Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S26CIRCUIT DESCRIPTION5-2. From the Drive output to the Antenna TerminalThe transmission signal sent to the CN2 (DRIVE) of thefi nal unit (X45-388 A/2) from the TX-RX unit (X57-827 A/2)is amplified to the specified power by the final unit and inputinto the antenna connector unit (X45-388 B/2) through theLPF. This transceiver includes a relay antenna tuner circuitthat operates in amateur bands.The transmission signal that is applied to the CN2 ofthe fi nal unit is amplifi ed by the pre-drive amplifi er (Q2) anddrive amplifier (Q3), and then power amplified by the finalamplifier (Q7) to 200 W. The harmonic components of thesignal are then removed by the LPF, and the signal is sent tothe antenna switch unit (X53-441 A/2).The final amplifier is a push-pull amplifier consisting ofa power MOS FET (VRF150MP) of 50 V type. Q7 (A/2) andQ7 (B/2) form a pair that is matched through VGS (TH). Q7(A/2) and Q7 (B/2) are packaged under a single part num-ber, therefore both of them need to be replaced even if oneof the push-pull elements is broken.The signal amplified to 200 W is applied to J7 on theantenna switch unit (X53-441 A/2) from J1 on the final unit(X45-388 A/2). The signal goes through the forward/reflectedwave detector, amplitude/phase detector for the antennatuner, transmission/reception switching diode (D19), andantenna tuner IN/THROUGH switching relay (K18 and K19),and is sent from J4 on the antenna switch unit.The signal is applied to J800 on the antenna connectorunit (X45-388 B/2), and is fi nally sent from the ANT1, ANT2,ANT3, or ANT4 antenna terminal via the antenna switchingrelay (K801, K802, K803, or K804). In order to reduce theoperating noise of the transmission/reception switching relay,the transmission path uses a diode switch and the receptionpath uses a relay circuit (as with the TS-940). The relay (K16)is turned ON during signal reception in order to maintain theisolation of the transmitter block from the receiver block.Fig. 27 From the drive output to the antenna terminalQ2 Q3Q7(A/2)Q7(B/2)TX LPF1.8-50MHzBANDL28SWRL25L24IC4IC3Drive inVSRVSFPhasedefferencialoutD37 D36 Q26D19K9RATK16GNDAmplitudedefferencialoutK18 K19AT inAT throughX45-388 A/2X53-441 B/2X53-441 A/2Q255-3. Antenna Tuner and Various ProtectionsThe antenna tuner is switched by antenna change overrelays (K18 and K19). If IN is selected, the signal is appliedto the antenna tuner unit (X53-441 B/2), where a capacitorand coil in combination tune the signal. Its operation is thesame as in previous models. IC4's phase error signal switch-es the input side capacitor of the tuning circuit, and the IC3'samplitude difference signal switches the output side capaci-tor. The SWR is decided by calculating the voltage of theprogressive wave (VSF) and that of the reflected wave (VSR)with the main MCU (X53-452 IC46).The transmit signal is applied to the antenna connectorunit (X45-388 B/2), and finally sent from antenna terminalANT1, ATN2, ANT3, or ANT4 through an antenna switch-ing relay (K801, K802, K803, or K804). If the main band andsub band use the same antenna, the signal passes the pathshown in Fig. 28 and the relay switches over the signal. Thedistribution circuit distributes approximately half the powerof the receive signal to the main band and the rest to thesub band. If the main band and sub band use different an-tennas, the antenna for the main band or the one selectedfor transmission is connected through a relay (K801, K802,K803, or K804) and the antenna selected for the sub band isconnected through a relay (K805, K806, K807, or K808) onthe sub reception side.The transceiver has RX IN and RX OUT terminals, thusmaking it possible to connect an antenna dedicated for re-ception to the RX IN terminal or an external BPF or trans-verter to the RX IN or RX OUT terminal. You can activate anRX ANT function for either the main band or sub band and