...from the eHam.net website...
Matchbox antenna coupler (model 250-30) built by E. F. Johnson in the late 1950s.
The Matchbox is rated up to one-kilowatt ("maximum input to the final amplifier") and couples 52-ohm coaxial transmitter output to antenna loads that range from 50-ohms to 1200-ohms for balanced lines and 50-ohms to 2000-ohms for unbalanced lines.
The coupler circuit consists of a parallel resonant network with an inductor and a coaxial wound coupling link, a dual tuning capacitor, and a dual differential matching capacitor.
The kilowatt Matchbox also has a switching relay system that is designed for fast make-slow break operation that allows the final amplifier plate voltage to be cut off before the transmitter load is removed.
The unit measures 17.25" x 12.125 x 10.875" and weighs 27 lbs.
See WB6FZH for additional information on the 275-watt version MatchBox.
http://www.frobenius.com/matchbox.htm -- Last Revision: 01 January 2011
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