At 09:17 PM 5/6/2003 -0400, you wrote:
>Hi group,
>
>Looking to add 6m to the VHF set-up. Currently running 2M with a Cushcraft
>17B2 on the tower with a Hygain TH5MK2 (HF tribander) about 5 feet below it.
>My dilemma is that I can only go about 5 foot more in mast height on the
>tower which would stuff the 6m beam between the HF tribander and the 2m beam
>(5 feet between each if equally spaced). Any comments on this spacing or
>similar mast configurations would be appreciated.
>
>Also, I'm gagging on the quoted shipping costs of a new mast pipe, anyone
>have a local Cleveland OH (or relatively close) source for chrome molly or
>similar ??
>
>Thanks for any replies !!
Hi Brad,
One possible suggestion (Others correct me if I'm wrong) would be to
consider the following:
First, consider your tri-bander is going to look like ground plane as far
as the other two antennas. The distance your tri-bander will have the least
effect on your 6m beam would be 1/2 wavelength or 3 meters (118 inches or
9.8 feet). At 1.5m distance (1/4 wavelength), the tri-bander will have the
most effect on the 6m beam causing it to change impedance and act as a
reflector placing much of your radiated signal away from the tri-bander in
the vertical direction!
Second, the effect of either the 6m or tri-bander is the same on your 2m
beam. Both will act as a ground plane. In an Ideal world, your best place
would be 1/2 wavelength above the 6m beam for least effect. For my station,
I chose to put the 2m beam in between the 6m and tri-bander when that was
my only three antennas.
The above information on stacking is from the 1972 ARRL VHF Manual (no
longer in publication and NOT covered by the RSGB version).
Of course you have to take into account the physical nature of the beast
and what your mast and tower can support. I've probably over done mine but
it did hold up quite nicely in 80mph winds last fall. You can place the
rotator way down inside your tower so not as much load is placed on it.
Mine is just above the bottom of the top section. When I started adding
move VHF antennas on the tower, I finally had to give up the tri-bander in
favor of 903 and 1296. Currently I have 6 antennas on my tower and am
looking at placing 2 more. You can see the evolution of my setup at
http://www.aa1yn.com and take a look at the tower link at the bottom of the
home page. The latest photo has not been put up yet but the arrangement is
almost the same.
The mast is a 22' galvanized 2" schedule 40 pipe I picked up from a local
chain link fence company for $55 and was able to drive the 1 mile to my
house with it. You can find chrome molly tubing at any steel supply house -
ask for DOM (Drawn Over Mandrel) tubing rather than seamless as it is much
less expensive and only a slight difference in structural strength.
Hope this gives you some ideas.
Lee Scott - AA1YN
Home of the VHF & Up Register http://www.aa1yn.com/vhf
Hooksett, NH
FN43gc52
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