On 12/13/2012 3:14 PM, Tom W8JI wrote:
Somehow they thought moving the feedpoint eliminated the need for
radials with an electrically short antenna, when the real mechanism
was a 1/2 wave vertical was converted to a 1/4 wave groundplane 1/4
wave above ground and it only got a tiny bit weaker. The groundplane
still had 8 radials, but they were hundreds of feet in the air.
There was some more stuff about offsetting the feedpoint in that
handout, but nothing that remotely applied to a fractional wavelength
vertical just sitting on the dirt with a few radials laying directly
on the lawn.
They got rid of lossy traps and loading coils by using even lossier
coax and some folded wires for a loading system.
This is all why, as frequency increases and the current and voltage
moves up the antenna, the GAP on most bands isn't terribly bad. This
also why it is a real dog of an antenna on 160 and 80, where it is
very short electrically, has no ground system, has an exceptionally
poor loading method, and where it folds the radiator back and forth
which suppresses radiation resistance.
This is why a ten foot mobile antenna can tie it or beat it on 160,
and why it is reasonably on par with anything else on most bands above
80 meters.
73 Tom
I got hold of a brand new voyager about 7 years ago. The first thing I
did was throw away all that yellow coax stuffed inside the bottom half.
The fiberglass "GAP" for the elevated feed point makes a nice insulator
for a center loading coil. Then I added some top hat wires with
dimensions per WX7G's recommendation and fed the antenna from the bottom
as a standard ground mounted vertical with a bunch of radials. For 80
meters, I put a short "yard arm" at the top with a pulley and hung a
wire in parallel with the aluminum radiator. For only being 45ft tall
this antenna has worked surprisingly well. I've since lengthened it to
56ft and added an additional parallel wire for 40 meters. I use an
Ameritron RCS-4 remote switch at the base to select between 160 or 80/40
(the 80 and 40 meter vertical wires are tied together). I use a 50 to
12.5 ohms Unun on the 160 side to raise the feedpoint Z up to 50 ohms.
With all these modifications done in haste before various contests it
aint pretty to look at, but it does seem to hold its own against folks
with shunt-fed towers and inverted-Ls (at least the ones who don't use
overly active antenna tuners :-) ).
Here are some pictures of it when I took a trip to one of the dry lake
beds north of here:
http://www.dellroy.com/W4EF's-Ham-Radio-Page/CQ160/2006.htm
73, Mike W4EF...............
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