SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
The antenna switching circuit toggles receive line and transmit line. This circuit does not allow transmit signals to enter the receiver circuits.
Received signals from the antenna are passed through the
While receiving, no voltage is applied to D151 and D152. Thus, the receive line and the ground are disconnected and L151, L152, C151, C152 and C153 function as an LPF which leads received signals to the RF circuits.
The RF circuits amplify signals within the range of frequency coverage and filters off
The signals from the antenna switching circuit are passed through the
The amplified signals are passed through another
The 1st IF signal from the 1st mixer is passed through the crystal filter (FI211) to suppress unwanted signals, and amplified at the 1st IF amplifier (Q211).
The amplified 1st IF signal is applied to the FM IF IC (IC231).The 1st IF signal is converted into the 2nd IF signal and
The 1st IF signal from the 1st IF amplifier is applied to pin 16 of IC231, and mixed with the 30.6 MHz 2nd LO signal coming from the doubler (Q221), to convert into the 450 kHz 2nd IF signal and output from pin 3. The 2nd IF signal is filtered by the ceramic filters (FI231, FI232) to suppress the heterodyne noise, then applied to IC231 (pin 5) again and amplified at the limiter amplifier section and demodulated by the quadrature detector.
The quadrature detector is a detection method which uses a ceramic discriminator (X231). The demodulated AF signals are output from pin 9.
The 1st mixer circuit converts received signals into the 1st intermediate frequency (IF) signal by mixing with local oscillator (LO) signal. The converted 1st IF signal is filtered at the 1st IF filter, then amplified at the 1st IF amplifier.
The signals from the31.05MHz 1st IF signal at the 1st mixer (Q191) by being mixed with the 1st LO signals generated at RX VCO (Q41,
AF signals from IC231 (pin 9) are passed through the AF mute switch (IC281 A; pins 1, 2), analog switch (IC282; pins 1, 7), LPF (IC261 C; pins
The level controlled AF signals are passed through the AF mute switch (Q411) and the
The
450 kHz 2nd IF filters FI232
"SQCON" signal |
|
| FI231 |
|
|
|
|
from the D/A converter (IC251) |
|
|
| 30.6 MHz 2nd LO signal |
| ||
|
| W/N | W/N |
|
| ||
|
| SW | SW |
|
|
|
|
|
| D232 | D231 |
|
|
|
|
8 | 7 | 5 |
| 3 | 2 | PLL |
|
|
|
|
|
|
| IC |
|
| Noise | Noise |
| ×2 | (IC1) | X1 | |
Active | AMP | detector |
| 2 |
| 1 | |
| Q221 |
|
| ||||
filter | Limiter |
|
|
|
| 15.3 MHz | |
|
|
|
|
| |||
|
|
|
|
|
|
| |
| AMP |
| Noise | Mixer |
|
|
|
FM |
|
| comparator |
|
|
|
|
detector |
|
|
|
|
|
|
|
|
|
|
| IC231 TA31136FN |
9 | 10 | 11 | 14 | 16 1st IF signal |
|
|
|
| from the IF amplifier (Q211) |
AF "DET" signal |
|
| "NOISV" signal to the CPU (IC661, pin 32) | |
|
| R5V |
| |
to the AF circuits |
|
|
| |
|
|
|
| |
| X231 |
|
|
|
4 - 1