Micro Technologies (NZ) Limited – 406-2 User Manual v .0.
Technical Information
Determination of Serial Number
The serial number of the beacon is determined based on the 406 beacon protocol used in the
transmission. The serial number shown should also be considered to be synonymous with MMSI,
radio call sign or Aircraft marking.
All Cospas Sarsat specified protocols are decoded. If the protocol used by the beacon does not
contain serial number information, then only the hex 5 code will be displayed.
Display Used
The 406-2 Decoder uses a 4 wide 7 segment discrete LED display. Visibility is good in most
conditions, except in areas with high levels of lighting. Although usable, the display is not as clear
as displays using 7 segments LED modules or LCD modules . There are some characters however
that are not particularly intuitive, e.g. 'K','M',W,Z. When these characters are required as part of a
serial number, aircraft marking or call sign, accepted representations of these characters have been
used.
Without familiarisation, displayed numeric serial numbers are not confusing, nor the hex Id or
power level.
Frequency Testing
The 406-2 decoder scans all used 406 beacon frequencies between 406.020MHz and 406.045MHz.
Signal Strength Indicator
If there is a desire to use the 406-2 decoder as a tool to determine power transmitted from the
beacon the following should be considered:
When the 406-2 decodes a message, the serial number and hex 5 code is displayed. Following this
an approximate beacon power level is displayed e.g. "P 9". The number represents the
approximate beacon power level in dBm based on the decoder received signal strength. Since the
beacon may not have the aerial released or unfolded, orientation of the beacon may not be ideal or
objects may be in the way, the beacon may not radiate its maximum power when tested. To allow
for this the user should consider any signal strength above 25dBm to be an "OK" result (when
aerial is fully deployed). Although this level for this test is a moderate level below the full beacon
transmit power, a 25dBm transmitter is still considered to be powerful (more than 4 times the power
level of the 2 .5MHz homing signal that is also used in the beacon for final location).
The generous pass/fail margin is to simplify testing in conditions that will probably be less than
ideal, and from analysis of beacon failure data, beacon power levels are likely to degrade
significantly in a transmission failure mode, and are less likely to have minor reductions in output
power levels.
Accuracy of the received signal strength by the tester in ideal testing conditions is to within dB,
but producing these ideal conditions outside the laboratory is difficult, hence the larger margin
allowed to consider a pass.
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