Netyjnd

Let's say for sake of example we are in the 40m band.

I've read articles and posts about riding the RF gain (or even just simply lowering it). And I can see how it is useful in overload situations.

What I don't quite get is how lowering the RF gain can help dig a weak signal out of the noise. A "weak signal" just means that it's not much stronger than the noise floor. Lowering the RF gain will lower the noise floor. But it will also lower the signal as well.

How is it possible that lowering the RF gain will attenuate the background noise faster than the desired signal. If you lower the gain by 3dB. Everything goes down by 3dB, right? The SNR doesn't improve.

I've also heard of "riding the RF gain" where you crank up the AF and use the RF as your volume control. How does this help? You are lowering the noise floor and the desired signal by the same amount with the RF gain. And then making it loud again with the AF gain.

There must be something happening when going from the IF to audio then benefits from having an overall quieter signal I guess. I just don't see how any of this can somehow know to attenuate static and amplify desired signal more.

Is dynamic range an issue with weak signals? I can see it being a problem with strong signals (hence the overload and need to attenuate). But with a weak signal, unless your noise floor is S9, you have enough dynamic range right?

Articles (i.e. forum posts)

https://www.eham.net/reviews/review/148466

Next, with the RF Gain still all of the way Counter-clockwise, so that the radio is nearly silent (don't move the RF Gain yet), we bring the AF Gain (volume) up to a quieted -- not quite normal listening level, where we cut hiss, but still just hear the signal clearly.

Once that AF Gain volume is set (about half for Icom 7300), you just leave it where it is, roughly, but you will twiddle it a bit up or down, to keep HISS down to lowest possible levels, as your slowly raise your RF Gain. You are now using your RF Gain as your volume control, by turning it clockwise to raise the volume, or counter-clockwise to lower the volume. While you are adjusting your RF Gain, you are looking for a happy medium between where signals are loudest, but the noise around them is quietest.

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I also twiddle with the AF Gain a little bit, if that helps the signal -- it really depends. Experiment!

https://forums.qrz.com/index.php?threads/rf-gain-more-powerful-than-nr.554997/

With AF gain on full, while using the RF gain to control volume, and aggressive EQ settings on upper-middle frequencies, signals barely readable often rise to an easy 56 to 57.

https://forums.qrz.com/index.php?threads/help-me-like-my-new-ic-7300-more.551169/

My KX2's RF Gain, when used with either ATT or Pre-amp, and EQ, will dramatically cut hiss noise while digging out signals.

I've seen this argument before and never been entirely convinced by it either, but I think the theory is that it comes down to nonlinearity. The silicon in the amplification and detection stages of your rig is never perfectly linear. Nonlinearity at the high end is what causes overload issues, but there's also nonlinearity at the low end, where a signal that is too small is greatly attenuated or causes no reaction at all. So if you can push the noise down far enough by reducing the input gain, the noise level in the output will suddenly fall off of a cliff, "revealing" your weak signal, or so the theory goes.

However, since the signal is (in this scenario) very close to the noise, we must be adding quite a bit of nonlinear distortion to it as well, and indeed the nonlinearity must be multiplying the signal with the noise (since the gain in the nonlinear region is dependent on the sum of signal and noise), so it's not clear that the result is any better than what we started with. Perhaps, since the mixing means that even most of the distortion products we hear are somehow correlated with the signal, copyability should improve even though the absolute fidelity doesn't?

There is some systemic noise created by the front end which is proportional to its gain. So, lowering the gain lowers that systemic noise, thus raising the SNR. Of course, the degree of improvement depends on the front end and the frequency. 'Riding the RF' simply keeps the front-end gain as low as possible. You're right, it isn't a dynamic range issue.

One factor at play here has to do with how human hearing works.

Generally (in my experience) the human hearing system (ears and brain together) does a better job of sifting information out of a low SNR when the overall sound level is low, than when it's high. That is, if you have a voice signal that's just perceptible against a background of white(ish) noise, you'll actually hear the voice better at output volume than when it's louder.

Since the recommendation is to set the audio gain and adjust the signal with RF gain (especially when working weak signals and low SNR), this means you're "chasing the RF" in order to optimize your own ability to hear the desired signal.

Of course, it doesn't hurt that lowering the RF gain may also lower internal noise more than received signal -- but even if it doesn't, you're likely to do your hearing a favor keeping it as low as you can and still hear the signal.