Hi Ray,
I have a 55ft tall aluminum tubing vertical for 160 meters which is
center loaded with an inductor and top loaded with 4 sloping wires. At
the top of the tubing vertical I have a yard arm made of a piece of
aluminum angle stock that holds up a pulley which is offset ~18" from
the aluminum tubing vertical. From that pulley I am suspending a wire
vertical for 80 meters in parallel with the 160 meter vertical. Since my
160 meter vertical is only 55 ft tall, the last 10 ft or so of the 80
meter wire bends down at the pulley level at an ~45 degree angle.
I am just using standard ~2" long plastic (or perhaps they are porcelain
- I forget) end insulators at the 55ft level (the rope going thru the
pulley attaches to the insulator supporting the wire at the 55 ft level)
and on the end of the ~66 ft long wire. I have never had any problems
with these insulators failing when running 1500 watts into this wire
vertical.
Have you tried leaving the base of the 160 meter vertical open instead
of shorted? I use an Ameritron RCS-4 at the base of my vertical to
switch from the 160 meter tubing portion to the 80 meter wire portion.
The RCS-4 leaves the unused ports open so the base of the 160 meter
tubing vertical floats when I am 80 meters and vice versa.
If your 160 meter vertical looks like an ~1/2 wavelength on 80 meters,
shorting its base may cause the mutually coupled RF from the wire to
induce a high RF voltage in the tubing near the end of the 80 meter wire
(it might be worth trying to model this in EZNEC). In the absence of
some sort of mutual coupling like that, the voltage at the end of a 1/4
wave wire vertical shouldn't be any worse than the voltage near the end
of an 80 meter 1/2 wave dipole and I have never had problems using those
standard ~2" long plastic or porcelain dipole end insulators on 80 meter
wire antennas when running legal limit. Of course, I should say that I
am only at a moderate altitude (~2700 ft ASL) and far away from ocean
salt spray.
I hope this helps.
73, Mike W4EF...............
On 1/31/2018 6:20 PM, Raymond Benny wrote:
I need the experience and wisdom of this group.
I have am 80m vertical hanging off the side of my 160m vertical and share
the common radial system. The 160m vertical is 4" and 3" irrigation pipe,
72 ft tall with 4 - 30ft top hat wires and a loading coil at the base. The
80m vertical is up 68 ft and hangs from a 14" side arms and has its own
coax and loading coil. I have to short the 160m vertical to ground to
operate 80m. I run near 1500w output.
The problem is that the 80m insulator at the top shorts and arcs out over
time. I understand there is perhaps 6 - 10 KV at the top of the 1/4 wave
80m vertical. I can see it now arcing at night and my swr is jumping
between 1.5 to 2.0. My original insulator what just a small, abt 1" x 2"
white porcelain wire insulator that lasted for 2 - 3 years before it
cracked and shorted due to mechanical strains. My second was some sort of
composite insulate about 1" x 4" long that lasted abt a month before it
melted. My last insulator that is arcing, I think it is some sort of
porcelain insulator. Maybe its cracked too.
I am tilting down the vertical tmw to replace the insulator and want to get
some ideas as what to replace it with. I have both white and brown guy wire
insulators, about 1 - 1/2" dia by 3" long, or I'm wondering if a synthetic
material type might work the best. I have three pieces of synthetic rods,
about 3/4 to 1" dia. One is from the center insulator of a yagi driven
insulator from my junk box and about 1" dia by 8" long. I think its
fiberglass, but not sure. I also have from my junk box, one round stock
that might be Delron another and other might be Teflon or some other
synthetic material. I just placed the 3 pieces in the microwave with a cup
of water. After 2 minutes, all three were slightly warm. After a second 2
minutes hit, two of the synthetic types were very hot. The yagi dipole
center insulator which I think is fiberglass was still only slight hot.
So, what conclusions can I deduce? Which one might be best for my use? I'm
tending towards using one of the porcelain insulators.
Any thought or experiences? Are there more tests I can do on the synthetic
material rods?
Tnx for your thoughts and recommendations.
Ray,
N6VR
Near Prescott, AZ
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