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Todays antenna project: HELICES made of PAPER



Some people did not get this message retransmitted via the listserv so here
it goes again:
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I have gotten many inquiries on the building of helices using copper tape. I
wanted to add a couple of ideas. The first helices I built a couple of years
ago used regular paper. Here is the process:

1. You take a roll of paper like those used on calculators. They are about 3
inches wide.
2. you cut a really long strip of 1.1 inches wide.
3. you buy a piece of 1.25 inch (I think) PVC tubing. this tubing has an
outside diameter of about 1.65 inches
4. The strip is closely wound around the PVC tube. Make sure it is wound
with RHCP. The strip can only go one way with the right turns per foot etc.
It can only go one way RHCP or LHCP.
5. The strip seams  will be separated by 1.1 inches (the paper width) which
is perfect for 2.4 GHz.
6. Next use copper tape of 0.25 inch width to tape the seam between the two
adjacent pieces of paper. Do this by putting .125 inch of copper tape on
each side of the seam.
7. Coil the copper tape for as many turns around the tube. I have gotten
real good results up to about 30 turns.
8. Place a  thicker tape either paper or plastic over the copper tape to
stabilize it.
9. remove the PVC tube very carefully. Rotating the tube in the right
direction helps. The wrong direction unwinds your helix :(
10 use fiberglass resin with a brush to completely coat the antenna. You
might also try some new epoxy based transparent coatings. I have tried the
fiberglass resin and it works. I have not tried the epoxy sprays.
11 the coated fiberglass antenna does not need anyother protection from the
climate.
12 you can also enclose the antenna in one of the pvc tubes or light tubes
mentioned before. To make the antenna fit in the transparent flourecent
tube, wind the paper helix on a tube of slightly less diameter than the 1.65
inches. It will not affect anything just keep it to around .1 inches.

Paper is a great material to wind antennas. It is low loss and can be
protected with fiberglass of other tubes.

I hope this info is useful. It only takes 30 minutes to build one of these
antennas and the dimensions come out a lot more accurate than trying to
space the copper coil just right. 73's

Pieter Ibelings
N4IP

PS. I'll try to get more pictures of the feed portion on my page soon. ONE
VERY IMPORTANT POINT IS:
I CANNOT DETECT ANY DIFFERENCE IN RECEPTION BETWEEN A MATCHED ANTENNA AND AN
UNMATCHED ONE. The 3 turn helix that I use on the 4.5 foot dish is unmatched
and it works great. remember that the average 2.4 GHz LNA used for mode S
reception uses a very simple matching at the front end. It only uses a small
inductor in series with the FET. Most amplifiers that I have measured have
about 5 or 6 dB return loss which is extremely bad SWR. This matching is low
loss and works great for noise figure.




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