[AMRadio] new antenna and matchbox a bust.

Jim Wilhite w5jo at brightok.net
Mon Jan 29 22:25:08 EST 2007

>> * The EF Johnson Matchbox's have in my experience limited
>> tuning range when
>> the load is reactive, and even if the load is resistive, 
>> they
>> don't like
>> anything under a few hundred ohms or so. Feeding a 
>> resonant
>> antenna with 450
>> ohm feedline, and a High Z antenna (like a folded 
>> dipole),
>> and they work
>> great.
> I noticed the caps are really small...(in capacitance)

The 275 watt matchbox has caps with the following numbers:


Here is how to decipher the ratings.

The first number is the max capacity.

The last number x 100 is the "approximate" flashover 

The type C is 5-1/2" wide x 5-3/8" high The type D is 4-1/4" 
wide x 4" high The type E is 2-5/8" square The type F is 
2-1/16" square

Dual section caps have second letter D. e.g., 150DD45 is a 
150 pf maximum Type D @ 4500V flashover measuring 4-1/4" 
wide x 4" high.



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