[Elecraft] increasing receive gain

[Ron D'Eau Claire]

Since the noise background drops when you disconnect the antenna with
the Preamp OFF, then you don't need it to help hear weak signals.
Adjusting R1 to increase the gain of the IF amp will do a better job
since it comes after the IF filter. Or increase the audio gain. Of
course, you want to run that test in the narrowest selectivity setting
you ever use. The narrower the bandpass, the more noise generated in the
stages after the IF filter will show up. 

As Bob pointed out, this is NOT an especially "quiet" IF amp, but as
long as the rig passes the "antenna disconnect" test after tinkering
with the resistor value, you ability to hear weak signals will not be
hurt at all. 

As you pointed out, you are NOT using  a "high gain" antenna there in
your attic, so the deleterious effects of running the preamp when you
don't need one won't show up as often as it might for someone with a
giant gain antenna on a tower. Even so, local sigs like a CB'er can
cause your preamp a lot of grief even on band well away from 27 MHz. 

Keep in mind when evaluating the effect of R1 that as you increase the
gain, the S-meter will be LESS active on weak signals. Since the S-meter
is measuring the control voltage used to turn down the gain if the IF
amplifier, adjusting R1 to keep the AGC action from starting will also
cause the S-meter to show stronger signals or noise levels as S-0 levels
(or whatever you have set the "meter" to show with no signal input"). 

Ron AC7AC
K2 # 1289

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Done that. ;-) Preamp on/Preamp off background noise drops in both cases
with antenna disconnected....

It's all a balancing act at my QTH. Attic antenna, in the middle of a
small city, LARGE apartment complex to one side, commercial buildings
less that 1/2 mile away.... Having the Preamp on helps me hear those
weaker signals, but at the price of more noise...like I said in my case
it is a balancing at. (That's why I like the Icom 746pro, the DSP
functions give me some advantage at times)...

73, Rod N0RC