[AMRadio] Modulation power required


Gary Schafer garyschafer at comcast.net
Thu Feb 14 20:33:18 EST 2008


Bob,

As John says it's just part of the definition of PEP that the FCC gives. I
would suspect that their wording is meant to preclude anyone coming up with
some creative ways to get around what they have in mind.

They say it must be measured over at least one RF cycle. That means that you
may measure as many cycles as you wish as long as you are measuring them at
the peak or crest of the modulation envelope. The easiest way to measure PEP
is to just measure the highest peak of the modulation envelope on your scope
like John mentioned. You measure the peak to peak value, divide that in half
for the peak value, multiply by .707 to give RMS, square that and divide by
your load impedance (50 ohms). That gives you average power at the peak of
the modulation wave form which is Peak Envelope Power.

73
Gary K4FMX


> -----Original Message-----
> From: Bob Macklin [mailto:macklinbob at msn.com]
> Sent: Thursday, February 14, 2008 6:33 PM
> To: garyschafer at comcast.net; Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Modulation power required
> 
> "E squared / R will give average power."
> 
> So how do you do that on a single cycle?
> 
> Bob Macklin
> K5MYJ
> Seattle, Wa,
> "Real Radios Glow in the Dark"
> 
> ----- Original Message -----
> From: "Gary Schafer" <garyschafer at comcast.net>
> To: "'Discussion of AM Radio in the Amateur Service'"
> <amradio at mailman.qth.net>
> Sent: Thursday, February 14, 2008 3:13 PM
> Subject: RE: [AMRadio] Modulation power required
> 
> 
> >
> >
> > > -----Original Message-----
> > > From: amradio-bounces at mailman.qth.net [mailto:amradio-
> > > bounces at mailman.qth.net] On Behalf Of Bob Macklin
> > > Sent: Thursday, February 14, 2008 5:19 PM
> > > To: Discussion of AM Radio in the Amateur Service
> > > Subject: Re: [AMRadio] Modulation power required
> > >
> > > Why not just calibrate a Trapezoid display for MAXIMUM PEP? The just
> watch
> > > the trapezoid display?
> > >
> > > Watching a single cycle on a scope is a difficult thing to do.
> > >
> > > HOW DO YOU AVERAGE PEP ON A SINGLE CYCLE?
> >
> > E squared / R will give average power.
> >
> > 73
> > Gary  K4FMX
> >
> >
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