Kenwood TK-860G Service Manual

Also see for TK-860G series: Instruction manual Instruction manual Service manual supplement Service manual Service manual

Contents

24TK-860G/862GFrequency ConfigurationThe receiver utilizes double conversion. The first IF is49.95MHz and the second IF is 450kHz. The first local oscil-lator signal is supplied from the PLL circuit.The PLL circuit in the transmitter generates the neces-sary frequencies. Figure 1 shows the frequencies.Fig. 1 Frequency configurationReceiver SystemThe receiver is double conversion superheterodyne. Thefrequency configuration is shown in Figure 1. Front-end RF AmplifierAn incoming signal from the antenna is applied to an RFamplifier (Q34) after passing through a transmit/receiveswitch circuit (D33 and D34 are off) and a BPF (L22 : two-pole helical resonators). After the signal is amplified (Q34),the signal is filtered by a BPF (L13 : two-pile herical resona-tors) to eliminate unwanted signals before it is passed to thefirst mixer. Band pass filters (L22 and L13) have varactordiodes (D28, D31, D18 and D23).The voltage of these diodes are controlled by to track theCPU (IC502) center frequency of the band pass filter. (SeeFig. 2) First MixerThe signal from the RF amplifier is heterodyned with thefirst local oscillator signal from the PLL frequency synthe-sizer circuit at the first mixer (Q15) to create a 49.95MHzfirst intermediate frequency (1st IF) signal. The first IF signalis then fed through two monolithic crystal filters (MCFs :XF1) to further remove spurious signals. IF AmplifierThe first IF signal is amplified by Q13, and the enters IC5(FM processing IC). The signal is heterodyned again with asecond local oscillator signal within IC5 to create a 450kHzsecond IF signal. The second IF signal is then fed through a450kHz ceramic filter (Narrow : CF1, Wide : CF2) to furthereliminate unwanted signals before it si amplified and FMdetected in IC5.Item RatingNominal center frequency 49.95MHzPass bandwidth ± 5.0kHz or more at 3dB35dB stop bandwidth ± 20.0kHz or lessRipple 1.0dB or lessInsertion loss 5.0dB or lessGuaranteed attenuation 80dB or more at fo±1MHzSpurious : 40dB or more within fo± 1MHzTerminal impedance 350Ω± 5% / 5.5pF±0.5pFTable 1 Crystal filter (L71-0551-15) : XF1Item RatingNominal center frequency 450kHz6dB bandwidth ± 4.5kHz or more50dB bandwidth ± 10.0kHz or lessRipple 2.0dB or lessInsertion loss 6.0dB or lessGuaranteed attenuation 55.0dB or more within fo± 100kHzTerminal impedance 2.0kΩTable 2 Ceramic filter (L71-0959-05) : CF1Item RatingNominal center frequency 450kHz6dB bandwidth ± 6.0kHz or more50dB bandwidth ± 12.5kHz or lessRipple 3.0dB or lessInsertion loss 6.0dB or lessGuaranteed attenuation 35.0dB or more within fo± 100kHzTerminal impedance 2.0kΩTable 3 Ceramic filter (L72-0973-05) : CF2Fig. 2 Receiver systemCIRCUIT DESCRIPTIONANTSWRFAMP1stMIXAFAMPTCXOMICAMPX3multiplyTXAMPPAAMPCF 450kHzMCF49.95MHzIF SYSTEMPLL/VCO16.8MHz50.4MHzANTRXTXSPMICSWANTL22BPF L13BPFQ34RF AMP Q13IF AMP IC4AF AMPQ15MIX XF1MCFD33,34ANTSWIC6D/AQ7X3 multiplyX1VCXOIC5MIX,IF,DET1st localOSC (VCO/PLL)DEOCF1 (Narrow)CF2 (Wide)TVCPU Q35Wide/Narrow SW