[CQ-Contest] Receiver Gain (Was TOP BAND RECEIVING ANTENNAS)

[Scott Ellington]

Most HF receivers do not have enough gain for decent AGC action on weak CW 
signals.  (The insertion loss of the CW filters can reduce IF gain 
considerably.)  This is particularly so on 10M, even with a beam in an urban 
location.  These receivers are sensitive enough, but for any signal that doesn't 
move the S-meter, you have to crank up the audio gain.  We all know what happens 
next, when a loud signal appears.

I prefer that the overall gain be high enough that the noise just moves the 
S-meter, so any signal will result in AGC action.  The proper way to achieve 
this is to have sufficient IF gain, which most receivers lack.  If there's an IF 
gain adjustment, one can turn it all the way up.  This will change the S-meter 
calibration, but probably not have any other adverse effects.  It's usually not 
enough, though.  Unless you want to modify the receiver, a preamp is the only 
alternative, but you'll have to switch it out when there are extremely strong 
signals around.  (I sense the purists cringing.)  The front end of most 
receivers provides adequate sensitivity and excellent dynamic range, and a 
preamp will almost certainly compromise the dynamic range.  Still, I find I use 
the preamp almost all the time on 10 and 15M with either the FT-1000D or TS-930. 
  I probably don't hear any better, but it's a lot more comfortable, and maybe 
I'll still be able to hear 30 years from now.

Needless to say, the preamp is often required with lossy receiving antennas.

I agree with Tom that your receiver is sensitive enough if you can hear a 
significant increase in noise when the antenna is connected.  Adequate 
senstivity, however, does not guarantee sufficient gain for good AGC on weak 
signals.  The AGC threshold could still be 20 dB above that noise level.  On the 
other hand, if your noise level moves the S-meter even slightly, you're better 
off without the preamp.


73,

Scott  K9MA


-- 
Scott Ellington
Madison, Wisconsin   USA

sdelling at facstaff.wisc.edu


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