Topband: Radials experiment results.
Mon, 14 Feb 2000 12:26:48 -0500
I have completed my experimentation with the radial system
of my 160m shunt fed tower.
Originally I had 24 insulated 1/4wl radials laying on the ground.
When I added each set of radials I was not seeing any change in SWR or
decrease in usable bandwidth whatsoever. I thought this was quite odd. After
going to the elevated system and seeing the 3 db increase in signal at a
local's station on groundwave at 23 miles away I decided to add 8 more
elevated radials for a total of 24 elevated radials at 8 feet. I also
replaced the 6 gauge 2 foot length of cable connecting the shield of the
coax to the bottom of the tower with a 7 foot length of 1/0 gauge welding
cable. This connects directly to the point of the tower where the 24
elevated radials are connected. I had to re-tune the series vacuum variable
since the swr had gone up from a 1.1:1 to a 1.6:1. Before making the move to
elevated radials my 1.5:1 to 1.5:1 swr bandwidth was 250 KCs and the 1.1:1
to 1.1:1 bandwidth was 20 KCs! After the move to elevated radials the 1.5:1
to 1.5:1 bandwidth dropped to 110 KCs with the 1.1:1 to 1.1:1 BW decreasing
to 10 KCs centered on 1832 after re-tuning the series capacitor. From what I
understand about efficiency and losses in a vertical system I believe all my
changes were for the better according to the results I have recorded. I
still need more on- the- air tests to see how much better it is but I don't
believe it could be any worse than it was before. VK6VZ was S9 plus 5 DB a
couple of days ago which is about the strongest I have seen him. He told me
in an e-mail that I was also hitting the S9 mark. We'll see how it plays in
the CQ 160m SSB contest.
BTW, I also tried connecting the radial system from the
75m parasitic vertical array together with the 160m elevated radials. I have
tried this numerous times before and the results have always been the same.
It screws up the F/B on the 75m array quite badly. It must have to do with
the fact that the 160m radials are affixed to the tower electrically and the
tower plays a big part in the performance of the 75m array.
So, I have found that, in at least my antenna scenario,
that elevated radials have improved my efficiency and that connecting the
radials of two different systems together does not work.
73 and see you all in the pileups. Ken, N4UK
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