For Yagi antenna do-it-yourselfers, one of the most important and problematic steps in the building process is deciding on the best method of matching the feedpoint of a low-impedance Yagi design (often 20-25 ohms at resonance) to 50 ohms.
Yagi builders strive to have the antenna’s input impedance at 50 ohms to match the 50-ohm coaxial cable. Then a 1:1 balun fed with 50-ohm coaxial cable can be used for balanced distribution of RF currents and a proper, predictable radiation pattern. The result: minimized ohmic losses, maximized beam antenna performance for optimal signal efficiency, and reduced RFI-causing common mode current. An unmatched system (2:1 or more) invites a host of troubles, including distorted RF radiation patterns and degraded signal efficiency.
What can you do to match your low-impedance Yagi to the higher-impedance feedline?
Gamma-Match, T-Match, and Hairpin Match, also known as Beta Match, are three popular methods of matching the driven element to the feedline. In a Gamma-Match system, the antenna’s driven element is fed at the center of the element and at a fraction of a wavelength to one side of center. It usually includes a capacitor in series with the rod designed to cancel the inductive reactance of the matching network. A major complaint among Hams is that this unbalanced system tends todistort the antenna radiation pattern. The T-Match method is basically two Gamma-Match systems on either side of the boom. While this may correct the imbalance, installation can be nightmarish and tuning can be difficult.
Hairpin Matching Systems, so called because of their U-shape, have been around for years. A few years back, the team of Amateur Radio operators and designers at DX Engineering looked for ways to improve on the mechanical and electrical aspects of this classic design.
The result was the DX Engineering Hairpin System for Yagis. It comes in three models: DXE-HMS-1P (10-30 MHz for 2 inch booms); DXE-HMS-2P (24.9-54.0 MHz for 1.250 to 1.750 inch booms) and DXE-HMS-4P (10-30 MHz for 3 inch booms). All models are balanced and can be installed and tuned in as little as ten minutes. They have enough capacity for almost any HF through 6 meter high performance Yagi design. Other features include:
- Using rods that are parallel to the boom, operators can quickly match the Yagi antenna by repositioning the boom clamp and shorting bar along the boom and hairpin rods, so the antenna is easier to adjust for minimum SWR than conventional wire-loop hairpins
- Increased rigidity for greater durability
- Better protection against ice and wind
- Depending on the Yagi design, the systems include all of the hardware items needed to match the Yagi antenna to a 50-ohm feedline without the need for drilling holes
- More professional appearance
Yagis that do not have a split driven element (insulated from the boom) will need the proper size DX Engineering Insulated Boom-to-Element Bracket and DX Engineering Boom-to-Element Bracket Hardware Kit. Depending on the driven element diameter, a DX Engineering Element Adapter may also be required.
What do Hams think?
“Just got through building my first mono-band Yagi antenna for the 17 meter band. The antenna is highly directional, has VERY good f/b performance, and f/s is also very good. So I’m thinking the matching device is working properly or the pattern would be badly skewed. Overall I am very pleased with the DX Engineering Hairpin Match.”
