Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

kc2rgw
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Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby kc2rgw » Wed Aug 12, 2020 5:02 pm

Just curious if anyone has ever tried what the results would be with SSB through a crude non-linear amp like a class C while using Pure Signal? Does it correct enough to allow for use of a crudely designed amplifier with maybe a very minimal low-pass filter.

Just daydreaming about cheap and easy amp builds.
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W1AEX
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby W1AEX » Wed Aug 12, 2020 7:28 pm

Just being curious, I flipped the switch on my AL-82 and ran SSB mode with the amp set for CW mode. In CW mode the amplifier sets the pair of 3-500 tubes very close to cut-off. The short story is that Pure Signal corrected the amplifier without any issue. The tubes barely showed any color when running full legal limit, which was a side benefit. Not sure how it would handle an amp biased at full cutoff for class C though.

73, Rob W1AEX
"One thing I am certain of is that there is too much certainty in the world."
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w-u-2-o
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby w-u-2-o » Wed Aug 12, 2020 10:33 pm

Very cool experiment, Rob!
kc2rgw
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby kc2rgw » Thu Aug 13, 2020 12:51 am

Very cool.
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FM5GB
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby FM5GB » Fri Aug 14, 2020 9:14 pm

Wow

does that mean that PS will make a class C amplifier feel like a true linear class A or AB ? Class C amps boosting FM or pure carrier signals
would not need PS. Did you check the behaviour on a separate SDR receiver or spectrum analyzer ?
This could simplify and cheapen PA in the future. It's hard to believe though no one had the idea before.

Phil FM5GB
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby AB2EZ » Sat Aug 15, 2020 12:38 am

An RF amplifier biased close to cutoff (just above cutoff) will still have a fairly linear relationship between the amplitude of the input envelope and the amplitude of the output envelope. Therefore it is no surprise that Pure Signal will work essentially the same as it does with a typical “linear” amplifier.

If the RF amplifier is biased well below cutoff (I.e. class C) it would be necessary for Pure Signal to add a DC offset to the input RF signal (in addition to performing the usual predistortion) to move the operating point to Class B.

I don’t know if Pure Signal, as presently designed, can do that.

Stu
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Re: Anyone ever run Pure Signal with a non-linear amplifier? Say a class C?

Postby K1LSB » Sat Aug 15, 2020 1:14 am

Stu,

To your point, my AL-80B runs SSB at full cutoff unless there is modulation on the audio. When I press the PTT and trip the amp into XMT mode, there is still no power coming out of the back of the amp (nor is there any grid current or plate current on the tube) until and unless I actually speak into the mic. PureSignal accommodates that arrangement exceptionally well.

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