Best rf-gain demo video I've ever seen

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nanZor

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Getting the most out of your HF radio (be it for swl, amateur, utils whatever) usually ends up in someone telling you to ride the rf-gain manually. That leaves out a lot of detail, and a newcomer usually goes right back to listening to an S7 noise floor.

So although the video here is demonstrated using the amateur bands, it is general enough to be used by anyone. Thought I'd drop it in here, because not ALL of us are amateurs.


The bullet points here would be:
1) Roll your rf gain back to about S1, just tickling the meter. Otherwise you are activating the agc with noise already.
2) If necessary, turn OFF your preamp.
3) Test your setup merely by removing your antenna. You can tell if you have gone too far with gain reduction, if by removing and reattaching the antenna, you don't hear any increase / decrease in noise.
4) Simply crank your audio gain up a little to compensate.

S-meter readings are a valuable tool, but one can get so used to the swinging eye candy, that trying to make it dance can actually degrade reception and over time, you can get used to the wrong adjustment and spend much of your hobby disappointed or frustrated with a noise problem that may actually be tolerable!
 

ka3jjz

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Interesting, but one point here - if you have a preamp in the radio, leave it off as a matter of course. Use it only when necessary...Mike
 

majoco

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Yes, agreed, it is a very good video and very well explains 'riding the RF gain' which is an old technique especially when trying to copy a fading CW signal - you don't want the gain too high as it brings up the noise between characters. In quite a few of the older tube receivers, the RF gain control was combined with the AGC on/off - you had one or the other, or there was a separate switch - even my Sony CRF-230 does that. Of course when receiving an SSB signal, there is no carrier to produce the AGC voltage anyway so the noise will return to maximum unless you reduce the RF gain - that's why some receivers have AGC with long time delays on signal fall.
In some non-SDR type radios, the RF gain control actually feeds a voltage into the AGC line and thus changes the readings on the "S" meter, turning the RF gain down actually moves the "S" meter up the scale, not down as shown on the video - a minor point but may get some confused.
 

nanZor

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In some non-SDR type radios, the RF gain control actually feeds a voltage into the AGC line and thus changes the readings on the "S" meter, turning the RF gain down actually moves the "S" meter up the scale, not down as shown on the video - a minor point but may get some confused.

That's a GREAT point - one which makes me go nutty with some modern receivers/transceivers.

But there's hope - just do what you have to do to reduce the band noise s-meter reading down as close to tickling S1 without choking the front end. Ie, if an on-board attenuator drops your band noise from S7 to say S3, then one is headed in the right direction.

In addition, one may have the ability to turn off the first preamp, ie Yaesu's "IPO", cleverly named as an intercept-point-optimizer. :)

Using either one singularly or in combination may be necessary and might be easier than the stupid rf-gain s-meter circuitry that raises the s-meter reading instead of lowering it.

What if you don't have an S-meter or have run out of options? Just disconnect and reconnect the antenna to see if you have a reasonable change in noise level.

What I love about the video is the mention of how the S-meter has been turned into a misleading tool. And how listeners may be hurting their front-end performance with eye-candy. It also explains why some experienced contesters and radio users will hand out a "five-nine" to a station that is barely moving the meter! Because it *is* 59 to the op, and anything other than a very local or lab measurement is meaningless to those disgruntled by receiving one from the other op. :)

I think this should be mentioned to users of amplified small vertical loops too, not just "normal" antennas. With an additional amount of amplification prior to the radio out at the loop, using the "just tickle the S1" reading with gain /attenuation control will allow you to get the most from the loop's preamp. Now you'll be able tell if there are any performance issues with the loop preamp itself.
 
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majoco

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Hertzian said:
What I love about the video is the mention of how the S-meter has been turned into a misleading tool.
...and how many actually have a calibrated "S" meter anyway. The IARU 'proposed' a standard "S" meter should show S9 for 100uV EMF, -73dBm, but I found when setting up a Kenwood R2000 I found they said set it to 30dBuV which is -83dBm, 10 dB lower than the IARU spec. If you don't have the required and calibrated gear, do you just take it for granted that the "S" meter is showing true? Anyway, most of them don't have a linear scale anyway, so even if you have set the "S" meter S9 point correctly, then what you see as S5 and what I see as S5 might be totally different.
 

nanZor

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Heh so right. :)

For those receivers where reducing the rf-gain makes the s-meter rise, you have to abandon the "tickle the S1 point". What you do here is open your gain up, make note of the band noise floor, say S4 for example, and reduce the gain until the S-meter just rises beyond S4. Or whatever your noise floor is.

If you have no visible noise floor, but by engaging a preamp that puts you back to S5 say, then rock the rf gain back to either tickle S1, or for backwards driving s-meter rf gain, roll gain back to tickle S5. Harder to explain than to just do it in person.

I guess someone figured that this would be easier than trying to just tickle S1 all the time.

Admittedly it took me a few decades of not really knowing all this, and sat around fat and happy with even low S3 noise floors without doing anything about it. Ie, not getting all that I paid for in the receiver front end. It just feels counter-intuitive to use attenuation when the receiver isn't just totally being blown away. Go ahead - rock it back - you paid for that performance, so might as well use it!

The other cool thing is that if one is also using noise-reduction circuitry, dsp or otherwise, you may not have to have your settings for that up so high, and better intelligibility and reduced listener fatigue are the result.

The light bulb went off when studying agc circuits, and viewing the S-meter needle as the "brake handle" that the gremlin inside is using to stop the front end of the train. :) When viewed like that, I lost the addiction of making the s-meter dance, and am now getting all that the front end can give me.
 
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Boombox

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Ironically Majoco, the Realistic DX-160 (and probably its predecessors) combined the RF Gain and AGC components into its RF Gain control. They probably were copying the tendency in communications receivers that you describe.

For most of us without the comm type receivers (i.e. portables, some with RF Gain, some without), it's a matter of turning it back so the AGC doesn't pump.
 
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