Distress Signal Emitted By Flat-Screen TV 514
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."
Signals (Score:5, Informative)
http://www.navcen.uscg.gov/marcomms/gmdss/epirb.ht m [uscg.gov]
Animah S/V Solaris
406MHz Digital Distress signal (Score:5, Informative)
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A better writeup (Score:5, Informative)
Re:Must have been quite powerful (Score:5, Informative)
See the official NOAA Press Release (PDF) [noaa.gov] for deteals.
Signal Details (Score:3, Informative)
http://www.cospas-sarsat.org/Beacons/121Bcns.htm
Re:Must have been quite powerful (Score:5, Informative)
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-.
Re:Signal Details (Score:5, Informative)
First, wait for a satellite pass will notify the Air Force. They will then verify it if they can, contact the FAA for missing flights, etc. The next call goes out to the Civil Air Patrol wing that is responsible for that area. They in turn will normally notify the local authorities who are in charge of S&R. Of course, when you broadcast on 121.5, that sound is audible in every Airtraffic Control center that it can reach.
Once they have done this, they will organize a ground based S&R party and try get a general area of where the signal is coming from. Remember, this is non-directional, so they have to go to a few different places, measure the direction and approx. strength of the signal, and then they will know about where it is. Triangulation sucks, esp. with trees and mountains.
Once they have done this, they'll start their search. Oh, if it's at night and it's not somewhere near them, they'll wait until the morning. Hope you don't keel over at night.
Finally, once they triangulate it, they home in on it. In this case, they homed it to an apartment. Questioned the guy, and went back out into the hallway and confirmed it was coming from there.
So, do you REALLY want a 121.5 ELT locator? I would get one of the new 406mhz ones which are digitally encoded with your information. In addition, some models offer GPS in them that will transmit your GPS coordinates when it sends it. Much nicer and easier to find.
Oh, and I'm not a CAP member any more. But, it was fun while I did it. Not enough time now, but, maybe after I'm done building my airplane I'll have time.
Re:Must have been quite powerful (Score:5, Informative)
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.
Re:Must have been quite powerful (Score:3, Informative)
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.
Re:Must have been quite powerful (Score:2, Informative)
Also, television systems operating within the aircraft bands must comply with FCC Rules and Regulations 76.611 -- signal leakage criteria [fcc.gov].
Re:Must have been quite powerful (Score:2, Informative)
this site [amsat.org] 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
Comment removed (Score:5, Informative)
Re:406MHz Digital Distress signal (Score:5, Informative)
Currently the 121.5/243MHz COSPAS-SARSAT system gets so many false alarms every day that teams do not respond rapidly to their calls. The San Diego Coast Guard Group has about 10 ELT's to investigate *every day* with nearly every single one an accidental activation. If there was one system I could use right now it would be a 406MHz PLB with GPS enabled. Because of the requirement to register your PLB and the serial number transmitted with the distress signal, instead of just a AM warble as on the 121.5/243MHz system, people are less likly going to set them off "just to test them" and are more likly to get in trouble if they do.
Nick
Butte County Search & Rescue [buttesar.rg]
Re:I bet he was hacking Dishnetwork... (Score:2, Informative)
Re:Signal Details (Score:4, Informative)
And most the time we don't wait until daybreak, we like the challenge
Nick
Butte County Search & Rescue [buttesar.org]
Re:Must have been quite powerful (Score:3, Informative)
Re:Must have been quite powerful (Score:2, Informative)
Re:Must have been quite powerful (Score:5, Informative)
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 relationship of 121.5 Mhz to NTSC video (Score:5, Informative)
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.
Re:Must have been quite powerful (Score:5, Informative)
Re:Must have been quite powerful (Score:5, Informative)
SirWired
Re:Actually...it's complaing about the fall lineup (Score:3, Informative)
Re:Error on the side of caution is great! (Score:3, Informative)
It is only about a mile from the Clyde estuary.
Re:Must have been quite powerful (Score:5, Informative)
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.
Re:Must have been quite powerful (Score:3, Informative)
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 [equipped.org] for more information.
Can affect Air Traffic Control (Score:5, Informative)
If you want to do wiring yourself, here's what you should be looking for:
Hope that helps
Re:Must have been quite powerful (Score:3, Informative)
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 [equipped.org] 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.
Re:EMI testing is a bitch. (Score:3, Informative)
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.
121.5 - 121.6 == HELP! (Score:3, Informative)
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
Re:Must have been quite powerful (Score:3, Informative)
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.
Re:Actually (Score:3, Informative)
121.5 NOT the "international distress frequency". (Score:3, Informative)
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.
Modem = Police (Score:3, Informative)
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-...-....