I have used center fed fan dipoles for some years. They can be used for
multi bands, or to gain bandwidth on 75 and 160.
I've used them as dual banders on 75 and 40 as well as for increased
bandwidth on 75. The 160 half sloper is down as it appears someone used
the ebd insulator for target practice
My tallest tower is a 100' ROHN 45G. It is currently supporting Center
fed, have wave, sloping dipoles for 75 and 40, in single band and a dual
band configurations.
Contrary to other's experience, I did find some effects, although small,
on 75 with the 74/40 dual band antenna. I don't bother trying to
broadband the 40 meter antenna as I normally operate below 7.200. The
big array is down for repair.
Spreaders: I also use 3' long, 1/2" PVC with holes drilled near the
ends. I use a simple equalizer to support the antennas.
The spreaders are attached close to the ends of the shortest antenna, or
element with small ceramic egg insulators at the end of each wire. From
there, I hook a single run of 5/16ths double braid Dacron rope to a
pulley and back to the other wire/element. The support ropes go to the
eyes of the pulleys. This means I only have to tension one rope to get
equal tension on each antenna wire. I use 5/16ths inch rope because of
the heavy tension required to minimize the feedpoint sag as it has to
support the common mode choke and feedline. Tension is roughly in the
200 to 300# range. The upper support rope goes through a pullet at
roughly the 90' level and then down through the tower. I thought I had
photos on the Web, but it looks like I need to update the page. It is
more than a bit out of date.
73, Roger (K8RI)
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|