My favourite antenna tuner is the single coil Z-Match. I tend to use ladder-line feeder instead of coax, so I believe a tuner designed for balanced feeder is a much better solution than a T-Match or SPC using an external 4:1 balun or similar. Many years ago, I used a standard Z-match with a doublet which worked well on the HF bands. In 1993, the single coil Z-Match was made popular by VK3OM and VK3AFW after their development of an earlier design of ZL3QQ. This design had the advantage of only one coupling link thus removing the necessity of bandswitching two links as used on the original Z-Match design. More information on the design can be found in "The W6SAI HF Antenna Handbook"
This QRP version by G3WQW, using a T130-2 toroidal inductor and polyvaricon variable capacitors was published in Sprat #84. An article in QRP Quarterly by Charlie Lofgren, W6JJZ
recommended using a T130-6 instead of a T130-2 for better Q and provided new turns values for use with the T130-6 toroid. Charlie also modified the design for better balance and 160m coverage. His Z-Match articles can be found on the NJQRP Club's Website
I have built two of the G3WQW design using polyvaricon capacitors and T130-6 toroids for QRP use and they both perform well. Two commercial versions, the Norcal BLT Tuner and the Emtech ZM-2 are available as kits. The Emtech ZM-2 is widely used by QRP operators.
As well as the two QRP Z-Matches, I have also built two QRO versions using the same design but constructed with more rugged components.
The 100 watt version in the photographs uses a T200-6 toroid and some fine vintage parts from my junkbox.
The tuning capacitor is a dual 500pF variable salvaged from an old valve BC receiver. |
The 300pF coupling capacitor is from a World War II B-2 "Suitcase" spy transmitter and the ceramic terminals are from a US Air Force Antenna Relay box.
The meter was removed from a MFJ SWR Meter and is used with Dave Stockton's bidirectional in-line wattmeter design from Sprat #61.
Slow motion drives are used on both variable capacitors because tuning is quite sharp on Z-Match couplers.
The completed Z-Match is housed in a custom case from HJ Morgan Smith who will supply one-off quantities to your own design. This case is the same width as my Astron SS-25 Switch-Mode PSU and finished in the same colour.