Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S10CIRCUIT DESCRIPTION3. Main Receiver Circuit3-1. From the Antenna Terminal to the PreselectorAmplifier (Q10 and Q11)Figure 5 shows a front part of the block diagram for themain receiver circuit.A double conversion is adopted for the main receiverprocess so that the 8.248MHz is used for the 1st IF and the24kHz (FM: 455kHz) is used for the 2nd IF frequency (Referto table 4).The received signal from ANT1~ANT4 is fed to CN1(MRAT) via K801 to 804 relays on the antenna connectorunit (X45-388 B/2) and K18, K19, K10, K14 relays on an-tenna switch unit (X53-441 A/2). (Fig. 28)A received signal enters CN1 (MRAT) on the RX unit(X55-313 A/2). The signal input to the RX unit is fed to theATT (OFF/6dB/12dB/18dB) selector, and is fed to the BPFunit (X55-313 B/2) via the surge current absorbing limiter,BC band attenuator (except 30kHz to 1.705MHz and 35 to40MHz). The two traps (11.7MHz and 15.5MHz) are embed-ded in the BC trap in order to prevent interference from highpower broadcast stations.The BPF divides in the range as shown in table 5. BPFsfor 30kHz to 1.705MHz and 35 to 40MHz are mounted on theRX unit, and BPFs for 1.705 to 60MHz (except 35 to 40MHz)are mounted on the BPF unit. In major amateur bands, thetoroidal coils and air core inductor are used to reduce in-sertion loss in the passband by the BPF, and the relay isused to suppress distortion by a large signal for the switch.In order to prevent intermodulation ranging from 522kHz to1.705MHz due to high power broadcasting stations, the ATT(attenuator) is mounted (ATT ON: CN50=open, CN60=short/ ATT OFF: CN50=short, CN60=open).The signal passed through the BPF is applied to thePRESEL unit (X42-343 B/10) where a preselector (tuningcircuit of the single-peaked characteristic) that can be se-lected with a preselector key ([P.SEL] key) is mounted.The preselector makes it possible to improve the selectiv-ity of the receiver. If the preselector is selected, the preselec-tor amplifier (Q10 and Q11) will be selected where the signalattenuated in the preselector will be compensated for.Fig. 5 Front part of the main receiver circuitMode SSB CW FSK AM FMRX-1 pathConversion method DoubleIF frequency1st 8.248MHz2nd 24kHz 455kHzTable 4 Mode, conversion method, and IF frequencyATTATT–6dB/12dB/18dBATTATTBC Trap BPFBPFLPF522kHz~1.705MHzLPF30kHz~522kHzBPFBPFQ10,Q11PRESEL AMPPreselectorTo PRE AMPPRESEL unit(X42-343 B/10)BPF unit(X55-313 B/2)MRATBPF35MHz~40MHz