Car FM antenna to VHF

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Cliff Harris:
I once saw a post on here for a fender mount FM radio antenna replacement, that had a splitter, one to your FM radio and the other to your VHF radio.  Is it possible to do that with just the stock FM antenna and a splitter.  Any help would be appreciated!  Thanks!

Steve Katz:
Not recommended.  The real answer depends on *exactly* what antenna design is used by the auto manufacturer, and those vary a lot.  But without having specifics, I'd have to say "no."

Reason is, mostly, because the car radio whip antennas used aren't just for FM, they're also for AM and that makes them special.  In many cases, the whip is a wire wrapped around a fibreglas (or similar) shaft and not extendable or retractable.  Much too much "whip" to work properly on any amateur VHF band except possibly six meters.

In other cases, the whip might be telescoping chrome plated brass tubing sections; if so, those whips are attached to "special" extremely low-capacitance coaxial cable having a hair-thin center conductor in an attempt to make the cable less lossy in the AM broadcast band, where 50 Ohm coax would be a terrible choice.  That stuff won't work with any kind of amateur VHF gear.

If the telescoping whip is motorized, usually you can't stop those at any particular length: They're all the way "up" or "down," and neither length is desirable.

Much better to buy the commercial aftermarket FM-VHF communications whip antenna product which is quite special in its design to allow it do work properly.  And it may not work on AM at all!

WB2WIK/6

Bob Lewis:
Sti-Co ( http://www.sti-co.com/ ) makes such antennas. They are solid whip antennas that include a splitter for VHF transceiver and FM radio use.

Sti-Co used to make (perhaps still do) a splitter box that had a tuner inside to match it to the old AM/FM antennas that used the special high impedance coax.

This stuff was (is) often used on police vehicles. They are a compromise but they do work, probably better than some of the 2M antenna installations I've seen.

Dennis Zabawa:
Factoid:  Most modern car antennas are a solid conducting shaft without a coil.  What appears to be a spiral wound coil is actually there to change the aerodynamics of the whip which stops it from whistling in the wind.

Dennis KG4RUL

Lon Kinley:
The AM/FM antenna on my '03 Windstar is a wire embedded in the right rear glass. :(

Lon - W3LK
Baltimore, Maryland

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