I finally put up a dipole for 70MHz (4m)

Anytone AT-588 on 70MHz

Anytone AT-588 on 70MHz

Today, I finally built a ½ λ dipole for 4m. I have previously been using a folded ½ λ dipole made out of 450Ω balanced feeder, suspended in the loft, which is not ideal. I still had the coax outside on the roof and the pole which were both used previously for my 2m/70cm co-linear, which has been relocated to the chimney, so once it was built, it was simple enough to put up.

Inside the waterproof box

Inside the waterproof box

I was thinking about building an end fed half wave dipole, having previously built a ‘prototype’ which worked well. This requires a matching section at the base, but no boom arm is needed. I also thought about a slim jim / J-pole, but the total length would be 3 metres. So, I decided to go with a trusty ½ λ centre fed dipole. I built it using two 1 metre lengths of 6mm aluminium tube, and all terminations are inside a waterproof electrical box. Inside, I also placed a coax choke balun, which is built out of a 25mm piece of pipe, with 11 turns of RG58 coax wrapped around it.

Coaxial choke balun

Coaxial choke balun.

I thought I might have to trim a bit off the 1m elements, but once I put it on the mast, the analyser showed the lowest VSWR of 1:1 at exactly 70MHz, so I left them as they are! The only thing I forgot was to put self amalgamating tape around the PL-259 plug after putting all my tools away! All watertight now though 😉

Hope to work you on 70MHz! John.

70MHz Dipole

The new 70MHz Dipole

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4 Comments

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  1. Thanks for the description, I now built one as well, suspended in the loft!

    Michael M0MPM – Reading area

    1. Nice Michael, perhaps work you soon on 70MHz!
      John.

  2. Hi John and Michael hope you don’t mind but I’m also going to make one of these antennas, can you tell me how it performs suspended in the loft many thanks Owen, M3OTM

    1. Should be OK, if you can fit it in! Noise level might be a bit high.
      Good luck, John.

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