Motorola Bpr40 Magone Detailled 6816102h01 A Manual
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Transmitter System and PLL Synthesizer2-3 3.0 Transmitter System and PLL Synthesizer The transmitter consists of: Microphone, Pre-emphasis, Modulator, Drivers, Power Amplifier, Low- Pass Filter, Antenna Switch and an Auto-Power Control. 3.1 TX Power Stage The TX VCO output signal is channeled by the TX power stage via an attenuator. The attenuator is pie style resister attenuator, and is used for isolation between the VCO and power amplifiers. The TX Power stage is consist of: pre-drive (Q401), drive amplifier (Q402) and final amplifier (Q403). The -4dBm TX RF signal from the attenuator is increased to around +25dBm by the pre- drive and the drive amplifier. The TX signal from drive amplifier is next amplified by final amplifier (Q403). It passes through a strip line for impedance matching, and a low pass filter to suppress unwanted harmonics via the antenna switch. 3.2 Antenna Switch The antenna switch is for enabling the TX section and the RX section to share the antenna. In transmit mode, PIN diodes (CR401, CR301, CR302) are forward biased and these enable the RF signal to pass to the antenna. 3.3 Low Pass Filter The TX Low Pass Filter consist of a fifth Chebyshev filter and reduces the unwanted spurious for TX output power from final Amplifier : C426~430, L409, L410. LPF ANT-SWFINAL AMP CURRENT DETECTDRIVE AMP APCP.DRIVE AMP VCO PLL PLL DATA VCTCXOREG. 5.8V U106 U701 Q401 Q402 Q403 R417 CR401 BATT.LOOP FIL. U401 AUDIO (From filter) 3DB ATTEN
2-4Transmitter System and PLL Synthesizer 3.4 Auto-Power Control The Auto-Power Control (APC) keeps the current constant to the final amplifier (Q403). The current into Q403 of the final amplifier is sensed across resistor R417. The voltage difference across R417 is amplified through U401 by the ratio of R423 to R417. The differential signal at the output of U401 is passed to Q404 and Q405 which then produce a constant power output to the antenna. If the current is changed due to a change of battery voltage or load, the APC controls gate voltage of Q403 and the collector voltage of Q401,402 to keep the TX power stable. This circuit stabilizes TX power at a pre-determined level adjusted by R425 (High Power), R426 (Low Power). 3.5PLL Synthesizer 3.5.1 12.8 MHz VCTCXO Reference frequency is 12.8Mhz VCTCXO (Voltage Controlled Temperature Compensated Crystal Oscillator). Main frequency can be adjusted by the chip trimmer of VCTCXO. This frequency provides a reference to the PLL. It has a frequency stability of ± 2.5PPM at -30º to +60º. 3.5.2 PLL IC and Loop Filter . The input frequency of 12.8Mhz is channeled into PLL IC (U701) pin 8. It is divided to 6.25Khz or 5Khz by a reference counter, R. The RF signal input from the VCO is divided to by prescaler (32/33), N counter in PLL IC. The internal phase comparator compares signal from the VCO with the reference frequency. The regulator 5.8V increases the internal charge pump voltage of PLL IC. The LPF contains C735, C734 and R718. This also reduces the residual side-band noise for the best signal-to-noise ratio. Loop filter VCTCXO +5V VCO VCO Control voltage CE CLOCK DATA STB Lock detector +5V +5.8V GND FLO CPO FIN-FIN VCC1 OSCIN GND CEGND CLOCK DATA LE FO/LD VCC2 VP LMX2316
Audio and Control Circuit2-5 3.5.3 Dual VCO The dual VCO module contains an RX VCO and a TX VCO. They are configured as Colpits oscillators and connected to power through cascade buffers. Only one VCO is selected at a time. The power source to each block is switched by transistors Q305 and Q111, and is dependent on the states of TX_EN1 and RX_EN. The varicap diodes CR701 and CR702 produce a change in frequency with a change in voltage. L703 and L706 are resonant tuning coils, which adjust the operating frequency with specified DC tuning voltage applied. The audio signals from low pass filter (U105-C) is applied to CR703 varicap diode in TX VCO to be modulated TX RF signal. 4.0 Audio and Control Circuit 4.1 RX Audio The RX audio signal comes through the de-emphasis pass six order elliptic 300 Hz HPF and 3 order 300Hz HPF. This 300Hz High Pass Filter (U203) removes all signals under 300Hz to keep any undesired signal from being heard from the speaker. After passing through this filter, audio signal is de-emphasized by R209,C212 to get 6db/oct response. The de-emphasized audio signal passes through volume control (SW/VOL1) and is amplified to a sufficient level to drive a loud speaker by U601 Audio AMP. U601 has mute/un-mute function by the audio-mute control in CPU. If U601 pin 2 is low, the audio amplifier goes into active mode. If pin 2 is high, the IC goes into mute mode. TONE-FIL LPF AF-AMP HPF MIC MUTE MIC N/S SW U104-A U104-C Q109 TONE-FIL U202 AUDIO- PATH Q103 AF PA U601 AUDIO- MUTEQ101 to SPK. TONE-GEN. U104-D, U105-C U105 MUTE- CON AUDIO-MUTE CON MOD. ADJ R159 6 Order Elliptic HPF 8 Order LPF to CPU RX LOGIC 3 Order HPF6 Order LPF 3 Order LPF to MOD. TX LOGIC + 3 Order HPF 260Hz From IF IC 300Hz 300Hz 3KHz SW/VOL1 Q108 De-EMPAUDIO-FIL U203 300HzR209,C212
2-6Audio and Control Circuit 4.2 RX Sub-Audible Decode Circuit The filter U202 is a 260Hz 8 order LPF to pass CTCSS, DCS signals and to block any other signals. The signals that pass the LPF filter changes this sub-tone to logic signals in the Q208 pass comparator (U202-D) so that the microprocessor can decode the CTCSS and DCS correctly. 4.3 TX Audio When the radio user pushes the PTT button, the microprocessor activates the entire transmitter section, including the microphone. The audio signal from the microphone passes through the 3 order 300Hz high pass filter and through the limiting amplifier (U104-C, A) that has a 6db/oct pre- emphasis function. The pre-emphasized audio signal is adjusted to a proper level by R159 and passes through a 6 order 3KHz low pass filter (U104-D,U105-C) before being modulated. Wide and narrow channel spacing is controlled by the N/S switch (Q108). 4.4 TX Sub-Audible Encode Circuit The encode circuit of CTCSS and CDCSS mixes signals from four ports of the microprocessor. This mixed signal passes through 3 order 300Hz LPF (U105-B) to obtain clear CTCSS and DCS signals. 4.5 Microprocessor U101 controls all functions of the radio as a Microprocessor. It is operated by an external 7.3728MHz crystal. It detects external activities such as the pressing of the PTT, muting/un-muting conditions, changing of channels, and then making the radio operate accordingly.
3-2RF Circuit Board and Schematic Diagram for VHF Band 1 (136–150 MHz)1.0 RF Circuit Board and Schematic Diagram for VHF Band 1 (136–150 MHz) VHF Band 1 (136–150 MHz) Main Board Top Side
RF Circuit Board and Schematic Diagram for VHF Band 1 (136–150 MHz)3-3 VHF Band 1 (136–150 MHz) Main Board Bottom Side
3-4RF Circuit Board and Schematic Diagram for VHF Band 1 (136–150 MHz)VHF Band 1 (136–150 MHz) Schematic Diagram
4-1 Section 4VHF BAND 2 (150–174 MHZ) INFORMATION (150–174 MHZ)
4-2RF Circuit Board and Schematic Diagram for VHF Band 2 (150–174 MHz)1.0 RF Circuit Board and Schematic Diagram for VHF Band 2 (150–174 MHz)VHF Band 2 (150–174 MHz) Main Board Top Side