|[AMRadio] Slew rate in plate modulated final|
k4kyv at charter.net
Sat Sep 6 10:22:17 EDT 2008
Here is the classic ultramodulation circuit based on the 1956 article in
QST. I tried this one back in the 60's and although it made the rf ammeter
kick up higher, the rf finals blush and the plate current meter kick upwards
on modulation peaks, over-the-air reports told me that the audio didn't
sound any louder but that the audio had fuzzy sounding distortion.
Here is WA1QIX's improvement on the above "ultramodulation" circuit that
actually reduces the splatter compared to normal overmodulation.
The purpose of the circuit is to suppress occasional negative overmodulation
peaks while offering protection to the modulation transformer, not to pile
extra audio on to the carrier by driving every cycle of the audio waveform
into negative peak limiting, hoping to make the modulation "louder".
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