A very common question that I receive from people inquiring about my antennas is “Does a J-Pole antenna need to be grounded?” Of course there is a very easy answer: no and yes.
J-Pole antennas are half wave antennas by design. Actually they are a half wave antenna sitting on top of a quarter wave matching section. One great advantage of a half wave antenna that it doesn’t require any special grounding or a ground plane to operate. That’s why you’ll find half wave antennas mounted in difficult antenna situations, like on a boat or a vehicle roof made out of fiberglass. I’ve got a antenna I use on my bicycle that ‘s a half wave, because there really isn’t enough metal in the bike to make a effective groundplane.
As for the second half of the question: yes the J-Pole should be grounded. But instead of an RF ground, the antenna should have an electrical ground to protect it in case of a lightning strike. An electrical ground doesn’t enhance the RF radiation of the antenna, but it is an important safety feature on any installation. A simple electrical ground would consist of a ground line from the antenna either bonded to the tower system or run to a buried ground rod.
The lack of a groundplane makes it easy to mount this antenna just about anywhere. You could put it in your attic, on a chimney or a temporary mast. In fact the lack of a groundplane makes the J-Pole a great choice as an emergency or field antenna since there is less parts you need to assemble in deploying the antenna.
Do you have a Slim Jim design for gmrs?
I’m in the process of testing UHF 70cm and GMRS versions of the Slim Jim. I will have one available within the next week.