[amsat-bb] Re: Helical Antenna on 70 cm

Bob- W7LRD w7lrd at comcast.net
Mon May 13 18:21:08 PDT 2013

the helix is a nice antenna...however...once wound for either RHCP or LHCP there's no going back. So switching from R to L or L to R is out of the question. Unless of course the chosen polarity is always compatible with the satellite in use. Unless you have L and a R helix and switch between them, that can get a "little" involved. Many times it is very convenient to be able to switch between L or R during a pass, at times it can make the contact happen. This is of course is easy with a L/R CP yagi. I have used a helix for L band (1.2ghz ) as well as feeds for a 2.4ghz dish. They are a fine antenna with a fair amount of bandwidth. For a 16+ turn helix I have used stainless steel "U" channel for the center support. If Clair, VE3NPC is listening, he's the resident helix guy. Just my opinion, your mileage may differ. 
73 Bob W7LRD 

----- Original Message -----
From: "Rolf Krogstad" <rolf.krogstad at gmail.com> 
To: amsat-bb at amsat.org 
Sent: Monday, May 13, 2013 9:22:57 AM 
Subject: [amsat-bb] Helical Antenna on 70 cm 

I am new to satellites and new to the design requirements for UHF and am 
looking for advice. 

I am looking to build a Helical antenna for the 70cm Band. I am 
considering the plans for such an antenna from the 2010 edition of the ARRL 
Satellite Handbook. The plans call for a 235 cm (7' 8") long, 2.5 cm (1") 
diameter center support made of either a wooden dowel which has been 
treated or a fiberglass tube. It also requires multiple 7.6 cm (3") 
spacers for the helical element. 

My question is would fiberglass rods made of "Isophthlic Polyester Resin" 
be a good choice of material at UHF frequencies? 
I hesitate to use treated wood because I plan to mount this on the top of a 
15 meter high tower and it isn't very accessible. 


Rolf NR0T 
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