Raymarine Limited. Registered in England. Company no. 1177969
Page 11
Registered Office: Anchorage Park, Portsmouth P03 5TD
Ray240 RF PCB Circuit Description
The RF PCB is the FM transmitter and receiver section for the Ray240 marine VHF radio with Class
“D” digital selective calling, and has one transmitter, one ‘channel selectable’ receiver (for audio
purposes) and one fixed frequency receiver which is used solely for the reception of digitally encoded
messages on Channel 70. The radio can only be in either a transmit or receive mode, and cannot do
both at the same time. As a result of this, there is a central VCO/Synthesiser whose output is used as
the transmit carrier when the radio is transmitting and LO for the first down converter for the
Channel selectable receiver. Below is brief summary detailing the main performance criteria of the
radio.
Power Supply
Supply v12V
Rx mode: 200 mA Max., Tx mode: 6 A Max
Supply v5V
10 mA Max
Transmitter
Transmitter Frequency Range
155.00 to 165.00 MHz with 25 kHz channel spacing
Transmitter Output Power
25 Watts, switchable to 1 Watt
Modulation
Frequency modulated at 16F3 (
±
4.5 kHz at 1kHz)
Receiver
Receiver Frequency Range
155.00 to 163.275 MHz with 25 kHz channel spacing
Receiver Usable Sensitivity
-3 db
µ
V (emf) or –116 dBm
Channel selectable 1
st
IF
21.4 MHz
CH 70 1
st
IF
16.9 MHz
Channel selectable and CH70 2
nd
IF
455 kHz
The RF PCB goes through an electronic alignment/set up procedure, and the resulting data from this
alignment process is stored in an EEPROM located on the PCB.
VCO/synthesiser
The VCO is phase locked to a 21.85 MHz crystal oscillator by using an LMX2306 synthesiser from
National Semiconductor. The frequency of the reference oscillator is fine tuned with a varacter
diode. The voltage across the diode is controlled be a D/A converter.
The synthesiser is programmed (via an SPI link) to enable the VCO to change its output frequency in
12.5 kHz steps. When the radio is transmitting, the VCO operates between 155.000 MHz and
165.000 MHz, and when the radio is in receive mode, operates between 133.600 MHz and 141.875
