William:
I use both shunt feed on 160M and reverse-feed 1/4 WL wire (sloper) for 80M on
the same tower. However, I have a ten-element Yagi atop the tower and I have
grounded all parasitic elements on it for capacitive loading of the entire
tower. I didn't model either of these antennas but climbed, set and measured
SWR a few times until I got the tower tap point just right (lowest SWR on my
MFJ-259 analyzer.) I also adjusted the length of the sloper wire for further
SWR reduction.
BTW - I did not merely hang the sloper wire off the center conductor of the
coax. I tied an egg insulator onto the tower near where I thought the tap point
ought to be (55 AGL on a 64 foot tall tower.) I tied the sloper (69 feet long
#12 insulated) onto the other side of the insulator but allowed about 2 feet of
length to hang off the insulator. (The far end is connected to another
insulator that is on a bungee cord wrapped around a roof vent on my house.) I
connected the center conductor and sloper wire with a wire nut and began my SWR
measurements. I was able to cut a few inches off the hanging wire at a time
until I arrived at an acceptable SWR. I didn't undo the entire wire until after
all the adjustments had been completed. Then I let the excess wire slip through
the egg insulator until I had only a few inches sticking out. I believe I even
kept the wire nut in place, rather than soldering the connection to the coax
center. I applied a couple wraps of electrical tape to
the center wire's insulation to protect it from sunlight.
BTW2 - As for the coax braid connection to the tower, I stripped about 4 inches
of jacket off the cable and twisted the braid into a single wire. I used a
Harger 213T cable-to-flat clamp to connect the braid to the tower angle steel
members. This is the connection I had to move around the tower to find a low
SWR spot initially. The clamp made it easy to do and undo. Round member
towers such as Rohn will probably need a different type of connector for the
braid.
BOTTOM LINE: Face it - you'll have to do some tower climbing to get this
right, but shunt feeding and sloper/reverse feed wires do work.
73 de
Gene Smar AD3F
On 12/15/15, wosborne44@gmail.com wrote:
I have a tower that has a base that is in concrete and grounded. I
would like to make it a vertical without installing insulators. Has
anyone used elevated radials with reverse feeding, i.e., connecting the
center conductor to the radials and the shield to the grounded tower? I
see this in the ARRL handbook but I cannot seem to make a model of it
work. Any help would be welcome.
Thanks,
William Osborne--K5ZQ
270-205-9565
Wosborne44@gmail.com
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