70cm Helix: getting close...

The 70cm helix kit has been going together nicely past few days.  Very nicely engineered by the maker, and a great surprise that we don't find these antennas much more widely.  Incredibly robust, this one won't be bothered by the wind!

Whilst this kit is the last of 170 ever made, it's pretty easy to make your own.  You just need a boom, easily-available aluminium mesh for the reflector, and plumbing microbore (10mm) copper tubing that you wrap closely around some kind of forming mandrel to the correct diameter (229mm.)  After that, it's just a case of stretching the tube confidently to get the helix.  The only 'hard' part is finding some suitable plastic like Delrin to make supports for the helix, and tap them so bolts secure them through the boom.

And if you're wondering why you'd bother with an antenna like this, rather than the simple straight elements of a Yagi, the answer is twofold: (1) Circular polarisation, which leads to improved terrestrial operation and, more especially, the near-elimination of fading due to satellite tumbling and Faraday rotation, and (2), the extraordinarily wide bandwidth (which also means a huge tolerance to errors in build dimensions.)  Add to that the fact that the maximum gain is constant over something like 20MHz at around 70cm, and there is very little not to recommend this antenna.  At 144MHz, the antenna does become unfeasibly large for most, but that's another story...

So, this is what the nearly-complete antenna looks like: