K3: AGC THR doesn't go low enough

[Ralph Parker]

Re:
>...the only way I get the quiet background I desire is to turn the AGC off..

and

>I had resigned myself to living with the AGC off because I can't stand
>the sound of the audio with it on in CW mode
>(I've come close to selling it because of that many times),

AHA!!!
Whenever I've posted a comment saying that my rx was noisy, it's generated
a flurry of responses saying that I'm crazy, and don't know what I'm
talking about or listening to.

I'll never sell ol' #1823, but I did put her on the back shelf for a while
until I added the DSPUPG board, and I'm giving her another critical listen.

Considering this and my never-loud-enough speaker amp, I must come to the
conclusion that NOT ALL THESE RADIOS ARE THE SAME!

Tnx John, and George - I feel your pain (to quote an ex-president).

VE7XF

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[P.B. Christensen]

>I had resigned myself to living with the AGC off because I can't stand
>the sound of the audio with it on in CW mode..

I have similar perceptions in CW mode and generally leave AGC turned off.
The only problem I've encountered living in Florida is that on the 40m-20M
bands, the 100 kHz/sec sweep from the Department of Homeland Security's
ROTHR system nearly leaves me with permanent hearing damage.

http://tinyurl.com/2egfnjo

The sweeps occur at regular intervals, usually around 12 minutes apart from
three ROTHR transmit facilities located in TX, VA, and PR.  With the SDR-IQ
running, I can usually react in time to activate AGC before the sweep
appears on my listening frequency.  However, when I'm not looking at the
screen, the result is pretty painful.  I know that the K3 firmware was
updated some time back to include a peak-limiter function, but it seems to
respond after the fact.

Paul, W9AC



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[W5UXH]

For me, it is more than a perception.  To demonstrate this to myself, I used the XG-2 set at 50 uV (so a good strong S9 signal) and for my normal operating setup I see a tone (from the XG-2) in the presence of very noticeable noise on an oscilloscope when looking at the K3 audio output.

I believe I understand why this happens in my case.  I believe it is because as a 100% CW  100% QSK type, I am not able to operate with the RF gain at maximum.  If I do this, then when I am talking, the band noise is greatly amplified in between elements by the AGC, in the absence of other received signals.

For this reason I have spent the last 50 years using the RF gain as my primary level control, keeping it as low as possible for the band conditions and signal I am in QSO with.

With the K3, the received signal sounds great with RF gain at max.  But it is not possible to think when transmitting with the RF gain at max, due to band noise.

With the RF gain turned down to an appropriate level for decent QSK (and the AF gain subsequently set higher), the "perceived" extra noise is very real as seen on the scope, and typically, in the absence of signals, there is no change in the noise when I ground the antenna.  Of course with RF gain at max there is a big change in noise when I ground the antenna.

So, I really doubt there is any "cure" for me.  I have played with the AGC SLP and THR parameters per suggestions in the main thread under this subject just in case.  But I suspect clean QSK and RF gain at max are just mutually exclusive with the K3.  If anyone can point me to a setup where this is not the case, I would be happy to investigate.

This is not the case with my FT-1000MP.  I have no idea what the reason for this difference is.  Unfortunately the MP keying waveform leaves a bit to be desired.  Maybe I will finally be forced to try one of the key click mods!

Chuck, W5UXH
Las Cruces, NM

P.B. Christensen wrote

>I had resigned myself to living with the AGC off because I can't stand
>the sound of the audio with it on in CW mode..

I have similar perceptions in CW mode and generally leave AGC turned off.