At the low-down end of the AM radio dial, around 530-540, there is a repetitive pattern of mechanical beeps that is present 24 hours a day. It sounds sort of like Morse code, three long beeps, a short beep, three long beeps, and then a pause – which I guess would spell “SES”? Does anyone know what the reason/purpose of this is? I’m in western Missouri, in case this is a local thing.
Thanks, and sorry if this has been asked before. I guess guests can’t search the message board archives?
I for one welcome our new alien overlords.
Finally being the first to use this line in a thread – yeah!
My best guess is what you have found is a navigational beacon.
Where abouts are you? I had a friend in Washington DC who had a radio monitoring and recording service as a sideline, and he was thoroughly familiar with the local radio spectrum. If you don’t want to say where you are, you might find an amateur radio club in your area on this page.It’ll be someone who’ll belong to a group like one of these in your neck of the woods who will be able to answer your question.
I’m near Kansas City. I blush to admit this, but the reason I was fishing around at that end of the dial was that a few months ago I accidentally picked up what seemed to be conversations on my neighbor’s portable phone. The navigational beacon idea sounds plausible. I didn’t know you could pick up stuff like that on “regular” radio, and now I’m sort of intrigued by the whole idea.
Mary
With some very old cordless phones the frequency of the base unit was just above the AM band. With a regular radio with an analog tuner, they were designed to go somewhat above and below the broadcast bands. Better that the radio could tune in more than was needed rather than too little, lest some stations not be receivable. From the way the signal is described, I have to figure it is a navigational beacon. Since the modulated signal is just a few letters repeated over and over, this broadcast station could serve no other purpose I can imagine.
I, for one, would eagerly welcome a new Doper who’d admit to having nefarious motivations, even in her search for the real truth, the STRAIGHT DOPE. I hope you subscribe. xo C.
The Master speaks on a somewhat related issue: The Mysterious Numbers Radio Stations.
Radio Geek checking in…
As others have mentioned, what you’re hearing is probably a radionavigation beacon. Although this type of beacon is largely obsolete now there are still hundreds of them in operation around the country. They operate from 190 Khz to just below the AM band (520 Khz, I think). From your description of the tones you hear (OEO in Morse code, not SES) the beacon in question would be Osceola NDB (nondirectional beacon) in Osceola, WI. That’s a ways from you but not so far away that it would surprise me - I’ve done a fair amount of NDB monitoring and sometimes the conditions are just right and you can hear signals from thousands of miles away.
The only thing that makes me unsure of the identification is the frequency - 233 Khz. Although it’s common for AM tuners to tune a bit past the ends of the band I suspect your AM tuner doesn’t go quite that low. You might be hearing a second harmonic at 466 Khz, but harmonics are usually 3rd-order, not second, and they’re significantly weaker than the primary signal. Also, since you say this is audible 24 hours a day it’s probably a nearby transmitter.
Another thing I’ve heard about is cases where something sounded like Morse code but wasn’t. I read a story about a guy who spent quite a while tracking down what sounded like Morse code, but which turned out to be a compressor on an air conditioner unit that was throwing off RF interference. It just happened to be switching on and off in a pattern that sounded like Morse code. So you might be hearing some nearby source of interference and nothing more.
Most AM radios have internal antennas that are directional, almost always oriented horizontally on a left-right axis. Try picking up your radio and turning it in a horizontal circle. At two points the signal should drop to nearly nothing - those are called the “nulls” and indicate the direction of the signal. There are two nulls, though, so there’s ambiguity - for example, for a transmitter to the north, you’ll know that it’s on a north-south line, but not whether it’s north or south. If you’re really curious you can drive to another location a mile or so away and take another bearing. If the signal appears to be coming from the same direction it’s probably quite far away, but if the direction changes significantly it’s likely nearby. If your radio’s portable and the signal is very close by (a neighbor’s house, or your own, for example) you might even be able to narrow it down just by walking around with the radio and aiming the null at it from various points.
Yes, this is what I do in lieu of having a real life.
73 de N1IHL
Thanks for the info! I tried turning around with a portable radio, and the sound is loudest to the SW and then drops off in a northwestish/southeasterly line. So this means that the origin would lie somewhere to the NW or SE? I took the portable along when I walked my dog a little bit ago, and the signal strength and no-sound direction didn’t change as far as I can tell, so this rules out really close origin, like my neighbor’s air conditioner, right? The portable radio has digital tuning, so I know I’m definitely hearing the sound at close to 530 KHz, or anyroad probably not a whole lot lower.
It’s the navigational beacon at the Johnson County Executive Airport, IIRC. There was a thread in here where I and Scooby, IIRC, figured it out.
(I’m in Johnson County and I’ve heard it since the 1980’s)
Damn it. Search won’t find it, but I know Scooby and I did figure this out once. It could have been Johnson County Industrial, but I’m remembering the Executive Airport. I could be misremembering the airport but I’m certain it is an aircraft navigation beacon in Johnson County, KS.
Hmm…
http://www.airnav.com/airport/KOJC
They have a beacon at 517 KHz, which would be easy to pick up on many AM radios. However, the identifier of the beacon is GQ, which is --. --.- in Morse code. That isn’t close to the OEO in Morse meowpossum reported.
The NORGE NDB is approx. 13 nm south of the Johnson County Executive Airport. It operates on 517 kHz. Could that be it? The morse identifier would be --. --.- (GQ).
Hmm. I’ve just heard it again, and it sounds like “—.---”, which is what the OP reports. I may be thinking of the wrong thing here, I freely admit. But I’m certain that this was worked out on here once before; wish I could find it and see if it’s just my poor memory (or if I am remembering right).
If it’s “O-E-O,” you’ve clearly stumbled onto the broadcasting service of the Castle Guards of the Wicked Witch of the West.
OK guys, just for you, I recorded a WAV of the code, to confirm what I’m hearing.
(340kb WAV file)
That’s OJ in Morse. — .—
Mystery solved!
It’s the LOM for the Johnson County Executive Airport. It transmits on 526 kHz, and the identifier is OJ, or — .—
Cool!
Approach chart is here , the beacon in question is the IAF right in the middle.
So…was I right, wrong, or somewhere in-between? Honestly, no snarkasm, I don’t know if an “LOM” is the same as a “navigational beacon”…at least I get points for posting a WAV, right?