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[AMPS] SB-200 parasitic chokes

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Subject: [AMPS] SB-200 parasitic chokes
From: (2)
Date: Mon, 6 Aug 2001 09:39:39 -0700
>Can anyone provide the value of the resistor used and the number of turns 
>the parasitic chokes used in the SB-200. The manual only lists them as a 
>"prebuilt" part that came with the kit. Thanks!
//  ... roughly 7-turns, 1/4 - 5/16 inch diameter with about 1 wire 
diameter air gap between turns.  The best resistors for this application 
are probably Matsushita 3W MOF-type.  I tested a 100-ohm 3W unit at 12W 
for 1-hour.  The resistor glowed dull red, the blue paint got pale, but 
the resistor did not fail.   The L of these resistors is low,:  11nH -- 
which is almost as low as an equivalent piece of copper tubing.  A low-L 
resistor is what's prescribed for VHF parasite suppressor service.  Also, 
by making the coil from resistance-wire, an approx. 60% improvement in 
suppression ability results.  
--  Notes:  Do not wind the wire on the film resistor because the 
conductive film is under the paint. / The coils should be at right angles 
to each other. / The suppressor resistors should get very hot and 
discolor during AØ on 10m.  

cheers, Mark

-  R. L. Measures, 805.386.3734,AG6K,  

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