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