Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S25CIRCUIT DESCRIPTION■ Blanking CircuitThe blanking circuit attenuates the IF signal by the signaldetected in the noise detection circuit and removes the pulsenoise.The SBLNK is set to “H”, Q483 is turned ON, and Q482is turned OFF when pulse noise is detected in the noiseblanker. Diodes (D481 to D484) are then turned OFF andthe IF signal is attenuated.Fig. 25 Blanking circuit5. Transmission Circuit5-1. From the Transmission Signal (TIF) to theDrive outputThe transmission signal (TIF) is divided by the analogswitcher (IC686) in the DSP unit (X53-453) in accordancewith whether it’s in FM mode or a mode other than FM.In FM mode, the transmission signal is switched by theanalog switcher (IC686), sent to the PLL (MAIN LO) unit(X50-322), and the frequency is modulated in audio signalsinto the 1st local oscillator (TLO1) signal. In modes otherthan FM, the transmission signal is switched by the analogswitcher (IC686), sent to the TX-RX unit (X57-827 A/2) andthen input into the balanced mixer (IC701). The 24kHz TIFsignal and 3rd local oscillator signal (SLO3) are input intothis balanced mixer to generate the 10.695MHz IF signal.The 10.695MHz transmission IF signal passes the IF filter(XF482) with a bandwidth of 6kHz through the buffer (Q702),and is amplified by the IF amplifier (Q703). The pin diodes(D703 and D705) operate the variable attenuator by the cur-rent control, and change the transmission IF signal gain. Thevariable gain provides the TGC function which controls eachband’s transmission gain.The 10.695MHz transmission IF signal is converted to73.095MHz by the mixer (D405 and D406). Signal attenu-ation is made variable by the current that passes throughthe pin diode (D707), and thus the level of the 73.095MHztransmission IF signal varies. The level control corrects thetransmission signal gain (PGC function) at the time of powercontrol. By varying the level of the transmission signal, cor-rection of the gain at the time of power control can be per-formed.The transmission signal passing through the MCF (XF401)with a bandwidth of 15kHz is converted to the target trans-mission frequency in the final transmission mixer (IC702).The MCF (XF401) helps reduce proximate spurious com-ponents. The 73.095MHz IF signal is applied to the 1st gateof the transmission IF amplifier (Q706) for ALC control, andthe ALC voltage is in the 2nd gate control to make gain ad-justments. The signal from the final transmit mixer passesthrough the receive BPF, and is amplifi ed to the power need-ed to drive the fi nal stage in the drive amplifi er (Q707).+8VBlanking ON : 4VBlanking OFF : 1.6VD481D482D483D484IF in IF outL490 L491SBLNKH : Blanking ONL : Blanking OFFBlanking ON : 8VBlanking OFF : 0VQ482, 483Fig. 26 From the transmission signal (TIF) to the drive outputXF482Q703XF401DriveoutDACALCTLO1SLO2IC686TIFSLO3IC70110.695MHzDSP unit (X53-453) TX-RX unit (X57-827 A/2)FMD703,705 D405,40673.095MHzIC702 Q706Q707 D707FM