A common perception of J-Pole antennas is that because of their design, they have a tendency to couple with large metal objects and buildings. This is true if you are attempting to mount a J-Pole along side a house with metal siding or a steel shed. But does this restriction hold true for side mounting the antenna on a tower?
Tower real estate is valuable and only one thing can be on the top. We often select our best, or most desirable omni antenna to hold that top piece of the tower. J-Pole antennas are great choices for your secondary radio, packet data radio, Winlink 2000 or APRS radio. These antennas often take lower priority to the prime voice antenna, so they get mounted lower on the tower. I’ve even had customers wanting to Tee off the top of a short mast and install a 2 meter J-Pole antenna and a 220 MHz J-pole side by side.
The good news is that in all of these situations is that the J-Pole can be side mounted on a tower or you can have two J-Poles of different frequencies mounted alongside each other. Antenna towers are metal, but because they are built our of tubular steel and are not a large metal sheet, they won’t couple with the antenna, as long as the antenna is at least 1/4 wavelength or more from the face of the tower. In fact the further you can move the antenna out from the face, the less and less the interaction (if any) there will be. My recommendation is to have the 2 meter or high frequency antennas out at least 2 feet and the 6 meter antenna at least 5-6 feet.
Side mounting two J-Poles alongside each other also won’t cause interference with each other. You can mount a 222 MHz, or 70cm J-Pole on the same plane as a 2 meter antenna. These antennas are on different frequencies and won’t cause the other antenna to resonate or cause interference. I wouldn’t recomend, though, mounting to two 2 meter J-Poles side by side.