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VE2HAR > MT63     12.03.05 23:31l 91 Lines 2625 Bytes #-7309 (0) @ WW
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Subj: Re: [MT63] Crest Factors
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At 02:09 PM 3/12/2005, karl larsen wrote:

>Mark Miller wrote:
>
> >Karl,
> >
> >My setup is a Bird 4431 (model 43 with a sampling port)
> >
>     Sorry I do not know that Bird 4431. What is the bandwidth of the
>sampled data? And what is it sampling? Is it sampling the power or the
>voltage?

You do know what a Bird model 43 is don't you?  The 4431 has a power sample 
output that is adjustable from -15 to -70 dB.  It is a directional 
coupler.  The frequency range is from 2 to 1000 MHz.


>     I assume you have a dummy load on your Bird watt meter. I did some
>peak power measurements using my Heathkit Antenna. It has a diode that
>picks off the voltage across the resistor which you can hook a scope to.
>It is quite accurate I found from testing.
>
>     With the antenna it would be easy to measure the difference from the
>resting power with the transmitter turned on, and then the peak power
>with data flow.

What is this resting power?  Please define.


> > 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,
> >
>Nope. The Crest factor is a Power measurement. And peak voltage is
>defined as the peak of the sine wave.

I disagree with you.  The definition of crest factor is the peak-to-rms 
voltage ratio of an alternating current (ac) signal.  The crest factor of a 
pure sine wave is 1.414.  It is definitely voltage.


>     I define peak power as the actual power when MT63 is being modulated
>continuously by digital data.

What do you mean by actual power?


>     I'm afraid your measuring something else.

I am afraid you do not understand crest factor.

73,

Mark N5RFX  




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