A 5/8th Wave Antenna for 146 Mhz.

Last weekend I did some work for WICEN with the National Capital Rally, and during the drive in I remembered how terrible access to the 146.900 Mhz repeater on Isaacs Ridge was for me in the Xtrail. Normally, the car simply has a stainless steel 1/4 wave that gets into Mt Ginini Just fine, but from home I can never get into 146.9.

While passing in times for my SOS checkpoint, I remembered that I used to own a 5/8 wave antenna for VHF – It was especially handy for getting just a little extra gain for locations that were a little ropey. I searched everywhere in the Garage, and I must have lent it out – Gone forever….

I have a handful of old CB antennas, so I decided to make one based on a little internet research. My memory was correct – The antenna is literally made from about 11 turns of wire over about 40mm to match the radiator, and a single vertical wire. The inductance on the base is to lower the angle of radiation while making the antenna look like a 3/4 wave whip – thus providing gain over a standard 1/4 wave whip. The length of the radiator was about 1200mm for 146 Mhz.

A quick trim with a knife cut the black heat shrink sleeve off, leaving the wire element which I unwound to allow it to be reused. I wound the necessary 11 turns at the bottom and secured the with a piece of clear tape. I then ran the wire in basically a straight line for 1300mm and dropped a piece of black double wall glue based heat shrink on it and loaded it onto the car.

My MFJ 259 quickly told me that the antenna was resonant at about 136Mhz, so I trimmed some length off and tried again. I quickly arrived at resonance at 146Mhz, and a SWR of 1.3:1, so I tried the non-accessible Isaacs Ridge repeater. Ker-Chunk!!! A S1, slightly noisy response, but a response nonetheless. I trimmed the excess biberglass of the stick, and shrunk the heat shrink down.

And now I own a 5/8 wave for VHF – Nice and robust!

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