Are Terrestrial Radio Stations Trying to Crowd Out Unused Frequencies?

In order to listen to my XM satellite radio in my car, I plug a gizmo into it that converts the satellite signal into an FM signal and broadcasts said signal at very low wattage, to my antenna about two inches away. I have a choice of which FM to broadcast on; all are at the low end (88.1 through 88.9, IIRC) or the high end (106.5 through 107.9, IIRC).

Until about two months ago, the best “empty” frequency on which to broadcast my XM was 107.5. However, at about this time a local terrestrial station started broadcasting their signal on two frequencies: their original 93.9 and, you guessed it, 107.5.

Ostensibly this was to allow their signal to be heard deep inside this city’s office buildings (so says the business writer in our local rag), but the cynic in me finds it a very odd coincidence that their repeating signal is on the one frequency in Springfield that had the least interference from other stations and, thus, was perfect for broadcasting my XM signal.

So is this just a coincidence, or is the cynic in me right? Are terrestrial radio stations trying to crowd out empty frequencies in order to render it difficult to interface satellite radios and MP3 players with car stereos?

In all seriousness, it’s just a coincidence.

I had a lengthy answer for you, but it comes down to this.

Terrestrial radio stations are competing for the same empty frequencies that you are. Given the physical and geographical issues limiting which frequencies are usable, 107.5 was probably the only frequency that was available for the repeater. As far as the FCC is concerned, that frequency was open and assignable, so they did. :shrug:

Radio Locator has a list of unassigned frequencies that you might try.


If the terrestrial stations are seriously trying, they’re doing a piss-poor job of it out where I live. Most of the possible slots here are empty.

I suspect that the radio station picked 107.5 for exactly the same reason you did. It was a clear frequency with little interference. They aren’t trying to stop you from using XM radio. They are just looking for a good frequency to broadcast on. Picking a frequency that won’t interfere with anything else is going to make it much easier to get FCC approval.

The entire FM band is allocated for FM radio stations. The fact that you can buy a converter for XM to FM band is irrelivant. FM is there for radio stations. If you have some whiz bang fancy device that converts XM to FM, as long as it doesn’t interfere with existing FM stations, the FCC really doesn’t give two hoots about it one way or the other. They aren’t even going to consider the operation of your device when they look at frequency allocations and where to put new transmitters. If one of their new frequency allocations interferes with your little device, tough noogies. The FCC will happily fill up all of the available FM bandwidth in your area with radio stations. That’s what the frequencies are there for.

Trying to penetrate city buildings is one of the more common reasons for a radio station to broadcast on two frequencies, and radio stations have been doing that for years and years (long before FM converter devices came out). It doesn’t sound to me like there’s any conspiracy here. It’s just the normal way radio stations do things. Radio stations may also broadcast on two different frequencies with directional antennas so that they can avoid interference with other stations and still reach their desired market size.

You can avoid all of the interference problems by buying a car radio with a line level input. Then you can plug your mp3, XM, or any other audio source into your radio without going through an FM converter.

Go to Buffalo. Thanks to the city’s proximity to Rochester, Hamilton and Toronto, you’ll be able to hear a station at every allocated frequency.

[highjack] I run much the same thing with an IPOD accessory gizmo that will play my IPOD over the radio speakers in my car on unassigned radio stations. However, when I drive into an area with a strong signal on the previously unassigned station it creates static and eventually breaks in. I cannot take long trips out of my area without this happening and needing to readjust my IPOD.

Are you, HeyHomie or anyone else, saying the same thing happens with XM? I would guess that XM is “higher tech” and once you find a blank station you are good to go - even driving say +50 miles into other media markets? – but maybe that is not the case? [/highjack]

The same thing is going to happen, no matter what generates the audio source. You can have the output of an XM receiver, the output of an IPOD, or anything else, it doesn’t matter. The problem is that you are modulating it up to FM, so any strong FM source (like a close radio station) will overpower it.

No, I have that problem pretty much wherever I go.

I keep my XM on 106.9 here at home, but when I drive to any other city I’ll have to change, often several times. This is a tad tricky when driving through urbanized areas, trying to pay attention to my driving and reset the XM frequency, often several times. :eek:

Springfield’s proximity to Decatur and Lincoln and, to a lesser extent, Peoria and St. Louis means that every frequency is open to at least some interference. Even my best one, currently 106.9, will sometimes get interference, especially at night.

It may not help you, but my XM came with a transducer (I guess it’s called) that plugs into the cassette player. It looks just like an audio cassette with a wire coming out of it. I mentioned to a buddy with Sirius that I was thinking of getting the FM modulator like his Sirius had, and he said he was looking for a hardwire solution to get around the problems you mention. Of course it wouldn’t do any good if your stereo didn’t have a cassette player, and there’s the extra wire hanging out of the dash (that’s what I wanted to do away with), but there isn’t any crosstalk with FM stations.

There are two factors to blame for this.

First, the terrain is flat. There are no mountains to stop or re-route signals. Thus, signals travel farther on the same power than they would in more mountainous terrain, leading to interference.

Second, the atmospheric conditions at night are more conducive to long-distance radio reception. Consequently, you’re going to get interference from other stations.

Finally, there is a condition called “podjacking” in which the signals from the transmitters of other users overpower yours and you get interference or the signals of the guy next to you.