While motoring around this afternoon I decided to listen to something different from my usual classical station. Just punchin’ my way through the spectrum with the seek button, I came upon a station I had not heard of before. It’s an oldies station whose ID jingle goes, “Golden oldies one-oh-seve-point-five!” Well, that made me curious, because they were at 97.1 on my dial, so I listened for a bit, and sure enough the DJ identified them as 107.5.
I thought for a minute I might be getting some fluke reception from another city, but no, it turns out they’re a relatively new Houston station. So I checked the other stations, and they’re all where they’re supposed to be. And nothing was received at 107.5. I will note that reception of this station included a wee bit of static (unusual for FM). The situation was unchanged when I rode in the car again a couple of hours later.
What’s happening here? Could some unusual atmospheric events be causing this (weather here today is beautiful; ~75°, nary a cloud in the sky)? Could these guys really be screwing up and broadcasting on the wrong frequency? Should I call’em and tell’em?
well, there’s a few things that could be happening.
the only thing that needs to be said for the id to be legal is the station’s call letters and station of license. but they could probably still get into trouble with the fcc for broadcasting misleading statements.
maybe they’re about to move frequencies.
maybe it’s an automated station with the wrong legal ids stuck in the cart player, or computer
maybe it’s a satellite station and the legal ids on your side aren’t firing at all.
the static kinda leads me to believe a computer is involved. can’t say why, it just does.
out of curiosity, i’d call em. make that a plan for tomorrow, would ya?
Hey Beatle
94.5 and 107.5 swaped channels about a month or so ago with a bunch of hype about how each station was going off the air.
We also have a new <gagging>Classic 80’s rock</gagging> station 106.9, it used to be a christian station before the change.
Later
Peace
LIONsob
I’m surprised nobody’s mentioned radio “images”, which is what it sounds like to me. It happens to me all the time, where I’m from there’s a station I like to listen to at 96.3. Whenever I drive near the local station (101.7) it interferes with 96.3, and I can hear 101.7 through 96.3. I don’t know enough about radio images to really give an explanation, but I found this, and I’m sure someone here will be able to give you a better idea what cause it:
A couple stations in St Louis recently changed formats, as have a couple DJ’s.
The reason you heard the station at the wrong place on the dial was because if you have a commercial license, you have to transmit something. It is required. Obviously there’s not a lot you can do about technical breakdowns, but you can’t just sign off for two weeks and send all the employees on vacation. If a station is undergoing a large staff restructuring, (by some agreement) they temporarily “borrow” another existing stations’ broadcast.
In St Louis, there’s a classic rock station at 94.7. Up until a few days ago, there used to be another at 97.1, but 97.1 has decided to switch formats. Their staff won’t be ready for a couple weeks, so they are transmitting 94.7’s signal for that long. 94.7’s identification says that it is being broadcast on both frequencies until the other goes to the talk format.
~
Radio “images” are something else entirely: when I was in San Antonio, I could only get four FM stations across the whole dial: two Mexican, one Christian/gospel and one country. The Mexican stations use ancient transmitting equipment that sends “ghosts”:
93.7: you’d hear it here at 40% volume, 60% static
94.3: you’d hear it here at 55% volume, 45% static
94.9: you’d hear it here at 70% volume, 30% static
95.4: you’d hear it here at 85% volume, 15% static
96.1: This was where the Mexican station was actually “transmitting” at-
96.9: you’d hear it here at 85% volume, 15% static
97.5: you’d hear it here at 70% volume, 30% static
98.3: you’d hear it here at 55% volume, 45% static
99.1: you’d hear it here at 40% volume, 60% static
!
Three Mexican stations just about cover the whole dial. - MC
My AM reception in LA has been bouncing around, but I think it may be a problem with the tuner. One preset station will jump to another preset station for a few seconds and then go back.
Like Lion said, 94.5 and 107.5 swapped a while back. Before the swap 107.5 was the Buzz, and broadcasted on both 97.1 and 107.5. I believe the 97.1 tower was the “cleveland-Houston” (Don’t ask me, I’m just remembering the commercials) broadcast, and the 107.5 broadcast was from Conroe.
So it’s not some weird slippage of frequency, they really were broadcasting on 97.1.
106.9 hasn’t been good for anything since it stopped being ZRock.
It’s not an image frequency problem unless you’re listening on a heathkit. Modern tuners have become very good at filtering out the image frequencies. I don’t mean to belittle heathkit (are they still in business?), it just took me back to my days teaching RF theory & tuner design. Half way through the course all the students had to build tuners on breadboards. Due to the cheesy nature of the kit & lack of shielding, image filtering was a big problem.
For the record, any frequency (besides the desired signal) that beats together with the receiver’s internal oscillator to produce a 10.7MHz (for FM) sum, difference, or multiple of the sum or difference signal is an image. In your example, you were tuned to 97.1MHz. The nearest image frequencies would be:
Therefore, any strong signals at these frequencies will result in an image being generated in your tuner. 107.8 is close to 107.5 (the station you imagined you were hearing) but I don’t think it’s close enough. FM boadcasts have a bandwidth of 200KHz (.2MHz) with a dead space “no man’s land” guardband of 25KHz on each side (straining to remember that number- I haven’t taught this crap in years). The image of 107.7MHz is the next available broadcast slot, and that is the station you should have heard, if any. Your tuner would have to be in really bad shape not to be able to reject an image that far away.
Having seen many many bizarre “that’s theoretically impossible!” problems with tuners as well as many other consumer devices, all I’m willing to say is that it was probably not an image you heard. I’m leaning more towards Lion’s answer.
[sub][sup]*[/sup]And so on using harmonics of 10.7MHz[/sub]