[time-nuts] retry: PRS10 has spurious frequencies
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Sun Apr 29 19:56:18 EDT 2007
Henk ten Pierick wrote:
> On Apr 25, 2007, at 23:38, Dave Brown wrote:
>> Do any of the spurious signals show on the SA with a search antenna
>> (located in your lab environment)connected instead of the PRS10?
> No, they are not. I can see spurious if and only if the PRS10 is
> powered. When I open the PRS10 and search with a loop antenna, then I
> see the whole spectrum up to 600MHz. Most of the power comes from the
> board with the micro which runs at 10MHz. I expect that there is a
> parasitic coupling of this micro 10MHz to the PRS10 output. This can
> explain why the spurious level increases with frequency to higher
> than the spectrum analyzer noise level at say 500MHz. The micro slew
> rate can explain why it decreases again into the noise above 700MHz.
> The spurious is only there if the micro runs. It is not clear to me
> why I can see this spurious and other PRS10 owners can not. May be a
> different run or version of the PRS10. My PRS10 has serial 5099.
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If indeed the micro is the source of the spurious frequencies that other
PRS10's do not exhibit, then either you've got an unusually fast micro
or there is something wrong/different in the micro supply decoupling
and/or EMI filtering. The PCB layout could differ or different or even
extra components may have been used in the other PRS10's.
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