[AMRadio] Power Levels

[Jeff Edmonson]

:        Thank you for your reasoned response.  I would expect nothing less
: from a group of real amateur radio operators.

I fail to see how you can accept his explanation of how it's correct, when
*essentially* I said the same thing, only to have you tell me it was wrong...

(and I quote)
(me:)#1, forget about a PEP reading wattmeter.
They're *close*, but not quite what you can read from an Osciliscope.

(you:)There is nothing wrong with PEP wattmeter readings and I'm sure
most amateurs use one to conform to the FCC requirment of 1500W
OUTPUT PEP.  For the sake of our discussion, PEP wattmeter
reading are adequate.

No, they're not.  And now you know why.

:        I read posts from this list for about a week before joining it and I
: saw quite a bit of ignornace and misinformation being spewed forth.

(me:)
Imagine an AM carrier on your o'scope(allow me to interject a quote I read from
the old AM Press Exchange; your carrier is set to occupy 2 divisions and those
divisions could be say 2v per division.


Let's just use that, as an arbitrary rate (?).  That gives us 4V peak to peak

Now, modulate that carrier at 100%.  Assuming symetrical audio, your peaks will
reach 2 more divisions (or 8v peak to peak)  4x the original.

(you:)
The foregoing is wrong and wrong by 50% (in the audio).  A carrier which is 2
divisions pk-pk requires only 1 division pk-pk (of audio) to modulate it 100%.
Fact:  A carrier of 100W requires only 50 Watts of audio to modulate it 100%.

:        It is difficult to believe that testing for Advanced and Extra Class
: licenses has become such a farce.

the positive peak of a modulated AM carrier is twice that of the carrier that is
un-modulated.
Double the voltage, double the current.  The load remains the same.

375w of carrier, modulated symetrically will deliver 1500watts PEP of Output
power.
375 / 1500 = 4

(me:)
 Much the same way that a 100w rice-box needs to be lowered to somewhere around
25 watts of carrier, to allow for full audio output.

(you:)
This again is in error....perhaps an old wives tale.  The reason that the rice
boxes need to be lowered to 25 watts is that the final transistors are not
specified (selected) for continuous AM operation because, in the SSB mode, the
duty cycle is quite low whereas in AM it is 100%.

No sir.  The transistorized finals in your Yaewoodcom will allow you to output
100w.
There are three components of an AM signal; Carrier, Upper Sideband and Lower
Sideband.
AT THE MOST, you can run 33.3 watts of carrier, because you'll need 33.3 watts
of Upper Sideband energy
as well as 33.3 watts of Lower sideband energy to complete the AM signal.

(me:)
25w of carrier, and 25w of sideband power in each sideband - upper and lower,
with a little for overhead.

(you:)
This again is in error.  There is only 25 watts TOTAL of audio in both
sidebands.

Now, you know... that just might be true.   But, using your reasoning, tell me
how
100w of carrier, modulated to 100% will equal 400watts PEP?

(me:)
RMS of course, means Root Mean Square.  And, you're measuring the actual power
output of the rf generator.

(you:)
(You mean PEP is not a measure of the actual power ?)

Not the unmodulated RF that's being generated, no.  I'm sorry if I didn't make
that clear.

(me:)
Adding an audio component to the carrier, is what causes Peak Envelope Power.

(you:)
Audio is added to the carrier of an AM transmitter...how does one measure the
PEP value of an AM transmitter?

by multiplying the carrier power by 4.  And, as was earlier stated in this
group, if you're modulation is that of say 125%, then you multiply carrier power
* 4 * modulation percentage greater than 100%. (125% is 1.25% more than 100%) is
how you come up with the PEP output of an AM signal.

(you:)
I ask again, if you tune your amp up for 1500W output PEP, and then, without
changing anything, switch to CW and key it, what does the wattmeter read?

You won't get the same level you would as if you were reading the carrier with
an O'scope.

Please remember, AM means Amplitude Modulation.  AMPlitude, where the audio
expands the carrier.
in FM, we could all run 1500w output and modulate no more than 5kc of deviation
and be legal, according to
part 97.  Yes, even on 75m.  It is said, somewhere in there, in regards to FM on
HF, that no FM signal below
28MC shall have a signal no wider than a typical AM signal.

:        Again, thank you.

: 73 de
: Dave in Dayton, WT8R
:
:
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: _______________________________________________

While we're at it, Dave, heed the above... This list accepts text messages,
only.
No HTML.

Would you answer a question for me, please?
Why did you create your reply to me, off-list, and in a Word document file?

Oh, and.. Answer it here, in the list.  ok?

73 = Best Regards,
-=Jeff/W5OMR=-