Martin Barr KH6MB End-Fed Half-Wave Tuner
Martin KH6MB designed an antenna tuner for use with end-fed half-wave vertical antennas for use during annual feld day events. The tuner is capable of handling bands from 10-40 meters at legal limit power.
Circuit Diagram
The rotor shaft of the capacitor is attached to the 50 Ohm side to keep the high voltage away from your hand while tuning. Keep about 2 inches spacing between the inductor and the capacitor.
The wires from the inductor to the ground connection on the coax connector are #12 gauge. This is where all the current is.
The wire to the antenna and the other ground is #16 gauge. These are low current lines.
Note the orientation of the inductor; wider spacing wire turns towards back of unit.
Assembly Photos
KH6MB EFHW Tuner
Inductor and Capacitor position and wiring
Knob position and spacing
Antenna (left) and ground / SO239 position
Coax RF input and ground on outside of box)
Antenna connection on outside of box
Photos and illustrations courtesy of Kimo Chun KH7U
Bill Of Materials
P/N, Description, Cost, Manufacturer
(Note: major parts only. Miscellaneous wire, hardware, etc. can be locally purchased)
1) RI-20, Roller inductor, 0.1 – 20.0 µH, $75.00, Palstar
2) Variable capacitor, 5.5 – 83 pF, $45.00, Palstar – <<Item: 9001200 CUSTOM MADE DIFFERENTIAL VARIABLE CAPACITOR WITH COUPLER ON END OF SHAFT. 5.5 TO 83 PF>> – <<REF: INVOICE NUMBER 23906 SALES ORDER NO. 29434>>
3) NBA-10142, Enclosure Box, $47.43, Bud Industries
Ant-Tuner-Parts <<– a detailed list of parts (PDF)
August 2012
