Topband: Fw: GAP VERTICAL QUESTION

[Michael Tope]

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...............