Tom W8JI wrote
>>There is one rule that always works.
Set your gain with use of preamplifiers or attenuators so you can just
comfortably hear a noise increase when the antenna is connected, and a
definite decrease with it removed. If your receiver can not take you
comfortably into the noise without overloading on the strongest 160 signals,
then you need to buy another receiver or have your receiver repaired...or
give up working some weak signals.<<
This is similar to what I used to do on SHF systems and we called it Noise
Overide.
We used 'a rule of thumb concept' to monitor the Rx noise from the detector
output on a scope and then add the preamp with the gains set so the noise
level doubled and no more. This way you can be sure you get the maximum
sensitivity (ie the noise figure of the preamp) and you did not decrease the
dynamic range of the system anymore than necessary. For LF situations a
Preamp reads as antenna since in SHF systems the antenna noise is swamped by
the preamp NF.
The noise can be seen on a scope or heard on phones but it will show an
increase when the antenna is connected.
If it does not show an increase then something is not working and you are not
seeing the antenna noise (or environment noise) overiding the receiver noise.
best 73s
Bob Parkes
G3REP
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