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VE2HAR > MT63 12.03.05 20:37l 120 Lines 2823 Bytes #-7312 (0) @ WW
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Subj: Re: [MT63] Crest Factors
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VE2HAR
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Karl,
My setup is a Bird 4431 (model 43 with a sampling port) and a Tektronics
2225 scope. I first calibrate my scope. I use a single tone to set the
output of my IC-746pro to 40 watts as shown on the Bird, then adjust the
trace on the scope for some convenient deflection. I ended up with 4
gradicules peak to peak. Then I fire up MT63. Since crest factor is Peak
voltage/RMS voltage, I read the peak voltage from the scope. I then look
at the average power on the Bird and calculate the RMS voltage by taking
the square root of P*R where P is the power measured on the Bird and R is
50 Ohms. I then divide the peak voltage by the RMS voltage to get the
linear crest factor, I then take 20*log10 of the linear crest factor to get dB.
My transceiver is linear up to 45 watts, so I typically use 40 W PEP when
transmitting waveforms that must be linear. That means when transmitting
MT63, my average power is somewhere around 12 watts.
73,
Mark N5RFX
At 07:23 AM 3/12/2005, karl larsen wrote:
> Hi Mark, No one I think knows what the crest factor is for MT63, but
>I am not surprised by your 10DB figure. I run it at about 20 watts out
>to a 100 watt transmitter so the peaks are not getting out.
>
> Please tell us how you made your measurements. Yours might become
>the "standard"...:-)
>
>
>Mark Miller wrote:
>
> >I have just recently measured crest factors (peak to RMS) for a few modes.
> >
> >MT63 10 dB
> >RDFT 8dB
> >WinDRM 12 dB
> >
> >Has anyone else measured crest factors for these modes? I am just
> >wondering how close I am to the theoretical numbers.
> >
> >73,
> >
> >Mark N5RFX
> >
> >
> >
> >
> >
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