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.


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


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.


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.


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.


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.


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.


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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