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

[Rolf Krogstad]

Thanks, Bob.

Is there a commercial yagi available for 435 MHz which is R-L switchable?

Rolf   NR0T


On Mon, May 13, 2013 at 8:21 PM, Bob- W7LRD <w7lrd at comcast.net> wrote:

> 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
> Seattle
>
> ------------------------------
> *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.
>
> Thanks
>
> Rolf   NR0T
> [EN34]
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