[AMRadio] Modulation power required


Bob Macklin macklinbob at msn.com
Thu Feb 14 19:53:56 EST 2008


I think that was my point. An instrument could be made to capture any peak
that went over the limit. It only takes one. But if you have one you
probably have more.

In my opinion the thing for the average ham to do is set their monitor to
display the maximum the want to transmit on their monitor. If they see the
trapezoid flashing over that point they will know they have a problem. But
they will never see a single cycle.

The thing to do is not worry about it until you get a notice. Just don't
push your modulation to the legal limit!

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "John Coleman" <jc at pctechref.com>
To: "'Discussion of AM Radio in the Amateur Service'"
<amradio at mailman.qth.net>
Sent: Thursday, February 14, 2008 4:32 PM
Subject: RE: [AMRadio] Modulation power required


Bob:
As you pointed out earlier it is nearly impossible to measure a
single cycle.  It is just a definition.  When looking at the trap pattern or
an envelope pattern one can get a pretty fair measurement of the peak
voltage of the envelope.  There is even meters that will give you the peak
RF of an envelope or just the peak RF of the carrier.  Then you can make the
assumption that the single RF cycle which exits at that most extreme point
of the envelope has the peak voltage of the envelope.  Calculate the RMS
value of that carrier voltage before putting the value in the power formula.
Power can only be calculated from RMS values of RF voltage or current.
(.707 Ep = Erms)  Ep is the peak RF voltage at the extremes of the RF sine
wave with respect to 0V center line.

Erms squared / 50 ohms of the dummy load = PEP for that envelope

With out modulation the carrier power is calculated the same way.

Measure the peak voltage of the RF
Multiply by .707
Square the product
Divide by 50

BTW if your using a scope to measure the RF voltage the peak will be 1/2 the
peak to peak of the RF on the scope.

Also I have a circuit using a 6AL5 which can be mounted in a small chassis
and affixed to the top of a Can-tenna which will allow measurement of the
peak RF voltage with very good accuracy.  If you interested.

John, WA5BXO






-----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 5:33 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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