Raymarine Limited. Registered in England. Company no. 1177969
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Registered Office: Anchorage Park, Portsmouth P03 5TD
DSC signals received on channel 70 appear as FSK at the receiver output and are passed to a phase
locked loop (PLL1). PLL1 is configured to demodulate FSK, and the recovered DSC message data is
passed to the microcontroller for processing. PLL1 also generates an interrupt, alerting the
microcontroller, when it is locked to an incoming signal.
A second phase locked loop (PLL2), monitors the audio signal from the all channel receiver. Radios
destined for the European market have PLL2 configured the same as PLL1 to detect FSK, in this case
ATIS signals appended to voice transmissions. In the event that PLL2 detects FSK, it interrupts the
microcontroller which then validates the incoming ATIS data and squelches the audio so that the
listener does not hear the ATIS burst.
Radios for the US market have no requirement for ATIS detection and PLL2 is instead configured to
detect the 1050Hz NOAA weather alert tone.
Handset Interfaces
A handset interface comprises
•
Line level audio signals to and from the handset.
•
Serial communications line that carries display information to the handset and key-press
information from the handset, utilising one of the microncontroller’s UARTs.
•
Discrete PTT signal that directly indicates when the PTT switch on the handset is pressed
•
Discrete mute signal to the active speaker, mutes the speaker in transmit mode
In addition to these functions, the microcontroller can signal an alarm by pulling the audio line from
the handset
to 12V. In the active speaker, this over-rides the volume control and forces maximum volume. The
alarm signal is issued concurrently with an alert audio tone in the event of special conditions such as
receipt of a DSC distress message.
Seatalk & NMEA0183 Communications
The second of the microcontroller’s UARTs is used for serial communications with external systems,
such as GPS. The UART can be connected either to a Seatalk interface (Raymarine’s proprietary
single wire half-duplex communications interface) or to an NMEA0183 transmitter and receiver.
The Seatalk interface and NMEA0183 receiver are opto-isolated to prevent ground loops occurring
on the vessel. Opto-isolating also protects against damage due to mis-connection of the Seatalk
power supply at the Ray240.
Seatalk2 Communications
Provision is made on the processor board to fit, as a future option, an NMEA2000 compliant,
“Seatalk2” interface.
Hailer
The processor board can operate a loudhailer in either “talk” or “listen” mode. In talk mode, the
talk/listen relay connects the horn to a power amplifier, audio from any handset may be routed via the
eight-step hailer volume control, to the power amplifier.
