[AMRadio] Re: Screen Modulated 813


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Tue Dec 12 19:13:22 EST 2006


No one talks about the nasty distortion you get in most
receivers when you get much over 100% modulation.

Most people sound MUCH nicer if they run the audio
under 100% modulation.

My transmitter might like doing 15 watts of carrier
and 1500 watts pep, but no one is going to think it
sounds good...

Brett
N2DTS 

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of ne1s
> Sent: Tuesday, December 12, 2006 2:55 PM
> To: bcarling at cfl.rr.com; Discussion of AM Radio in the Amateur Service
> Subject: [AMRadio] Re: Screen Modulated 813
> 
> 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 
> correct. 
> 
> > 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. 
> 
> 73,
>  -Larry/NE1S 
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