[time-nuts] Unexpected problem found
magnus at rubidium.dyndns.org
Fri Oct 28 22:15:28 EDT 2016
On a related note, I remember when Pendulum was testing a rubidium and
it had more jitter than motivated by the integrated phase-noise slopes,
so they where curious about it. As I had just brought in my SIA3000 for
them to have fun with, I hooked it up and already in the oscilloscope
view I found small bumps spread out over the sine. Turned out to be the
100 MHz used for the rubidium lamp that polluted the output. You rarely
do a plot out to 90 MHz offset of the 10 MHz carrier on phase-noise
plots, you rather call it harmonics which wasn't listed.
On 10/29/2016 03:58 AM, Bob Camp wrote:
> 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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