Monday, March 4, 2019

When should you use a halo?

Almost all mobile antennas are vertically polarised. It's not hard to see why. They have a small footprint. They radiate equally in all directions. So you don't lose the signal when you turn a corner. And the vertical polarisation suits FM and repeater work.

But there are a few times when you want horizontal polarisation. For instance if you're operating SSB on bands like 6 and 2 metres. Nearly all SSB operators use horizontal polarisation. If you don't follow suit then your signal may well be 20 or more decibels weaker. That's a loss you can't afford to have.

Consider a horizontal dipole, you may say. Well, for 50 MHz, at nearly 3 metres end-to-end, that's too big for a vehicle. One for 144 MHz is more compact. But you've still got the directionality problem with a dramatic drop in signal when the antenna is end-on to the station being worked.

If only there was an antenna that's both horizontally polarised and omnidirectional. Luckily there is. The halo. And its small size means that even a 50 MHz one can be used mobile. And if you don't like to make people think you're some sort of self-proclaimed saint it could be made square instead.  That's sometimes known as a 'squalo'. Similar performance and it might be slightly easier to make with some materials. 

What about at home? There are times when you want an omnidirectional horizontally polarised antenna for casual listening. A halo can be good for that as well. Though with no more gain than a dipole don't throw away your beams just yet. 

I've never built a halo. But plenty of people have. Learn from their experiences here:

* G3XBM 10m wire halo
* PA3HCM 6m squalo
* Homebrew 6m halo by W3DHJ
* N6TWW 2m halo
* KR1ST 2m tree friendly halo

PS: Puzzled about some of the terms you hear? This dictionary can help with over 1500 explained.

 Link to Ham Radio Dictionary

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