RadioBanter - View Single Post - Poor vertical performance on metal sheet roof

August 8th 03, 07:46 AM

(Jeffdeham) wrote in message . com...
W5DXP wrote in message ...
Kristinn Andersen wrote:
Any comments, anyone, before I remove the vertical and turn to another
design?

I spent considerable time and effort erecting a 33ft vertical 40m
antenna with 8 elevated radials at 20ft. Average signal strengths were
about 2 S-units below a dipole and the noise level was about 2 S-units
higher than the dipole. At my QTH, it was a dog.

I had exactly the opposite results. It was 2-3 S units better at low
angles of radiation compared to my low dipole. I've heard other
experiences like this too. I just wonder if there some part of antenna
theory that's missing that could explain why that happens. Murphy's
law, blind luck, who knows. 8-)

73!

Jeff

It's simple. Cecil did not use enough radials for the low height he
mounted the vertical. Also, he didn't use it to work much long haul or
dx, which is what the vertical is best for. His antenna was just a bit
higher than an 1/8 wave. For an antenna that high to equal a GP at 1/2
wave with 4 radials, he really needed nearly 40-50-60 radials. A 1/2
wave high GP with 4 radials = a 1/4 wave high GP with 8-10 radials = a
1/8 wave high GP with 50-60 radials = a ground mount with 120 radials.
They all have the same appx ground loss. Now look at Cecils GP at a
bit over 1/8 wave and only 8 radials. Thats not much better than a
ground mount with 16-20 radials. No one will ever confuse a vertical
with 120 radials against one with appx 16-20 in the real world. I ran
a 40m GP at 36 ft, which is a bit over a 1/4 wave up. I used only 4
radials, but my antenna was appx equal to a ground mount with about 60
radials. My ground cdx are better than his also, so if anything he
should need more radials than I did. To me, his results are about as
to be expected. Heck, on 40m at night, my mobile vertical antenna will
outdo my home dipole at 42 ft to anyone at least 1000 miles away. I've
tested it many times. And my mobile antenna was a peanut whistle
compared to the full size GP I ran here at the house. To VK, Japan,
EU, etc, my GP would always be 3-4 S units better than my dipole at 36
ft. Heck, I'd give Tokyo a 20 db over 9 window rattling when I ran
that GP and a full KW. My dipole would be lucky to be S 8-9 with the
same power. MK