[CQ-Contest] Re: 2-Radio Interference
Scott Ellington
sdelling at facstaff.wisc.edu
Tue Dec 26 09:25:06 EST 2000
The "rules" about the effect of attenuation on intermodulation products is just
a mathematical consequence of nonlinearity. You do a power series expansion of
the nonlinear transfer function, apply some sine waves of various frequencies,
apply some trig identities to the result, and you get the rule. One way to look
at it is that, for example, third order intermod results from three
multiplications: One signal squared times the second signal. If you double the
amplitude of the input, the third order product increase by a factor of 8.
The change in signal level occurs AHEAD of the nonlinearity. Saturation
shouldn't be an issue unless some OTHER signal(s) are causing saturation, or
saturation is occurring further down the signal path, like the last IF stage.
One way to avoid the S-meter calibration problem is to turn the AGC off, reduce
the RF gain to prevent IF overload, and measure the change in audio level with a voltmeter.
73,
Scott K9MA
--
Scott Ellington
Madison, Wisconsin USA
sdelling at facstaff.wisc.edu
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