[amsat-bb] Re: 70cm Helicoil Good/Bad expensive?
ko6th_greg at hotmail.com
Mon Jul 11 21:13:54 PDT 2011
I second Jim's assessment here. Helical antennas are the only way I will build an antenna at 1.2 ghz or higher. It's not worth the stress trying to measure things to the precision needed for a Yagi at those frequencies. The less stress (and time) taken to build the antenna, the more enjoyment you will get from actually using it!
For 2m and 70cm, Yagis are good, but also consider making a Quad or a Quagi (a 2 element Quad with more Yagi elements in front). I used a home-built 8 element Quagi from the ARRL Antenna Handbook for several years as a satellite antenna, until I found a crossed Yagi antenna at a Ham Swap for a price I couldn't pass up. Still have the Quagi, just in case.
> Date: Tue, 12 Jul 2011 01:38:17 +0000
> From: kq6ea at verizon.net
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] Re: 70cm Helicoil Good/Bad expensive?
> 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
> > KF7MYK
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