2. 121.5 MHz Homing Signal - History
At the 2010 SSARCC meeting, one of the Federal Partners gave a presentation on “SARSAT and Beacon Modernization”
MEOSAR – new system of satellites for locating beacons
New beacons – called Second Generation Beacons (SGB)
Asked the coordinators to complete a questionnaire
SAR Resources
406 MHz
Beacons
RCC
USMCC (NOAA)
Medium Earth Orbit (MEO) Satellites
2 U.S. Ground
Stations

3. Beacon Modernization Objectives
Overcome limitations of current 406 MHz beacons operating through the LEOSAR-GEOSAR system
Identify operational ‘requirements’ of SAR personnel…things they need or want…for new beacons operating through MEOSAR
Develop Cospas-Sarsat and other national and international standards for new beacons and for the MEOSAR ground system that match the ‘requirements’
Expand beacon usage within communities that should use beacons
Dramatically improve Cospas-Sarsat performance and capabilities
Slide from the 2010 presentation

4. MEOSAR/New Beacon Needs and Wants for SAR?
System locations?
Encoded locations?
Time to first alert?
Alert intervals?
Homing?
Operating time?
Alert message content?
Temperature extremes?
Return Link?
Slide from the 2010 presentation

5. 121.5 MHz Homing Signal - History

6. 121.5 MHz Homing Signal - History
Question 31 asked for any other comments. Of the 26 comments, these referenced homing.

7. 121.5 MHz Homing Signal - History
2011 SSARCC meeting - one Federal Partner said that there would be no MHz homing signal on the SGB, another said that no decision had been made yet
Some discussion ensued
2012 SSARC meeting - a Federal Partner said that there would be no homing signal, no rebuttal from any other Federal Partners
Lively discussion followed
2012 NTSB forum on General Aviation SAR
A Federal Partner said there would be no MHz homing signal on Second Generation Beacons
Two Federal Partners noted that there may be a lack of 406 MHz ground DF equipment
2013 SSARCC meeting - no discussion on homing due to sequestration and a Himalayan expedition reunion

8. 121.5 MHz Homing Signal - History
2014 SSARCC meeting – some discussion on homing and SGB
The US position paper on homing, to be presented at an upcoming Cospas-Sarsat meeting, was available for reading
At the Cospas-Sarsat meeting it was determined that
Although the ultimate desire would be to remove MHz from the homing equation
it is clear from the SAR response community that is currently not possible.
There are little to no 406-MHz ground DF capabilities/tools available and
several countries have stated that they currently cannot afford to transition their SAR units from to 406 homing.

9. 121.5 MHz Homing Trials
A proposal was made to make the MHz homing signal intermittent to accommodate the needs of the SGB
Current international ELT specs allow an intermittent signal and that an “ON period of 0.75 seconds followed by an OFF period of 1.5 seconds gives satisfactory results.”
Only a few beacon models world-wide have an intermittent homing signal
This on-off pattern was chosen as the goal for all types of SGB, not just ELTs
Some C-S participants wanted testing of the intermittent signal to ensure that existing DF equipment would still be able to locate the beacon
Australia, Canada, UK and US offered to perform tests

10. 121.5 MHz Homing Trials
The Cospas-Sarsat Homing and Intelligent Transmit Scheduling (HITS) working group developed test criteria
Three reduced duty cycle (intermittent) transmissions would be tested and compared to a control beacon with a continuous signal
33% seconds ON, 1.5 seconds OFF, repeating
50% seconds ON, 1.1 seconds OFF, repeating
66% seconds ON, 0.75 seconds OFF, repeating
These reduced duty cycles are independent of the required half second, every 50 seconds, signal interruption for transmission of the 406 MHz data burst
DF equipped aircraft would fly at specific altitudes
The ranges at which the beacon signal was detected or lost would be recorded
Any difficulties with DF processing of the signals would be noted

11. 121.5 MHz Homing Trials - Australia
The first trials were conducted by the Australian Maritime Safety Authority (AMSA)
Used modified GME MT600 EPIRBs
Simple ground distance tests were done using a VHF air band transceiver (Icom IC-A24)
The reduced duty cycle beacons (33% and 66%) could be detected at the same distance (up to 0.8 km) as the 100% duty cycle beacon
Some simple beacon direction finding exercises were conducted from about 50 metres using an L-Tronics Little L-Per
Again, no differences were noted between the reduced duty cycle beacons and the control

12. 121.5 MHz Homing Trials - Colorado
The Colorado Department of Military and Veterans Affairs, Division of Civil Air Patrol sponsored the next trials which would include air and ground DF equipment
Participants were from Colorado Wing Civil Air Patrol and three Mountain Rescue Association teams – Alpine Rescue, Douglas County SAR and Larimer County SAR; assisted by the Colorado Search and Rescue Board
DF experience ranged from nearly 40 years to trainees working under qualified supervisors
The test beacons were factory modified ACR PLBs
One each on the 33%, 50% and 66% duty cycle
One unmodified control beacon with a continuous, % duty cycle

13. 121.5 MHz Homing Trials - Colorado
DF equipment used
Three models of ground DF units
One model of aircraft DF
Non-DF handheld receivers
L-Tronics LH-16 Little L-Per
L-Tronics LL-16 Little L-Per
VK3YNG Mk 4 Sniffer
Photos courtesy CAP and Bob Miller Enterprises
(not taken during the homing trials)

14. 121.5 MHz Homing Trials - Colorado
L-Tronics Little L-Per
LH-16
Rhotheta SAR-DF 517 Aircraft DF
VK3YNG Mk 4 Sniffer
L-Tronics Little L-Per LL-16

15. 121.5 MHz Homing Trials - Colorado
The starting point in all trials was miles away from the beacon
SAR personnel were given only a general location of where the beacon was
Personnel were not told that the homing signal was intermittent
One crew initially thought their DF was defective
Another group thought the beacon was defective or that the battery was dying
A different team thought the signal gaps were due to interference

16. 121.5 MHz Homing Trials - Colorado
Three test locations were selected in relatively flat, open terrain of the high plains to minimize terrain and ground clutter effects on the signal. In a fourth location, the beacon was placed in an area with signal obstructions.
Mobile DFing was performed by driving trucks with a 1/4 wavelength MHz whip (monopole) antenna mounted to the roof of the vehicle. This is a standard practice (in some places).
This was the primary means to determine the max detection range
Only relative signal strength, not direction, is found by this method
Where the signal was weak or lost on the vehicle system, or where higher terrain was encountered, handheld DF units with a higher gain antenna were used to check for a signal

17. 121.5 MHz Homing Trials - Colorado

18. 121.5 MHz Homing Trials - ColoradoX

19. 121.5 MHz Homing Trials - Colorado
Overall results
All of the DF equipment was able to receive and home-in on the intermittent signal. The non-DF receivers were also usable in locating the beacons.
Searchers DF’d the signal right up to the beacon at all sites.
There was no noticeable difference in detection ranges between the intermittent and continuous homing signals.
Ground DF techniques were adjusted to locate the intermittent signal beacon
The intermittent signal often caused the DF operator to pause during the 1.5 second off-time
This pause came naturally but is unnecessary
The 33% signal was tested first. Due the success DFing this signal, no testing was done with the 50% and 66% beacons.

20. 121.5 MHz Homing Trials - Colorado
Distance
Altitude
Descriptive
from Beacon
MSL
AGL (approx.)
Signal Reception nm
feet DF
COM
19.7
12,500
7,200 No
19.1
Int
17.7 OK
12.9
Weak
13.8
11,100
5,800
12.0
10.0
8.3
6,800
1,500
N/R
7.0
5.0
Table 1 Key: nm – nautical miles No – no signal detected
MSL – (above) Mean Sea Level Int – intermittent signal, unusable
AGL – above ground level Weak – weak signal, but usable
DF – direction finder OK – strong signal, usable
COM – aircraft VHF-AM N/R – no report
communications transceiver
Table 1 - Search Aircraft Beacon Reports for the MHz 33% Intermittent Signal

21. 121.5 MHz Homing Trials - Colorado
The results of the Australian and Colorado homing trials were presented in a paper at the 30th meeting of the Cospas-Sarsat Joint Committee (JC-30) in September, 2016.
The paper was also presented at the ICAO/IMO Joint Working Group (JWG) on Harmonization of Aeronautical and Maritime Search and Rescue (JWG-23), also in September, 2016.
US Coast Guard testing is to start soon.

22. Questions in the future?
Questions now?
Questions in the future?
Mike McDonald
Cell:
Work:

24. Beacon Limitations/Concerns
Slide from the 2010 presentation
Beacon cost, size and weight
Power hungry…beacon operating 24 hours needs a battery able to produce 1,728 five watt signals (or 2,456 signals for 48 hours) plus any homing signals and other functions
Mix of complex coding protocols
Sub-optimal for 406 MHz homing (e.g., non-continuous signals)
GPS capability is not ubiquitous (encoded locations)
Transmissions of 406 and MHz signals are both compromised by sharing an antenna
Communications are one-way

25. 121.5 MHz Homing Signal - History
Radio distress beacons have transmitted on the international distress frequency MHz since the late 1950s
In 1971, the 406 to MHz band was “reserved solely for the use and development of low-power (not to exceed 5 W) emergency position-indicating radiobeacon (EPIRB) systems using space techniques.” EPIRB referred to all beacons, not just maritime beacons, as it is used today.
The Cospas-Sarsat system was optimized for beacons in this reserved frequency band.
Maintained backward compatibility with MHz beacons
Phase-out of MHz by 406 MHz was planned from the beginning

26. 121.5 MHz Homing Signal - History
Mandatory carriage requirements of MHz ELTs during the 1970s moved faster than 406 MHz beacon development
Search and rescue direction finding equipment was designed for MHz
FCC authorization for 406 MHz EPIRBs became effective in October, 1988, ELTs in June, 1993 and PLBs in July, 2003
USAF, USCG and NASA commented to the FCC that
a MHz homing signal was required because
it was not practical nor feasible to replace existing DF equipment
406 MHz DF equipment was costly and not readily available
Replacement of MHz beacons with 406 MHz beacons was not required