I have one of those (cheap) players that plug into the cigarette lighter thing in my car. It has three frequencies it can transmit to and when I set my car radio to those frequencies, I get the music from my iPod.
My wife asked my how it worked and I patiently explained to her that it was essentially a tiny radio transmitter that my car radio picked up. She seemed satisfied. When we got interference from other stations and had to change frequencies, I explained that the radio waves from those stations were so ‘strong’ that they were interfering with the frequencies from our little unit.
However, when we go into an underground garage, we don’t get any signal at all from the device. I would have thought that the music would have been crystal clear because there’s very little interference from radio station waves. My wife now thinks I’m a dumbass. I need to regain her trust.
You’re correct about how it works. I also would have thought that being underground could only make the reception better. The only thing I can think of is that there is something underground with you that is causing massive interference. A generator? Lots of underground power lines?
Yes, it’s a tiny (and thus, very weak) FM transmitter. There’s no obvious reason why it wouldn’t work in a parking garage, other than JSexton’s suggestions.
I think when you go into a tunnel its not that you get no outside FM signals, it’s just that the whole spectrum gets scattered and your cars radio picks this up as noise. If the signal to noise ratio gets too high modern radios will just shut down rather than blast static at you.
I was in a car with one of these in Colorado once. It was a few years ago now and my memory ain’t what it used to be, but I definitely remember experiencing something similar. It might have been when driving with towering mountains on either side, or going through a long tunnel.