Siren noise on 121.5

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GKolo

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Anybody know what would cause a siren type noise on 121.5 ? Whatever it was had the chan locked up for 20 minutes????
 

GKolo

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Thats the first thing that came to mind when i heard it. Wonder how far away you can pick up the signal on the ground ??
 

gewecke

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I would call your local airport and ask them to check any planes on the tarmac for a transmitting EPIRB.
Sometime when they're towed and hit a strong bump,that can set off the EPIRB in the plane.
n9zas
 

davidmc36

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Thats the first thing that came to mind when i heard it. Wonder how far away you can pick up the signal on the ground ??
Not far, a few miles likely for and ELT on the ground. Could have been in a passing airplane if you heard it for a long time, or it was close and activated for the 20 mins you heard. If at an airport with a controller of any sort they would have alerted people on the field about it to track it down.
 

FoeHammer

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It does fit the description of an ELT , When I worked at the airport as part of our aircraft inspections there was an elt testing procedure , it could be turned on in the test mode only during the first 5 minutes of the hour & only for 3 sweeps , for testing purposes , anything longer than that would either be a legit activation or an accident caused by a bump , but during my time working on aircraft I had never seen one accidentally activated , they are generally a small orange box located in the tail section , I would think any signal like this on this frequency would immediately set the search & rescue teams into motion...
 

davidmc36

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.......but during my time working on aircraft I had never seen one accidentally activated.......I would think any signal like this on this frequency would immediately set the search & rescue teams into motion...
I have seen a half dozen times or so in 25+ years in Aviation that one got set off. Even high winds and and aircraft that is not properly tied down can do it.

121.5 is mainly defunct now and not monitored by satellite any more so it is unlikely that any SAR effort would be launched soley on the basis of an obsolete ELT signal.
 

Thunderknight

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121.5 is mainly defunct now and not monitored by satellite any more so it is unlikely that any SAR effort would be launched soley on the basis of an obsolete ELT signal.
That is true, however it's not really "defunct". 121.5 is still used for radio direction finding for land, air, sea assets. The satellites will give you a general area (or a good one if it's GPS equipped, but lost people/ships still move), and then 121.5 is used for homing in on the signal.

406 MHz is what is now monitored by satellites, and that data stream includes a unique ID (makes it easier to figure out if it's a real activation or not) and can also include a GPS location.
 

GKolo

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The closest airport is about 6miles away, Could the ELT be heard that far away by a ground station ?

The 406 MHZ, Can it be monitored by radio or is it mainly satelite ? And if it can be monitored is it 406.000 or other ? I havent seen anything to indicate.
 

KF4ZTO

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Long ago, CAP used 121.600 as their practice ELT frequency, for doing direction-finding drills and such, but nowadays they use 121.775 mostly, unless that frequency is in use, then they use 121.600 as a backup.

ELT's are pretty low powered transmitters, so if the one you're hearing is on the ground...its probably really close to you.
 

GKolo

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I assume that since i had the signal for 20 minutes, It was either in someones garage and accidently activated or it was on a aircraft flying over and went off for some unknown reason.
I think the airport is to far away to pick up the signal.
 

davidmc36

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I assume that since i had the signal for 20 minutes, It was either in someones garage and accidently activated or it was on a aircraft flying over and went off for some unknown reason.
I think the airport is to far away to pick up the signal.
While at the airport my scanner had a hard time breaking squelch when one was going off unless I was right on top of it. Recieved just great from a fair distance if parked on the freq. I would concur that 6 miles is too far if you and it are on the ground. Especially if you have a small antenna.
The 406 MHZ, Can it be monitored by radio or is it mainly satelite ? And if it can be monitored is it 406.000 or other ? I havent seen anything to indicate. .
Cospas-Sarsat (satellite) compatible beacon frequencies
  • 406 MHz UHF- carrier wave at 406.025 MHz ± 0.005 MHz[1]
  • 121.5 MHz VHF ± 6 kHz (frequency band protected to ±50 kHz)[10] (Satellite detection ceased on 1 February 2009, but this frequency is still used for short-range location during a search and rescue operation)
  • 243.0 MHz VHF ± 12 kHz (frequency band protected to ± 100 kHz)[10][11] (prior to 1 February 2009)
Just digital data on 406:

406 MHz beacons transmit bursts of digital distress information to orbiting satellites, and may also contain a small integrated analog (121.5 MHz) homing beacon

Distress radiobeacon - Wikipedia, the free encyclopedia
 
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