[AMRadio] Slew rate in plate modulated final

D. Chester 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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