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Do's and Don'ts in weak
signal communications |
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Be sure to have enough gain
in your system, this is to prevent loosing performance in your
system |
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Calculate overall
performance and check it by measuring |
| Calculations can be done using
VK3UM calculator |
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Measurements can be easily
done using SDR Spectravue program |
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For moon- and sun noise measurements use Continuum mode from
Spectravue |
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Work as hard as possible to gain each 0.1 dB performance |
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Weak signals communications is a fight for each 0.1 dB |
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As general rule of thumb: losses before the pre-amp will degrade the
echo's by a factor 2 |
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Calculate overall system Noise figure including transceiver |
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Be sure to have good image rejection of at least 20 dB |
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Be sure that phase noise of your LO at your IF range is well below
the noise floor at your mixer |
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For 10 GHz use an IF of 432 MHz or higher |
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For 5760 MHz when using a good filter an IF of 144 MHz is just
acceptable |
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When turning on and off the pre-amp you should have at least a 20 dB
rise in noise floor |
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Too much gain is hardly ever a problem |
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Use Spectravue and FFT averaging to find extreme weak signals |
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Signals with a S/N of -18 dB@3KHz are just strong enough to copy in
CW |
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Using Spectravue S/N of -18 dB@3KHz show as S/N of 6 dB@12Hz so
clearly visible |
With enough overall gain your receiver is just a detector,
performance like phase noise is not very important
(as long as there are not very strong signals in your system) |
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Check your dynamic range taking into account your operating mode |
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On EME you don't need a very large dynamic range; 20 dB for most
setups will be enough |
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In other modes you will need more dynamic range; 23 cm tropo will
need at least 80 dB |
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If possible use frequency referenced oscillators coupled to a stable
10 MHz source |
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If possible use automatic Doppler correction |
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