I have an external vertical antenna on my 2001 Ford F-250 pickup.
It's OEM, for the AM-FM broadcast radio in the cab of the truck.
This is a metal antenna, tapered from base to tip.

This antenna is about 32 inches long, and sticks straight up in the
air. It appears to have something spirally wrapped on the exterior of
it, helically wound, with about 1 turn per inch of antenna length.

Does this antenna serve both AM and FM? I can't tell for sure, but
it looks as though there is coax running from the radio to the base of
the antenna. No markings on the coax that I can discern, but it hard
to see up under the dash, with a flashlight!

What would be a probable ohmic value for this coax, if indeed that
black cable IS coax!? Would it most likely be approx. 50 ohm........or
75 ohm........or what?

What is the likely (or "common") configuration of the above
antenna? Would I call it a ¼ wave vertical for the FM freqs? As you
can tell.......I don't know much about how an AM-FM auto radio and
antenna are designed.

Any chance that the AM part of the radio uses a ferrite rod antenna,
and that the external, visible antenna is FM only?

This radio is a VERY good receiver, compared to 3 other AM-FM receivers
that I have.....Sony, GE, and a Grundig. It "pulls in" weak
stations in an impressive manner.

Please, someone fill me in a bit here, or direct me to a good website.
I _HAVE_ GOOGLED around, but found mostly nothing pertinent to my
questions.

Thank you so much........ Lee Carkenord