Moshe:
One possible source of the phenomenon you've observed could likely be "beating"
caused by assynchronous clocks. It's even more defined when the frequencies are
slightly skewed by an amount slightly less than your receiver bandwidth.
Take for example, you have two processors running off their own 100 MHz clock
(VCXOs). These clocks are not only assynchronous but due to tolerances,
there'll be some slight delta in actual operating frequency. The beat frequency
formed by the vector addition of these sources at your transducer appears
as an erratic emission (amplitude instability).
There are two ways to verify this:
- scan up to higher harmonics until the delta in frequency is greater than
resolution bandwidth of the receiver--you'll observe two "humps" instead.
- continue to lower the receiver bandwidth until the BW is less than the
delta between the frequencies--you'll see two "humps" again.
Regards,
Geoff Skanes
EMC Engineer
Nortel
In message "Re[2]: modeling RFI sources "randomness"",
moshe_vald...@isr-rhv-p1.ccmail.compuserve.com writes:
> I understand what you mean, but I'm not sure this is the whole story.
> I often check a product which is in "idle" mode, i.e. the processor is running
> in a tight loop, repeating itself every X microseconds (which is probably less
> than the measurement equipment integration time). In this situation everything
> should be "static", but still the Spectrum Analyzer /receiver give an unstable
> reading (+/- several dB).
> What other factors could be related to this? Maybe it is related to the
> measurement equipment limitations?
>
> thanks for your opinions
>
> moshe valdman
>
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