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VE2HAR > MT63 13.03.05 15:07l 86 Lines 3023 Bytes #-7305 (0) @ WW
BID : 1463SENTTO
Read: GUEST
Subj: Re: [MT63] Re: Crest Factors
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<DB0EEO<DB0RES<ON0AR<VA2HAR<
VE2HAR
Sent: 050313/1343z @:VE2HAR.#MTL.QC.CAN.NOAM Laval #:42118 $:1463sentto
karl larsen wrote:
>
> We want to know what the POWER out is when MT63 is not being
> modulated by data to the POWER out maximum when it is. It is a ratio of
> POWER to POWER, not rms to peak voltage.
>
> The guy who thinks the method he found on a web page is right, is not
> able to see and not capable of proving that he is wrong. It is very wrong.
>
> karl
I think you've identified the wrong person as being wrong.
Apologies to those on the reflector who think we need to be on
the air using the mode rather than discussing its technical
characteristics -- but a certain amount of technical discussion
is necessary in order to properly understand HOW to use it.
And, if one thinks about it a bit, without a little technical
discussion and off-the-air work, there wouldn't BE any modes
to use on the air :)
Regardless of what the number is called -- crest factor,
SpongeBob's Ratio, or whatever, it is important to know how to
set the power level on your rig in order to cleanly transmit.
MT63 has a high peak-to-average ratio, PSK31 has a lower peak-to-
average ratio, and for MFSK, peak power IS average power.
It has nothing to do with the presence of data (if MT63 has no
data, it transmits an idle pattern -- which is still, from the
perspective of modulation, data), we're looking for the ratio
of power when the peaks of all the carriers hit their maximum
at the same time compared to the average power. It is certainly
a ratio of power to power, but there's no reason one can't
use voltage computations and square the results, or express
it in decibels where the conversion squares it for you (the
10*log for power vs the 20*log for voltage).
In looking over the e-mails again, I did find what appears to be a
minor flaw in the methodology presented (using the peak value
of the waveform vice the RMS value of the waveform at its peak),
but I think it's much more constructive to identify and fix the
minor flaw than to toss the entire concept out the window.
By the way, one of the first things I learned as an engineer is
to stay on the good side of the techs, in much the same was as
a smart military officer to listen to the senior enlisted people.
While they may not have the entire theoretical education, you
definitely don't want to discount their practical experience.
73,
Paul / K9PS
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