[AMPS] Use of the Johnson Matchbox

[Rich Measures]

>
>Jim says:
>
>>  >I am pondering ways of actually measuring the efficiencies of these
>> tuners,  >but am not sure how to proceed.  
>> 
>> 
>measure the load impedance, measure the current with a thermo ammeter.
>Calibrate the thermoammeter with DC: measure its RF resistance (not easy!)
>at the frequency in question, ,measure the DC resistance and calculate a
>correction factor. Taking into account the inaccuracies, and the fact that
>the tuner should hopefully be 98% efficient or better, you may well find
>that the measurements tell you that the tuner is really an amplifier!
>
>Seriously, I think the best way to get an idea of tuner efficiency is
>temperature rise after ten minutes of key down at full power. And if the
>Delrin catches fire before then, you know it ain't that efficient..........
>
Unsubstantiated rumour has it that in the ARRL lab test of the MFJ "3kW" 
tuner Delrin ignition occurred at c. 30% of the mfg.-rated power level.  
>
-  later, Peter


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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