Total posts : 45366
As has been stated here, a properly designed “top hat” does not radiate but does aid an antenna in radiating by changing the distribution of current on the antenna. It also adds capacitance to the antenna which, although not physically longer. becomes electrically longer.
In my case, the antenna which I built and featured on my website some time ago utilizes a capacitance hat to lower the resonant frequency of the antenna even though it was not at the top. It does so by increasing the total capacitance of the antenna which offsets the fact that the antenna was a tad shorter (read smaller inductance) than required.
I’ve read pros and cons regarding the FCC’s take on a 3 meter antenna with a top hat. But, in either case there is nothing wrong with using a top hat on a Part 15 transmitter in so much as it is not going to harm the transmitter. Yes it will alter the resonant frequency but that is designed into the antenna to work with the transmitter to which it is attached. By the same token, a properly designed ground counterpoise does not radiate but definitely aids an antenna by reducing ground losses. There again the FCC probably frowns upon artifical grounds such as that.
Carls idea of parallel wires is not unlike that of some antennas I’ve seen. Fed from a common point, three radiators each slightly different in lenght are each resonant at slightly different frequencies; ie 1505, 1500, 1495 kHz. Like the “Fan Dipole” but covering a very small range of frequencies the bandwidth is larger, more suitable for AM than a single radiator. Many discussions here have pointed out problems with electrically short antennas having very narrow bandwidths. I wonder how the FCC would view that type of antenna? Would it be the same as a single conductor, Litz wire or using a top hat?
This started out as trying to answer one question but seems to have raised many more…