Understanding Linearity of a station in the water fall

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  • Updated 3 years ago

Spurs or feathers I call it.
I know all of you have seen this many times.
This was a strong S-9+ signal.
Is it from the Radio,un-Linear amp, or Propagation from transmitting station?
Garbage in garbage out?
So if the radio was not in passband an amplifier would magnify this issue or not?
Improperly tuned HF amplifier create this on its own?

Looking for education for myself and others on this.

73 Jeff

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Posted 3 years ago

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Mike W9OJ

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I have a friend with a 6500, an SPE 2K-FA and an OM-4000. When he runs the 6500 barefoot or drives the SPE the signal in the waterfall has perfectly straight edges with no spurs to the sides. When he drives the OM-4000 it has a lot of spurs sticking out. It sounds OK to my ears but you definitely can see it using SSDR and my 6300. I thought the OM would be cleaner than the SPE but not so according to the waterfall.

Mike W9OJ
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EA4GLI - 8P9EH - Salvador

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This is very interesting! I would have thought the same... the way people speak of the OM amps....
I am very happy with my 1k and 1.3k SPEs.
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You would have to look at the panadapter view and see how many DB down that fuzz is.  If a guy is 20 over then that might be 70-80 db down which meets his rigs specifications which might be much less than  that.
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Al K0VM, Elmer

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With most amateur rigs and amps the distortion products are usually down only about 40db ( at best) at full output even when well adjusted.  ( HPSDR with Pure\Signal can be much better)
The panadapter can provide a better reading than the waterfall.

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Mike, someone listening to a signal like this may not hear any adverse effect. The real problem is that the distortion products (feathers, spurs, whiskers or whatever) manifest as "splatter" on the adjacent frequencies. So on a busy band it's antisocial at best. The example signal is taking up roughly 3 x the necessary bandwidth.

Adaptive pre-distortion should help eliminate the problem by improving the linearity of the output and can also include the "linear" amp in the loop. I look forward to seeing an FRS implementation.
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Steven G1XOW

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Obviously the OM-4000 would also be about twice the output of the SPE, so not really a fair test. Most recent solid state amps don't meet the minimum emission regs so wont get CE approval.
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Tim - W4TME, Customer Experience Manager

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It could be exciter phase noise too, but this looks like splatter.
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Looks like the average contest station
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Martin Ewing AA6E

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This is one of the advantages of running with a panafall Rx:  You get to see how awful many of the signals are on the band.  Many rigs are overdriven and give you excess intermodulation distortion (IMD) -- splatter.  If people would only back off a dB or so from full power!

The key thing you can't (easily) see is what your own signal looks like on the band.  You need full duplex and you need a sampler that feeds back a highly attenuated version of what's going up the feedline.  That's the setup you need for predistortion equalization operation.  Some day!
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Larry - W8LLL

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The Telepost LP-500/700 are going to be excellent for monitoring your signal with the trapezoid to make sure your amp is linear. watch the first video at the 7 minute mark


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Martin Ewing AA6E

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The Telepost monitors are amazing.   A lot of this functionality could be incorporated in SSDR, I'd think.  It's mostly "just software", after all. :-)
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Jon - KF2E

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This is a valid point. I would much rather pay Flex for this functionality than buying another device for the shack. Maybe they could offer a station monitor software option for an additional fee? I would be willing to pay.

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As well as local monitoring I find that looking on a "websdr" gives a good indication of my transmit spectrum. Just need to find one where you are a reasonable signal. Anyone can access them so there's really no excuse for signals like the earlier example these days;

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Simon Lewis

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yup I see it on HF all the time - the owner of this signal emailed me after I publicised his terrible signal here and on my FB page! - my answer - well tidy your signals up then and you won't get complaints!


It's a myriad of problems, over drive, poor tuning, too much compression etc

But the panadater sees all :)

Said VK was suggesting it was my receiver or how strong he was - funny how his companion VK's around him were straight sided and clean!

The pandapter tells no lies :)

As for the example above I'd bet without a doubt that if I was close in to that signal it would be splattering all over the band