[AMRadio] Re: max output off dip

[RABRUNER at aol.com]

I have never seen a plate modulated AM transmitter that didn't put out more 
RF off dip.  In fact, this phenomenon was used in many AM broadcast 
transmitters.  The RCA BTA-1R series of transmitters (2 4-400s modulating 2 
4-400s) had fixed output coupling.  The instructions were to adjust the 
output loading by moving taps on the coils until you achieved about 80 per 
cent of the required power, and then run the plate tuning off dip until the 
desired power was obtained.  Even transmitters which had adjustable output 
coupling would offer the same instructions.  Transmitters that I engineered 
that worked this way included the Gates BC-5P, BC-1E, BC-1G, the Collins 
30-V3, and RCAs referenced above.  In fact, on the RCA, if you tired to load 
it up 'on dip' you would not make power.  You get more efficiency out of a 
class C plate modulated amplifier if you tune it to the 'High" side of dip, 
often referred to as the capacitive side of dip.  You can improve the 
efficiency of your finals better than 10 percent this way.  This is because, 
while the input to the stage increases as you run the tuning 'Hi C', the RF 
output is going up faster.  Even linear amplifiers work this way. Anyone who 
has experience with a Heathkit SB-220 for instance will not that the 
instructions are to dip the play and then adjust the final for maximum output 
using both the tuning and loading.

Bob Bruner
WB4TAJ/9


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