DF 406 Beacon Without 121.5 Homing Signal

[sardak]

Anyone have any experiences they would like to share about locating a 406 distress beacon that didn't have a 121.5 homing signal? The Second Generation [406] Beacon (SGB) specifications are being written and one of the proposals is to drop the 121.5 homing signal. The SGB is based on the new MEOSAR system which will locate the beacons using Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) of the 406 signal to the satellites, similar to the way a cell phone is located by the phone system.  Imagine the beacon as the phone and the satellites as the towers, with 75 satellites. MEOSAR Initial Operational Capability (IOC) is scheduled for 2018.

Mike

[NIN]

Mike: I am not completely sure off the top of my head, but you might want to get in touch with Colonel Bill Moran from New Hampshire Wing. We had a mission up here about 60 days ago where a hiker touched off 406 PLB, and the coordinates that we were getting from the GPS and the Doppler calculations were all over the map.

Because of the way the PLB was oriented, I don't believe a 121 homing signal was a player in this situation.

At the very least this mission was a very serious examination of real world employment of a 406, to include the limitations of the coordinates that come through from RCC.

[Al Sayre]

Here's the simple answer:  We have several thousand DF sets available around the country that can find a 121.5MHz beacon on the ground.  I know at least in our wing, we do not have any equipment that can DF a "406MHz only" signal on the ground.  Unless someone is going to cough up the pile of money for the necessary equipment to track "406MHz only" beacons, this will delay or prevent a ground team from finding a crash site and/or survivors.  While our (some) aircraft Becker's can do it, there are many instances due to weather, location etc where an aircraft would not be available for a day or two, and even if available could not get enough of a pinpoint location to put in a ground team.

[LTC Don]

Required reading -- Especially the Summary --
http://www.capmembers.com/media/cms/Prosecuting_406_MHz_Distress_Beacon_DAE24A42EC69E.pdf

9. Summary: 
Search planning and execution personnel must understand that prosecuting a 406 MHz Distress Beacon requires a different methodology than performed when prosecuting the older 121.5 MHz signal.  The following guidelines summarize this approach:

a. It is critical for personnel involved in 406 MHz Distress Beacon and Missing Aircraft
missions to be cognizant of the 406 MHz technology, its capabilities, our resources'
limitations (e.g. Becker SAR-DF 517 frequency limits, lack of Ground SAR Team 406
MHz Data
-Burst DF/Processing, etc.), and effective mitigations.

b. Incident Commanders and Incident Planning Staff (PSC, OSC, AOBD, & GOBD) should
ensure that the AFRCC provides the following information:
1) Distress Beacon Frequency –Is it supported by the Aircrafts' Direction Finder?
2) Position Source (Composite based on Satellite Cross-Fix, GPS Coordinates in Data Burst, GPS Data validated with Composite Satellite Cross-Fix)
3) Distress Beacon Type (ELT, EPIRB, PLB)

c. The Position Source information provides Planners with an increasing level of confidence
regarding the location of the Distress Beacon.  For 406 MHz Distress Beacons, it is most
always prudent to send the Search Assets directly to the location identified by the
AFRCC.  Given the ability to much more accurately locate the 406 MHz source and the
significantly reduced radiated power level of the 121.5 MHz Homing Signal, it is critical
to place the Search Assets within the immediate proximity of the derived signal source's
location.  Natural and manmade obstructions may limit the accuracy of the GPS sensor;
however, geo-location can be validated by Satellite Cross-Fixes (Composite Positions). 

d. Search Assets may monitor for a 121.5 MHz Homing Signal while enroute to the prescribed location, but they may not detect reduced-level signal until they are within relatively close range. For that reason, everyone involved should be aware that searching the
area away from the reported position (which occurs at an alarming rate) may not be an efficient use of the time and resources available. Such actions will typically induce delay, may result in additional suffering of injured persons and can severely impact the overall success of the mission.

e. These are new concepts that must be integrated into CAP's Emergency Service's Training and Exercise Programs.  Failure to address our 406 MHz Distress Beacon knowledge gaps severely inhibits our ability to leverage the significant improvements that have occurred over the last 20 years in Distress Beacon and Satellite Detection/Processing capabilities.

[brent.teal]

Just did one this past weekend.  A plb that did not emit a 121.5 signal in an urban commercial and residential area.  GPS coordinats were not pin point accurate.  spent 12 hours no joy.  Tried using my wouxon to body block with some success but due to the .5 second duration and 50 second repeat, was not able to really narrow down a bearing.  Best I could do was a 90 degree cone. 

Has anyone tried using any of the lower cost doppler DF solutions out there?  The plane was unable to use the Becker to definetly pin point it either. 

There is a DF2020T for approx $400.  found here.  http://kn2c.us/
or picodopp at http://www.silcom.com/~pelican2/PicoDopp/PICODOPP.htm  This is a kit in the true sense of the word.  I ran across one site that claimed the df2020t was a picodopp that had been assembled.  May or may not be true.

Only other thing I was thinking was trying to go old school and use a high gain uhf beam antenna on the wouxon.  Though it would be nice to have some osrt of digital signal meter like on the newer elppers.  Would have been nice if hte elper would have been capable of that frequency as well.  We could have tried using recieve mode to get a bearing, but again very time consuming.   

 

[SarDragon]

There is a DF2020T for approx $400.  found here.  http://kn2c.us/
or picodopp at http://www.silcom.com/~pelican2/PicoDopp/PICODOPP.htm  This is a kit in the true sense of the word.  I ran across one site that claimed the df2020t was a picodopp that had been assembled.  May or may not be true.

They may be similar electronically, but they are different units. The antennas are different.

I investigated the Picodopp several years ago, and haven't found the motivation to build it yet.

[sardak]

Has anyone tried using any of the lower cost doppler DF solutions out there?  The plane was unable to use the Becker to definetly pin point it either.

I know someone who used one of the DIY Doppler units on the 406 signal and it didn't work. I don't think it was either of the models you listed, but I believe the basic innards of all of them are based on the same design published a number of years ago.

What was the make and model of the beacon you were looking for? RCC can tell you that and whether it is supposed to have a 121.5 homing signal. There are a few 406 beacons that don't have a 121.5 homer, and despite being illegal for sale and use in the US, there are some around. And as always, there is a remote chance of a defective beacon.

Mike

[brent.teal]

We found out later that it didn't have a 121.5 signal as it was from a foreign country. 

I'm going to try a couple of things.  Since I am an HAM radio operator i've purchased a 440mhz 100mw beacon.  I am hoping to emulate a 406 mhz type signal to with .5 second burst at 50 second intervals. 

Also a 5 element hand held uhf beam and a uhf df loop. to try to old school df it. 

problems I may have
a plb is pulse modulation while my beacon will be straight FM. 
A regular beacon is 5 watts of power, mine will be only 100mw.  I'll try using better antennas to boos the signal a bit.

If I can work out some techniques to get a good bearing, perhaps we can graduate to an actual 406 beacon in test mode sometime down the line.  This is allowed but takes coordination with NOAA and should be coded with the Test User Protocol.  Whatever that actually might be.

Hoping to come up with something to bring up to the higher ups. 

http://www.sarsat.noaa.gov/Policy%20-%20Emergency%20Beacon%20Tesing%20and%20Training%20_v1.1_March2014.pdf


http://www.sarsat.noaa.gov/Beacon%20Test%20Request%20Form%20Revised_2014v2.pdf

[sardak]

Every wing at one time was issued a 406 training beacon when the Seimac Pro/No-Find DFs were distributed. It was a Seimac EPIRB coded as a test beacon with a homing signal on 121.775. Ours is still maintained (we put in rechargeable batteries and a charging port), gets used and is listed in ORMS.

Mike

[brent.teal]

Hopefully I can use ours if this works out.