Antenna matching devices are simple electrical circuits that match the output of radio transmitters to antenna systems. Variously known as antenna tuners, antenna trans-matches and antenna matching networks, these versatile devices protect transmitting equipment while optimizing the amount of radio signal that reaches the antenna. Amateur radio operators frequently purchase or build and use antenna matching devices to experiment with various antennas, to use antennas on a wide range of frequency bands and to convert practically any metal object into a functional antenna under emergency operating conditions. Build your own low-cost antenna matcher from a few recycled electronic components.

Things You'll Need

Metal, plastic or wooden cabinet box
Surplus 0-25 microhenry (uH) roller inductor coil
2 variable capacitors: 0-500 picofarad (pF)
12 ceramic standoff insulators
3 large plastic dial knobs
2 female coaxial cable connectors
No. 12 insulated copper wire
13 bolts (3/16-inch by 1-inch), washers and nuts
8 machine screws, 1/8-inch by 1/-inch
Schematic diagram (AA5TB.com)
Drill with 1/8-inch, 3/16-inch and 1/2-inch bits
Soldering iron and acid-free solder
Pliers
Standing wave ratio (SWR) meter
2 short coaxial cables

Instructions

1.Gather the tools and materials needed for the antenna-matching network. Obtain or create a cabinet box to house the device. The cabinet can be metal, plastic or wooden as you desire. Recycle a cabinet from another electronic device or make one from scratch to match physically and aesthetically your radio station equipment. A metal file box or breadbox will suffice as a cabinet housing. Military surplus sales and hamfests often have large metal boxes as well as capacitors and inductor coils available.

2.Install the two capacitors on either side of the roller inductor coil so that the three major components are evenly spaced on the front panel and supported by standoff insulators from the cabinet floor. Drill three 1/2-inch holes in the front panel of the housing box. Drill four 3/16-inch holes for the four corners of each of the three components in the floor of the cabinet. Secure the 12 standoff insulators with 3/16-inch by 1-inch long bolts and nuts. Attach the three components to the insulators and to the front panel with the hardware that came with them.

3.Drill three 3/16-inch holes in the back cabinet panel – one each near the left and right edges of the panel for coaxial connectors and one near the center of the panel for a ground connection. Install a female coaxial connector over each of the left and right side holes. Drill four 1/8-inch holes for each connector while using the coaxial connector base as a drilling template. Attach the two coaxial connectors to the rear panel using four 1/8-inch metal machine screws for each. Install a 3/16-inch bolt outward from the rear cabinet panel to serve as a grounding lug.

4.Wire your antenna tuner using No. 12 insulated copper wire, a soldering iron and acid-free solder. Follow the schematic diagram for a T-network antenna tuner (AA5TB.com). As you face the front panel, the left side of the tuner is the transmitter side and the right side is the antenna side. C1 and C2 are the left and right tuning capacitors respectively. Wire one side of each capacitor to the center conductor of their respective left and right side coaxial connectors.

5.Wire the other side of each capacitor in series with the roller portion of the inductor coil, one end of the coil, and with each other. Wire the other end of the coil to ground along with the shield sides of each coaxial connector. If the back of the housing is metal, simply connect the grounded end of the coil to the grounding lug; the outer shields of the coaxial connectors are already grounded by default.

6.Complete the construction by ensuring that all electrical connections are mechanically tight and neatly soldered. Install the three large plastic adjustment dial knobs. Connect an SWR meter between your transmitter and the left side of your new tuner using two short coaxial cables. Connect your antenna to the right side of the tuner. Connect the grounding lug to a good earth ground system. Transmit a low power signal as you tune through each of your intended bands of radio operation while looking for the three tuner adjustment settings, which give you the lowest SWR. Record these dial settings for future reference.

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