[Elecraft] AGC OFF --> S-meter gone?

[Ron D'Eau Claire]

> I found a strange thing on my K2 (#2555).  A S9 + 20db CW station with
> AGC ON does not make the S-meter move when I turn off the AGC.  The
> signal itself stays just as loud in the speaker.
> Any ideas?
> Andreas, DL6UST/W7

That' is normal, Andreas. Here's why.

The AGC helps maintain a relatively constant output at the speaker or phones
by creating a voltage that REDUCES the gain as needed. In the K2 it works
just like the "RF Gain" control  except that it adjusts the gain
automatically. (In the K2 the "RF Gain" control is actually an i-f gain
control, adjusting the gain of the intermediate amplifier).  That's why you
must have the RF Gain control full UP for the AGC to work properly. The AGC
circuit will then take over and reduce the gain as needed, depending upon
the signal strength.

All the "S" meter does is to measure the gain control voltage that the AGC
or the "RF Gain" controls use to adjust the i-f gain. The greater the
control voltage (meaning the more the gain is REDUCED), the HIGHER the
S-Meter indicates. That way a very strong signal requires a big reduction in
the gain, so S-Meter reads very high.

If you turn the AGC Off, the i-f gain is now set by the "RF Gain" control
alone. Normally you have this full up. With the AGC Off, try turning the RF
Gain control DOWN, and you will see the S-meter display move UP the scale.
Now you are controlling the i-f amplifier gain manually, and the "S Meter"
is showing you how much you have reduced the i-f gain, just like it does
when the AGC is on.

The K2 has excellent 'dynamic range' meaining that it is hard to overload
the receiver. So when you turned off the AGC, the change was not really
apparent. Actually, you should have had heard the volume increase. If the
signal was strong enough, it would begin to sound distorted.

It is ALWAYS a good idea to keep the "RF Gain" at the lowest level needed to
avoid having strong signals overload the receiver. Overload can cause noise
that sounds like QRN or splatter that spreads across the band as well as
causing the strong signals to sound distorted. That's why Elecraft included
the Attenuator as well. Have that ON any time you have adequate signal
strengths coming in, and keep the RF Gain turned down (or the AGC On) to
avoid overloading the receiver.

If you don't use the AGC, it is a good idea to set the Audio Gain just below
the point where you can hear noise in the speaker or phones with a dummy
load on the receiver and leave it there. Then use the RF Gain control to
adjust the volume.

I prefer to operate with AGC off because it makes the bands sound more
natural and a LOT quieter! When you use AGC, it turns up the gain to full
between signals so the background noise between stations is nearly as loud
as the strongest signal.

Ron AC7AC
K2 # 1289