Kenwood TK-790 Service Manual

Also see for FleetSync TK-790: Specifications Instruction manual Specifications Instruction manual

27TK-790/(B)/H(B)2. Receiver CircuitIncoming signals from the antenna pass through a low-pass filter in the final unit of the transmitter system, and areswitched to the front-end of the receiver system via a re-ceive/transmit switch (switching diode D3 and D4 : TK-790/(B), switching relay K1 : TK-790H(B)).The signal is then passed through an antenna matchingcoil. After passing through the BPF (L.C filter), it is amplifiedby the RF amplifier (Q101). The tuned varactor BPF(L110~112) is then passed, and it enters the 1st mixer.The 1st mixer use a double balanced mixer (A101). TheDBM is an excellent IM (intermodulation distortion) and im-age. The 1st mixer mixes the signal with the 1st local oscil-lator frequency and converts it to the 1st IF (44.85MHz).The signal is amplified by the 1st IF amplifier 1 (Q102).The signal then passes through two monolithic crystal fil-ters (XF101 : Wide, XF102 : Narrow) to remove unnecessarynearby frequency components. The signal from the XF101or XF102 is used as the 1st IF signal.The 1st IF signal is amplified by 1st IF amplifier 2 (Q107)and fed into IC101 in the FM IF IC. The IF signal is thenmixed with the 2nd local oscillator frequency of 45.305MHzto generate the 2nd IF of 455kHz. The 455kHz signal is thenpassed through a ceramic filter (CF101, CF103 : Wide,CF102, CF104 : Narrow) and fed back into IC101 for addi-tional amplification.The AF signal output from IC101 then passes throughthe control unit's HPF and D/A converter IC. After enteringthe AF power amplifier (IC522), the signal is output from thespeaker.CIRCUIT DESCRIPTIONItem RatingNominal center frequency 44.85MHzPass bandwidth ± 5.5~7.5kHz or more at 3dBAttenuation bandwidth ± 25kHz or less at 40dBRipple 1.0dB or lessInsertion loss 3.0dB or lessGuaranteed attenuation 85dB or more at fo+400~+1000kHzfo–200~–1000kHzTerminating impedance 3.2kΩ / –1.0pFTable 1 Crystal filter (L71-0512-05) : Wide(TX-RX unit XF101)Item RatingNominal center frequency 44.85MHzPass bandwidth ± 3.5kHz or more at 3dBAttenuation bandwidth ± 15kHz or less at 40dBRipple 1.0dB or lessInsertion loss 4.0dB or lessGuaranteed attenuation 85dB or more at fo+400~+1000kHzfo–200~–1000kHzTerminating impedance 3.0kΩ / –0.5pFTable 2 Crystal filter (L71-0513-05) : Narrow(TX-RX unit XF102)Fig. 5 Receiver circuitANTSWLPFL7,5,4LPFL9,8,7 D3,4ANTBPFIC101IC504 IC515AMP HPF BEFRF AMPQ101RF AMPQ104BPFL110~1121st MIXA101 LPFTVD306ANTT/RSWRAK1CF103 CF101CeramicfilterWIDECF104 CF102CeramicfilterNARROWX10145.305MHzFM SYSTEM ICNOISEAMPNOISEDETRSSIDETRSSIDETQ109D103SQ455kHz1st IF AMP2Q1071st IF AMP1Q102MCFXF101MCFXF102WIDENARROW44.85MHzVCORX VCOf RX +44.85MHzIC518(2/2) IC524(1/2) IC524(2/2)DE-EMP EXPIC512IC518(1/2)IC522VOLBUFFAF PAVOLIC516CPU2726 RSSIASQSPFINAL UNIT : TK-790H(B) TX-RX UNITCONTROL UNIT DISPLAY UNITFINAL UNIT : TK-790/(B)Fig. 6 Double balanced mixerLO GND GNDGND IF RF21 3456