Post by BBB on May 13, 2013 8:03:50 GMT -5
After removing the ground plane kit from my isolated IMAX antenna, I was getting CMI (common mode interference) and /or stray RF in the house from my LMR400 coax. The better half could not come to terms with the ground plane radials 
The antenna is mounted to a 10' fiberglass mast above my fireplace chimney. Since I was cleaning up the coax runs to the roof anyway, I decided to construct an Very Ugly Balun and mount it out of sight on the back side of the chimney a few feet down.
I read that if your using the larger LMR 400 coax, that the balun needs to be at least 6"-8" in diameter. Looked around in the garage and found a suitable ugly windshield washer fluid jug and plenty of weather resistant ty-wraps. I wrapped about 10 wraps of coax around the jug. This was a bit of a workout using the stiff LMR 400 coax but it was easy to just poke the ty-wrap mounting holes thru the plastic jug. I left about 8' of coax to run past the balun to reach the connector on the IMAX. In one continuous 125' run, the rest ran across and down the side of the house then into the shack. To hide all the coax, the overall run was increased by about 60' from what I originally had run up to the roof.
The results were very satisfying. SWR was reduced from 1:1.7 down to 1:1.1 across the 11 meter band. The peanut gallery didn't hear me thru there speakers as much and I lost some of the white noise static I was getting for some reason.
Just wanted to let those who run the IMAX Antenna know that this relatively easy add on worked for me in a positive way.
I may try to sneak the GPK back on the IMAX as I painted it earth brown this weekend
The antenna is mounted to a 10' fiberglass mast above my fireplace chimney. Since I was cleaning up the coax runs to the roof anyway, I decided to construct an Very Ugly Balun and mount it out of sight on the back side of the chimney a few feet down.
I read that if your using the larger LMR 400 coax, that the balun needs to be at least 6"-8" in diameter. Looked around in the garage and found a suitable ugly windshield washer fluid jug and plenty of weather resistant ty-wraps. I wrapped about 10 wraps of coax around the jug. This was a bit of a workout using the stiff LMR 400 coax but it was easy to just poke the ty-wrap mounting holes thru the plastic jug. I left about 8' of coax to run past the balun to reach the connector on the IMAX. In one continuous 125' run, the rest ran across and down the side of the house then into the shack. To hide all the coax, the overall run was increased by about 60' from what I originally had run up to the roof.
The results were very satisfying. SWR was reduced from 1:1.7 down to 1:1.1 across the 11 meter band. The peanut gallery didn't hear me thru there speakers as much and I lost some of the white noise static I was getting for some reason.
Just wanted to let those who run the IMAX Antenna know that this relatively easy add on worked for me in a positive way.
I may try to sneak the GPK back on the IMAX as I painted it earth brown this weekend
