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Distress Signal Emitted By Flat-Screen TV
pinqkandi writes "CNN is a running a story on an Oregon college student's flat-screen Toshiba TV which was releasing the 121.5 MHz international distress signal. He was unaware of the issue until local police, search and rescue, and civil air patrol members showed up at his apartment's door. Apparently the signal was strong enough to be picked up by satellite and then routed to the Air Force Rescue Center in Virginia. Quite impressive - luckily Toshiba is offering him a free replacement."
http://www.navcen.uscg.gov/marcomms/gmdss/epirb.ht m
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Corvallis Gazette-Times has more details and a picture of the guy posing with his TV. Apparently, he mostly watches public broadcasting and has acquired a taste for all the quality children's programming it provides, especially "Arthur".
The 121.5 MHz (as well as 243 MHz) Distress call response is being phased out, and the newer 406 MHz call is becoming a more accepted (and used) standard.
See the official NOAA Press Release (PDF) for deteals.
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I, too, was wondering about the specifics of this "international distress signal". Getting lucky (google) with "121.5 Mhz" gives the following link which specifies a relatively simple AM signal with less than 100 mW radiated power! That's not much these days, and I'm rather shocked (har har) that it's taken this long for a device to accidentally trigger such a search. Anyway...here's the URL...
http://www.cospas-sarsat.org/Beacons/121Bcns.htm
Basically, that frequency was getting way too many false positives, so they're phasing it out. To quote the release, "121.5 MHz false alerts inundate search and rescue authorities. This is another major factor in influencing the decision to stop the satellite processing."
121.5 MHz is in the middle of cable channel 14. Frankly, it's rather surprising that this doesn't happen -constantly-.
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Actually, not that powerful, relatively speaking. A typical 121.5 EPIRB puts out 75-125 milliwatts. Keep in mind this is VHF and the satellites are typically NOAA birds in low-earth orbit expecting a line of sight signal, so 100 milliwatts is very workable.
The issue with 121.5 EPIRBs is all they do is send a warble tone -- no ID, location, nothing. All the processing is done by the rest of the infrastructure, and even then the output is basically a position (still no ID) to within a mile or so -- with people using radio-direction finders narrowing it down more.
The newer 406 MHz EPIRBs have specific user data and location information transmitted in their digital packets, so not only do they know the where, but they also know the who -- so when they get a boat beacon originating at someone's house they pretty much already know it's a false alarm.
Another writeup, from the town paper where it happened: Corvallis Gazette-Times, and another from the Eugene Registar-Guard here. On a side note, I'm suprised they responded so quickly, less than 24 hours between recieving the signal and a response team at the door. I used to live in the area, and Corvallis is a small (pop. 50k) college town, with some hills and rivers in the area but nothing like a mountain that would require a large search & rescue squad. I guess it's good to know they're there, though.
As for the transmission strength, from the article - " Mandrell has heard of this sort of thing happening with customized computer gear. Sometimes CAP equipment will pick up these signals, he said, but they are usually weak enough to ignore. "This was really strong," Mandrell said. "This was abnormally strong. It kind of surprised us."" I don't know anything about these distress signals, but I imagine that if they're designed to work from a battery-powered tranciever, anything connected to a wall socket should have enough power to work.
It is in the gap between the video carrier (121.25) and aural carrier (125.75) of Standard and IRC cable systems' channel 14, broadcast channel 14 is at 471.25 (visual) and 475.75 (aural) this should not cause much interference, especially as Cable Television is run on Shielded Coaxial Cable.
Also, television systems operating within the aircraft bands must comply with FCC Rules and Regulations 76.611 -- signal leakage criteria.
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powerful signals are not necessarily needed for a satellite to pick up. Keep in mind that (generally) any satellite link is going to be line-of-sight so there is little to disrupt any signal already propagating between the source and the satellite itself. Also, amateur radio operators have been talking with sattelites for years. You could even talk to the MIR space station when it was in operation.
:)
this site lists an amateur radio satellite with link power between 1/2 and 1 watt on frequencies higher than the 120ish mhz of the distress signal. It really doesn't take much to receive a low-output signal with the proper listening equipment.
I'm just trying to put things into perspective, so that hopefully the tinfoil hat can be taken off
I just checked the frequency of channels for TWC Austin. (digital cable)
Ch 6 = 85Mhz
Ch 7 = 177Mhz
Ch 8 = 183Mhz
Ch 9 = 189Mhz
Ch 10 = 195Mhz
Ch 11 = 201Mhz
Ch 12 = 207Mhz
Ch 13 = 213Mhz
Ch 15 = 129Mhz
Ch 16 = 135Mhz
Ch 17 = 141Mhz
Ch 18 and above keep climbing past 141Mhz
Notice that Channel 14 doesn't exist and how the lower chanels skip around a bit. But the closest to 121.5Mhz is Channel 15.
Life is not for the lazy.
I live in Oregon and he is not far from my home, and we have this story on the local newspaper. Anyway, in the story he doesn't even have a cable or sat. He can only get 4 channels and his favorite channel is OPB (oregon public TV). The story also says that the built-in DVD player died just days before it started sending the signal. Maybe it just asked to be fixed :-)
The devices designed to operate on the 406 MHz System (and the system itself) support unique identifiers, and distress signal is more than just a tone as it is in the 121.5/243 system. This should remove 'invalid' (erroneous) broadcasts from the system.
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The phase-out was announced in 2000 and won't be complete until 2009, and I suspect that after then they will still monitor the old system, but not be as responsive (the technologies that allow the current approximate location of the signal may be phased out as well). Also, if you are at sea WITH THE BOAT, you would most likely transmit an alternate distress signal [mayday style] giving your approximate location. Most of the distress signal transmitters are battery powered and hand-held.
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The signals are received by three satellites, to triangulate the position of the transmitter. I don't know what kind of antenna the receiver uses. Bloody big ones, I would think.
The frequency of the NTSC color subcarrier (the TV color system used in analog video standards in North America and Japan) is defined as exactly 5 MHz times 63/88. That works out to 3.579545454.... (infinitely repeating 54's) MHz. The horizontal scanning frequency is then defined as a 2/455 times the color subcarrier frequency. That works out to 15734.26573426.... (infinitely repeating 573426's) Hz (very nearly the original monochrome horizontal frequency of 15750 Hz). This is where the problem lies. 121.5 MHz divided by 7722 is exactly the same frequency as the horizontal in an NTSC color video signal.
The 7722nd harmonic shouldn't really be that strong, right? Usually not. But the harmonics can get to be very strong overall even at such high orders when dealing with modulating the high voltages needed for the horizontal sweep. There should be some low pass filters that prevent that from getting into the VHF range. But if the filters are absent, or were incorrectly installed, or were damaged somehow, and if some wires formed some resonance near 121.5 MHz (like wires going out to cable, speakers, etc) ... a wavelength of about 2.47 meters or 8.1 feet ... it is possible that harmonic, and a bunch of others near it, could be enhanced and radiated.
The local oscillator in the tuner is a remote possibility. But it would have to be tuned to be receiving a video carrier at 75.75 MHz based on the common satndard of 45.75 MHz for the IF stage in the tuner. But there is no TV broadcast on that frequency in the US ... though I could not rule out there being something on that frequency from a cable system. Still, it wouldn't be an expected place for a TV to tune to. But if the TV has a non-standard IF frequency, the local oscillator getting on 121.5 MHz by some expected channel could be possible. Those leak a lot and it's how the snoops can tell what channel you are tuned to by spying on the RF emitted from your house.
If just this one TV had the problem, then apparently it must be a manufacturing defect or shipping damage (or maybe user damage or tampering). If it were a design problem, I'd sure we'd hear more about it. That probably rules out the CPU clock frequency.
now we need to go OSS in diesel cars
Cable Channel 14 does exist, they just aren't using it. The Minions of Satan, I mean Time-Warner Cable, in my area reshuffled the deck awhile back and quit using it as well. Cable channels 2-6 (low VHF) and 7-13 (high VHF) use the same frequencies as their over the air counterparts, but where over the air 14-83 (UHF) is in one continuous block of frequencies (around 470 to 890 MHz), cable uses frequencies for 14 and up that are used for many things other than television as far as over the air use is concerned.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Even if the ELS frequency is being moved, it is still quite important to keep 121.5 clear, as that is also the standard voice aviation distress frequency. Aircraft voice radios can't tune into 406MHz.
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Could we perhaps give these coastguards a map, marked with areas such as "ocean" (likely place for ships to sink), and "land" (unlikely place for ships to sink)?
It is only about a mile from the Clyde estuary.
Mod parent up.
For those of you who might be wondering what this costs: Replacing an ELT on an aircraft is not like replacing an EPRIB on a ship. You need to ensure the shock switches fire appropriately, and that the unit is mounted such that it will survive a crash.
The last time I explored that option for our airplane we were staring at something around $1200 to do this upgrade. It's hardly chump change.
Further, we need to get our navigation gear coordinated so that the 406 MHz signal has GPS to feed to the world. That's not easy to do for aircraft without panel mounted GPS navigation receivers.
Also, new regulations regarding the pointless ADIZ around Washington DC practically require pilots to monitor 121.5 to respond to an intercept if one happens. If you hear callsign "huntress" on the air and they're operating in your vicinity, remember to be on your very best behavior.
Nearly fifty percent of all graduates come from the bottom half of the class!
You can get a hand-held system using the new frequency for under $500. Check HERE if you don't believe me. Less than $500 is not quite the same as "thousands of dollars."
The 121.5 system is entirely separate from the "GPS sats." GPS has NOTHING to do with EPIRBs and PLBs (except that you can hook up a GPS receiver to a PLB for better accuracy).
I suggest reading HERE for more information.
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If you want to do wiring yourself, here's what you should be looking for:
Hope that helps
What also can be encoded on the signal is the lat/lon coordinates from a GPS. That information allows the initial search location to be pinpointed down to the size of a football field. Without GPS, it's 25 square nautical miles. With the old 121.5 MHZ system the initial search area is 500 square nautical miles.
What I'm curious about is how the CAP and the Air Force got so exicited about a signal that wouldn't have been the whooop-whooop of real 121.5 MHZ ELT. They must have been hearing this TV for quite a while before they got down to locating it. It can take a day or more to locate a REAL 121.5 ELT.
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The main thing that we've found over the last few years is that
(a) Sometimes the FCC test house that you send your stuff to does the tests wrong, or with improperly calibrated equipment, and they may say that you fail where you should have passed.
(b) You can't trust a manufacturer's reference design to have good harmonic performance, so while you're getting good range, you may also be contaminating the second and third harmonic bands with crap. (c) When you have your own anechoic chamber, you can do development and tuning much more quickly than having to outsource that stage of product design. We never intended to be an RF design company, but since our products use wireless technology, we really couldn't do without an investment in basic RF test equipment, and from there it was a series of small steps to where we are now.
Less is more.
If I remember correctly from my CAP (Civil Air Patrol) days, 121.5 is the "test" emergency freq while 121.6 is the actual "live" freq. (Any cadets reading this, please feel free to correct me if I'm wrong - it's been a LONG time).
Most aircraft are fitted with a small transmitter (about the size of a pack of cigarettes) that will start squaking on certian conditions. Sometimes a hard landing would be enough to set one off.
Back in the day (late 80's), SAR (Search and Rescue) teams used a device called an L-per which was basically a reciever mounted on a large hand-held directional antenna. The operator would go to the appoximate location of the crash, determine which direction the signal was coming from and then move about a mile in a perpendicular direction. The op would take another reading and repeat the process one more time, triangulating the position of the downed aircraft.
Of course now they probably have fancy-schmancy wiz-bag computers to do all of that for them.
Any other CAP members out there?
C/FO Martin Dinstuhl (Ret.)
Alpha Flight Commander, 144th Air Rescue & Recovery Squadron
TN Wing
I'm not surprised. In Oregon, the Sheriffs have assumed the responsibility for downed aircraft search and rescue. They have staff to deal with this, and it is a very serious issue. We have three or four radio-oriented volunteers on call to help look for this stuff, and probably a dozen general SAR people. After all, the one call that gets dropped may very well be a real crash where people's lives are at stake. Twenty four hours is a long time.
Yes, there are mountains here. There is also a lot of national forest and wild areas. Mary's Peak is the largest mountain, and you can find one group online if you google for Mary's Peak Search and Rescue. We also host Corvallis Mountain Rescue in this county. They operate state-wide on many of the actual climbing rescues.
In this case, the "squad" was pretty small. Six or seven CAP cadets, a handful of city cops, and two county people. One of them was the county ES manager. I was the other. I got called in after the signal was localized to a small apartment building. Almost nobody was home and the ES manager wanted help identifying which apartment in case he needed to gain access.
In the longer articles, you read about someone saying "the signal's gone". That's me. The real question was "before you answered the door, did you turn something off?" When he turned his TV back on, it was obvious.
I was able to pick the signal up a block away, and when I was inside the building I had to take the antenna off my radio because the signal was so strong. It was also very strong near the electrical panel for the building, so I know that some of it was leaking out the wiring.
I'm glad Toshiba is helping him out. It was a very dissappointing result to have to say "you can't watch TV" and not be able to help him fix it. We had to explain why we couldn't just ignore any satellite hits from his TV: his TV could interfere with a real emergency beacon and either keep the satellite from seeing it at all, or make it harder to find it on the ground.
www.electoral-vote.com is showing Kerry with 51% and Bush with 38% in New Jersey. That data is also consistent with the Dem/Rep split the state saw in 2000. Their source is Eagleton-Rutgers from Oct. 17th. To me 13% is a pretty commanding lead. I'd have to say that Bush has no hope of winning New Jersey based on the poll data I'm seeing.
-matt
121.5Mhz is used in Emergency Locator Transmitters (ELTs) that go in civilian aircraft. When the aircraft crashes (or even has a hard landing every once in a while) it starts trasmnitting. The military uses 243Mhz (harmonic). The transmission is picked up by SARSAT (search and rescue satellite) and then the relevent emergency services resources are called into action.
There actually IS a frequecny for international distress calls (which i don't remember off hand) but it's not 121.5Mhz or 243Mhz. It's illegal to broadcast a distress call on those frequencies. If you use one of those hiker distress thingies that they sell in catalogs don't be surprised to meet a frustrated CAP ground team and an angry Sherrif.
"Let him go, Ralph. He knows what he's doing." --Otto Mann (simpsons)
As a phone tech support guy, I got a call from someone complaining "whenever I try to use my laptop to dial up the company computer, the police show up at my front door."
Turns out the guy had gone to a hotel on business. Getting an outside line required dialing 9-1, then the desired phone number: 1-800-...-.... Upon returning home, the unmodified dialer dutifully dialed 9-1-1-800-...-....
Can we get a "-1 Wrong" moderation option?