FM transmitters for Apple Computer's iPods can be great conveniences, allowing motorists to pipe their tunes magically through their car radios without messy cables. Seemingly just as often, the wireless devices are static-y abominations.

Given my good and bad luck with such devices, I urge you to shop carefully.

Above all, don't buy an FM transmitter you can't return for a refund. You may end up needing to get your money back on one — or two or three — of the devices before you find a model that makes magical music with your particular kind of car radio. You may never find one that works as well as you'd like.

When I tested a number of transmitters last year, I found two that worked perfectly with a factory-installed radio in a 2004 Mazda 6.

One of these, Griffin Technology's iTrip mini, fit conveniently atop an iPod mini and allowed me to designate any of several spots on the FM band. The other, NewerTech's RoadTrip!+, offered no such tuning flexibility — it only used 87.9 — but did double as an iPod charger courtesy of cable-like design with a prong that plugged into the car's lighter port.

I was so taken with these transmitters (both are still available) that I was eager to road test new versions intended for Apple's recently released iPod video and nano players. To my dismay, I have yet to find a new-model transmitter that works as well as those older ones.

The prolific Griffin has released several fresh, feature-laden iTrips, including the first such transmitter to also work as a charger. None of these, however, performed as miraculously for me as the iTrip mini did. Often, the music coming over the car speakers was intolerably static-y.

I also tried XtremeMac's new AirPlay2, which is cosmetically designed for an iPod nano but compatible with other iPods. This transmitter worked far better for me but not as well as the RoadTrip+ (which also works with any of several iPods with a so-called Dock Connector port).

Your mileage may vary. My loaner transmitters performed even more poorly in another test vehicle, an older domestic sedan with a more primitive radio. I take this as evidence transmitter performance may largely depend on which car and radio you use. In fact, one of Griffin's iTrips may work wonderfully for you. There's only one way to find out.

I'd still recommend the RoadTrip+ as the best option for a variety of iPod models, based on my admittedly limited road testing. Macintosh guru Ted Landau likes it, too: www.themacobserver.com/columns/userfriendly/2005/20050614.shtml.

I don't recommend it for St. Cloud drivers, though. I got loads of interference at the 87.9 setting during a road trip last year — perhaps due to radio towers on the city's outskirts — and did not have the option to retune.

As for the iTrip mini, it will work with several older iPods but not the newest ones that require bottom-loading Dock Connector devices.

For details on the various FM transmitters on the market, try the authoritative iLounge (www.ilounge.com) site and its reviews of individual models. If you can spend a bit more and want to investigate options for hard-wired iPod-to-radio hook-ups, try Apple's "car integration" site at www.apple.com/ipod/ipodyourcar.

Good luck.