[TowerTalk] mounting a dipole to the side of a tower

[Dave Hachadorian]

For tough insulating material, this stuff is good:
http://lists.contesting.com/archives//html/Towertalk/2006-09/msg00158.html

Attached is a picture of what it looks like on one of my 
antennas.  Maybe the reflector strips attachments, but you will 
get it by direct email.

Dave Hachadorian, K6LL
Yuma, AZ


-----Original Message----- 
From: Dave Sublette
Sent: Saturday, March 31, 2018 4:03 PM
To: Ron Young W8RJL ; kj6y--- via TowerTalk
Subject: Re: [TowerTalk] mounting a dipole to the side of a tower

Very good questions, Ron.  I will attempt to clarify.  The 
antenna always
hangs or bolts to the tower horizontally.  To raise it, I strung 
a trolly
cable to a point well out from the base of the tower.  The 
raising angle
was less than 45 degrees.

The guys are all non-inductive. Phillystran.

Although I haven't measured with an ohmmeter, I would be very 
surprised to
find either half of the antenna shorted to the tower.  The saddle 
clamps
hold it about a half inch away from the mounting plate and each 
side of the
dipole is insulated with the split PVC pipe under the U-bolts 
between them
and the saddle clamp.
I've never noticed any change in SWR as the antenna rotates.

Dave

On Sat, Mar 31, 2018 at 4:54 PM, Ron Young W8RJL 
<youngron at verizon.net>
wrote:

> You said dangling. Vertical or horizontal???   Was it the same 
> distance
> from the guy wires when dangling and bolted???  Did you check 
> for
> resistance between either side of dipole and tower??
> Does SWR change as it is rotated???
>
> Ron W8RJL
>
> Sent from AOL Mobile Mail
>
> On Saturday, March 31, 2018, Dave Sublette 
> <k4to.dave at gmail.com> wrote:
>
> I have a Rohn 55 tower that rotates. I recently built a rotary 
> dipole for
> 40 meters. It is full size. The center section tubing is 1.625 
> inches in
> diameter. It is a split construction. I feed it with an RF 
> choke and 50
> ohm coax.
>
> Hoisting the dipole up to 100 feet or so and leaving it dangle, 
> the antenna
> shows an almost perfect SWR curve. It has a 1.1:1 SWR at the 
> bottom of the
> band and rises gently to 1.5:1 at 7300. Since I operate mostly 
> CW, I
> didn't bother to shorten it.
>
> However, after I have bolted it to the mounting plate, the SWR 
> goes bad,
> raising to 5:1 at the band edges and being at 3:1 at about 7200 
> Khz. It
> still works great and has a good pattern.(Nulls off the ends).
>
> My mount is made from two aluminum plates bolted to two pieces 
> of Angle
> steel, one on the top edge and one on the bottom edge. They run 
> the entire
> width of the tower face. The edges of the angle are within an 
> inch of the
> dipole, so that makes it practically enclosed on three sides. 
> I'm guessing
> the stray capacitance is killing me.
>
> I propose to redesign and get rid of the angle pieces, leaving 
> a flat
> plate. I presently insulate the dipole with a full length 
> (tower face)
> piece of schedule 40 PVC that is split and slides between the 
> U-bolts and
> the saddle clamps.
>
> The diameter of the tubing in the center is 1.625 inches. If I 
> were to
> replace the saddle clamps with insulated type, is there a 
> product available
> that does
> this, or should I just go ahead and make them? If so, What sort 
> of
> material? I am also thinking of ditching the metal plate and 
> using Marine
> plywood.
>
> The antenna uses dacron support ropes out about 25 feet from 
> the center so
> a lot of the stress is relieved by doing this.
>
> This thing works great. The change in SWR drives me nuts. So 
> I'm going to
> try to fix it.
>
> Building stuff is not a problem for me, but I don't have a lot 
> of
> experience with tough insulating material. Any advice is 
> welcome.
>
> Thanks and 73,
>
> Dave, K4TO
> _______________________________________________
>
>
>
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