I'm not sure of your application but I was playing around with one to link a GPS to my radio and didn't like it. There are too many stations around here andI would constantly be changing frequencies to get a clear channel.
Not sure of any brand or model names, it's been a while. I got one and it seems to work pretty well, but I live in the Ozarks - not the middle of nowhere, but I can see it from here.
When I was looking to get one, I saw some would disconnect the input from the antenna and switch to the input of the connected device. Unless the radio signal very strong (like next to the tower)the interference is minimal. If you have the device plugged in to bike power you may get an alternator wine. You might get a noise filter when you get the modulator.
Scosche makes one, plugs into the antannae under the seat and has its own on off switch...No problem with station interference or having to change station all the time either like with ones that plug into cig lighter outlet...An in line modulator actually kills the radio antannae feed for you...think the scosche one is around 30 bucks on ebay..
When I was using one, I had the Scosche FMMOD01 and never had a problem with stations bleeding in. But instead of tapping into the antenna wire under the seat, Itapped it directlyat the radio. That worked like a charm. I live in a large urban area with a lot of FM stations and still never had an issue. Now Scosche has the FMMOD02. The actual modulator is the same but the interface was simplified and easier to use. It can be found for under $30.
Rick, if you are saying that the sound quality is better with the radio mod than with an inline FM modulator, can you say whether you can hear this improvement when confronted to the ambient noises at highway speeds?
IMO, yes. I don't have to push the volume as much which in general produces cleaner sound quality. I am able to push my iPod more which is better able to handle it and back off on the bike volume.
I have used the iPod FM transmitter, weak signal and never stayed locked on. Audiovox FMM100 stayed locked on but the added cabling and connectors seemed to always have some kind of static or clicking. The internal mod is soldered in and is rock solid and Sierra does excellent work. And no I am not affiliated with Sierra
Keep in mind, speaker quality also plays a huge role. About 3 months after getting the mod, I installed EdSets in a new helmet and they also improved the quality over the 8 year old speakers that were in my old helmets. I am not able to listen to music from the bike speakers at anything above about 40 MPH