ORIGINAL MESSAGE:
On Thu, 9 Aug 2007 20:55:38 -0400, "Gedas" <w8bya@mchsi.com> wrote:
>Hi Bill. Got all excited when I saw your post ref the parallel dipoles. I
>have had very little luck in getting even a pair going for 75m and 40m.
>Could you please share with me the exact details of your setup. Basically
>everything I would need to duplicate one at this end. I would like one for
>160m/80m/40m and would so much appreciate it.
>73
>Gedas
------------ REPLY FOLLOWS ------------
I'd be glad to share. My tower is 80 feet tall and the three dipoles
are in an inverted vee configuration with the apex at 70 feet. I cut
them all to be about ten percent longer than the standard 468/f
formula calls for, figuring I would trim them using the MFJ-259. Since
I have lots of room, I ran the longest one out at a fairly shallow
angle with the ends being about 20 feet above the ground. I used a
one-foot piece of one-inch PVC pipe for the end insulator and ran a
piece of galvanized fence wire out to a concrete block which just sits
on the ground and anchors the ends. Same for the 80 and 40 meter ones,
keeping the same angle so of course the wire to the anchor block is
longer. All three blocks on each end are fanned out about 20 feet
apart from each other.
As for tuning, I found that the 160 meter and 40 meter dipoles did not
require much trimming, which means they ended up noticeably longer
than the 468/f formula would indicate. The 80 meter one initially
resonated lower in proportion to the others, around 3.2 MHz. About an
hour's work cutting and trumming ended with all three nicely in-band.
The 2:1 SWR bandwidth on the 160 meter antenna is about 70 kHz with
the minimum SWR of 1.1:1 at 1831 kHz. On the 80 meter antenna, the SWR
is higher, with the minimum SWR of 1.8:1 at 3555 kHz and the 3:1 SWR
bandwidth of 165 kHz. On 40, the minimum SWR is exactly 1:1 at 7172
and the 2:1 SWR bandwidth covers the entire band.
The built-in tuner on my IC-756Pro3 has no problem matching any
frequency in all three bands.
Spreading the end anchor points farther away from each other changes
the point of minimum SWR only about 10-15 kHz on each band. I have not
yet experimented with bandwidth vs spreading the anchor points. I will
get around to that one of these days, but I don't expect a lot of
change.
Hope this helps, let me know if you have any more questions.
Bill W6WRT
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