7-18 Adjustments 8525B/8528 Technical Service Manual
Issue 6 Publication No: 15-02036
7.6 Emergency Call Frequencies
8525B/8528 RFDS
Select an RFDS channel and disconnect dual coax socket to PA and Filter
PCB. Press the Emgcy Call pad and measure the frequencies on pins 10 and
13 of IC12 on the Microprocessor Controller PCB. Frequencies should be
880Hz ±2Hz and 1320Hz ±2Hz respectively. Reconnect dual coax socket.
8528S Marine
On pressing the Emergency Call Test pad the marine emergency call is
generated for approximately 45 seconds by the two-tone generator on the
Microprocessor Controller Assembly (pressing the Test pad alone generates
the tones without keying the transmitter.) The signal consists of alternate
bursts of 1300 2Hz and 2200 2Hz; each burst lasting approximately 250ms.
This can be monitored at pin 10 of IC12 on the Microprocessor Assembly
08-02451, using an oscilloscope with the time base set so that these 250ms
bursts can be seen as two different frequencies. The individual frequencies
can be measured using a Lissajous figure technique.
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