Re: K3: RF Gain, Squelch

Posted by Alan Bloom on Jan 12, 2010; 4:51am
URL: http://elecraft.85.s1.nabble.com/K3-RF-Gain-Squelch-tp4289745p4289840.html

On most radios, the term "RF Gain" is actually a misnomer.  The control
should really be called "IF Gain".

The way most HF receivers work is that turning down the "RF Gain"
control simply applies a DC voltage to the receiver's AGC circuitry.
For example, if an S9 signal causes the AGC voltage to rise to 1.23
volts, then when you set the RF Gain control to place 1.23V on the AGC
line, the S meter will read S9 even when no signal is present.  In that
case, signals below S9 do not change the gain or S meter reading.
Signals above S9 cause the AGC/S meter to rise as before.

Turning down the RF gain control causes the receiver to sound less noisy
because the IF gain is limited to some maximum value.  If you set it
right you can still hear the weak signals (taking advantage of the human
ear's dynamic range) but you don't have to put up with so much noise.

On the noisy low bands I generally set the RF Gain control so that the S
meter reads nearly constant when no signals are present, bouncing up
slightly only on the biggest noise peaks.

Al N1AL




On Mon, 2010-01-11 at 20:11 -0800, Phil Hystad wrote:

> I have never really understood the connection between RF gain and squelch controls.  I first saw this when I got my first modern rig, the Icom 756 Pro III.  And, I see this kind of combo with the K3 too.  I never had experience with this back in my early ham operator days (~1960s).
>
> So, can someone explain the behavior.  Let's assume that I have squelch operative for FM only.
>
> On CW or SSB I see that RF gain maximized is the control knob turned all the way clockwise.  But, as I back off the RF gain (counterclockwise) there comes a point where the S-meter starts to increase even though there is no apparent signal.  Turning the RF gain fully counter clockwise pins the S-meter.
>
> So, what is going on here.  What is this connection between turning "down" RF gain and the S-meter increasing.  Now, I have the same behavior (roughly) on my Icom Pro III and I never understood that either.
>
> Thanks for any explanation you can contribute.
>
> 73, phil, K7PEH
> K3 owner for one full week now.
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