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Re: fiberglass boom



On 9 Feb 2002, at 14:29, Tracy wrote:

Ah ha . . . then what are you saying . . my set up is possibly bad?  I
wouldn't think the boom would affect the Dish and helix at 2.4 Ghz and being
5 feet long and only somewhat conductive at UHF wouldn't seriously interact
with the 70 cm uplink yaggi.  Should I change it out for expensive
fiberglass?

73's  Tracy

----- Original Message -----
From: "Luc Leblanc (VE2DWE)" <luclebla@sorel-tracy.qc.ca>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, February 06, 2002 7:10 AM
Subject: Re: [amsat-bb] fiberglass boom


>
> I"m using a standard PVC pipe with a 1 feet (30cm) wood dowl cut from a
showel
> replacement handle the end is not capped (later modifications). You can
see
> pictures at     http://www.qsl.net/ve2dwe/
>
> Just a quick note PVC is NOT A GOOD INSULATOR AT MICROWAVE
> FREQUENCIES but losses are acceptable at UHF frequencies.
>
> Luc Leblanc VE2DWE (AMSAT 33583)
> SITES WEB:http://www.sorel-tracy.qc.ca/~luclebla/
>           http://www.qsl.net/ve2dwe/
> C.P.341
> Sorel-Tracy
> J3P 5N6

You extrapolate much more than my quick note said Tracy. I'm just refering to 
conductivity of materials and to my own test who are conclusive with those noted 
on BB.

I give you an excerpt from the 1987 ARRL handbook regarding ANTENNA CROSS 
BOOM CONSTRUCTION (chapter 23 page 14)

One requirement not commonly discussed is that of using a nonmetallic elevation 
axis boom for antennas that have their boom-to-mast mounting hardware in the 
center of the boom. A metal cross boom WILL SERIOUSLY DISTORT THE BEAM 
PATTERN of a circularly polarized antenna, so it is important to make the cross 
boom from nonmetallic material.

>From a structural standpoint, the best nonmetallic material for this job is glass-
epoxy composite tubing, because its stiffness is excellent....A less expensive 
alternative is to make the cross boom from a combination of metallic and 
nonmetallic tubing. For strenght and stiffness, use a short lenght of steell or 
aluminium tubing throught the middle of the rotator. Let the metal tubing extend for 
about 6 inches on each side of the rotator. Then install nonmetallic masting such as 
COMMON PVC PIPE....Unlike glass-epoxy tubing, PVC pipe is not very stiff; it 
need help. The secret to making PVC pipe capable of supporting satellite yagis is 
to insert a wooden dowel into the PVC pipe, along its entire lenght...

I use a look a like version of this mounting, i just added a couple of pictures of it on 
my website   http://www.qsl.net/ve2dwe/ be patient pictures are long to be 
downloaded and if some are missing just make a couple of refresh.

On 2.4GHZ i'm using an BBQ grill who is commercially installed on metallic tower or 
pole and i bolted it to the metallic mast.



Luc Leblanc VE2DWE (AMSAT 33583)
SITES WEB:http://www.sorel-tracy.qc.ca/~luclebla/
          http://www.qsl.net/ve2dwe/
C.P.341
Sorel-Tracy
J3P 5N6

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