SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUIT
Note: [Main]=Main band, [Sub]=Sub band
4-1-1 VHF TRANSMIT/RECEIVE SWITCHING CIRCUIT (PA UNIT)
Received signals from the antenna connector (CHASSIS; J1) are passed through the
The transmit/receive switching circuit leads receive signal to the RF circuit from a
The passed signals are then applied to the RF amplifier cir- cuit.
4-1-2 VHF RF CIRCUIT (PA UNIT)
Received signals from transmit/receive switching circuit are applied to the RF amplifier circuit (Q507) via the RF attenu- ator (D515), limiter (D514) and tunable band pass filter (D513, L560) circuits.
The amplified signals are then passed through the another
4-1-3 VHF 1ST MIXER CIRCUIT (PA UNIT)
The 1st mixer circuit converts the received signals into a fixed frequency of the 10 MHz IF signal with a PLL output frequency. By changing the PLL frequency, only the desired frequency will pass through a pair of crystal filters at the next stage of the VHF 1st mixer.
The filtered signals from the bandpass filter are mixed with 1st LO signals at the mixer circuit (Q511, Q512) to produce a 1st IF signal (10.85 MHz [Main] or 10.95 MHz [Sub]). The 1st LO signals (125.15
The 1st IF signal is then applied to either the Main or Sub band 10 MHz IF circuit in the MAIN unit via P501 [Main] or P510 [Sub].
4-1-4 UHF RF CIRCUIT (PA UNIT)
The received signals from the UHF antenna connector (CHASSIS; J2) are passed through the
4-1-5 UHF 1ST AND 2ND MIXER CIRCUIT (PA UNIT)
The filtered RF signals from the bandpass filter are mixed with a 1st LO signal at the 1st mixer circuit (Q220, Q221) to produce a 1st IF signal (71.25 MHz [Main] or 71.35 MHz [Sub]). The 1st IF signal is passed through a crystal filter (Fl280 [Main], Fl281 [Sub]) to suppress
The 1st LO signal (348.75
• RECEIVER CONSTRUCTION | PA unit |
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430 MHz |
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1st mixer |
| 2nd mixer | ||
| Q220, Q221 |
| Q11 | |
LPF | BPF |
| BPF |
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| 1st LO | BPF | 2nd LO | |
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| B1LO |
| B2LO | |
144 MHz | 1st mixer |
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| Q511, Q512 |
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LPF | BPF |
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1st LO
A1LO
MAIN unit |
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| FI51 |
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| FI151 | IC351 | for MAIN band | ||
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| BPF |
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| BPF |
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| 10.85 MHz |
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| AF selector circuit | |
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| BFOM |
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| to FM IF IC (IC401) | for SUB band | ||
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| FI651 |
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| FI751 | IC851 | |||
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| 10.95 MHz |
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| AF selector circuit | |
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| BFOM |
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| to FM IF IC (IC951) |
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4 - 1