(1) AM DETECTOR CIRCUIT
The filtered signals are applied to the AM detector circuit (Q201, Q202) to demodulate the 2nd IF signal into the AM AF signals.
(2) FM AND WFM DETECTOR CIRCUIT
The filtered signals are applied to the limiter amplifier section in the FM IF IC (IC151, pin 5), and then applied to the quad- rature detector section to demodulate the 2nd IF signal into FM and WFM AF signals.
The demodulated AM, FM or WFM signals are applied to the AF amplifier circuit.
4-1-6 AF AMPLIFIER CIRCUIT (AF UNIT)
The AF amplifier circuit which is included a
(1) AM AND FM AF SIGNALS
The demodulated AM or FM (“DETO” signal) AF signals from the AM detector (Q201, Q202) or FM detector (IC151, pin 9) circuits are passed through the
(2) WFM AF SIGNALS
The demodulated WFM (“DETO” signal) AF signals from FM detector (IC151, pin 9) circuit are bypassed the
The amplified AF signals from the 1st AF amplifier (Q205) are applied to the AF mute switch (Q251) which is controlled by “MUTE” signal from the CPU (LOGIC unit; IC1, pin 48), and are then applied to the electronic volume control circuit (IC251, pin 6). The level controlled AF signals are output from the volume IC (LOGIC unit; IC251, pin 7) and are then applied to the AF power amplifier (IC252, pin 4). The power amplified AF signals are then applied to the internal speaker (LOGIC unit; SP1) through the “INTSP” signal via the [EXT SP] jack (J253) when no plug is connected to the jack.
The AF filter circuit (LOGIC unit; IC241, pin 5) removes AF signals below 300 Hz (CTCSS signals) for clear AF output and these are applied to the CPU (LOGIC unit; IC1, pin 7) for the CTCSS squelch detection via the “CTCIN” line.
The electronic volume control circuit controls AF gain, there- fore, the AF output level is according to the [VOL] setting and also the squelch conditions.
4-1-7 SQUELCH CIRCUIT(AF AND LOGIC UNITS)
• NOISE SQUELCH
The noise squelch circuit cuts out AF signals when no RF sig- nals are received. By detecting noise components in the AF signals, the squelch circuit switches the AF mute switch.
A portion of the AF signals from the FM IF IC (IC151, pin 9) are applied to the active filter section (IC151, pins 7, 8). The active filter section amplifies and filters noise components. The filtered signals are applied to the noise detector section and output from IC151 (pin 13) as the “NOISE” signal.
The “NOISE” signal from IC151 (pin 13) is applied to the CPU (LOGIC unit; IC1, pin 47). The CPU analyzes the noise con- dition and outputs the “MUTE” signal to AF mute switch (Q251).
Even when the squelch is closed, the AF mute switch (Q251) opens at the moment of emitting beep tones.
• TONE SQUELCH
The tone squelch circuit detects AF signals and opens the squelch only when receiving a signal containing a matching subaudible tone (CTCSS). When tone squelch is in use, and a signal with a mismatched or no subaudible tone is received, the tone squelch circuit mutes the AF signals even when noise squelch is open.
A portion of the AF signals from the FM IF IC (IC151, pin 9) passes through the
• 2ND IF AND DEMODULATOR CIRCUIT |
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| 2nd IF filter |
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| 450 kHz |
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| FI151 |
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| R159 |
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| 8 | R158 | 7 | 5 |
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Q201, | R167 |
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Q202 |
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AM | C158 | filter |
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| Limiter |
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| Mixer |
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detector |
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| C156 |
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| from IC351, pin 6 (RF unit) |
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| "NOISE" signal to the CPU |
AF signal to the mode switch |
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(AF unit; Q203, D201) |
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| WFM |
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| "SD" signal to the CPU | ||||
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filter (LOGIC unit; IC241) |
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