[time-nuts] Unexpected problem found
kb8tq at n1k.org
Fri Oct 28 21:58:11 EDT 2016
Probably what is going on is that the OCXO’s have a parasitic oscillaton in the UHF
region. It has injection locked to the 10 MHz. You get a signal that is much higher
level than any harmonic relation would predict.
I’d try fiddling the bypassing and load ….
> On Oct 28, 2016, at 8:43 PM, Joseph Gray <jgray at zianet.com> wrote:
> 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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