Re: Slightly off-topic


sdwillingham
 

It is unlikely this problem involves the Si4734 AGC. There is no threshold used in the AGC processing of the IF signal. The time constants are very fast and the only artifacts of AGC I've heard are for very weak signals with carrier fading flutter. In that case, the AGC tries to keep the volume steady and succeeds, but the resulting pumping of the noise floor is more distracting than if one just let the signal flutter.

The threshold you might be referring to is the soft-mute property, which is only an audio attenuation when the SNR is too low (3 dB on a PL-380, larger for others). You are correct that off-tuning defeats the soft-mute pumping on weak signals. Again, it's only an audio processing effect, equivalent to volume control, so off-tuning doesn't compromise RF sensitivity.

As for the chuffing, I think it is an RF interference problem. (I don't have a Kchibo radio, so I can't verify this.) In all of these radios, there is a main "applications processor" which manages button presses, tuning dials, the display, and of course the Si4734. To save battery power, this processor sleeps most of the time. It wakes up when a button or dial is moved, then goes back to sleep some time later. If this circuitry (or the display) is not shielded properly, it emits interference right to the antenna and radio front-end. I believe that's what you are hearing as "chuffing".

In these cases, one way to diagnose this problem is to try putting another radio nearby with its antenna near the same position as the Kchibo's antenna. See if you can hear the interference in the second radio when pressing buttons on the Kchibo. If so, you have verified that the problem is emitted interference. If not, the problem could be something else, or it might be that you can't get the antenna close enough to the problem area. But it's an easy experiment.

-Scott-

--- In ultralightdx@..., "dhsatyadhana" <dhsatyadhana@...> wrote:

Ah, that chuffing! I call it pumping, but whatever you call it, my understanding is that signals that fade in and out below a certain SNR threshold (10 dB?) cause the AGC to pulse on and off. I think it disappears when you tune off-frequency and make the SNR go to zero - in that case, the AGC doesn't "come on" since it thinks the signal is very weak.

Experts, please chime in!

Kevin

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