[amsat-bb] Re: 70cm Helicoil Good/Bad expensive?

Jim Jerzycke kq6ea at verizon.net
Mon Jul 11 18:38:17 PDT 2011

A "Helicoil" is a threaded insert used to repair stripped threads.

I think you're asking about a HELICAL antenna.

They work very well, and are easy to build. They're very forgiving in 
construction errors, but have a few pitfalls you want to watch out for.

You do NOT want to wind one on PVC pipe for a support, as the dielectric 
constant of the PVC will throw off the antenna from the design numbers 
you use to wind the "coil".

This type of helical is called an "Axial Mode" antenna. A "Normal Mode" 
helical is how a rubber duck is made, and is not what you want.

The ARRL Antenna Handbook has several designs that work well, and 
there's a TON of information on the Web about building an "Axial Mode 
Helical Antenna".

They're fixed polarization, determined when you wind it, and the only 
way to switch between left-hand and right-hand is to have another 
antenna, and switch to it.

I've built several, and they work pretty well. They get pretty big at 2 
Meters, but are manageable (at least for me!) at 70cm and up.

73, Jim  KQ6EA

On 07/12/2011 12:39 AM, Kevin Deane wrote:
> Hello all, whats the take on these antennas? I am sure someone on here has used them and they certainly look cool but how do they perform?
> Dont you have to switch polerization on a cross polerized yagi?
> I know there is not a perfect antenna, just wondering about the Helicoil...
> Kevin
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