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Re: Converter gain and noise..



There is no problem in principle in having a high noise level in a
receiving system, provided the noise figure is good and there are no
excessively strong signals around.  My AO-40 receiving system noise floor
runs at about "S5" and I would not be bothered if this were "S9" (or more).
 On 10GHz EME, my system noise floor is at about S9+20dB.

Signals on the AO-40 downlink are never going to be so strong that ground
station receivers will suffer cross-modulation.

On microwaves, we are accustomed to dealing with signal strengths in dB
above noise (often referred to as dBn), and this is much more useful when
comparing performance of one receiving system to another.  Calibrating the
receiver S-meter is needed of course before any values can be quoted, and
you may be surprised that the number of dB between s points is not
constant, and rarely the oft-quoted 6dB.  My IC735 averages about 3-4dB per
s-point.  Likewise the dB scale above "S9" is probably wrong too.

The only time when gain may be an issue is if you have any strong
out-of-band signals around, in which case the non-linearity problems will
probably be in the front-end of the RX converter, and adding attenuators at
IF will do no good.

Charlie G3WDG
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