All Channels Receiver - Raymarine RAY230E Owner's Handbook Manual

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4.1.2.3 All Channels Receiver

4.1.2.3 All Channels Receiver
4.1.2.3 All Channels Receiver 4.1.2.3 All Channels Receiver 4.1.2.3 All Channels Receiver
1) RF Amplifier
The RF amplifier consists of the FET amplifier (Q18) and a Band Pass
Filter (BPF) having variable bandwidth by variable capacitance diodes
(D12-D16). The response is automatically corrected by the control
voltage supplied from the CPU to a proper value corresponding to the
receive frequency. The BPF is provided with an attenuation
characteristic of 15 dB or larger at the detuning point 3 MHz lower than
the lower limit of the receive frequency (156 MHz). Then the RF signal,
having been mixed with the 1st local oscillator signal by the 1st mixer
(Q19) after passing the BPF, is converted to the 1st Intermediate
Frequency (IF) signal (21.6 MHz).
Note:
The 1st local oscillator signal generated by a synthesizer has a frequency
lower than the desired frequency by 21.6 MHz. The 1st local oscillator
signal is fed to the 1st mixer (Q19) after being amplified by the buffer
amplifier (Q14).
2) First Intermediate Frequency (1st IF)
The 1st IF signal of 21.6 MHz supplied via the crystal filter (F1) is then
amplified by the 1st IF amplifier (Q20).
3) 2nd IF
The 1st IF signal, having been mixed with the 2nd local oscillator signal
(21.145 MHz) in the IC (IC7 Mix, Osc, Amp, Limit, Det) for the 2nd IF, is
converted into the 2nd IF signal with a frequency of 455 kHz. Further,
after subjected to amplification and successive amplitude limitation
via the ceramic filter (F2), the signal is demodulated by the Quad detector
(quadrature detection) into an audio signal.
4) De-Emphasis
An audio signal is subjected to a correction in the frequency
characteristic to -6 dB/oct by the de-emphasis circuit (IC8).
5) Squelch
Within IC 9, high frequency noise outside the voice band from the DISC
output of IC 7 is amplified by the noise amplifier and converted into a DC
voltage by the detection circuit. Then, this voltage is further amplified by
the DC amplifier (IC374B on the control PCB) to a BUSY1 signal, which is
Technical Description