In article , Frank writes:
If your radio has a coaxial connector for the FM antenna, a simple dipole
will match the radio better than a folded dipole. A folded dipole will
work OK but a simple dipole will transfer a little more signal.

Or use a 75:300 ohm balun. I know, balun losses. But then a dipole
of the sort you recommend has issues, too: the balanced to unbalanced
transition leads to antenna currents in the feed line. Assuming you
have one.

Also: a folded dipole is a broader band device than a simple dipole.

Another simple one is a loop. I believe the length is 1055/f,
making it about 10.5' long. It's lower impedance than a folded
dipole and may actually be a good match to a 75 ohm input.

Shape isn't too important - a circle or a square is common.
A square antenna is commonly called a quad.

If you want to try something quick and dirty, put the bare end of
a thin wire about 5 feet long into the center terminal of the radio's
coax antenna connector. This is hardly ideal but it's easy and might
work well enough.

Well, the hams use 468/f for a dipole, 234/f for a 1/4 wave. So for a center
frequency of 100Mhz, that would translate to 2.34' . Assuming you have a
ground plane. Hmmm. Never heard of anyone building a ground plane antenna
for FM radio. Be the first on your block to try it!

George