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Scott Dorsey
 
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Default FM radio antenna height for car... ?

WideGlide wrote:

The height of the stock FM radio antenna on a new car I bought is about 31"
high. It hits some things that hang from the garage ceiling so I'd love to
be able to shorten the antenna. I realize that doing so will most likely
decrease the quality of reception etc. Someone mentioned that if I shorten
the antenna I would need to keep it at a certain specific length... a
multiple of something... in order for it to work effectively...? Is this
true? I was just going to hack off maybe 6"... thus the total height would
now be 26" as opposed to 31"... but, is there some formula or rule about
antenna height that I need to pay attention to? I don't mind if I reduce
the overall effectiveness of the antenna by a little bit. If I cut 20% of
the length off the antenna, will I simply loose 20% of the antenna's
effectiveness? Thanks.


Most car antennae aren't resonant anyway. They are shorter than a quarter
wave and go into a high-z input rather than have a normal antenna system
where the antenna resonates in the band and feeds a low-Z input.

This is part of why car radio reception is so crappy.

Anyway, you could trim it down. Or you could stop at your local truckstop
and get a wound fibreglass FM antenna that will be shorter AND give you
better reception.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."