A very strange thing happened today… almost as strange as when I started hearing very, very faintly my local low power AM station on my landline telephone.
I live in Manchester New Hampshire and listen to WTKK 96.9 Boston. Admittedly, that’s on the fringe of their listening area and if there were another station on a nearby frequency, I probably couldn’t recieve it well.
Today I recieved another station cutting back and forth from the WTKK broadcast. Not so weird. The problem is that the station I was recieving was WDJR 96.9 in DOTHAN, ALABAMA! Aparently, they actually transmit from Florida. I’m positive on the station ID.
Isn’t this much too far for atmospheric conditions to propogate that far? Is WDJR operating above legal power? Is it being repeated by Mexican radio? Or is a strange coincidence of engineering problems and an errant open microphone to blame. I called WTKK and they said “sure is some strange weather we’re having” although I don’t think I got anyone particularly tech savvy on the line. Is this situation possible?
FM doesn’t bounce through the atmosphere very well, partly because of the frequency band they use and partly because the signal is horizontally polarized. FM signals are usually they are limited to line of sight. They generally don’t go over the horizon, even if they boost the power level.
That said, under rare circumstances FM can bounce off of the atmosphere and get reflected back down. It’s not a likely thing to happen, but it’s not impossible either. I’d say that under the circumstances it’s fairly likely that this happened.
AM signals are vertically polarized, and the frequencies they use bounce much more easily through the atmosphere. A lot of AM stations actually have to reduce their power at night so they don’t interfere with other distant AM stations on the same frequency.
Doesn’t sound so crazy. Atmospheric conditions can propagate radio waves hundreds of miles. It’s not very common, but summer creates the best conditions for it to happen. Skimming through this wiki page, Sporadic-E propagation seems to be able to keep a signal going for up to 3000 miles.
Several years ago, I was driving through rural west Texas, turned on the car stereo, and found a station at every spot on the dial, all from the west coast of Florida - Tampa, Sarasota, and Naples. If I was still a radio geek, I would have stopped, taken notes, and sent off signal reports for QSL cards.
The most common time for picking up very distant FM stations is high noon in the summer, in the case of Sporadic-E propagation. The most distant FM station I remember picking up was a Maine station I heard on my car radio while driving in southeastern North Carolina.
I have Sirius XM radio and since it was after market, the radio transmits on a “clear” FM channel to your radio. In my area 107.7 is clear, usually.
Lately I’d been getting interference in the morning while listening to Howard Stern.
I got fed up with the noise and turned off my Sirius radio. Instead of static I hear a fairly strong “country-ish” station. I think, great, I need to find a new empty channel, someone in NY must have been assigned 107.7. I listen for a few minutes and hear the announcer say “Hot Country 107.7” They are in Delaware.
Must be a lot of that not-so sporadic E propagation, because it’s happening pretty regularly. That or Hot Country had their transmitter cranked.
The VHF/UHF fanatic on my amatuer radio mailing group reported several sporatic-E contacts lately. This is on 2m (~144 MHz) - a bit easier to skip than broadcast FM but probably not THAT much harder.
Just FM? Harumph. I once watched a TV station for one evening that was over 1200 miles away. (Got to watch “Sea Hunt” an hour early. Yes, I’m that old.) Since it lasted so long it couldn’t have been a meteor. So most likely ducting. Note that VHF and FM frequencies intermix. The antenna was just 10 feet of twin lead and in a basement.
And I hate TV tuners that go “blue” when the signal is weak.
“FM frequency” is commonly understood in the U.S. to be the frequency band allocated by the FCC for FM modulated radio broadcast, which is approx. 88 to 108 MHz. Since this is an FCC thing and not a worldwide thing, it’s not necessarily true for other countries. Japan for example uses 76 to 90 MHz.
Similarly, “AM frequency” in the U.S. is going to be about 540 kHz (0.54 MHz) to 1700 kHz (1.7 MHz).
Obviously AM and FM signals can be broadcast on other frequencies as well, but if someone says “FM frequency” it’s generally understood what they mean.
Don’t forget to take in consideration the effect of the transition to digital TV.
Almost all stations that broadcast on VHF Channels 2 - 6 have vacated those channels and moved to other channels.
You don’t notice it because of a thing called PSIP which allows a virtual channel. For instance in Chicago WBBM-TV broadcasts on channel 12 but through the use of PSIP it’s virtual channel is its old analog channel number, channel 2. WMAQ-TV used to broadcast on channel 5 in Chicago, it now broadcasts on UHF channel 29 and through PSIP uses a virtual channel of channel 5.
What does this have to do with the OP quesitons? Oddly enough a lot. The FM band in North America and most of the world lies just above channel 6.
The fact that most (but not all) TV has left the lower VHF (channel 2 -6) had cleared up a lot of airwaves and a result a lot of FM stations are doing weird things because there is nothing around them to interfere with their signals.
Of course there are still channel 6’s in the USA and Mexica and Canada hasn’t change over but the vast vacancies has an had an unsual side efffect. Over at Radio-Info (dot) Comyou ever since digital people have reported pulling in FM and TV stations from all over the place where they normally would’nt have and it seems the reason given has to do with the vacant frequencies, even if that FM station or TV station does use it.
There’s some sort of technical reason why having less frequencies allows the FMs to expand beyond their normal range.
Sorry, I’m being pedantic. The frequencies allocated for FM broadcasting are just as capable of being amplitude-modulated, although you’ll probably be building your own equipment to accomplish it. Then there’s the issue that the spectrum allocated for broadcast operations in the US is not the same worldwide, as engineer_comp_geek noted.
“FM frequency” means nothing more than a radio frequency modulated with frequency modulation as opposed amplitude modulation or one of the many other schemes of modulating a carrier frequency.
What people generally understand should be given less consideration, because the general understanding is incorrect.
9 out of 10 people here will say FM frequency when referring to a radio frequency within the USA FM band of 88.1-107.9 MHz. The fact that someone with the right equipment could broadcast an AM signal within that band is irrelevant.
The same loose usage of terminology is common for SW frequencies too.
See the Sirius XM page here that uses the terminology that you say is incorrect.
I’m guessing you actually mean 103.1–was it a classical station? When I lived in Rochester proper, you could pick up this station (CFMX out of Cobourg, ON) quite clearly all the time. It’s just that powerful (or was 15 years ago, at least).
Of course, depending on how far south of Rochester you were, it might have been a cool atmospheric moment.
