A few weeks ago I thought it would time to build another UHF-Satcom Antenna and thought that a Helical would be ideal, because most of the Signals are Circular Polarzised. I took a look on the Uhf-satcom.com UHF-Antenna section where a building instruction for a 5 Turn RHCP Helical is published.
There are two matching sections possible, one version uses a adjustable reflector plate which is good the get the inpendance close to 50 Ohms and is better when you want to build a helical for transmitting.
The other version is, to wind the first 1/4 turn prallel to the ground plate.
I only want to rx with this antenna so I prefered the last version.
I bought some things I needed and a couple of days later I could start with building all together.
At a steel factory around the corner I could find a ideal steel (reflector) disc and the wire-mesh for the reflector.
For the wire I used ca. 7 Meters of 4,75mm copper break pipe.
The boom is made from 50mm plastic pipe from a local DIY Superstore.
For the Support rods I used 10mm Roundwoods which are screwed together inside the plastic boom.
After I completeted the whole reflector section and the boom and the support rods were installed, I started with bending the wire.
That was a bit tricky, because I could not find a suitable pipe or similar with an diameter of ca. 36 cm to bend the wire around.
I started to bend every turn "manually" and fasten it to the wood support rods.
I already drilled little holes for the wire and the cable ties into them at that point, so that the mounting and bending was a bit easier.
As the wire was roughtly in place I had to begin with the fine tuning/bending.
That took me a few hours, but the wire is nicely in place now with the correct diameter and turn spacing.
Then I only had to cut the rest of the copper pipe and solder it to the N-Connector on the backplate.
I tested it first on the AOR with my handheld receiver outside in the garden and the signals were really strong!
Then I also tried the Helical with an preamp and my Icom IC-R7100 on IOR.
I firstly tried it on the Fleet Broadcast channel on 250,650(IOR) to peak the signal a little bit which is also very strong.
Btw, I wondered a bit as I heard portuguise pirates on a few Frequencies who I didn´t suspect to hear on IOR, as that Satellites aren´t in sight of South Amerika.
Now I´m planning to mount it on the attic, as it´s ~1,55 Meters long, and a bit difficult to mount it outside on a pole.

If you are also planning to listen to UHF-Satcom in future I really can suggest you to build this antenna. Maik´s 4 Element UHF-Yagi is also exellent as a starter antenna, as it´s not too difficult to build and not too big. The Signals with the Yagi are also really strong.

Links :

5 Turn UHF-Helical : http://www.uhf-satcom.com/uhf/uhfantenna.html
Maik´s 4 El. UHF-Yagi : http://www.satellitenwelt.de/yagi260mhz.htm

Regards, Nils