Nonetheless, your FM reception should improve nicely with a "real"
antenna too, since less of the signal will be blocked/interacted with by
the car body. It's best if that antenna is straight vertical because FM
signals are typically polarized in both the vertical and the horizontal
planes, never any angle in between. The receiving antenna works best if
it's at the same angle as the transmission. Angled car antennas look
nice and racy, but it's not the best way to get a good signal into the
Antennas are typically a simple fraction of the actual wavelength. But
they can simply be too short. A window antenna is not very good at
matching typical AM-band wavelengths, as Mr. Garcia implied.
The old car radios (both tube and transistor) came with an adjustment
screw that matched the radio to the antenna for AM reception (FM never
needed it). I think that the digital sets don't use this any more.
AM car radio circuits in recent years have seemed to me to be far
inferior to typical car radios of the past. This is similar to the poor
performance of the AM section of home stereo equipment.
The typical FM station broadcasts a certain percentage polarized
vertically and the rest horizontally. As I recall, a common ratio is
something like 80% horizontal and 20% vertical. It may have changed
since I worked in radio. Horizontal antennas are great for homes since
homes don't drive around curves. There's a reason why most car antennas
are vertical whips (in England, TV is vertically-polarized). If you're
using a horizontal antenna in a car windshield, you can go around a
corner and now, your windshield and its antenna are at a right angle to
the radio station, resulting in almost no reception. That's where the
vertical whip gives quite an advantage.
Whips are nice and cheap -- and you've got to drill a big hole someplace
to mount one.
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