Setting RF Gain

[jk77]

This is a very elementary question, but it is one that I can't seem to find a clear-cut answer to. What is the correct method to set the RF gain?

Since the noise level depends on the RF gain setting, when people say they have, e.g., S7 noise how did they determine the RF gain setting that gave them the S7 noise floor?

Thanks.

 

[RFBOSS]

It is usually at full gain, unless otherwise specified. And at that not all S meters have the same signal level calibration.

The correct method of setting the RF gain may vary with the radio used, local conditions and band conditions and operator preference.

Back in the day there was a standard level for an S9 signal that was used by some manufactures, but not all.

This was 50 microvolts for an S9 signal and 6 dB change for each S unit below S9. Signals above S9 were what they were, whether it was a plus 1 dB signal or a plus 30 dB signal that was how much larger it was than an S9 signal.

 

[Sporrt]

You are correct, there is no clear cut answer. An individual adjusts the RF gain accordingly.

I've even seen RF gain set to 0, volume at max, and RF gain slowly rotated until signal is heard. Seems to reduce the noise.

 

[jk77]

Thanks, guys. I appreciate the responses.

So when people report, say, S7 noise the RF gain is usually set to max? When I turn up my RF gain, the noise on the S-meter decreases which somehow seems counter-intuitive to me. If I am to adopt that method, then I am in a very low-noise (S1 or S2) environment which should be true since I live in a rural area.

 

[majoco]

I've even seen RF gain set to 0, volume at max, and RF gain slowly rotated until signal is heard. Seems to reduce the noise.

This is the standard method for listening to SSB or CW morse on a basic radio with a BFO. Otherwise when the is no voice or CW carrier, the background noise comes up and when the signal starts again, there is a loud burst of audio until the AGC catches up - called 'pumping' - extremely irritating. Proper modern communication receivers have audio derived AGC with longer time constants. I wouldn't put the audio to max though, you'll probably hear all the audio amp noise and hum.

 

[majoco]

When I turn up my RF gain, the noise on the S-meter decreases which somehow seems counter-intuitive to me.

I believe you are confused about the relationship between signal strength, RF gain and AGC (automatic gain control) action.
The purpose of AGC is to keep the audio output relatively constant with widely varying signal strength. It does this by detecting the level of the signal and using this voltage to control the gain of the RF stages - the more the voltage, the less the gain. This voltage also drives your "S" meter. As you turn down your RF gain control, it adds a voltage to the AGC line so reducing the gain but it also moves the "S" meter up - even though there is no signal. The antenna noise you were hearing then goes down. So if you want maximum sensitivity, turn the RF Gain full up and you will hear the antenna atmospheric noises - hopefully your "S" meter will read 0 in your quiet rural area - if you connect your dummy load instead of the antenna you can set the "S" meter to 0. However, as I replied to Sporrt above, the noise gets annoying so you can back the RF gain off until the noise is just audible - a signal will still get through! I find the best setting with a high background noise (sometimes from next door's TV!) to just back off the RF gain until the "S" meter just starts to rise.

 

[majoco]

No answer? No Comment? It would be nice to know that you have made sense out of the above and your radio now works better.

 

[prcguy]

My suggestion would be to ignore the S meter when adjusting RF gain. Close your eyes and adjust until your ears are happy.
prcguy

 

[Jimru]

On HF, for a weak signal, I turn off the AGC, turn the RF gain up and turn the volume down. I adjust the RF gain as I would AF gain, instead.
Usually works fairly well, just remember to turn the AF gain way down before turning off the AGC!

 

[majoco]

Sure, the "S" meter is a 'nice to have' but doesn't actually tell you anything that you can guess with the Mk1 ear! Any commercial HF receivers I have used over the years often have a meter that indicates the AGC voltage but often on an arbitrary scale. The meter is often used to indicate voltages all round the receiver including audio level if you're feeding a decoder but often just with a 'green/red' scale to indicate good/bad.
After all, if you can copy the received signal with no errors then the object has been achieved - "S"1 or "S"9+20dB - who cares!