| | VE2HAR > MT63 13.03.05 01:04l 118 Lines 2910 Bytes #-7308 (0) @ WW
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Subj: Re: [MT63] Re: Crest Factors
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Sent: 050312/2346z @:VE2HAR.#MTL.QC.CAN.NOAM Laval #:41886 $:30236sentto
Mark Miller wrote:
>At 03:57 PM 3/12/2005, you wrote:
>
>
>>This term "Crest Factor" is a new one on me. I admit to doing my
>>Postgraduate School work way back shortly after WW2. I see Mark Miller has
>>clarified the term to be peak to RMS. That appears to be akin what we SSB
>>pioneers called the "Peak to Average" power ratio.
>>
>>
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Exactly. The SSB work back then was very similar to what we want to
measure. We want to know, if the average power was Wa what was the peak
power ever measured Wp? The Peak to Average number is P-to-A= Wp/Wa. Now
we can do some factoring of terms.
W=E*I = E(sq)/R. So we can rewrite P-toA = E(sq)p/E(sq)a. By the way,
E(sq) means the square of the number E.
Wa is defined as MT63 in transmit with zero data flow. On my system that
is 20 watts.
Wp is defined as the power measured when a lot of data is being sent.
So, we can measure the voltage across a load with a rf probe. We
need to measure the RMS voltage.
An example is that Ea = 3 volts RMS, and Ep= 10 volts RMS. To find a
number for P-to-A we square 3 and get 9, and square 10 and get 100 and
P-to-A= 100/9. This is correct and straight forward. You could do this
with your gear.
>I agree that peak to RMS voltage ratio is the same as the peak to average
>power ratio when stated in dB. I looked at my original findings. Note that
>peak power is not the same as PEP.
>
>My average power when using MT63 was 7 Watts as read on the Watt
>meter. This is 18.7 Vrms. The scope measured 60 Volts peak. 60/18.7 is
>3.2 which is the crest factor.
>
>
>
This has nothing to do with what we want to know about MT63. Period.
karl
>Using only power I had 7 Watts average and 60 volts showing on the
>scope. 60 volts indicates 72 watts peak. 72/7 = 10.3. The square root of
>10.3 is 3.2 which is the crest factor.
>
>Using dB, 20 log of 3.2 is 10.1 dB. 10 log of 10.3 is 10.1 dB. Everything
>is the same.
>
>73,
>
>Mark N5RFX
>
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><< Try MT63 on 80m - great fun!>>
>
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