The only thing I know is that I’ve heard that the optimal length of the antenna is a whole-number multiple of the wavelength it is intended to receive. If that is so, it seems that the cable from the antenna to the tuner would have to be included; doesn’t that act like part of the antenna?
What happens when EMR hits an antenna? Is there a current induced in the antenna somehow? If not, how is the signal transmitted through the antenna?
Is there an advantage in an antenna being straight vs. curved? I have two car antennas that seem to have a coil wrapped around a central post, which results in a shorter antenna.
The EMR is a wave phenomenon involving electrostatic field and magnetic field vectors that are orthagonal to each other and to the direction of travel. Conductors in this field will have charge sloshing back and forth due to Coulombic attraction and/or due to electromagnetic induction, especially if the inductance and capacitance of the conductor create a resonant frequency the same as the signal. If the conductor is broken somewhere and lines close to one another join that break to a circuit input on a radio receiver, the sloshing of charge corresponds to a low power signal entering the radio, and you start calling the conductor an antenna. Different antenna designs change the resonant frequency, change the breadth of frequencies and the degree of resonance (which are exclusive goals), and change the importance of the antenna’s orientation (that is, change the directionality).
Oddly enough I was just going to ask whether trimming my truck’s radio antenna by six inches or so would have a negative impact (I recently started to park in my garage and the antenna scrapes along the door and some ladders that are stored against the ceiling on hooks). So maybe we can kill two birds with one stone here…
Probably to some extent but you’re not likely to notice much, if at all. In any case, automotive antennas are rarely paragons of efficiency so a few inches plus or minus is as likely to improve things as worsen them. If the stations you tend to listen to are local and strong, you won’t be able to tell the difference.
Also the optimal length of the antenna depends on the wavelength of the signal, which differs for each station. When I was a tranee radio operator umpteen years ago, the elderly C42 sets we trained on had a separate antenna tuner which electronically matched the fixed-length antenna to the wavelength of the signal frequency. Presumably, there is something similar built into your truck radio, as there is no guarantee that you wouldn’t replace it with a generic antenna of unknown length if it was damaged.
The signal in the cable between the radio and the antenna is confined between two conductors. In the case of coax cable, the signal is confined between the outer surface of the inner conductor and the inner surface of the outer conductor. An antenna, by contrast, is designed to radiate the signal (in the case of a transmitter) into open space, or capture the signal (in the case of a receiver) from open space. An explanation of how it actually does this can become quite complex.
Nah. As I insinuated, automotive antennas are pretty much “let the chips fall where they may.” I think the formula is roughly a quarter-wavelength of some frequency in the general ballpark of the FM broadcast band, give or take 20%. Either that or the height of the CEO’s daughter’s three-year-old son plus the length of one average watermelon. Either of those produces an antenna which is good enough for reception of strongish local stations. Ever see a car with a coat-hanger antenna? It’s as good as anything else.