[Elecraft] [K3] Setting RF gain & AGC correctly

[Al Lorona]

Again and again, I have asked (privately) those reporting 'bad K3 audio' to furnish me with settings, measurements, recordings -- anything-- but I haven't ever received anything with which I could diagnose the problem.

Bad. Noisy. Fatiguing. These adjectives have been used continually to describe K3 audio. I believe you, I just don't know exactly what you're hearing.

In the meantime, the analysis and recommendations that Ian, GM3SEK made here on 23 March are excellent and what I would consider required reading for anyone plagued with 'bad audio'. I must second all that he said.

In conjunction with Ian's tips, if you're not in the habit of using Bob, K4TAX's technique [see below] to set your RF gain correctly, please consider doing so. I have come to believe that many hams may not want to turn down their RF Gain (or turn off their preamps, or turn on their attenuators) perhaps for fear of not hearing very weak signals? However, you can't hear anything below the atmospheric noise level... so once the receiver can hear the external noise floor, any further sensitivity or gain doesn't buy you anything and only increases the noisiness -- which is what many of the complainants complain about.

I think it was about six years ago that I conducted a double-blind survey here on the reflector in which I presented hi-fi recordings of four different receivers-- including an unmodified K3 with the old DSP board-- and asked folks to identify the K3. I hypothesized that the 'noisy' and 'fatiguing' audio that many reported would make it easy to pick out the K3 from the group. [The other receivers in the test were an Omni VI, a K2, and a Ten Tec 1340.]

The results were exactly the same as random chance guessing, and the loudest critics of the K3 at the time were conspicuous by not participating. I don't know why; this only served to increase my frustration. At the time (and up to this day) my K3 AGC parameters were almost exactly those recommended by GM3SEK.

Anyway, please try all of these great techniques that have been presented in the past few weeks because I really believe they can help. Thanks for letting me beat this one to a pulp. [Now, if you want, you can beat me to a pulp privately instead of overloading the reflector.]

Al  W6LX


> My technique is to observe the S meter, no signal, RF Gain at max for 
> the given band and antenna.  Then with the antenna disconnected, 
> actually by a switch, I adjust the RF Gain until the S meter indicates 
> the same value as the noise coming in on the antenna. Then switch the 
> antenna back to the receiver.  The result is signal present and no noise.

> 73
> Bob, K4TAX