[Icom] pwr IC746

[Sheldon Daitch]

Adam,

The only reason to mention the VU vs PPM was not to compare
them in terms of actually measuring PEP but to discuss the
effects of meter ballistics on measurements of something
other than a steady state sine wave, specifically "fast"
meters and "slow" meters will read much more closely
on a steady state tone than with voice audio.  Then again,
we could get into the realm of reading peak power vs RMS
power.

But that same effect is very apparent in SSB operations
when the modulation is a multi-tone "tone pack" for multiple
channel RTTY, in which case the PEP of the transmitted
signal approaches the rated power output of the transmitter,
but the average watt meter would read perhaps 15 dB below
that power level.  I don't have the numbers here at the office
for how far down a 16 channel tone pack needs to be, below
PEP rating of a transmitter to reduce distortion products to an
acceptable level, but it is much more than one might think.
(In the case of multiple tone transmissions, the transmitter
has to be able to handled the in phase power of all the tones in
use, but that phase relationship varies and does not result
in a high average power.)

I would submit that for the best accuracy in measuring
performance of a SSB transmitter would require a good
calibrated spectrum analyzer, but with proper metering one
could achieve fair results with the metering provided.

Thanks,

73
Sheldon

Adam Farson wrote:

> Hi Clete,
>
> As a rule, one can safely assume that a solid-state 100W-class transmitter
> will deliver 100W PEP on SSB when it is adjusted for 100W CW output. This is
> how I set up my radios; I set output power in RTTY mode, adjust Mic Gain for
> mid-scale deflection on the ALC scale (on voice peaks) and set COMP for 3 to
> 5 dB compression (also on voice peaks). This procedure will be adequate if
> the radio's Po scale is average-reading (as most seem to be).
>
> The digital (peak-reading) Po scale on the IC-756Pro and Pro II is fairly
> close to a true fast-attack slow-decay peak-reading meter, as is the peak
> output scale on the Quadra. I use those scales to check PEP. For a more
> exacting measurement, I use the procedure on my homepage.
>
> The question of PPM vs. VU meters is not really all that relevant to the
> topic of accurate SSB PEP measurement.
>
> http://www.qsl.net/ab4oj/peptest.html
>
> Best 73,
> Adam, VA7OJ/AB4OJ
> North Vancouver, BC, Canada
> http://www.qsl.net/ab4oj/
> Icom FAQ site:
> http://www.qsl.net/icom/
>
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