[Boatanchors] 813 grid to filament short

[Gary Schafer]

It doesn't matter one bit if the modulation is symmetrical or not when
measuring PEP. We are only concerned with the POSITIVE PEAKS.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of rbethman
> Sent: Friday, October 02, 2015 5:44 AM
> To: boatanchors at mailman.qth.net
> Cc: wv2zow at gmail.com; SDAITCH at bbg.gov
> Subject: Re: [Boatanchors] 813 grid to filament short
> 
> 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
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