As Bill says "there is no RMS power". RMS power is a common misconception and
it confuses things when you start to convert things. There is only average
power that is derived from RMS voltage and RMS current or RMS voltage and
resistance or RMS current and resistance.
RMS voltage squared divided by resistance gives average power.
RMS voltage squared times resistance gives average power.
Average power is 1/2 of peak power. (.707 times .707 = .5)
If you try to figure things with RMS power you will get totally confused.
If you multiply peak voltage by peak current that gives you peak power. (this
is not PEP)
To find AVERAGE power you multiply peak voltage times .707. That gives RMS
voltage. Then multiply peak current by .707. That gives RMS current. Now RMS
voltage times RMS current gives AVERAGE power.
NOTE that .707 times .707 = .499 or rounded to .5. So AVERAGE power is 1/2 of
peak power.
If you try to find RMS power by multiplying peak power by .707 you will get 70%
of peak power. Not 1/2 of peak power that is average power.
Peak envelope power is average power of 1 cycle of rf at modulation peaks. It
is the same as average power of CW. In other words 1000 watts of CW power is
also 1000 watts PEP.
Average power in the PEP formula is not to be confused with average modulation
power as we see on the watt meter when we talk into the mike.
73
Gary K4FMX
Joseph DiPietro wrote:
> The RMS power of an RF signal is a mathamatical approximation of the
> equivilant amount of DC power.
>
> For example, if an RF signal were to dissapate in a resistive load then the
> RMS value of that signal would model the amount of DC power needed to cause
> the same amount of heating in the load.
>
> I don't quite understand what PEP is supposed to be but according to
> http://www.its.bldrdoc.gov/fs-1037/dir-027/_3903.htm
> peak envelope power (of a radio transmitter) [PEP, pX, PX]: The average
> power supplied to the antenna transmission line by a transmitter during one
> radio frequency cycle at the crest of the modulation envelope taken under
> normal operating conditions. [NTIA] [RR] (188)
>
> JoeD
> N2UF
>
> ----- Original Message -----
> From: <wb8jkr@juno.com>
> To: <Maximo.Martin@icm.siemens.com>
> Cc: <amps@contesting.com>
> Sent: Thursday, November 07, 2002 1:25 PM
> Subject: Re: [Amps] RMS-PEP & 2x8877
>
> >
> > The negative peak occurs 180 degrees away from the positive
> > peak, so they don't occur at the same time. You can't add them
> > together.
> > PEP power is the same power level as you would have KEY DOWN
> > at a given power level except whatever little extra you'd obtain
> > from power supply dynamics, typically 5 to 10 %.
> > A amp that runs 1000 watts output carrier is going to run 1000
> > watts PEP output plus maybe 5 to 10 % during SSB use, its
> > the average power that is going to vary considerably.
> >
> > Mark WB8JKR
> >
> >
> > On Thu, 7 Nov 2002 10:20:59 -0500 "Martin, Maximo"
> > <Maximo.Martin@icm.siemens.com> writes:
> > > RMS is an average measurement, efective power instead PEP, it's peak
> > > to
> > > peak.
> > > If you take one peak without flat-topping you have the RMS, but it
> > > is from
> > > the half of the total, in a graphic you use only the upper half part
> > > of the
> > > signal, but PEP is from the top peak to the bottom peak so it is
> > > more than
> > > double, it is 2.25 times.
> > >
> > > Max.
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: DF3KV@aol.com [mailto:DF3KV@aol.com]
> > > Sent: Thursday, November 07, 2002 9:52 AM
> > > To: Maximo.Martin@icm.siemens.com; amps@contesting.com
> > > Subject: Re: [Amps] RMS-PEP & 2x8877
> > >
> > >
> > > I
> > >
> > >
> > >
> > >
> > > 2 x 8877 are able to run about 4.5 to 5 Kw out, but this is a RMS
> > > measurement. The PEP value is the RMS x 2.25 so; 4.5 x 2.25= + 10000
> > > W
> > >
> > > Max.
> > >
> > >
> > >
> > >
> > > Hello Max,
> > >
> > > Please explain why PEP should equal 2,25 x RMS wattage?
> > >
> > > For my knowledge so far PEP ist the RMS wattage at the peak of the
> > > envelope without flat-topping.
> > >
> > > 73
> > > Peter
> > >
> > >
> > >
> > >
> > >
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