Hello Wally,
The fiberglass is used more for it not being a metalic support . This
becomes more important as you go up in frequency. The metal mast on a 20mtr
beam is so small in relation to wave lenght it would nnot be considered.
When you get up to VHF, this is not the case. It then dependends on how the
antenna was modeled, and if the mast/cross boom is going to be in line with
the elements or not. I will has impact both ways, not not the same. So what
to do? These antennas are very good antennas, but are not as touchy as one
like the 17B2. If you want a perfect, clean, non distorted pattern on VHF
and up, use fiberglass . At least to within a wavelenght of the antenna. A
very good way would be to space them at the ideal seperation using the metal
in the center, and fiberglass on the ends if they need to be farther apart
than your fiberglass boom is long.
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| | <-- antenna ____________________________ antenna
---> | |
| |--------------------------
----------------------| |
| |fiberglass Metal Boom
fiberglass | |
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|-------------------------___________________________----------------------|
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I hope this drawing shows up correct when sent.... Bruce
Wally Klinger wrote:
> Good morning,
>
> I am in the process of putting up a new tower, and have a question. I
> intend to put up a 13 el 2 meter FM cushcraft ans 15 el 220 FM cushcraft
> on the tower. To save space (and maximize the height) I want to use a
> crossboom. I was thinking of 10 feet of 1 1/2 inch galvanized water pipe
> (with appropriat mast to cross boom plate) This would give me 5 feet of
> separation from the mast on either side, and 10 feet from each antenna
> respectfully. Is this a good idea? Too long?? Not the right type/grade
> of pipe?? Any better ideas?? Apparently KLM sells a 7 1/2 foot
> fiberglass cross boom (used by the OSCAR guys) Which I surmise would be
> lighter. Is there enough separation here?? Or should I stay with my
> origional idea?
>
> The plan this saturday is as follows.....
>
> Discone at 85 feet
> Below it crossboom w/ 2 meter and 220 beams vertical polarization
> JUST below it 6 el 440 FM beam mounted on main mast
> Below this 4 el hygain 6 meter beam
> Below this at roughly 71 or 72 feet, TH11DXX
>
> Hope it stays up!
>
> Let me know what you think!!
>
> 73's
> Wally W9BEA
> Wklinn@hotmail.com
>
> ______________________________________________________
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>
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--------------------------------------------------
Bruce Richards / WD4NGB (No Good Bum) (ex HL9JV)
DX Web Page http://home.sprynet.com/sprynet/wd4ngb
Mirror Site http://members.xoom.com/wd4ngb
Space A DX http://members.xoom.com/space_a
50 Miles North West of Nashville Tn
--
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