1. Update on 121.5 and 406 MHz Homing for Second Generation Beacons
Mike McDonald
Douglas County SAR Team (MRA)
Colorado Wing Civil Air Patrol
Colorado SAR Board
Cospas-Sarsat Homing and Intelligent Transmit Scheduling Correspondence Working Group
State Search and Rescue Coordinators Council
Washington, DC
February 27-28, 2018

2. Update on 121.5 and 406 MHz Homing
Background
A proposal to the Cospas-Sarsat Programme sought to eliminate the option of a MHz homing signal on Second Generation Beacons (SGB) because
This signal is the primary user of battery power, which is needed for other SGB functions
Improved accuracy of beacon location due to MEOSAR and increasing number of beacons which transmit position from Global Navigation Satellite System (GNSS) receivers (e.g. GPS) reduces the need for a homing signal
More search and rescue units (SRU) with capability to DF the 406 MHz beacon signal
A homing signal is optional per C-S regs, but the MHz homing signal is required by most administrations and international regulatory organizations

3. Update on 121.5 and 406 MHz Homing
Background
C-S members voted to keep the option because of the world-wide lack of 406 MHz DF equipment and cost to upgrade
Need for a longer period to transition from MHz to 406 MHz homing
Look at ways to reduce the homing signal power consumption
The Homing and Intelligent Transmit Scheduling (HITS) Correspondence Working Group was established to find solutions to the homing and power conflict
HITS proposed a reduced duty cycle (intermittent) homing signal based on a note in the ELT technical spec (but with rare exceptions, not utilized in current ELTs)
0.75 second on, 1.5 seconds off, repeating

4. Update on 121.5 and 406 MHz Homing
Background
121.5 MHz DF Units
L-Tronics LL-16 Little L-Per
$750
VK3YNG Mk 4 Sniffer
$450
L-Tronics LH-16 Little L-Per
L-Tronics closed last year after making DF units since the early 1970s.
Photos courtesy CAP and Bob Miller Enterprises

5. Update on 121.5 and 406 MHz Homing
Background
121.5 / 406 MHz Portable DF - $17,000
Rhotheta RT-500-Manpack Wideband RDF/Location System
Production unit
Prototype unit developed for USCG

6. Update on 121.5 and 406 MHz Homing
Current Status
The International Maritime Organization (IMO) requires EPIRBs to have a continuous homing signal
It would consider changing its regulations if testing shows that existing DF units can locate a beacon with a reduced duty cycle signal
Known testing to date
Australian Maritime Safety Authority (AMSA) – land test success
Colorado Search and Rescue Board (CSRB) – land/air test success
Norwegian Maritime Authority (NMA) – maritime test success
Report of a test in which the DF on an aircraft traveling 150 kts was reportedly not able to locate the intermittent signal

7. Update on 121.5 and 406 MHz Homing
Current Status
HITS is also studying the addition of a low-power, short interval 406 MHz homing signal for close-in or on-scene homing and locating
The fundamental 406 MHz signal (5 watt data burst, ½ second long, every 50 seconds) is OK for long-range and enroute homing, but is difficult to use in-close
Low power 406 MHz locating signal with an interval much less than the 50 seconds of the primary signal
Intermittent low-power MHz homing signal

8. Questions in the future?
Questions now?
Questions in the future?
Mike McDonald
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