[TowerTalk] Reverse Fed Towers

[Gene Smar]

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 at 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 at gmail.com



_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk