66 Foot End Fed Wire with Charlie Lofgren Design Z Match Tuner (2008)
This is my version of the Lofgren Z-Match tuner. It seems to be a refinement of the circuit used in the Emtech ZM-2. Input is from the BNC connector on the left. Below this is a switch to go from the operating position to the tune position. In the tune position a Tayloe resistive bridge is used. These can be purchased as a kit or easily made up. When the LED below the switch goes out, you are at 1:1 SWR. Very convenient. It is in a Radio Shack 2" x 2.375" x 5" plastic box.
The knob at the lower left is for the tuning capacitor in the radio side of the circuit. The three vertically oriented switches above it are for additional capacitance for this part of the circuit. The large knob is for the tuning capacitor on the antenna side of the circuit. The three horizontally oriented switches above it are for additional capacitance for this part of the circuit.
The the right are two binding posts. The red one is for the antenna wire. and the black one is for a counterpoise. The switch below the binding posts is to change the ratio of the toroid transformer. This gives the tuner the maximum possible amount of tuning range.
This tuner can tune high impedance half wave wires which is a big advantage over many other types of end fed wire tuners. A half wave antenna has such a high impedance to ground that it is almost ground independent and does not require a counter poise. Lofgren recommends a 3 to 6 foot counterpoise just to give the circuit a minimum amount of capacitance. I use a 6 foot wire. It is a great advantage to not have to fiddle with different length counterpoises. A 66 foot half wave on 40 meters wire tunes to 40, 20, 15 and 10 meters with this setup. This is the most versatile setup I have found for end fed wires.
Many of the QRP end fed wire tuners offered for sale are not strong enough to tune out the impedance of a half wave wire. They either require separate wires or even tuners for different bands. Some require a magic length of wire like 55 feet to tune more than one band. I consider this tuner design the best out there.
The complete article by Charles Lofgren is here:
http://www.seboldt.net/k0jd/z-match.html
Be sure to read the full article as the mods mentioned at the end of the article are what I used.
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On the right is the Tayloe bridge.
Note how the toroid is attached to |
Here you can see the taps on the toroid transformer. |
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This shows the parts for the Tayloe resistive bridge. |
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33 foot Jackite pole. Very light. The 26 gage stranded copper clad steel stealth wire is very light, strong and invisible. |
With battery, K2, and SWR analyzer. |
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