Thursday, June 13, 2024

Rebuild of the EA642ZB7 (Part 1)

 Recently acquired some antennas from PA7NTH. Unfortunately Nanne had to stop with the radiohobby due to a stroke. Very sad as he had just placed a big tower behind his house full of all kind of antennas. Life goes on though. He has to live with some complications, listening to radio is a no go for him. Anyway, among the antennas are a 3 band beam (10,15/20m), a 3 band beam (2/4/6m) and a 40m dipole. I decided to sell the 40m dipole as it is just too long for me. 

Some of the antennas are damaged and one of them is the EA antenna EA642ZB7 which consists of 2 elements for 6m, 2 elements for 4m and 3 elements for 2m. It is a so called open sleeve design.

I guess the design is ok, but the mechanical strength of this antenna is not that good. It is obviously designed to fit in a small box with as few parts as possible. Costs might also be playing a role. First of all the isolation between te dipole halves is probably made of POM which is not really UV resistant. I personally prefer PTFE, it is UV resistant, heat resistant and water resistant. Disadvantage of PTFE is that it is not as hard as POM, at least the PTFE 10mm rod I have. Well you see what happened to the dipole of this did get brittle and snapped. The challenge is to repair everything and make a stronger antenna that will last.

It was the first thing I wanted to repair. I thought it would be the most difficult part to remake. But in the end it was easy. I just drilled a 10mm hole through the old center part and pushed the new PTFE rod in. As you can see it looks pretty well.

The antenna was still assembled and I know why. The stainless steel bolts have been mounted without greasing them first. There was nothing on the antenna connections to protect it from nature elements either. Stainless steel and aluminium are not the best friends and so everything was heavily corroded and very difficult to remove. I had to apply brute force to remove everything and even had to drill out one bolt. Results in the photo, these are aluminium connecting pieces to connect the half 6m and 4m elements together inside the boom.

The choke used is consisting of about 11 windings of RG58 (would not be my first choice) on a alu tube. I've been thinking of removing it and use a piece of teflon coax which would probabely be a lot better especially on 2m. However the PL chassis is glued into the aluminium tube and removing it would destroy everything. I decided to clean everything and solder new wires to it. When I reassemble everything I will mount it again and cut the wires at length. It's not the best but I guess it will work anyway.

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