Channel 70 Receiver; High Frequency Amplifier; 1St If; 2Nd If - Raymarine RAY230E Owner's Handbook Manual

Technical Description
fed to the squelch control port (A/D). The operation level of the squelch is
determined by the electronically controlled volume (IC313 on the control
PCB) and the set value for the A/D action of the CPU.
4.1.2.4 4.1.2.4
4.1.2.4 4.1.2.4 4.1.2.4

1) High Frequency Amplifier

The front-end part of the Channel 70 receiver consists of the FET
amplifier (Q21) and a narrow bandwidth BPF. The BPF has 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).
The amplified RF signal is mixed with the local oscillator signal in the
Mixer (Q22) and converted into the 1st IF signal of 16.9 MHz. The 1st
local signal, generated by an oscillation circuit (Q24) using the 3rd
over tone of the crystal (X3, 46.5417 MHz), has a frequency of 139.625
MHz. The signal is fed to the mixer (Q22) via the buffer amplifier (Q25).

2) 1st IF

The 1st IF signal of 16.9 MHz supplied via the crystal filter (F3) is
amplified by the 1st IF amplifier (Q23).

3) 2nd IF

The 1st IF signal is mixed with the 2nd local oscillator signal (16.445
MHz) in the IC (IC9 Mix, Osc, Amp, Limit, Det) for the 2nd IF and is
converted into the 2nd IF signal with a frequency of 455 kHz. After
further amplification and successive amplitude limitation via the ceramic
filter (F4), 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 its frequency
characteristic to a -6dB/oct by the de-emphasis circuit (IC8).

5) Squelch

Within IC9, 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 converted voltage
is supplied as the BUSY2 signal to the squelch control port (A/D) of
the CPU. The threshold level is set with the VR4 on the PCB, free from
any external adjustment.

Channel 70 Receiver

Channel 70 Receiver
Channel 70 Receiver Channel 70 Receiver Channel 70 Receiver
4-3