Re: [SI-LIST] : bare board resonance test

alterra@adnc.com
Wed, 01 Oct 1997 18:17:52 -0700

Hans,

I have done this sort of test before. I recommend that you use a network
analyzer and very lightly capacitively couple to your board under test.
Observe S11 over the frequency range of interest. If you adjust the
coupling so that the peaks of any resonances are at least 30-40 dB below
your drive signal, then you can be reasonably certain that you are not
'pulling' the resonances as is likely to occur in the strongly coupled
configuration in your note. This is important if you really want the
resonances of the board and nothing else. Of course the resonances will
change when you stuff the board or connect it to external circuirry (e.g.
bypass capacitors) because the boundary conditions are different.

Best regards,

Eric
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At 04:00 PM 10/1/97 -0700, you wrote:
> Colleagues:
>
> What is the simplest way to test the bare board resonance? use a 50
> Ohm resistor in series with the power and or ground plane, drive it
> with a sweeping oscillator and observe using a Spectrum analyzer
> connected with a "T"?
>
> SG----50ohm---PCB
> |
> |
> SA-----------
>
>
> In this configuration, the pcb appears as a stub to the 50 ohm line
> from the SG to the SA. It seems it would work but?.. there probably
> are many better ways?
>
> Thanx in advance
>
> Hans
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Eric Wheatley Ph.D. (760) 942-9426 (phone)
Alterra Technology Co. (760) 942-2366 (fax)
Encinitas, CA 92024 alterra@adnc.com
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