K3 weird RF gain behaviour

[G3TCT]

I've just upgraded from firmware 3.27 to 3.63, and the gain balance in the
rx has been altered significantly.  The rf gain now reduces the S/N quite
noticeably as soon as it is rotated counter clockwise from max, suggesting
the gain is being mostly backed off at the rx front end, leaving the IF
stages on full gain.  This can be best heard by tuning in a steady
unmodulated carrier on AM, at say S7. Turn rf gain to max, af gain up to
hear background noise. Now reduce rf gain - the noise goes up! Then as I
reduce the rf gain further, the s meter reaches 9+25, then there's a click
and the meter jumps down to S7 and the signal is audible again!

Things I've tried:-
- reverting to 3.27 - problem disappears. RF gain at minimum shows 9+25 on s
meter.
- updating to 3.63 again - problem returns
- re-did the rf gain calibration - problem remains
I have agc dcy=soft; hld=0.30; pls=nor; slp=012; thr=005

Seems the gain calibration function was changed in 3.41.
Can anyone duplicate this?

Graham

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[Grant Youngman]

On Nov 29, 2009, at 11:51 AM, Graham Kimbell (G3TCT) wrote:

>
> stages on full gain.  This can be best heard by tuning in a steady
> unmodulated carrier on AM, at say S7. Turn rf gain to max, af gain up to
> hear background noise. Now reduce rf gain - the noise goes up! Then as I
> reduce the rf gain further, the s meter reaches 9+25, then there's a click
> and the meter jumps down to S7 and the signal is audible again!

I'm hearing something similar.  It's quite noticeable on AM, but I don't really hear it happening on CW/SSB.  It may just be less obvious.

What I'm not seeing at all is the sudden meter reduction you referred to.  As I turn down the RF gain, the meter just tops out.  My AGC settings are about the same as yours.  They don't seem to have an effect in any case.

Gran/NQ5T

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