406 Decoder

Major Lord · March 30, 2009, 09:05:28 PM

I think a portable, low cost 406 receiver/decoder would be of value to ground teams. I know there are test receivers out there that use PDA's the brain, but don't know how they work at a distance.

Major Lord

JoeTomasone · March 31, 2009, 12:07:50 AM

I can see why a GT could use a receiver (5W signal is close by, sir!), but not a decoder. Even if it's the wrong objective, if you hear it, you're gonna prosecute.

Major Lord · March 31, 2009, 02:14:45 AM

Joe, My consideration was that the unit may be damaged and sending a low powered signal that has not been uplinked, and a ground team MIGHT possibly be able to read the GPS data and assess whether its reasonable to go off-road to pursue. ( I think in light of the number of low quality ELT signals pursuant to an actual crash this is reasonable) I don't know how many crashes have resulted in a succesful activation with valid data uplinks and how many just got extra crispy, destroyed or seriously damaged on impact, so perhaps my idea is overly optimistic. It would be mighty tricky using conventional DF'ing techniques to find a 5 Watt bursting transmitter! Besides, it would be cool! (only if it does not cost as much as a Becker though!)

Major Lord

es_g0d · March 31, 2009, 04:08:10 PM

A low-cost 406-band receiver would be great for CAP ES personnel. A decoder wouldn't be terribly more complex and provide a useful capability. And either of these would be a good first step towards a reasonably-priced DF unit for 406, technical challenges aside. The bottom line is, if you could build it, I'll buy it!

I'm also curious about what we do when the 406 signal ceases. In the case of at least 2 ELT manufacturers, this is the case after 24 hours. The idea is that the battery will be preserved for the low-power homer.

argentip · March 31, 2009, 04:54:20 PM

I still don't see what the purpose of having a receiver for 406MHz is. You can't track on the 406 because it is only a burst of data. All 406 beacons have a 121.5MHz homing signal that operates just like the older 121.5-ony beacons. I've worked one 406 mission so far where the beacon was unregistered. The lat/long we got from AFCCwas very close to where it was located and we were able to track it just like an older beacon.

JoeTomasone · March 31, 2009, 06:01:18 PM

The 406 burst is a 5w signal - meaning that you might be able to pick it up a little further away than the 121.5 - helping you to realize that you're in the right area.

BigMojo · March 31, 2009, 07:15:42 PM

I don't think there is any audible quality to the 406 signal burst...I may be wrong though. I would think it would have to be a decoder to be of any use. But I think it would be more of a "cool gadget" than an essential tool.

JoeTomasone · March 31, 2009, 07:45:22 PM

Quote from: BigMojo on March 31, 2009, 07:15:42 PM
I don't think there is any audible quality to the 406 signal burst...

Sure there is. A quite audible "braaaaaaap" every 50-60 secs.

lordmonar · March 31, 2009, 08:30:41 PM

Quote from: JoeTomasone on March 31, 2009, 07:45:22 PM
Quote from: BigMojo on March 31, 2009, 07:15:42 PM
I don't think there is any audible quality to the 406 signal burst...

Sure there is. A quite audible "braaaaaaap" every 50-60 secs.

How did you hear this Braaaaap? Were you listening on AM, FM or what?

sparks · March 31, 2009, 10:12:43 PM

Does anyone know if the 406 TSO requires a secondary 121.5 signal or is it an extra cost option. I tried to find the operational requirements but was referenced to a technical committee paper which wasn't available without paying for it.

JoeTomasone · March 31, 2009, 10:30:44 PM

Quote from: lordmonar on March 31, 2009, 08:30:41 PM
Quote from: JoeTomasone on March 31, 2009, 07:45:22 PM
Quote from: BigMojo on March 31, 2009, 07:15:42 PM
I don't think there is any audible quality to the 406 signal burst...

Sure there is. A quite audible "braaaaaaap" every 50-60 secs.

How did you hear this Braaaaap? Were you listening on AM, FM or what?

FM. I have a WAV and MP3 of it if you're interested. PM me an email to send it to.

Quote from: sparks on March 31, 2009, 10:12:43 PM
Does anyone know if the 406 TSO requires a secondary 121.5 signal or is it an extra cost option. I tried to find the operational requirements but was referenced to a technical committee paper which wasn't available without paying for it.

AFAIK it is mandatory.

lordmonar · March 31, 2009, 10:34:20 PM

Quote from: sparks on March 31, 2009, 10:12:43 PM
Does anyone know if the 406 TSO requires a secondary 121.5 signal or is it an extra cost option. I tried to find the operational requirements but was referenced to a technical committee paper which wasn't available without paying for it.

The 121.5 is part of the 406 transponder. Only the GPS unit is optional.

♠SARKID♠ · March 31, 2009, 11:23:53 PM

Quote from: Major Lord on March 30, 2009, 09:05:28 PM
I think a portable, low cost 406 receiver/decoder would be of value to ground teams. I know there are test receivers out there that use PDA's the brain, but don't know how they work at a distance.

Major Lord

So how do we go about it? Like in the thread I started a while back, I'd love to be able to do this.

Major Lord · April 01, 2009, 12:24:28 AM

Dan,

The Tigerstrike people talked about it in the locked thread, and raised the question as to whether there would be value to it. I believe their thinking was as an adjunct to their DF unit. I don't know of anyone else actively pursuing it. There are not too many receivers that would do a very good job of acting as a front end for this kind of a device.

Major Lord

sardak · April 01, 2009, 05:52:50 AM

QuoteDoes anyone know if the 406 TSO requires a secondary 121.5 signal or is it an extra cost option. I tried to find the operational requirements but was referenced to a technical committee paper which wasn't available without paying for it.

TSO-126 for 406 MHz ELTs refers to RTCA Document No. DO-204 (the one you have to pay for) for technical requirements.

RTCA DO-204 says "If a homing transmitter is incorporated in the 406 MHz ELT, it shall conform with the applicable application specifications of this document."

FCC reg 87.199(b) says "The 406.0–406.1 MHz ELT must contain as an integral part a homing beacon operating only on 121.500 MHz that meets all the requirements described in the RTCA Recommended Standards..."

So there is a requirement for the 121.5 homing signal, coming from the FCC - for beacons sold in the US. Equivalent requirements sequences exist for EPIRBs and PLBs in the US. A 121.5 homing signal is not required by Cospas-Sarsat (C/S T.001 sec. 4.5.3) so beacons from other countries might not have the 121.5 homing signal.

There was a recent incident in California where the 121.5 signal from a 406 beacon wasn't detectable until less than 100 feet from the beacon. The GPS location didn't get the 121.5 receivers close enough, a 406 DF detected the beacon. So the ability to detect the 406 signal is desirable. Whether it's necessary to decode it is a different story. The only useful info would be the lat/lon data, which should be coming from AFRCC, but for whatever reason might not be.

Mike

sparks · April 01, 2009, 12:03:51 PM

If the 121.5 signal was only detectable only 100 yards from the unit, a ground team would have an almost impossible task finding the target. Even though it may not be the best solution it seems that a 406 receiver/reader with the ground team's may be the fix. If a Becker quipped aircraft is on the scene it also would be a fix. Since most of our aircraft aren't equipped with the Becker odds are they'll only have an airborne tracker available. I wonder what NHQ is thinking about this?

california IC · April 01, 2009, 05:56:49 PM

Here are some facts based on experiences df'ing 406 beacons.

Some military 406 beacons can selectively transmit on 406.xxx only or a combination of 406, 121.5, and or 243.0 as well as other NATO frequencies that are not publicly known. The ones we found only were transmitting on 406.xxx due their design and the registration came back to the US Goverment in Florida, not the Navy in San Diego. Hence, the registration provided no valuable information. The SARSAT was within 1 mile but again, no homing signal.
Df'ing the 406 pulse signal got us to the signal.

Many PLB signals in shipment that have no registration and no GPS fix have been located with the 121.5 homer not being of any practical use. When shipped, the antenna is not deployed which tends to make 121.5 usefull only within 100 yards or less. The SARSAT accuracy has been within 5 mile. The 406 signal is what got us there.

We had a PLB that was activated by two hikers injured in the backcountry. They kept the PLB with them and stayed in a small cave to avoid the weather. The GPS signal was never received, the homing signal was not usefull either. Weather kept any aircraft away until 12 hours into the mission. The 406 signal was df'ed from 7 miles away and the homing signal wasn't heard by any SAR team until the 406 triangulation was provided to the. At that point, the 121.5 signal was heard from about 1/4 mile away. The SARSAT was within 5 miles.

A PLB at Bass Pro Store (again, unregistered) had a homing signal that was heard only 50 feet from the PLB. The 406 is what got us there, the SARSAT was within 1 mile.

An EPIRB on shore had a homer that could only be heard from 3 houses away. The SARSAT was within 3 miles, the aircraft never heard the 121.5 signal. The 406 got us there.

The moral to the story, we need to be able to df 406 pulses and due to weather, we cannot count on Becker equipted aircraft.

♠SARKID♠ · April 01, 2009, 08:32:08 PM

Were you using the airborne Becker to DF the 406?

california IC · April 02, 2009, 01:27:21 AM

No...a ground df unit.

es_g0d · April 02, 2009, 02:29:58 AM

I just would like to interject that the membership of CAP is often at the head of expertise when it comes to matters like this. The good people at National Headquarters are our employees! Simply put, there's no possible way for them to be the experts on everything. They ARE some very good folks, however, and they do an excellent job at keeping up with current events. When you ask, "I wonder what NHQ is thinking about this," what you should be doing is forming your own educated opinion and then sharing that through proper channels TO CAP HQ.