmitted and received. Upon power on, every one was receiving a
strong carrier on the programmed frequency of 460 MHz. Firing up the
service monitor with a small whip antenna, I found a -70 dBm carrier,
right on 460 MHz.

Taking a handheld scanner around the house and outside, it seemed that
the problem was in my house, but I couldn't localize it with the
scanner. I started turning off circuit breakers until the carrier went
away. Then I went around, unplugging things individually. You won't
believe what the culprit was.

I have had some 10 MHz, Micro Crystal OCXO's (DIP 14) aging for quite
a while, intending to use them in a few projects eventually. Yep, it
was the OCXO's. I am surprised that the OXCO's would be putting out a
carrier at 460 MHz, and such a strong one.

This has been going on for quite a while. If I hadn't had these
Motorola radios that just happened to be programmed for 460 MHz, who
knows if or when I would have noticed this.

Joe Gray

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