Kenwood TK-7100H Service Manual

Also see for TK-7100H: Specifications Service manual

TK-7100H15Frequency 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 necessaryfrequencies. Figure 1 shows the frequencies.CIRCUIT DESCRIPTIONReceiver 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 (Q353) after passing through a transmit/receiveswitch circuit (D603, D605 are off) and a band pass filter(L357, L356 and varactor diodes : D353, D354). After thesignal is amplified (Q353), the signal is filtered through a bandpass filter (L354, L355 and varactor diodes: D351, D352) toeliminate unwanted signals before it is passed to the firstmixer.The voltage of these diodes are controlled by tracking theCPU (IC101) 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 synthesizercircuit at the first mixer (Q352) to create a 49.95MHz firstintermediate frequency (1st IF) signal. The first IF signal isthen fed through one pair of monolithic crystal filter (MCF :XF351) to further remove spurious signals.ANTSW RFAMP1stMIXAFPATCXOMICAMPX3multiplyRFAMPPOWERAMPCF 450kHzMCF49.95MHzIF SYSTEMPLL/VCO16.8MHz50.4MHzANTRXTXSPMIC1/2Fig. 1 Frequency configuration■ IF AmplifierThe first IF signal is amplified by Q351, and the entersIC301 (FM processing IC). The signal is heterodyned againwith a second local oscillator signal within IC301 to create a450kHz second IF signal. The second IF signal is then fedthrough a 450kHz ceramic filter (Wide : CF301, Narrow :CF302) to further eliminate unwanted signals before it is am-plified and FM detected in IC301.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 attenMuation 80dB or more at fo± 1MHzSpurious : 40dB or more within fo± 1MHzTerminal impedance 350Ω / 5.5pFTable 1 Crystal filter (L71-0591-05) : XF351Item 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) : CF301Item RatingNominal center frequency 450kHz6dB bandwidth ± 4.5kHz or more50dB bandwidth ± 10.0kHz or lessRipple 2.0dB or lessInsertion loss 6.0dB or lessGuaranteed attenuation 60.0dB or more within fo± 100kHzTerminal impedance 2.0kΩTable 3 Ceramic filter (L72-0999-05) : CF302ANTL357,356D353,354BPFQ353RF AMP Q351IF AMP IC161D/A CONVERTERQ352MIX XF351MCFD602D603D605ANTSWIC161D/AQ302X3 multiplyIC4021/2 divider X401TCXOIC301IF system1st localOSC (VCO/PLL)W/NO(EVOL2)CF301 (Wide)CF302 (Narrow)TVCPUL354,355D351,352BPFFig. 2 Receiver system