1-18 (No.RA018)2.4.6.5 Low Battery WarningThe battery voltage is divided using R40 and R41 and is detected by A/D converter (IC900). When the battery voltage falls below thevoltage set by the Low battery warning adjustment, the red LED blinks to notify the operator that it is time to replace the battery. If thebattery voltage falls even more (approx. 5.8V), a beep sounds and transmission stops.2.4.6.6 DSPThe DSP circuit consists of a MPU/DSP (IC702) and processes the baseband signal. The DSP operates at 288MHz (MAX) clock, theI/O section operates at 3.3V/1.8V and the core section operates at 1.2V.The DSP carries out the following processes:• 4 Level FSK processing• Analog FM pre-emphasis/de-emphasis• Vocoder processing between audio codec and modulation/demodulation• CAI processing, such as error correction encoding• QT/DQT encoding/decoding• DTMF encoding/decoding• MSK encoding/decoding• 2-tone encoding/decoding• Compressor/expander processing• Voice scrambler processing• Transmit/receive audio filtering processing• Microphone amplifier AGC processing• Audio mute processing• Modulation level processing• Active Noise Reduction• Voice recording/playback processing• Voice announce processing2.4.7 Power Supply CircuitThe battery voltage (+B) is provided from battery terminal. The battery voltage passes through the 3.15A fuse (F1), and goes to RFfinal amplifier, AVR ICs (IC31, IC82, IC801, IC36, IC63, IC65, IC64), DC/DC converter (IC33), transistor (Q32, Q71 through the 1Afuse (F2)), and voltage detector IC (IC20). Voltage detector (IC20) watches battery voltage. If the battery voltage is enough higherthan 5.6V, detector outputs High. Then, IC31 (31BU) outputs 3.1V, and IC32 (12BU) outputs 1.2V, and Q31 is turned on.When the VOL SW is turned on, SB1 becomes high (battery voltage). The DC/DC (IC33) operates if both SB1 and output of detectorare high. IC33 (38M) outputs 3.8V, and A30 (12M) outputs 1.2V. Then, IC34 (18M) and IC37 (18BT) outputs 1.8V. Then, IC80 (30M)outputs 3.0V, and IC38 (33BT) and IC35 (33M) and IC81 (33OPT) outputs 3.3V. Then, IC39 (33A) outputs 3.3V, and IC82 (50A) out-puts 5.0V. Then, IC701 (18M_3) outputs 1.8V, and Q71 (53AF) is turned on. Voltage detector (IC704) watches IC33 (38M) outputvoltage. If the 38M output voltage is enough higher than 3.5V, detector outputs High. As a result, the MPU/DSP operate.The SBC signal becomes High after the MPU/DSP operates, and IC61 (33C), IC36 (50C), IC63 (50VCO) and Q32 (SB2) are turned on.When SD_EN signal becomes High, IC30 (33SD) operates. When 5UC signal becomes High, IC801 (50U) operates. When TXC signalbecomes High, IC65 (50T) operates. IC65 (50T) is turned on in transmit mode.When RXC signal becomes High, IC64 (50R) operates. IC64 (50R) is turned on in receive mode. Switches are controlled by the MPU/DSP.When the VOL SW is turned off /PSW signal becomes Low. After detecting /PSW signal, the MPU/DSP changes SBC signal to Low.The 50C is fed to IC60 (130C). IC60 (130C) is the DC/DC boost converter. IC60, D60, C64 consist of a DC/DC boost converter. The130C circuit then outputs approximately +13VDC.Low battery warning Battery conditionThe red LED blinks during transmission. The battery voltage is low but the transceiv-er is still usable.The red LED blinks and the warning tonebeeps while the PTT switch is pressed.The battery voltage is low and the trans-ceiver is not usable to make calls.
