On Thu, 28 Jun 2001 04:16:26 -0000 "Billy Ward"
<billydeanward@hotmail.com> writes:
Hi Billy,
>
>I am having quite a debate with a group of hams and cb'ers about the
subject
>of RMS power. I have been a Ham for almost 44 years and have never had
>anyone deny that there is such a thing as RMS Power. I am aware that
there
>are other amplifier manufacturers on this reflector and I would like
some
>input on how to calculate RMS Power of a linear amplifier. I have heard
or
>seen in a book somewhere that Average power is equal to the RMS voltage
>times the RMS current. It seems to me that if one is measuring RMS
voltage
>and RMS current, the product would be RMS power but it also seems that
the
>reference that I read that said otherwise was one of the main
respectable
>ARRL OR Orr handbooks.
(True) RMS power is probably best measured with a caloric instrument.
If you are dealing with anything besides a single tone signal, the peak
to average ratios will deceive most simple meters.
>One of the gang that I have had the discussion with says that when you
>measure a modulation envelope peak to peak symetrically modulated signal
>across a dummy load with a calibrated scope and calculate the power
using
>Esquared/R = P, that the Bird 43 will show 1/3 of that value when
looking at
>the dead key instead of 1/4. He therefore thinks that the Bird is a POS.
I
>happen to like the Bird 43 and have a lot of respect for it. Has anyone
here
>got a comment on that?
The Bird 43 (without a peak reading module) is an average reading
meter.
Sounds like AM... then, 1/4 is the correct figure above. If the peaks
aren't 4X the carrier value then, either you don't have 100% modulation
or something is operating non-linearly.
>It has been years since I had everything set up on the bench to make
these
>measurements accurately but I would swear that when I used to frequently
>make these type of tests that I came up with carriers that were 1/4 the
>modulated peaks. I know that the modulation envelope is double the size
>during 100% modulation and that calls for 4 times the power of the dead
key
>value. I also am aware that the carrier does not actually change in
size
>and that the modulation is a mixing process.
Likewise correct.
Note that during modulation the average power, contained in the
carrier plus the two sidebands of a 100% modulated AM signal, is 150% of
the unmodulated carrier power which is what a Bird 43 would read.
73 & Good evening,
Marv WC6W
*
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