Satgen 444  Sats for Antenna Tests  by GM4IHJ  (BID SGEN444) 27Sept 97

Recent trials using Chris Bock's excellent Wxsat software, has
permitted some interesting comparisons between this station various
attempts at omni directional satellite reception antenna manufacture.
Copying a Wefax picture from NOAA12(137.5), NOAA14(137.62) or Meteor
3-5(137.85) in a real urban environment full of hills, houses and
other impedimenta, is the ultimate test for any so called omni
directional antenna. As the Wefax picture unfolds , you are presented
with a continuous record showing every fade, every burst of noise, and
evidence of just how different reception is between, horizon and
overhead, and, in the course of several passes, how much results
differ from one point on the horizon , to another.

Tests a few years ago, when everyone was writing about Lindenblad
antennas, prompted the conclusion here that Turnstiles were better for
sat reception. But times and fashions change , The turnstiles are down
and in their place is a pair of Quadrifilar Helices for 137 and 437
MHz respectively. The impetus for this change came from GM4JJJ who
suggested we each build one of these antennas to see if it real was as
good as W3KH (reported in QST Aug 96) and further supported in his
excellent article about Wefax reception ( QST Aug 97). Using W3KH's
articles, a 137 MHz QF Helix was built after something of a struggle .
The struggle arose because of lack of expertise in drilling plastic
piping and, problems threading the antenna elemments through the
supports. The second QF Helix ( for 70 cms) however was put together
without trouble. Indeed W3KH's explanations are fine , the quality of
the local labour is the problem. 

Once up , the 137 MHz QFHelix soon demonstrated it superiority over
everything that had gone before. Copying pictures gave almost no
fading at all, and results were surprisingly good even down at very
low elevation on the very strong Meteor 3-5 signal as it produced
picture of ice around Disko in Western Greenland and the northern
approaches to Hudsons Bay. Horizon performance it not quite as good on
the weaker NOAA signals but the pictures are fade free, demonstrating
very satisfactory antenna performance. With good results on the
Weather sats attention then turned to making a QFHelix for 437 MHz for
Pacsat monitoring . With the experience of building the 137 antenna ,
the 70cm version went together like magic, and good results on Fuji20,
Webersat 18 and Lusat 19 , confirmed its excellent performance.  There
remains of course the endurance test about to be posed by the Scottish
winter, when it is hoped that mechanical performance will withstand
the whole thing being turned into a wicker basket ice ball, which will
then be savagely tested by galeforce winds.But so far things look good

Notes for would be builders - The W3KH version illustrated in QST has
no suitable location for clamping to a mast . In the IHJ version the
centre plastic tube is extended 6 inches lower below the antenna
elements , the coax is fed up inside the tube to a point just below
the lowest element support , where it emerges from the tube through a
hole. A strap on the coax braid just inside where it emerges feeds
across to the adjacent B1B conductor bottom connection. The much
smaller 70 cm QFHelix fits into the top of the 137MHz antenna main
plastic tube.