So, I was cleaning in the basement this weekend and happened upon an old CB mag mount antenna stuck on the side of a refridgerator. I got to thinking --
When you use a magmount CB or ham radio antenna, there is no direct connection between the ground side of the antenna and the car body -- there's a plastic layer on the mag mount and several layers of paint and primer. Yet the car becomes the ground plane for the antenna through capacitance coupling. Or so I've read. I never really thought about it before.
Additionally, I recall years ago in the days of the big ol' cell "bag phones" -- you know, those big three watt jobs from Motorola in the leather carrying cases -- that we had external antennas mounted on a window of the vehicle that stuck on the outside, and a matching coupler that stuck on the glass on the inside of the car -- the signal would pass through the glass to the antenna, again, referred to as a capacitive coupling, I believe.
Naturally this brought the questions to mind. Why wouldn't this concept work for Part 15? Would it work at all, and would it be legal?
Example. Get a base magnet from an old mag mount antenna, connect to your transmitter ground, make sure the layer of plastic is still in place on the bottom of the mount, get a matching size disc of metal, stick it on the bottom of the magnet, run a lead from that to your chosen ground. In my case, an elevated installation, this would give me a way to ground my transmitter with no direct connection between the transmitter and ground lead. Clearly, running a plain ol' ground lead would clearly be a violation as a "long ground lead". But if you could demonstrate with an ohmeter that there was NO connection between the transmmitter ground and the ground lead, would it be legal?
Further, say you had the standard 3 meter antenna, as I do, as provided by Procaster. If I were to put a plastic sleeve over, say, the top 3 feet of that antenna, and then slid another 10 foot section over that would it in effect create a longer, more effective antenna that would be legal, since it was not actually connected to the legal antenna? Again, an ohmeter test would show the extended section was not connected to the actual legal antenna.
Perhaps this has all been discussed before. But see what finding junk in the basement leads to? Answers to the effectiveness and legality need to be investigated! Now, I don't do ANY sort of experimenting with my installation, as quite simply, it's been on the air for 18 months, I actually have listeners, and I have what I like to refer to as a "blatantly legal" installation. So, I don't want to screw with it while it's on the air and negatively impact my listenership. But it DOES make me think about purchasing another transmitter simply to experiment with. I have the equipment necessary to take actual field strength readings at, say, 30 meters. And can readily deterine if any of these schemes actually work. Hmmm.
Tim in Bovey