Kenwood TK-980 Service Manual

Also see for TK-980: Programming instructions Instruction manual Instruction manual Programming instructions Specifications

25TK-980/981Frequency ConfigurationThe TX-RX unit (A/2) incorporates a VCO, based on a frac-tional N type PLL synthesizer system, that allows a channelstep of 12.5kHz to be selected. The incoming signal fromthe antenna is mixed with a first local oscillation frequencyto produce a first intermediate frequency of 44.85MHz.The signal is then mixed with a second local oscillationfrequency of 44.395MHz to produce a second intermediatefrequency of 455kHz. This is called a double-conversionsystem. The transmit signal frequency is generated by thePLL VCO, and modulated by the signal from the micro-phone. It is then amplified by TX amplifier and PA amplifier,and sent to the antenna.Fig. 1 Frequency configurationReceiver System OutlineAn incoming RF signal from the antenna terminal passesthrough the antenna switch (D208, D209, and D210 are off)and then the bandpass filter (L203). The signal is amplifiedby RF amplifier Q201, and passes through the bandpass fil-ter (L207) again. The resulting signal goes to the first mixer(Q203), where it is mixed with the first local oscillator signaloutput from the frequency synthesizer to produce the firstIF 44.85MHz. AF Signal SystemThe detection signal (DEO) from the TX-RX unit (A/2)goes to the audio processor (IC504) of the TX-RX unit (B/2).The signal passes through a filter in the audio processor toadjust the gain, and is output to IC502. IC502 sums the AFsignal and the DTMF signal and returns the resulting signalto the TX-RX unit (A/2). The signal (AFO) sent to the TX-RXunit (A/2) is input to the D/A converter (IC5). The AFO out-put level is adjusted by the D/A converter. The signal outputfrom the D/A converter is added with the BEEP signal (BPO)and the resulting signal is input to the audio power amplifier(IC10). The AF signal from IC10 switches between the inter-nal speaker and speaker jack (J1) output.Fig. 2 Receiver systemCIRCUIT DESCRIPTIONANTSW RFAMP1stMIXTXAMPPAAMPCF 455kHzMCF44.85MHzIF SYSTEMTK-980806.15~825.15MHzTK-981890.15~896.15MHzPLL/VCOVCXO16.8MHzTK-980TX 806~825MHz851~870MHzRX 851~870MHzTK-981TX 896~902MHz935~941MHzRX 935~941MHzTK-980806~825MHz851~870MHzTK-981896~902MHz935~941MHz44.395MHzAFOMDMBANTANTL203BPF L207BPFQ201RF AMP Q151st IF IC2AF AMPQ2031st MIX XF1MCFD208~210ANTSWCF1IC11MIX,DET,IFX22ndlocal OSC1st localOSC (PLL)DEODET DETAUDIOPROCE.SUMAMPD/ACONV.IC504 IC504 IC5AF PAIC10 SPDTMF BPOAFODEOTX-RX UNIT (B/2)Fig. 3 AF signal system Squelch CircuitThe detection output from the FM IF IC (IC11) is ampli-fied by IC2 and the signal (DEO) is sent to the TX-RX unit (B/2). The signal passes through a high-pass filter and a noiseamplifier (Q503) in the TX-RX unit (B/2) to detect noise. Avoltage is applied to the CPU (IC511). The CPU controlssquelch according to the voltage (ASQ) level. The signalfrom the RSSI pin of IC11 is monitored. The electric fieldstrength of the receive signal can be known before the ASQvoltage is input to the CPU, and the scan stop speed is im-proved.IC2AMPIC503AMPQ503NOISE AMP D509IC11 IC511DEORSSIHPF DETCPUIFSYSTEMTX-RX UNIT (B/2)Fig. 4 Squelch circuit