Kenwood 144MHz FM TRANSCEIVER K2E Service Manual

TH-K2AT/K2E/K2ET6CIRCUIT DESCRIPTIONFrequency ConfigurationThe frequency configuration is shown in Figure 1 andTable 1.Fig. 1 Frequency configuration174.850~212.845MHz(K,K2,M,M2)182.850~184.845MHz(E,E3)144.000~147.995MHz(K,K2)136.000~173.995MHz(M,M2)144.000~145.995MHz(E,E3)136.000~173.995MHz(K,K2,M,M2)144.000~145.995MHz(E,E3)144.000~147.995MHz(K,K2)136.000~173.995MHz(M,M2)144.000~145.995MHz(E,E3)RX :TX :ANTSWMCF38.85MHz 38.4MHz12.8MHz450kHzCFMIX, IF,DETAFAMPSPPREDRIVEFINAL TCXODRIVETriplerx 3RFAMP1st MIXPLLVCOMICAMPMICANTReceiver System■ Front EndThe received signal from the antenna passes through a low-pass filter and then through a transmission/reception switchingcircuit (antenna switch) and enters the band-pass filter (L40,L41, L38).The signal passing through the band-pass filter (L40, L41,L38) is amplified by with an RF amplifier (Q17), passes througha band-pass filter (L32, L35) and enters the first mixer (Q16).These band-pass filters are tuned to a desired frequencyby varicaps (D21, D20, D19, D18).Double super heterodyneReception method 1st IF Frequency 38.85MHz (Upper)2nd IF Frequency 450kHz (Lower)Transmission method VCO direct oscillation amplificationModulation Variable reactance phase modulationTable 1 Basic configurationANTSWSPLPFVCOBPF/APCMPUIC8PLLIF AMP,DETTriplerx 3TCXOBPFL41,L40,L38 BPFL32,L35 MIXERQ161st Local OSC(PLL)RF AMPQ17ANTMCFXF1 IF AMPQ24 FM ICIC3Q232nd Local OSCX1AF AMPIC65R5RD20D21LV6Tuning voltageD1838.85MHz12.8MHzD19A tuning voltage corresponding to the desired signal isapplied to each varicap through the BPF/APC terminal (pin 6)of the MPU (IC8) to tune to the receive frequency.■ First MixerThe received signal passing through the band-pass filter(L32, L35) is mixed with the first local signal generated by theVCO by the first mixer (Q16) to produce a first IF signal (38.85MHz) (Upper heterodyne).The first IF signal passes through a MCF (Monolithic crystalfilter: XF1) to remove unwanted components.The first IF signal passing through the MCF (XF1) is amplifiedby an IF amplifier (Q24) and the resulting signal enters the FMIC (IC3).Fig. 2 Receiver section configurationItem RatingNominal center frequency (fo) 38.85MHzPass bandwidth ±6.0kHz or more at 3dBAttenuation bandwidth ±25kHz or less at 35dBUltimate attenuation 70dB or more (fo –910 kHz)Spurious response 40dB or more (fo +1MHz)Ripple 1dB or lessInsertion loss 4dB or lessTerminating impedance 610Ω ±5% // 3pF ±0.5pFTable 2 MCF (L71-0619-05) characteristics (TX-RX unit XF1)Item RatingNominal center frequency (fo) 450kHz3dB bandwidth ±6.5kHz or more50dB bandwidth ±15.5kHz or lessRipple 2dB or less (fo ±6.5kHz)55dB or moreGuaranteed attenuation (fo ±18kHz to ±33kHz)50dB or more (fo ±100kHz)Insertion loss 4dB or lessI/O matching impedance 1.5kΩTable 3 Ceramic filter (L72-0968-05) characteristics (TX-RX unit CF1)