de Ward, N0AX
For any measurements such as spectral quality to be reliable the instrument
must not be overdriven into its non-linear region of operation...this can be
checked by inserting, say, 10dB of attenuation in the input signal (ie; at
the rubber duck antenna) and observing a corresponding drop in ALL observed
signal components of the same amount. If they don't all drop in amplitude by
the same amount that you attenuated the input, then the measuring device is
being over-driven and more attenuation is required. Keep adding attenuation
in the input (NOT at some intermediate stage...it's GOTTA be in the input)
until all observed signal components begin to drop at the same rate. Then,
and only then, can you trust your measurements.
Front-end overload is probably one of the three biggest problems associated
with interference on a crowded band and is certainly the most noticeable as
it shows up as distortion products within the passband of the receiver. It's
also incredibly difficult to explain to some of our more non-technical sistern
and brethern.
The sentence, "Your receiver RF gain is too high and it's overloading." Usually
gets them to check (most of them don't know where the attenuator switch is, IF
the radio they're using even HAS one...) and at least consider the possibility.
Remember, not everybody has a >$1k radio with an attenuator feature, but they
all seem to have an RF gain, seemingly stuck wide open.
A parallel consideration on their behalf is that I have heard, on a number of
occasions, boorish contesters blast right over major nets, ongoing QSOs and
round tables, etc. etc. without the slightest consideration for others. This
inflames the passions all-round and slams shut the window of communication.
Most of us seem to have reasonable manners, but a few bad apples are irritating
a large number of people who have just as much right to the band as anyone
else and are not afraid to complain about it to the League and others. Just
a thought...
73, Ward
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