TR-751A_E_serv.pdf

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1、I Photo is TR-751A. CONTENTS- CIRCUIT DESCRIPTION . . . . . 2 ELEMENT FUNCTIONS . . 14 PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 EXPLODED VIEW . . 50 LEVEL DIAGRAM . . . . 52 ADJUSTMENT . . . . 52 BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . 60 PC BOARD VIE

2、WS/CIRCUIT DIAGRAM CONTROL UNIT (X53-1460-XX) . 60 SUB VCO (X581000-XX) . . . 62 FM MIC AMP (X59-1090-00) . . 62 -6V DCDC (X59-1100-00) . 62 AF PRE AMP (X59-111 0-00) . . . . . . . . . . . . . . . 62 SQUELCH SWITCH (X591 120-00) . 62 CW BREAK IN (X59-113000) . 62 FM MIC AMP (X59-3000-00) . . 62 FM M

3、IC AMP (X59-300001) . : . . 62 FINAL UNIT (X45-1490-11) . 62 COMPOSITE UNIT (PLL, TX) (X60-1310-XX) . 63 COMPOSITE UNIT (RX) (X60-1320-XX) . 64 SCHEMATIC DIAGRAM S/No. 705- 707XXXX (K,M1,M2) . . . . 66 S/No. 708XXXX-(K,M1,M2,W,T) . 67 S/No. 705- 707XXXX (W, T) . . . . . . . . . . . . . . . 68 TERMIN

4、AL FUNCTION . . 69 MU-1 (MODEM UNIT) . . 70 TU-7 (TONE UNIT) . 71 VS-1 (VOICE SYNTHESIZER) . 71 PACKING . 72 SPECIFICATIONS . . BACK COVER TR-751A/E 2 CIRCUIT DESCRIPTION -MODEL TR-751A (K, M1, M2) -TR-751E (W, T) UNIT - FINAL UNIT X45-1490-11 X45-1490-11 - CONTROL UNIT X53-1460-11 (K, M1) X53-1460-

5、51 (T) X53-1460-21 (M2) X53-1460-61 (W) r- - - . COMPOSITE UNIT (PLL, TX) X60-1310-11 X60-1310-01 - COMPOSITE UNIT X60-1320-11 X60-1320-00 (RX) Table 1 TR-751A/E PC board chort FREQUENCY CONFIGURATION The TR-751A/E utilizes a PLL synthesizer system in- corporating a digital VFO, which covers each ba

6、nd in 50Hz steps. (See Fig. 1 . ) Received signals are mixed with the first local oscillator (133.305 to 137.295MHz) to produce the first intermediate frequency of 1 0.695MHz. In SSB or CW. the receiver operates as a single conversion system. The 1 0.695MHz IF signal is applied to crystal filter XF1

7、 (L71-0249-05). and the signal is then applied to the ring detector to obtain the audio output. In FM. the receiver operates as a double conversion system. The 10.695MHz signal is mixed with the PLL re- ference frequency of 1 0.24MHz to produce the second intermediate frequency of 455kHz. The transm

8、itter system operates as a double conversion system. In SSB mode, output from the carrier oscillator is modulated by a balanced modulator to produce an inter- mediate frequency signal, which is then mixed with the first local oscillator signal to produce the two rneter transmit signal. The carrier o

9、scillator circuit is controlled by the microprocessor according to the selected mode. During USB or CW receive. the carrier oscillator fre- quency is 1 0.6935MHz. During LSB receive. it is 10.6965 MHz. During CW transmit. it is 10.6943MHz. In FM, a SP SSB.CW OET 455kHz CF 10.695MHz XF 10.695MHz crys

10、tal oscillator frequency is used that is directly modulated and then mixed with the first local oscillator signal. To minimize internai heterodyne tones and spurs in the frequency generator and analysis are controlled by a microprocessor. The P L L -based frequency system consists of two PLL synthes

11、izer loops controlled by a 4-bit high- speed microprocessor and a stable, analog R IT oscillator circuit. Item Rating 1- - Nominal frequency 10.695MHz - Allowable center freq deviation Within 200Hz at 6dB - - Pass bandwidth and 2.2kHz or more at 6dB attenuation bandwidth Within 1.5kHz at 20dB (based

12、 on minimum loss) Within 2.4kHz at 60dB - -r- - Ripple 2dB or less - Minimum loss 5dB or less - Guaranteed attenuation 60dB or more within 40kHL r-. - - 1/0 terminating imped mce 1.2kn 5%/6pF5% Table 2 Crystal filter 10F2.2S (L71-0249-05) characteristics (Composit unit (RX) XF1) SSB, CW FM MHz 10.69

13、5MH -10 -20 0 !l 0 -30 C) c ., ;: (!) -40 - , - v v v , 0 -50 0 2 3 4 G2 Voltage (VI -3SK76 MOSFET -3SK !29 GoAsFET Fig. 2 AGC attenuation comparison 3 Downloaded by RadioManuai.EU - TR-751A/E 4 CIRCUIT DESCRIPTION The TR-751A/E AGC circuit has been designed to allow the AGC voltage to control the G

14、aAs FE T si rn i lar to the control that was obtained with the MOS FET. As shown in Fig. 3, AGC voltage from an amplifier similar to that used in previous models is fed into the intermediate fre- quency amplifier. The AGC voltage is approx. 4V when no signal is present. The AGC voltage is amplified

15、by the non-DC current inversion amplifier circuit that is corn posed of Op Amplifier (IC3). Its output is then applied to the GaAs FET. The output voltage is set to approx. 2.5V when no signal is present, or at minirnurn RF gain. The AGC characteristics are shown in Fig. 4. The AGC time constant is

16、automatically S.vitched to slow in SSB mode or to fast in CW mode. The high sensitivity of the receiver systern is thus obtained without sacrificing any two signal characteristic. Additionally, the RF gain control, provides a convenient method of tuning out undesired signals even when receiving sign

17、als that are too strong from near by local stations. 0 C) .r; , 0 0 - 10 -20 -30 -40 -50 -60 RF AMP GAIN / I 1 /1SK129 I I v .no o o o o o.n riri N NN I I I G2 Vohagll (V) Fig_ 4 AGC attenuation comparison AGC TIME CONSTANT .-B_u_ F_ FE_R _ -, ,.:.:.:.:.=.:.:.:.:., ,A_G_c_A_M_P-, SWITCHING CIRCUIT R

18、FAMPAGC VOLTAGE SHIFT CIRCUIT 02,03 3SK73 C20 SSB IF AMP o-Jt-H .-.-.-O+BV To ._.11/;.,_J RF AMP AGC LINE SSB SOL TIME CONSTANT SWITCHING Fig. 3 AGC circuit black diagram SSB squelch circuit The TR-751A/E SSB suqlech circuit is a noise operated type squelch. As compared with signal type squelch, noi

19、se detection squelch may be opened even by very weak signals, such as are frequently encountered in SSB. The high sensit ivity of the squelch circuit provides advantages when receiving VHF signals from distant sta- tions and when scanning. Generally, signal type squelch cannot surpass noise detectio

20、n type in sensitivity, since they are opened by changes in the AGC voltage. It means that, to open a signal type squelch, sufficient voltage level of signal to deflect the S rneter is required. The sensitivity of the TR-751A/E squelch is 0.1,uV or less (a weak signal which will not deflect the S met

21、er.) The squelch signal is applied to IC2 used in FM rnode, through the SSB filter, SSB IF, and buffer amplifier. This IC, rnixes the signal with 1 0.24MHz to produce 455kHz. Like the FM IF, the 455kHz signal is also amplified by IC2 and applied to the same squelch circuit as that used in FM mode. S

22、ince SSB signals do not contain carrier. unlike FM signals, the time constant circuit is switched between FM mode and SSB mode to get an appropriate response time. Downloaded by RadioManuai.EU I TR-751A/E CIRCUIT DESCRIPTION TRANSMITTER SYSTEM General The transmitter system operates as a single conv

23、ersion system. Audio signals from the microphone are amplified by a low-noise transistor (025) and applied to the SSB or FM circuits which provide approx. 26d8 gain. In SSB. the amplified signal passes through the SSB microphone gain control, and is amplified by (027) and applied to the balanced mod

24、ulator (IC4). The balanced modulator consists of an IC that provides stable carrier suppression without being influenced by changes in tem- perature. Signals from the micrphone amplifier are mixed with the carrier to produce a OSB signal. The OSB signal is applied to the SSB filter (with a center fr

25、equency of 1 0.695MHz) to produce the SSB signal. In FM, the signal amplified by the SSB/FM common micro- phone amplifier (025) is applied through the buffer ampli- fier (024) and FM microphone gain control, and then to the pre-emphasis circuit, amplified by (ICl), and limited by Op amplifier (IC1 )

26、. High frequency components are then removed from the signal by a 18dB/oct splatter filter, and the signal is sent to the FM modulation circuit. In the FM modulation circuit, signals from the 10.695 MHz crystal oscillator circuit are directly modulated by varactor diode (021). variable capacitor. Th

27、is direct fre- quency modulation enables a flat transmitter frequency response to be obtained from low frequencies to high frequencies. If the frequency deviation becomes excessive, the deviation level will vary from the upper to the lower portion of the signal. The TR-751A/E is designed so that the

28、 upper and lower portions of the signal are balanced even with maximum frequency deviation. SSB/FM switching is performed by diode switching cir- cuit according to the selected mode, and then amplified by the transmi Lter IF cirCLiit. This IF amplifier circuit con- sists of a dual-gate MOS FET, whos

29、e second gate is pro- vided with A LC voltage to control the transmitter output. The transmitter IF signal is then mixed with the PLL signal by balanced mixer consisting of two FETs (01, 02) to produce a 144MHz signal. Undesirable components are removed from the signal by a band-pass filter to mini-

30、 mize spurious emission. The signal from the band-pass filter is then amplified twice, once by a dual-gate MOS FET (03) and once by transistor (04). to raise the signal to the level necessary to drive the Final unit. The TR-751A/E contains an additional transistor amplifier (05). The signal from the

31、 drive circuit is amplified by the power module (01) in the Final unit, and goes through the ANT switching and diodes (05, 06) and low-pass filter to remove higher hArmonics, and is supplied to the antenna. CW circuit description In CW, the balanced modulator is unbalanced by AGC signal to allow the

32、 carrier w pass. CW keying is performed by switching the balanced mixer in the drive circuit and a bias voltage is applied to the first gate of amplifier. Fig. 5 shows the keying waveform. The leading and trailing edges are smoothed to prevent key clicks. To facilitate CW communications, the CW circ

33、uit con- tains CW semi break-in and side tone circuits. The CW semi break-in circuit is a Schmitt circuit consist- ing of transistors (0 1-04) or the break-in sub assembly. The delay time can be adjusted with VR7. The side tone circuit operates whenever the key is closed. The side tone circuit opera

34、tes in modes other than CW, so key adjustment and morse code practice can be performed. Transistor (09) is used as the oscillator. Signals from the side tone circuit are amp I ified by the audio amp- lifier (IC1 ). The output frequency of approx. 800Hz can be adjusted with potentiometer (VR4). I I I

35、 I I I I i ! I I l-. -= 1 11 I r 1 I l II I I .1 I, msec Fig. 5 CW waveform 5 Downloaded by RadioManuai.EU 6 CIRCUIT DESCRIPTION ALC and SWR protection circuits Fig. 6 shows the basic ALC and SWR protection circuits. ALC detection is made by amplifying a sample from the power module in the Final uni

36、t. The DC output signal is amplified by transistor (07) lower the ALC which controls the gain of the IF amplifiers. Low power is selected by controling the ALC Amplifier (07) with transistor (08). If the linearity of the Final is not well balanced with ALC feedback, SSB distortion may occur. The TR-

37、751A/E is designed to minimize SSB distortion. -, The SWR protection circuit detects and amplifies any reflected power due to mismatching in the antenna with a CM coupler. Output from the SWR protection circuit lowers the ALC reference voltage to reduce the gain of the power module for protection. F

38、INAL UNIT (X45-1490-11) TX IF AMP I ALC DETECTOR SWR PROTECTION DETECTION 024:3SK73(GR) .- I 0 i : M57727 _j +-:J-r:-rr - LOWPOWER SW LOW 0 I POWER SWITCHING 1 u I I I I I I L ALC AMP l 9V Fig. 6 ALC and SWR protectioncircuits PROTECTION AMP t.) Downloaded by RadioManuai.EU TR-751A/E Cl RCUIT DESCRI

39、PTION PLL SYNTHESIZER Fig. 7 is t he PLL system block diagram. The most important feature of the TR-751A/E PLL system is that it the rna in loop VCO (Loop A) is composed of a sub-unit to avoid the unit being influenced by outside forces (especially vibration), which improve the frequency stability D

40、uring mobile operation in SSB or CW, this provides a great increase advantage in reliability. The PLL system uses two loops to form a digital VFO which covers each band in 50Hz steps. Each of the loops uses a PLL IC (TC9172P) with pulse swallow type pre- scaler. The B loop utilizes a 2.5kHz comparis

41、on frequency. The range of its VCO output freqency is from 28 to 27iv1Hz (frequency division ratio 11200 to 10800 : 1). The B !oop VCO output is frequency divided by 50 (to produce 560 to 540kHz). which is used to produce a signal that covers 20kHz from 9.68 to 9.70MHz in 50Ht. steps. This signal is

42、 then mixed with the reference oscillator frequency of 10.24MHz. NA N8 sc BUFF FM SCAVH 2SC: SC -: SN 1 !:i913P IC:) : fA1310P MIX 9 68- 9 70IHt r -, -. 4 - l Q- 1 L_l-1-_ T_j - : I I 1 0 2 , : I I 9.esr.,1H2 .:;:.o /:.:V D T O I TO If( OUTI , -, I I I J-(l;Al I OPHON I WUI J -fR:XRt.TA I L _ _j M(

43、+-IMOOEM ENA9L() OR MIC MUTE Downloaded by RadioManuai.EU TR-751A/E CIRCUIT DESCRIPTION MPU interface circuits Fig. 9 shows how the three MPUs are interfaced. To exchange data between the MPUs, three clock and data 1/0 lines (SCK, Sl and SO) and two each of control lines SCK, SQR, DCK, and ORO are p

44、rovided. Reset backup circuit Fig. 9 also shows the reset backup circuit. When the transceiver power is turned on, an approx. 20ms H level pulse is sent from the reset circuit using a dedicated reset IC (IC201) to the RES line. Since the RES line is connect- ed to all MPUs (MPU-1, MPU-Il, MPU-III),

45、the MPUs begin operation at the same time. When the power is turned off, IC202 recognizes that the voltage of the 5V line fell to 4.5V or less. and sets the low voltage fallen detect line (VFD) to a low level. The VFD signal is sent to MPU-1 POO and MPU enters the backup mode. Output voltage from th

46、e lithium battery for backup is supplied to MPU-J and MPU-H providing backup for two MPUs. IMAIN CHASSIS l (X53-1460-XX) (A/6) 28 -Q-P 63 -Q-2 7 P 62 1 SV LINE MPU-II IC 301 I VFD RES voo 5 C E I 0/0 r RESET CIRCUIT I I ,-, -. LOWVOLTAGE DETEcT-l I !J -;r- - 0 OUTPUT r- IC202 PSTJZJC I 0Vwhentho5VIInofalls ) II EQUIVALENT 3 to 4.5V or less dunng powr on I I UIT l ij-IC 201 H RESET OUTPUT 2l SCK 24 S l 22 so 20 POO 15 RESET 0- I!) I!) n.O- P41 I I - L _: .: 10-rll. 8 11 lZ. :; T Ire: : -:J .l. ;f_vsseecc_ TP5,o-+-+._ _ _.!:= I L I 30m s TP40-l-._ _ -.: P50 12 RE