[TUNER] Z MATCH TUNER

[유재복]

Z-match for QRP

he Z-match is a very popular antenna tuner in the world of QRP hams. Surfing the internet pages you can find kits like the NorCal's Balanced Line Tuner and the commercial ZM-2 sold by Emtech™.
A lot of information about the working of the Z-match is described by Charlie Lofgren, W6JJZ.
Now my NC20 project is finished, I was looking for a antenna tuner which fits in the compact line of QRP my gear. Inspired by Charlie's work I have build a prototype combining a few designs. The schematic shows what I have done. Unfortunately I could not find a T130-6 toroid, so I used a T130-2 which would do the job too, I read. The variable capacitors are 7-345pF polyvaricon types from the junkbox.
The primary winding of the transformer consists of 30 turns 0,9mm enameled wire, tapped at 7 turns from the bottom (ground tap) and at 15 turns. On the secondary side there are two windings, both centered on the 7-turn ground tap. A high impedance link of 14 turns and a low impedance link of 6 turns, both 0,7mm enameled wire.
With an extra switch, one end of the balanced output is connected to ground while the other end is lead to a BNC connector for connecting coax fed antennas.
The series input capacitor is made switch able with a center-off toggle switch. (a. one section, b. two sections, c. both sections plus an additional 470pF padder.)

The final cabinet will include the famous N7VE LED SWR indicator circuit. Dan Tayloe invented this several years ago, and it has been proven a great addition to the QRP fraternity. The circuit is an absorptive bridge, which means that the transmitter sees a 50 ohm load when tuning the antenna. For the 50ohm resistors I used two 100ohm/1Watt types in parallel, so the bridge is rated at 5Watts.

Below are three pictures of the prototype tuner. The prototype was also made to determine the dimensions of the final cabinet I still have to make. I used the BLT cabinet sold by the AM-QRP Club as a guideline.

The schematic of my balanced line tuner. I need to experiment with the series diode whether to use a 1N4148 (Si) or a AA117 (Ge) type. The LED is a transparent bright red type.