[Elecraft] increasing receive gain

[Ron D'Eau Claire]

It's hard to beat the "disconnect the antenna and see if the background
noise drops" test. No laboratory equipment can do better to tell you if
you have enough "preamp" gain and a low enough receiver noise figure. If
the "S-meter" on other rigs seems to indicate higher, it may be that
those receivers have a less-desirable gain distribution than the K2, and
so a lower tolerance for strong signals. 

Ideally ALL amplification in a receiver should come after the IF filters
that set the receiver bandwidth (and so after the "S-meter" circuits
too).  The ONLY function of any amplification ahead of the IF filters is
to make background "atmospheric" noise picked up by your antenna
stronger than the noise generated in the receiver itself so the noise
generated by the receiver won't limit what you can hear when you dig for
a really weak signal. 

I've never found a case in which the preamp was desirable on 40, from
the standpoint of adequate sensitivity. I can understand wanting it on
if the K2 receiver, overall, is anemic, but if the noise level drops
when you disconnect the antenna with the preamp off, turning the preamp
ON will compromise the overall dynamic range of the receiver.

The "RF Gain" on the K2 does not control the level of signals at the RF
input. It is simply a manual control of IF amplifier gain. So  turning
it down to compensate for having the Preamp On still exposes the Preamp
and receiver "front end" to overload from strong signals that you cannot
hear  because they are outside of the IF filter passband. Well, often
you CAN hear them, but they come through as hash and QRN and you don't
even realize they ARE signals.

Ron AC7AC
K2 # 1289

What test(s) would anybody suggest to evaluate the suitability of a
particular R1 value? (tests that can be preformed without a full
compliment of lab equipment preferred)

What I noticed most during the Sprint was the elevated noise level on
40m, I was running the K2 with Preamp on. Usually I have the preamp on,
RF gain at max, and AF control between 9-11 o-clock (depending on the
other station's signal strength). With R1=33k, while on 40m with preamp
on, I found setting the RF gain control to 3 o-clock a better choice to
reduce background noise. Noise on other bands was not a noticeable and
running RF gain at max, preamp on, and AF gain at ~9 o-clock worked
well.

73, Rod N0RC