Re: K3 Sub RF gain

Posted by Stan Gibbs, KR7C on Oct 23, 2010; 11:04pm
URL: http://elecraft.85.s1.nabble.com/K3-Sub-RF-gain-tp5659334p5666590.html

Mike Scott-7 wrote

Still full CCW on the sub is about 12:00 O'clock on the main.

At full RF gain both are about equal. Strong signals are still copyable on
the sub Rx with full off RF gain, the main is dead when RF gain is minimum.

With my XG2 as a 40m source, I observe a similar phenomenon with my K3 (SN 4181) Main/Sub RF gains, though the details are quite different.  I'm running without PRE or ATT and the behavior is the same whether the BW is 2.8 kHz or 100 Hz.

At max gain, both the Sub and the Main generate the same audio level in my two ears (precision instruments). And, as the gains are reduced, the audio falls off similarly such that they are both just about inaudible at the 11:00 position on their respective gain knobs.  But the behavior on reducing the gain further is very different.

The Sub remains inaudible all the way to full CCW.  However, by about 10:00 on the Main gain, the response goes through a non-linearity where the audio jumps up to a level similar to about 3:00 on the gain dial.  Further reduction of the main gain reduces the audio again, but never to inaudibility.

Interestingly, the S meter also displays this non-linear response, climbing from S7 to S9+30, as the main gain is reduced from the max, until at the 10:00 position it suddenly falls to about S8.  Further reduction of the gain does not affect the S meter level.

I've repeated the RF Gain Calibration several times with both the 40m and 20m XG2 signals.  I have seen no change in the behavior as a result.

Does anyone else see this kind of behavior?