43
APPENDIX J TESTING LIMITATIONS
STARTUP DELAY The 406 Mhz. devices are required to not transmit immediately on a normal
activation but until one recycling period has elapsed, approximately 50 seconds. Since in many
cases it is difficult if not impossible to accurately determine, measuring the delay then becomes
more a factor of a random starting point. Therefore probably the best way would be to time
this with a second hand of a watch. Note: this requirement does not apply to the test signal
when using the self-test function of the beacon.
SELF TEST All beacons on the COSPAS-SARSAT system are required to incorporate a self-test
feature. This feature has several limitations. If a beacon is required to have an automatic
activation device as a part of its operation, the self- test, while it may check for electrical
continuity of the circuit, does not check the actual operation of the automatic device that is
used. While some self-tests check for excessive reflected energy from the antenna system,
there are some failures of an antenna system which will absorb the RF energy rather than
reflecting or radiating it resulting in a good self-test of a faulty system. The only way to verify
the proper operation of an antenna system is by measuring its radiated field. Another
shortcoming of the self-test is that some key elements used in generating the signal are also
being used in the self-test and can result in, for example, one or more of the critical timing
parameters being incorrect. Or if the transmitting frequency is wrong and can’t be detected
when the testing reference is the same as the source being used to generate the signals. The
self-test can’t check the recycling rate of the transmissions since it only sends one transmission,
therefore, it can’t determine if the beacon will send additional repeated signals following the
first one. This is important since the COSPAS-SARSAT routinely discards the first transmission if
not followed by additional transmissions. This is to verify the validity of an alarm. Finally, while
the correct information may be internally presented to the transmitter, the self-test does not
check the resultant signal to verify that the message has been properly sent, in other words the
transmitter has been properly modulated.
To Previous Page
Loading...