E.F. Johnson Matchbox 250-23 275 watt

THIS ANTENNA TUNER IS CLEAN INSIDE NO FLASHOVERS

OUTSIDE CONDITION  5 OUT OF 10 THERE ARE  EXTRA   HOLES IN TOP , WORKS NORMALLY, NEEDS CABINET  RESTORATION IF YOU WANT A SHOW PIECE.

IF YOU NEED A GOOD PARALLEL RESONANANT NETWORK  " LADDER LINE FED ANTENNAS " THIS IS IT

EF Johnson Viking Matchbox Antenna Tuner (Model 250-23)

• GENERAL DESCRIPTION (From EF Johnson Instructions 2/58)
  • The Johnson Matchbox is an antenna coupler designed for matching antenna and transmission lin impedances to a 52 ohm impedance within the amateur bands from 3.5 to 30 megacycles. The Matchbox also provides band switching and transfer of the coupler from transmitter to receiver and in addition mutes the receiver and grounds the receiver antenna terminals during transmission.
  • The Matchox is capable of matching the 52 ohm coaxial output of a transmitter into loads ranging from approxiamately 50 ohms to 1200 ohms for balanced lines, and 50 to 2000 ohms for unbalanced lines. Large amounts of reactance can be compensated for by the coupler, the amount depending upon the frequency, line or antenna resistance. The Matchbox, or any coupler, installed at the transmitter end of the transmission line cannot corrrect the standing way on the transmission line. This standing wave is a matter of impedance match between the antenna and the transmission line and may be eliminated in various ways described in antenna and transmission line literature.
  • The coupler circuit consists of a parallel resonant network utilizing an inductor with a coaxialwound coupling link, a dual tuning capacitor, and a dual differential matching capacitor as shown in Figure 1. Impeadance matching for either balanced or unbalanced transmission lines and antennas is accomplished by the front panel controls of the dual capacitors without resorting to the customary coil taps or link adjustments.