How does lowering the RF Gain help with SNR?












1












$begingroup$


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.




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.











share|improve this question











$endgroup$












  • $begingroup$
    The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    it might be very helpful to steer the answers by linking to one of these articles!
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    added a few to the question
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    @MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
    $endgroup$
    – Paul
    yesterday


















1












$begingroup$


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.




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.











share|improve this question











$endgroup$












  • $begingroup$
    The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    it might be very helpful to steer the answers by linking to one of these articles!
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    added a few to the question
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    @MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
    $endgroup$
    – Paul
    yesterday
















1












1








1





$begingroup$


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.




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.











share|improve this question











$endgroup$




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.




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.








equipment-operation noise






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday







Paul

















asked yesterday









PaulPaul

1258




1258












  • $begingroup$
    The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    it might be very helpful to steer the answers by linking to one of these articles!
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    added a few to the question
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    @MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
    $endgroup$
    – Paul
    yesterday




















  • $begingroup$
    The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    it might be very helpful to steer the answers by linking to one of these articles!
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    added a few to the question
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
    $endgroup$
    – Marcus Müller
    yesterday










  • $begingroup$
    @MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
    $endgroup$
    – Paul
    yesterday


















$begingroup$
The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
$endgroup$
– Brian K1LI
yesterday




$begingroup$
The RF receiving system is very complex. An approach that works with any given signal, using a particular receiver, under specific conditions of propagation, with unique combinations of atmospheric, man-made and cosmic noise, might not work well with any other combination.
$endgroup$
– Brian K1LI
yesterday












$begingroup$
it might be very helpful to steer the answers by linking to one of these articles!
$endgroup$
– Marcus Müller
yesterday




$begingroup$
it might be very helpful to steer the answers by linking to one of these articles!
$endgroup$
– Marcus Müller
yesterday












$begingroup$
added a few to the question
$endgroup$
– Paul
yesterday




$begingroup$
added a few to the question
$endgroup$
– Paul
yesterday












$begingroup$
@Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
$endgroup$
– Marcus Müller
yesterday




$begingroup$
@Paul I tried to add the quotations from the links; didn't find anything clearly related to your question in your third link; if you could copy and paste the appropriate section yourself, I think this would help my understanding.
$endgroup$
– Marcus Müller
yesterday












$begingroup$
@MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
$endgroup$
– Paul
yesterday






$begingroup$
@MarcusMüller The ones you added are pretty much the ones I'm wondering about. They all seem to imply that it improves the SNR. One going so far as to say the S meter reading goes up a unit. I'm starting to think the qrz and eham forums are full of more misinformation than I thought. How apropos when talking about poor SNR.
$endgroup$
– Paul
yesterday












3 Answers
3






active

oldest

votes


















2












$begingroup$

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?






share|improve this answer









$endgroup$













  • $begingroup$
    I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
    $endgroup$
    – Marcus Müller
    yesterday



















1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
    $endgroup$
    – Digiproc
    yesterday












  • $begingroup$
    I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
    $endgroup$
    – Cecil - W5DXP
    yesterday










  • $begingroup$
    @Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
    $endgroup$
    – Mike Waters
    yesterday



















-1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    Wouldn't lowing the AF achieve the same effect?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
    $endgroup$
    – Zeiss Ikon
    yesterday










  • $begingroup$
    That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul Think you mean "atmospheric" noise rather than "antenna" noise.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    @Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
    $endgroup$
    – Zeiss Ikon
    yesterday











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3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes









2












$begingroup$

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?






share|improve this answer









$endgroup$













  • $begingroup$
    I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
    $endgroup$
    – Marcus Müller
    yesterday
















2












$begingroup$

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?






share|improve this answer









$endgroup$













  • $begingroup$
    I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
    $endgroup$
    – Marcus Müller
    yesterday














2












2








2





$begingroup$

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?






share|improve this answer









$endgroup$



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?







share|improve this answer












share|improve this answer



share|improve this answer










answered yesterday









hobbs - KC2Ghobbs - KC2G

83828




83828












  • $begingroup$
    I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
    $endgroup$
    – Marcus Müller
    yesterday


















  • $begingroup$
    I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
    $endgroup$
    – Marcus Müller
    yesterday
















$begingroup$
I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
$endgroup$
– Paul
yesterday




$begingroup$
I hadn't considered non-linearity at the low end. But that does make sense. Like you said, however, if the signal is just above the noise then it would be hard to find a spot where the noise is attenuated more than the signal. I assume that linear to non-linear "cliff" is not a clean cut line. I suspect that most people who try this method are going in with a bias that it works. They try to "dig" out a signal and it sounds good. And confirmation bias dictates it was their method that made it sound good.
$endgroup$
– Paul
yesterday












$begingroup$
the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
$endgroup$
– Marcus Müller
yesterday




$begingroup$
the nonlinearity on the lower end is typically done away with by the magic of dithering – for every time instant, the received amplitude isn't just the low signal amplitude, but biased with the random noise amplitude (which tends to be larger). By low-pass filtering after the amplification, we use the fact that the "lifting" noise is temporally uncorrelated and hence falls prey to the low-pass filter, and the correlated desired signal remains amplified. But that only works if the filtering happens after the amplification! If you start with a narrowband filter, you'll get nothing.
$endgroup$
– Marcus Müller
yesterday











1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
    $endgroup$
    – Digiproc
    yesterday












  • $begingroup$
    I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
    $endgroup$
    – Cecil - W5DXP
    yesterday










  • $begingroup$
    @Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
    $endgroup$
    – Mike Waters
    yesterday
















1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
    $endgroup$
    – Digiproc
    yesterday












  • $begingroup$
    I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
    $endgroup$
    – Cecil - W5DXP
    yesterday










  • $begingroup$
    @Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
    $endgroup$
    – Mike Waters
    yesterday














1












1








1





$begingroup$

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.






share|improve this answer









$endgroup$



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.







share|improve this answer












share|improve this answer



share|improve this answer










answered yesterday









DigiprocDigiproc

26914




26914












  • $begingroup$
    How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
    $endgroup$
    – Digiproc
    yesterday












  • $begingroup$
    I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
    $endgroup$
    – Cecil - W5DXP
    yesterday










  • $begingroup$
    @Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
    $endgroup$
    – Mike Waters
    yesterday


















  • $begingroup$
    How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
    $endgroup$
    – Digiproc
    yesterday












  • $begingroup$
    I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
    $endgroup$
    – Cecil - W5DXP
    yesterday










  • $begingroup$
    @Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
    $endgroup$
    – Mike Waters
    yesterday
















$begingroup$
How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
$endgroup$
– Paul
yesterday




$begingroup$
How strong is the systemic noise in relation to the background noise on the antenna? I would expect the antenna noise to be the issue and not the internal noise of the radio.
$endgroup$
– Paul
yesterday












$begingroup$
The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
$endgroup$
– Digiproc
yesterday






$begingroup$
The higher the frequency, the more systemic noise becomes a problem. In fact, many cheaper/older UHF radios are swamped by their systemic noise. It's typically never a problem for HF bands, though. You'd have to look at your receiver specs to know for sure. Or you can do your own measurement.
$endgroup$
– Digiproc
yesterday














$begingroup$
I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
$endgroup$
– Paul
yesterday




$begingroup$
I'm talking mainly the HF band. And to be even more specific: 40 meters. I will update the questions.
$endgroup$
– Paul
yesterday












$begingroup$
The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
$endgroup$
– Cecil - W5DXP
yesterday




$begingroup$
The DSP noise reduction circuitry in my transceiver is the only thing I have found that works on 40m QRN.
$endgroup$
– Cecil - W5DXP
yesterday












$begingroup$
@Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
$endgroup$
– Mike Waters
yesterday




$begingroup$
@Cecil-W5DXP There's a lot to be said for some DSP noise reduction circuits! Which transceiver do you have?
$endgroup$
– Mike Waters
yesterday











-1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    Wouldn't lowing the AF achieve the same effect?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
    $endgroup$
    – Zeiss Ikon
    yesterday










  • $begingroup$
    That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul Think you mean "atmospheric" noise rather than "antenna" noise.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    @Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
    $endgroup$
    – Zeiss Ikon
    yesterday
















-1












$begingroup$

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.






share|improve this answer









$endgroup$













  • $begingroup$
    Wouldn't lowing the AF achieve the same effect?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
    $endgroup$
    – Zeiss Ikon
    yesterday










  • $begingroup$
    That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul Think you mean "atmospheric" noise rather than "antenna" noise.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    @Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
    $endgroup$
    – Zeiss Ikon
    yesterday














-1












-1








-1





$begingroup$

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.






share|improve this answer









$endgroup$



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.







share|improve this answer












share|improve this answer



share|improve this answer










answered yesterday









Zeiss IkonZeiss Ikon

625113




625113












  • $begingroup$
    Wouldn't lowing the AF achieve the same effect?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
    $endgroup$
    – Zeiss Ikon
    yesterday










  • $begingroup$
    That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul Think you mean "atmospheric" noise rather than "antenna" noise.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    @Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
    $endgroup$
    – Zeiss Ikon
    yesterday


















  • $begingroup$
    Wouldn't lowing the AF achieve the same effect?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
    $endgroup$
    – Zeiss Ikon
    yesterday










  • $begingroup$
    That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
    $endgroup$
    – Paul
    yesterday










  • $begingroup$
    @Paul Think you mean "atmospheric" noise rather than "antenna" noise.
    $endgroup$
    – Brian K1LI
    yesterday










  • $begingroup$
    @Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
    $endgroup$
    – Zeiss Ikon
    yesterday
















$begingroup$
Wouldn't lowing the AF achieve the same effect?
$endgroup$
– Paul
yesterday




$begingroup$
Wouldn't lowing the AF achieve the same effect?
$endgroup$
– Paul
yesterday












$begingroup$
Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
$endgroup$
– Zeiss Ikon
yesterday




$begingroup$
Chasing the AF doesn't keep the internal noise minimized, so won't preserve SNR to let your hearing do it's best work.
$endgroup$
– Zeiss Ikon
yesterday












$begingroup$
That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
$endgroup$
– Paul
yesterday




$begingroup$
That makes sense. But on 40m the antenna noise way higher than the internal noise. At that point is internal noise even a factor?
$endgroup$
– Paul
yesterday












$begingroup$
@Paul Think you mean "atmospheric" noise rather than "antenna" noise.
$endgroup$
– Brian K1LI
yesterday




$begingroup$
@Paul Think you mean "atmospheric" noise rather than "antenna" noise.
$endgroup$
– Brian K1LI
yesterday












$begingroup$
@Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
$endgroup$
– Zeiss Ikon
yesterday




$begingroup$
@Paul Internal noise is always a factor. It's added to atmospheric noise. If the total noise is louder than your signal, you have a problem.
$endgroup$
– Zeiss Ikon
yesterday


















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