Kenwood TK-8102 Service Manual

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Contents

10TK-8102Frequency 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.n Front-end RF AmplifierAn incoming signal from the antenna is applied to an RFamplifier (Q26) after passing through a transmit/receiveswitch circuit (D31 and D32 are off) and a BPF (L36, L38,L48, L49 and varactor diodes: D25, D26, D28). After thesignal is amplified (Q26), the signal is filtered by a BPF (L30,L32 and varactor diodes: D21, D22) to eliminate unwantedsignals before it is passed to the first mixer.The voltage of these diodes are controlled by tracking theCPU (IC6) center frequency of the band pass filter. (See Fig. 2)n 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 (Q21) 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.n IF AmplifierThe first IF signal is amplified by Q19, 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 (Wide : CF1, Narrow : CF2) to furthereliminate unwanted signals before it is amplified and FM de-tected 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 / 5.5pFTable 1 Crystal filter (L71-0591-05) : XF1Item RatingNominal center frequency 450kHz6dB bandwidth ± 6.0kHz or more50dB bandwidth ± 12.5kHz or lessRipple 2.0dB or lessInsertion loss 6.0dB or lessGuaranteed attenuation 35.0dB or more within fo± 100kHzTerminal impedance 2.0kΩTable 2 Ceramic filter (L72-0993-05) : CF1Item 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 3 Ceramic filter (L72-0994-05) : CF2Fig. 2 Receiver systemCIRCUIT DESCRIPTIONANTSWRFAMP1stMIXAFAMPTCXOMICAMPX3multiplyTXAMPPAAMPCF 450kHzMCF49.95MHzIF SYSTEMPLL/VCO16.8MHz50.4MHzANTRXTXSPMICSWANTL36,38,48,49D25,26,28BPFQ26RF AMP Q19IF AMP IC3AF AMPQ21MIX XF1MCFD30,31,32ANTSWIC3D/AQ6X3 multiplyX1TCXOIC5MIX,IF,DET1st localOSC (VCO/PLL)DEOCF1 (Wide)CF2 (Narrow)TVCPUL30,32D21,22BPF