QRP HF/VHF/UHF mobile antenna

This is a homemade version similar to a commercial antenna. I built it for fun, not to try and improve on the commercial design. So I didn’t use the highest possible standards. Experimentation was the name of the game. It is based around an L-Match ATU.

lmatchThe above is the circuit for the L-Match.

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The above image is the finished unit. It an be used with the telescopic whip or a longer wire can be connected.

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The above is the variable inductor. It is a T130-2 ferrite toroid wrapped in wire. The wire insulation is removed and soldered on to a 12 way switch every second turn.

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The above image is the switch I used. It is a cheap 12 way rotary switch. There are two types of this switch, one that breaks the contact before making the next one and one that doesn’t. I suggest that you use the break before make variety.

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The above image is the variable capacitor. It is a Varicon type. often used in Radio receivers. It is low voltage and limits the maximum power handling of the ATU.

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This is the ATU squeezed into a box. At the bottom we have a BNC plug, to connect the antenna. The top left is the SO239 socket. This allows us to connect a coax feeder. The tape inside is to cover the exposed terminals and prevent accidental shorts.

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Here is another view of the ATU. We have two knobs. One controls the variable inductor, which selects the band from 40 meters ( 7 Mhz ) to 70 CM ( 430 Mhz ) the other is the variable capacitor. Which is used for trimming. I have added a pl259 to pl259 adapter to the SO239 socket. Which allows me to connect it straight to my FT817.  This can be removed and a fly lead used instead.

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The above image shows the ATU and whip connected to my FT817. Which is receiving a signal on 14.155.50 Mhz at S8 inside my house.

The ATU can be used with the whip for portable operation. A maximum of 10 watts is recommended. You can also connect a long wire to the BNC antenna socket. The L-match ATU should be able to tune it. Adding a ground or counterpoise will improve efficiency.

Have fun experimenting.

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