Re: [amsat-bb] Commercial Helix Antennas?

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

Bob,

As I have previously stated mode LS and other microwave modes are well
suited to the apartment dweller that can't have large or permanent
antennas.  The two manufacturers are all I am aware of.  OAL and Directive
both have excellent products.  Might be a bit expensive on shipping to Korea!

Making a helix is really not too difficult, especially at these
frequencies.  I made a HB 437 MHz helix in 1996 for copying the Mars Global
Surveyor beacon, and this year I made a little 3-turn helix for 1420 MHz
for radioastronomy using my 8 foot dish.  THe latter antenna was made using
1/8 inch dia. copper tubing commonly used for refrigeration.  It was
mounted on a small piece of 1/2 inch plywood attached to a square sheet of
aluminum on which a panel coax connector was attached.  Not expensive nor
difficult.  Helix antennas are very wide bandwidth so very forgiving in
their construction.

Regarding a tripod or camera mount.  Usually the camera mount is rotatable
up-down and panning side-to-side using a hand lever.  The small camera
mount pad has a 3/8 inch screw for attaching the camera.  The trick for
mounting antennas would be using a well balance system.  I would think of
using something like pvc tubing [or 2x2 wood] as a crossboom and attaching
the helix antennas at either end at their midpoint rather than from the
rear.  You would need to make a small plate attached at the crossboom
midpoint and tapped for the 3/8 camera screw.  Sorry this is not a picture
so I kind of leave it to your immagination and innovation.

I previously stated that almost everything could be purchase for microwave,
now.  Well not 100% and antennas systems are one area that are often home
assembled.  So I guess it is up to what you are comfortable attempting.
The electronics will be available from Downeast Microwave, SSB Electronics,
or Kuhne Electronic typically upconverting from 144 or 432.

I will be publishing the 3-turn helical dish feed antenna design [done with
NEC4WIN] on the SETI-League web page once I have the article completed.  It
is simple to physically scale for 1296 or 2400 MHz.  The 3-turn design can
easily extended by adding more turns up to 16 turns.

Ed

>From: "Bob McElligott" <bmcellig@kornet.net>
>For those of us who lack the resources, time and mechanical ability to
>construct small helix antennas, are there any commercial sources to buy
>these antennas?  Looking on the web, I have found two manufactures.  One is
>Directive Systems, sold thru Downeast Microwave, who makes both a 1.2 and
>2.3 GHz 15 turn version for $175. each plus shipping, and the other is a
>dual bander for 1.2 and 2.3 GHz which is made by OAL for $190.00.  These
>prices seem high, but they might be quality products and the price is
>justified.
>
>Is anyone in the group familiar with these antennas, and/or are there any
>other companies making them?
>
>Living in one of those "High raise apartments" in Korea, my only choice will
>be for balcony mounted antennas on modes L/S and higher.
>
>Also I have read a lot here on the net about "tripod" mounted antennas.
>Being unfamiliar with this procedure, would some one be kind enough to send
>me some type of drawing or picture as to what the mount to the camera tripod
>should look like.  I would like to mount a 1.2 and 2.4 helix on one tripod,
>but due to the weight I am not sure it will handle both.
>
>73
>Bob McElligott
>KK4UZ/HL9WH
>
>kk4uz@amsat.org  or bmcellig@kornet.net
>
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