Copper J-Pole by: KB9VBR Antennas
I was searching for an inexpensive antenna to use in the shack for 20 meter / 70cm operation. I had heard about people using an antenna called a J-Pole and thought I would research it a bit.
During internet searches, I came across a web site called www.jpole-antenna.com.
The web site is run by a fellow ham, Michael Martins, who makes different types of antennas for different bands made of copper pipe.
Coax type: RG-8X from ABR Industries LLC
# 218XATC
Premium Quality RG-8X sized cable,
Unlike regular RG-8X this cable has a direct burial jacket.
(Uses UG-176 reducers like regular RG-8X, when needed)
100% Bonded Foil + 95% TC Braid
Closed Cell Polyethylene Dielectric
82% Velocity of Propagation
Very Flexible. Moisture Proof
Ultra-Violet Resistant
Similar to LMR-240-UF
Attenuation @ 100ft/Pwr/Efficiency
0.9dB @ 10MHz/2.16kW/80% E
1.4dB @ 30MHz/1.24kW/69% E
2.1dB @ 50MHz/.96kW/62% E
3.6dB @ 150MHz/0.55kW/43.5% E
6.3dB @ 450MHz/0.31kW/23.2% E
RoHS Compliant. Made in America
I got his antenna ($36.00) and about 6 snap on ferrite beads ($18.00), for common mode current. The antenna rediates very well in an omni-directional pattern. When I first mounted the J-pole it was on a push up pole at 17 feet. Below are graphs made with a Mini600 antenna analyzer for 2 meter and 70cm at 17' and 25' fo RG-8X coax with Amphonal PL-259 connectors.
I later decided to place the J-poles on my tower which is 60' to the peak of the mast. This time I cut a 100' foot length of RG-8X with the same connectos and ran that out to the J-pole. The distance I was able to reach and hear increased dramatically!!! At 17' I was hitting repeaters solid at 20 miles and was fuzzy beyond that. At 60' high, I was easily able to hit repeaters over 100 miles away. The graphs I produced were almost identical as the ones above and were only off by .1 +- in certain areas of the graphs.
Then on 6/6/2020 I snagged the coax, that I was going to hang up the following day. The coax got caught on the bumper of the Cab Cadet while I was cutting grass and pulled it out of the electrical box that weather sheilds the hole through the wall to the shack into the shack. I guess it got pulled pretty hard because, it broke clean at the electrical box. I lost 15' 8" off of my 100' run of coax. I pulled the 15' section out of the wall and stuck the other end of the coax through the wall and back into the shack. After I put a new Amphinol PL-259 connector on, I put it back on the Mini600 antenna analyzer and did a new graph. Below are the screen shots for 2 meter and 70 cm.
So, breaking off 15' 8" of coax from my 100' run left me with 84' 4". Very interesting to see the difference in the graphs above. Both bands tested better overall and may be even better with LMR-400 or similar coax.