On 1/13/13 12:57 PM, Pete Smith N4ZR wrote:
Do back-to-back diodes across a receiving antenna degrade receiver
performance before they begin to conduct? what I'm considering is
back-to-back series strings of diodes to limit RF voltage at the front
end of an SDR. My working assumption is that the conduction threshold
could be set below the damage level but above the ADC clipping level,
but if it affects performance before the ADC clips then that's no good.
The challenge is that diodes actually begin to conduct pretty early
(it's sort of a square law leading to a linear) so it's not so much the
clipping, but the IMD when the diodes are partially on.
Back to back diodes (zeners) work as a limiter to do damage protection,
but reverse biased diodes make fine noise generators. I think, if the
knee is sufficiently far out, this might not be a problem: and if you've
got your diodes in series, the forward conduction isn't an issue.
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