In article ,
Bill Freeman wrote:

Another car antenna question, why do they use such a small diameter
wire inside the coax? The wire inside this coax is about .010 inches
in diameter. Is it this small to save on copper, or is there some
technical advantage to a small diameter wire.

Car antennas are really, really short at AM wavelengths; for that reason
they are sensitive almost entirely to the "E" component of the EM field
only.

Interestingly, if that kind of antenna is hooked to a truly *infinite*
load, the voltage induced in it is entirely independent of its length
(it depends only on the total voltage swing from the E field of the
signal that it encounters). With a very-high-impedance load, it doesn't
take very much shunt capacitance to really attenuate the signal. The
lead-in from the antenna isn't properly a "coax" at all; it's just a
shielded cable, and it's constructed in a way that minimizes the shunt
capacitance as much as possible -- very large shield diameter, very
small inner conductor, nearly all air dielectric; concentricity is of no
concern since its impedance doesn't matter.

If cost was not an object, an insulated gate FET directly at the base of
the antenna would produce the best results.

Isaac