[Boatanchors] 813 grid to filament short

[rbethman]

On 10/2/2015 5:05 AM, Sheldon Daitch wrote:
> Bob,
>
> thanks.  I think the ERP got tossed in perhaps in error, but in defense of ERP on the broadcast bands, FM and TV stations have, in the past, used their ERP power levels in promotion material and nothing about their true transmitter power output.
>
> I remember many years back WBBQ in Augusta, GA, used to claim 137,000 watts - 100kW in the horizontal plane and 37kW in the vertical, as I think they had a split antenna system to cover both polarizations.  This may have been before circular polarized FM antenna systems became the norm, and I believe they added the vertical polarization antenna years after they went on the air.
>
> I note that Terman doesn't discuss asymmetrical modulation and his discussions appear to be based on sine wave modulation characteristics.
>
> Yes, voice audio is very asymmetrical and negative modulation peaks and positive modulation peaks in AM can give very different peak readings.
>
> The AM broadcasting industry has been well aware of this for years, and  Leonard Kahn was one of the first, when he manufactured, and marketed to broadcasters his Symmetra-Peak device, taking advantage of this, changing audio phase the higher of the peaks was on the positive side of modulation.  Most modern audio processors designed for AM transmitters have this capability built in.
>
> As we know, 100% negative modulation is a hard limit - carrier cut-off, but positive modulation on the AM band is limited by either the FCC (now 125%) or the modulation capability of the transmitter and perhaps how much distortion the listener was able to tolerate.
>
> As for monitoring, let me ramble here and if I am wrong, please correct me.  Assume a relatively accurate method of measuring 375 watts output, then use a scope to look at the transmitter output when 100% modulated with a sine wave, that peak level, top to bottom of the wave form, that would be your 1500 watt PEP level, right?  Any major audio greater than that peak to peak level, even on voice modulation, wouldn't that exceed the 1500 watts PEP?
>
> 73
> Sheldon
Sheldon,

You have it correct!  Indeed, 375Watt output, modulated with 100% sine 
wave would show the 1500 Watt PEP.

That is really where the fly gets into the ointment so to speak. Neither 
music nor human speech is symmetrical.  That is why the entire 
discussion is really moot in terms of measuring the mystical 1500W PEP!

It is just about the same as hunting a Unicorn!

Regards, Bob - N0DGN