[Amps] IMD

[Dan Mills]

On Mon, 2012-01-02 at 13:01 -0500, Fuqua, Bill L wrote:
> If the amplifier is extremely non-linear it can produce key clicks.
> Class-E amplifiers requre a enevelope modulating power supply to 
> prevent key clicks. 
>   I can see that it is possible for hard driven, class-c amplifier 
> with 2 or 3 times cutoff bias
> could produce very noticable  key clicks. 

I was assuming something basically designed to be linear..... 

I have actually been playing with a modulating power supply in a SSB rig
using cartesian feedback to linearise the modulation response and
envelope feedforward to the power supply from the DSP that handles the
modulation, heat comes way down as the drain match improves and the fets
spend more time closer to saturation. 
The next step with that project is to add dynamic bias into the mix,
start off in AB at low levels, gradually fade to zero bias class C as
the envelope comes up, then (possibly) back to AB as the exciter starts
to run out of drive power, 40dB of envelope feedback cures many ills. 

It is not (quite) full on EER, because the feedback loop varies the
exciter output amplitude and phase, but it should come fairly close in
efficiency. 

73, Dan.