Amps
[Top] [All Lists]

[AMPS] Use of the Johnson Matchbox

To: <amps@contesting.com>
Subject: [AMPS] Use of the Johnson Matchbox
From: measures@vc.net (Rich Measures)
Date: Wed, 31 Mar 1999 02:26:00 -0800


>
>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  


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm


<Prev in Thread] Current Thread [Next in Thread>