antenna tuner circuits
The Johnson 275 watt and Kilowatt Matchboxes are both unnecessarily exaggerated and unnecessarily maligned. They are not exceptional tuners, and are not poor designs. The primary drawbacks are the fixed coupling link, and the fact they are balanced VOLTAGE sources, not the generally more ideal current source. C2 is special and expensive. C2 is a d
ual-differential MATCHING capacitor with four capacitor sections. C2 has two insulated rotor areas in differential tied to the balanced outputs, two independent stators, and two commonly-connected stators. C2 is overcomplicated, with unnecessary sections in C2. The unnecessary sections of C2 are the two sections connected to ground. The two unnecessary grounded sections neither benefit nor harm tuner performance significantly. The tuner works almost identically when grounded inner sections of MATCHING capacitor C2 are eliminated. The fact Johnson included unnecessary grounded sections of C2 does not make it a bad tuner. The inclusion of unnecessary (basically harmless) sections only means Johnson wasted money and space inside the tuner by including the nearly-useless grounded C2 MATCHING capacitor sections. In the 1980`s, I designed an Ameritron ATR-10 antenna tuner (not related to any current Ameritron products). The ATR10 Ameritron was a companion to the AL84, and was designed as a companion bandpass 600-watt antenna tuner. The Ameritron ATR10 antenna tuner used a network functionally identical to the Johnson Matchbox series. The ATR-10 was a single-ended tuner with an output balun. The ATR-10 used a tapped inductor instead of a coupling link. The basic simplified ATR10 antenna tuner matching circuit is shown below: Tap A is from a standard rotary switch contact. This tap always leads tap B toward the hot end of the tank....