[AMRadio] Re: Screen Modulated 813

ne1s ne1s at neandertech.com
Tue Dec 12 14:55:07 EST 2006

Bry Carling writes: 

> Lary - I was talking about the kind of set-up with the 6DE7 
> that produces a SMALL carrier of say 6 or 8 watts
> and then does 90 watts p.e.p. on the voice peaks. 
Right - that is the question I addressed. 

> I may be nuts, but my empirical sense tells me that is 
> far more impressive sounding in the receiver n the other 
> end than the signal from the typical "novice rig" that runs
> 75 watts carrier input with Heising mod. OR even a plate 
> modulated class C rig with 22.5 watts carrier input and 
> 90 watts p.e.p. 
I think by "impressive" you mean the ratio of power in the sidebands to 
unmodulated carrier power - if so, I'd agree. 

> The power is turned DOWN during the inefficient phase 
> of the transmission in other words. 
We need to be careful here, because this created a misunderstanding about a 
year ago. With efficiency modulation (be it a linear amplifier stage, or 
screen suppressor, or control-grid modulated amplifier) PLATE EFFICIENCY (RF 
power output/DC plate power input) is lowest when the instantateous output 
is lowest. Therefore, the lower the output of the unmodulated carrier, the 
lower the PLATE EFFICIENCY. If we think of efficiency in terms of power in 
the sidebands/total power consumed (integrated over time), your statement is 

> WIth less and less quiescent signal the transmitter appraoches 
> the efficiency level of a DSB rig. 

Yes - in the limit, as the carrier level is reduced to zero, that's exactly 
what your left with: DSB w/o carrier. But the above comments on efficency 
still hold - plate efficiency in this case will be zero when no modulation 
is present, because there is no RF output, with finite DC plate power 
consumed. But, integrated over time, I believe less power will be consumed 
to convey the intelligence, so in this sense, "efficiency" is better. 


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