Should input of amp be tuned with a deadkey or modulated with a tone?

[loosecannon]

This question came up during a local CB group chat and i had to admit that i hadn't ever really given it much thought, and always just used a deadkey.

Then someone brought up "what about SSB" and i feel like they may have a point. or do they?

So i figured i'd bring up the question to this group. it made good discussion locally so why not here where people actually get into the "why" and not just the "what".

let's assume for the sake of discussion that the radio driving said amp would be a CB type radio that has both AM and SSB and the user uses both modes equally, and the amp is a solid state amp.

so what say you all?
do you have a preferred method?
care to explain why you use that particular method?
LC

 

[Shadetree Mechanic]

If the reflect on the input of an amp changes with mode or modulation, then I would say that the amplifier stability is more likely the problem than input match. And the output match can affect stability too, so the input problem could really be an output problem. Or the amp could use more negative feedback. That's the way I think of it.

 

[linearone]

Carrier

 

[nomadradio]

There will usually be a "spread" between where an input adjustment shows minimum reflected with carrier alone, and with modulation. The spread may be narrow, it could be large.

The more it rises when you modulate, the more you want it adjusted for minimum reflected power with modulation. But if it forces the mismatch with carrier alone to too high, a compromise between the two settings will probably stress the radio as little as possible.

And if that spread is just too high, fixing the amplifier's input circuit may be the only solution.

73

 

[loosecannon]

thank you for the reply nomad.

I have seen that spread that you speak of and that is partially what made me ask the question.
since we know that input power changes the impedance that the amp sees, which way should we be leaning when it comes to input tuning on an amp?

This local discussion got started by two people here, one of whom runs a ham radio with a tube amplifier that has an input tuning control on it.
he talks 99% SSB and of course always tunes the input of his amp, as well as the output, using a tone on SSB.

this prompted another who has started tinkering with solid state cb amp building to ask if he too should be using a tone on AM when he's adjusting the variable input cap on the two pill he just built.

my opinion was for him to just use a deadkey, but when pressed i had to admit a really didn't have a good answer for why.

regardless of whether or not this all comes down to opinion and preference, i think it's at least a worthwhile discussion to have.
LC

 

[nomadradio]

A tone isn't really any better than a long "helloooooooo". Achieves the same thing.

Every amplifier is different. The ideal compromise between carrier input match and modulated input match is determined by how that amplifier behaves.

Or doesn't.

73