Home > APRS, Home Brew > Of Antennae and Trees – Part 2

Of Antennae and Trees – Part 2

Today I continued the work with the cherry picker.

After reconnecting the refurbished 2 meter J-Pole, I decided to test it with the antenna analyser. I made the j-pole when I was an F call. I wanted it just to access the local repeater, but have since used it for APRS on 145.175 MHz. The design was one I found on the net.

When I tested it with the analyser, I found it resonant near the frequency of interest, but the SWR was  1:2.1, which suggested an impedance mismatch. A quick google found the answer. The plan I had used suggested no balun was needed but in fact a 4:1 balun is required. I had a homebrew 4:1 balun available from a previous project, so I set to altering the antenna feed point.  I removed the coax socket and soldered a short section of 450 ohm ladder line to the antenna. I then fitted the balun and connected the ladder line to the output of the balun.

The original feed point design

The new feedpoint

You can see how battered the antenna is after damage and repair, but with the balun fitted, the SWR is now 1:1.4

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Categories: APRS, Home Brew
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