Signals over S8?

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  • Updated 10 months ago
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Over the last while I noticed signals over S8 tend to spread out at the bottom on the panadapter and show images out past the TX band pass on the waterfall. If they go near S10 then they lock really bad. I have noticed this when talking to stations I know are transmitting very clean. When their signal falls below say, S7 they clean up. Their audio does not change, no distortion.

Dave W2OX and I have talked about this and we still do not know what to take from this yet.
I wonder if this is an under the hood fix? It looks like an overload.
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Bill -VA3WTB

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Posted 10 months ago

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Ken - NM9P, Elmer

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Official Response
Let's say that your noise floor is S4.
That gives you 5 S-Units to S9.
Each S-Unit = 6dB.
5 x 6 = 30 .

S9 is 30 dB above your noise floor.

If your rig/amp has intermod products that are 30 dB down from your peak signal, then at S9 they would just begin to show above the noise floor, showing up as the beginning of shelves on each side of the TX passband.

I'd you go up to S9 plus 10 dB (there is no such thing as S10) then the shelves on the sides of the TX skirts will begin to show increasingly wider.

As the noise floor, signal strength, or intermodal distortion products change, then the position, strength, and width of the skirts will change according to the numbers in the formula.

If the station is S9+30 dB, or even higher, then the bottom of the signal could look very broad, indeed.

Most modern amps are in the 35-45 dB range. Some are worse. Some are below 30! And if the amp is not tuned properly, or is overdriven, the numbers go downhill quite rapidly.

The thing about the Flex is that you can SEE it.

This is why many are salivating over Adaptive Pre-Distortion, which has been shown in some cases to exceed 50 dB down or more.

Ken - NM9P