At 23:13 26-12-05, Bill Coleman wrote:
As mentioned, 68' at the apex.
>68 feet is not very high with respect to 160m. Consider that a half
>wavelength is 270 feet. 68 feet is barely 1/8 wave high. At that
>height, and with the inverted V configuration, the main lobe of the
>antenna is going straight up.
Hrmmm. So much for that idea, I suppose <grin>. NVIS!
>>I'm not expecting miracles off this antenna, but I'd at
>>least like to have a shot into the Caribbean and Europe.
>
>You need a vertically-polarized antenna. A lot will depend on what
>sort of supports you have available. An inverted-L will work hung in
>a tree with lots of radials on the ground. You could also suspend one
>from your tower.
>
>Or, you could do like me and shunt-feed your tower against a good
>radial system. I have 25 60 foot radials down and a 15m high tower
>with a modest tribander on top. I have a matching network for 80m and
>160m. The shunt works well on both bands. Antenna is nearly a 1/4
>wave on 80m, closer to 1/10 wave on 160m.
I've gotten some great advice from those on the reflector, and from
all the replies I've gotten, these two choices are clearly what I
have to choose from. Couple of questions:
The tower is behind the house, so no possibility of putting radials
out to the east or southeast, and to the other directions, I won't be
able to put out more than a couple of full-size 240-foot radials bent
all over creation, another 4 or 5 128 footers and a bunch of 33's and
66's. Will this be enough, do you think?
How exactly does one shunt-feed a tower? I'm reading the ARRL antenna
book and I'm afraid I don't really understand what they're describing
fully. Vacuum-variable caps at $600 a pop are a little scary to the
budget of this new home owner, too!
If I go with an inverted-L suspended from the tower, how is it fed,
and how far from the tower should it be run? Will it interact with
the tower itself and the yagis on top? If so, favourably or
unfavourably? I have a C31XR and Force12 2/2/1 up top so I'm hoping
this could help things, i.e. capacity hat.
What size wire should be used for radials? I've got insulated #14
from Home Despot (about $25 for 500'), but I think that may be
overkill. I suspect i'll have to bury them, as much as I realize that
elevated radials work better -- but this is a suburban house first
and a ham-shack second <grin>. At least that's what SWMBO needs to believe!
Am I correct in believing that two separate feedlines are needed for
this, one for 80 and one for 160?
Are there any known RFI pitfalls to either of these methods? After a
couple of days with this multi-band dipole, for example, I think I'd
have done better with a balun-fed solution.
>Bill Coleman, AA4LR, PP-ASEL
- Peter
W2IRT (also PP-ASEL)
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