[Elecraft] K3. RX too sensitive for me - S-meter/RFgain/absolute mode...

[Ron D'Eau Claire]

Don't forget that the K3 *is* a largely analog radio. The signal path only
goes digital at the second I.F.

I believe the K3 (and K2) handle manual RF gain control just like any analog
radio does - they insert an adjustable d-c bias gain control voltage that
replaces voltage originally created by the received signal. 

So turning the RF gain down simply fools the receiver into acting as if a
very strong signal was being received. The gain is reduced and the S-meter
displays the "presumed" signal strength. It's just a fancy way of handling
the method I mentioned in an earlier post when some early receivers without
AGC simply "calibrated" the front panel gain control with S-units around the
knob. On the Elecraft rigs, the S-meter replaces the knob calibration.

Also, when the RF gain is turned down, it behaves just like the RF gain on
other analog radios; the AGC will take over and further reduce the gain if a
signal stronger than the "phantom" signal produced by the RF gain control is
received (provided you haven't actually turned the AGC off). 

Of course, in the K3 and K2 the "RF" gain is really an "IF" gain control.
That is, they control the gain of the signal at the intermediate frequency
(first I.F. for the K3), not the level of the RF signal at the input to the
first mixer. That came about with the development of really robust, quiet
solid state mixers. Back in vacuum tube designs, that first mixer needed a
lot of protection from strong signals, so controlling the level of the radio
frequency ahead of the mixer was really important. 

In the K3 it all goes "digital" at the 15 kHz second I.F. and, in the K2,
digital starts at audio if it's equipped with the DSP option. 

Ron AC7AC 

-----Original Message-----

I wholeheartedly agree.  This behaviour has always irked me.

73 Stephen G4SJP

On 18 May 2011 17:27, Guy Olinger K2AV <olinger at bellsouth.net> wrote:
> They're not likely to see this, rolling up to Dayton, but rolling the
> s-meter up scale as you roll the RF gain back is making a digital
> radio behave like an analog radio just to keep from all the complaints
> that it's broke because it doesn't act analog.  The designer knows
> full well that we tolerate changes very poorly, even changes that are
> huge improvements. Remember that the analog S-meter was a voltage on a
> bus that controlled gain all over the RX. When you manually reduced
> the gain, that changed the resting voltage on that circuit and
> "buried" any movement less than that voltage.  Hence the familiar
> covering up of voltage changes for signals less than the increased
> threshold.
>
> If one has chosen "absolute" s-meter performance which is already
> un-analog, it would be nice to see the input level regardless of the
> RF gain setting, and perhaps just slow "plink" only the top segment
> that would be "covered" with the analog convention.
>
> 73, Guy.
>
> On Tue, May 17, 2011 at 11:40 PM, Ron D'Eau Claire <ron at cobi.biz> wrote:
>> Sometimes we're just too picky about that "S-Meter". Many years ago
(almost
>> before my time) a number of receivers had no meter but instead calibrated
>> the gain control in S-units (or the S-unit's ancestor, the "R-unit"). If
you
>> wanted to see how strong the signal was, set the gain for a comfortable
>> volume and check the position of the knob. Of course 99% of us reported
>> signal strength "by ear" and didn't need a "calibrated" knob, Hi!
>>
>> I'm not entirely sure today's rigs are an improvement, at least in the
area
>> of receiver gain control. They are, however, much more "automatic" and
with
>> that comes limitations. I'm a heavy user of the ATTEN, Preamp and RF gain
>> control in any receiver.
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