Assessments - 5, GPA: 4.6
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Install the optional unit as follows. © Rotate [VOL] to turn the power OFF, and remove the battery pack. @ Remove the unit cover as below. (The removed unit cover can not be used again.) © Install the unit as below. © Cut the pattern on the PC board at “MIC” and “DISC” as below. (This modification is not necessary for UT-108R installation.) "DISC “MIC" © Remove the paper backing of the supplied unit cover, and attach the unit cover and the battery pack, then rotate [VOL] to turn the power ON. © Set or modify the scrambler or decoder settings using optional CS-F3020. j^NOTE: When uninstalling the unit 0Be sure to re-solder the cut points as below when you v 'Aremove the unit. Otherwise, no transmit modulation or ^receive AF output is available. 4 - 1 SECTION 5 CIRCUIT DESCRIPTION 5-1 RECEIVER CIRCUITS 5-1-1 ANTENNA SWITCHING CIRCUIT (PA UNIT) The antenna switching circuit toggles the receive (RX) line and transmit (TX) line. The received signals from the antenna are passed through the low-pass filter (ANT UNIT; L801, L802, C802, C803, C807) and antenna switch (D701, D704, D706). While transmitting, the voltage on the T5V line is applied to D701, D704 and D706, and these are ON. Thus the TX line is connected to the antenna. Simultaneously, the RX line is connected to the ground (GND) to prevent transmit signal entering. While receiving, no voltage is applied to the D701, D704 and D706, and these are OFF. Thus the TX line and the antenna are disconnected to prevent received signals entering. Simultaneously, the RX line is disconnected from the GND and the received signals are passed through the low-pass filter (L712, L714, C750, C751). The filtered signals are applied to the RF circuits. 5-1-2 RF CIRCUITS (MAIN UNIT) RF circuits filter and amplify the received signals within the frequency coverage. The received signals from the antenna switching circuit are passed though the two-staged bandpass filter (BPF; D19, D24, L7, L8, C22, C25, C27-C29, C369) to filter-out unwanted signals, and the filtered signals are applied to the RF amplifier (Q5). The amplified received signals are then applied to the 1st mixer (Q6) via another BPF (L47-L49, C19, C40, C437-C439, C443). 5-1-3 1st IF CIRCUITS (MAIN UNIT) The received signals are converted into the 1st IF signal, filtered and amplified at the 1st IF circuits. The received signals from the BPF (L47-L49, C19, C40, C437 -C439, C443) are applied to the 1st mixer (Q6) and converted into the 46.35 MHz 1st IF signal by being mixed with the local oscillator (LO) signal from the RX VCO (Q17, D9, D11, D33). The converted 1st IF signal is passed through the 1st IF filter (FI1) to filter-out adjacent signals, then applied to the 1st IF amplifier (Q7). The amplified 1st IF signal is then applied to the FM IF IC (IC9, pin 16). 5-1-4 2nd IF AND DEMODULATOR CIRCUITS (MAIN UNIT) The 1st IF signal is converted into the 2nd IF signal, and demodulated. The 1st IF signal from the 1st IF amplifier is applied to the 2nd mixer in the FM IF IC (IC9, pin 16), and converted into the 450 kHz 2nd IF signal by being mixed with the 45.9 MHz 2nd LO signal from the reference frequency oscillator (X2) via the tripler (Q22) and BPF (L33, C163, C164, C166). The converted 2nd IF signal is output from pin 3, and passed through the 2nd IF filters to remove sideband noise. The 2nd IF signal is passed through the 2nd IF filter (FI2) and applied to the FM IF IC (IC9, pin 5) again. The filtered 2nd IF signal is amplified at the limiter amplifier, and FM-demodulated by the quadrature detector (IC9, pins 10, 11, X1). The demodulated AF signals are output from pin 9, then applied to the AF amplifier circuits. 5-1-5 AF AMPLIFIER CIRCUITS (MAIN UNIT) The demodulated AF signals from the FM IF IC are amplified and filtered at AF circuits. The demodulated AF signals from the FM IF IC (IC9, pin 9) are passed through high-pass filter (HPF; IC5, pins 2, 1) to remove tone signals. The filtered AF signals are passed through the de-emphasis circuit (R142, C249) to obtain the 6 dB/oct of frequency characteristic. The de-emphasized AF signals are passed through the RX mute switch (Q32, Q33), AF switch (Q36, Q37), HPF (IC5, pins 13, 14), analog switch (IC3, pins 1, 2), AF mixer (IC5, pins 6, 7) and analog switch (IC3, pins 10, 11) in sequence. • 2nd IF AND DEMODULATOR CIRCUITS 5 - 1 The AF signals from the analog switch (IC3, pin 11) are applied to the volume buffer amplifier (IC6, pin 9). The buffer-amplified AF signals are adjusted its level (= audio level) by volume control pot (R315), then applied to the AF power amplifier (IC15, pin 4) and amplified to the 0.5 W of audio output power (max., at 8 Q load). The power-amplified AF signals are output from pin 10, then applied to the internal speaker (CHASSIS; SP1) or an external speaker via [SP] jack (J2). 5-1-6 SQUELCH CIRCUITS (MAIN UNIT) 5-1-6-1 NOISE SQUELCH The squelch mutes the AF output signals when no RF signal is received. By d...
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