Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S11CIRCUIT DESCRIPTIONTable 5 BPF rangeBand Filter range SW135kHz 30~522kHz DiodeBC 522kHz~1.705MHz Diode1.8MHz 1.705~2.5MHz Relay3.5MHz 2.5~4.1MHz Relay5MHz 4.1~6.0MHz Diode7MHz 6.0~7.5MHz Relay10MHz 7.5~10.5MHz Diode14MHz 10.5~14.5MHz Relay18MHz 14.5~18.5MHz Diode21MHz 18.5~21.5MHz Relay24MHz 21.5~26.5MHz Diode28MHz 26.5~35MHz Diode35MHz 35~40MHz Diode40MHz 40~46.5MHz Diode50MHz 46.5~60MHz Diode3-2. From the preselector amplifier (Q10 and Q11)to the 1st IF frequency (8.248MHz)The output signal from the preselector amplifier (Q10 andQ11) is applied to two amplifiers, i.e., preamplifier 2 (Q20)and preamplifier 1 (Q25 and Q26) (Refer to Fig. 6). The pre-amplifier key ([P.AMP] key) is used to select preamp ON orOFF. When it is ON, preamplifier 1 is selected at 30kHz to21.5MHz received frequency, and the preamplifier 2 is se-lected at 21.5 to 60MHz received frequency.The signal from the preamplifier passes through the8.248MHz IF trap and is mixed with the MLO1 output (rangingfrom 8.278 to 51.752MHz) in the 1st mixer of the double bal-anced grounded switch type consisting of IC7 and IC8 andconverted into the 1st IF (8.248MHz).The diplexer enables the wide-band matching of the mix-er output impedance. The 1st IF signal from the diplexer isdivided into two in the branch circuit, one of which is appliedto the scope unit (X42-343 A/10) and the other is applied tothe post amplifier (Q46). The post amplifier is selected onlywhen the preamplifiers (preamplifier 1 or preamplifier 2) areON and has a gain of approximately 8 dB. The 1st IF is ap-plied to the blanking gate circuit (D26 to D29). If the noiseblanker is ON, the path to the noise blanker filter (2-poleMCF x 2: XF1) and the noise blanker circuit is active. Theblanking signal by the noise blanker drives the blanking gatecircuit, and the noise is removed. The 1st IF signal passesthrough the IF filter (roofing filter). One of 5 filters is selected,depending on the frequency and mode (Refer to Table 6). Al-though the IF filter is usually automatically chosen accordingto the DSP filter bandwidth, it can also change the IF filterchosen with the filter setting menu. An additional roofing fil-ter prepared by the user can also be set up.The 1st IF signal passing the IF filter is applied to theAGC amplifier (Q70) that uses a dual-gate FET. The AGCvoltage (MAGCV) output from the DSP is applied to the gateof the AGC amplifier (Q70). The gain varies by approximately60 dB with an AGC voltage change. The 1st IF signal is am-plified by approximately 20 dB in the IF amplifier (Q49 andQ52) and passes through the attenuator circuit (D30) usinga PIN diode. The voltage determined while in adjustmentmode is applied to D30 to compensate for the insertion lossof the IF filters (270Hz, 500Hz, 2.7kHz, 6kHz and 15kHz fil-ters).Fig. 6 From the preselector amplifier (Q10 and Q11) to the 1st IF frequency (8.248MHz)IC7, IC81st Mixer8.248MTrap8.248M 15kXF3MAGCVQ70AGC AMPQ49,Q52IF AMP8.248M 6kXF48.248M 2708.248M 2.7kXF88.248M 500XF5XF6MIFGCIF output(8.248M)D30ATTQ20PRE AMP2FromPRESEL AMPQ25, Q26PRE AMP1 8.278~51.752MHzML01Diplexer BranchSCOPEQ46POST AMP8.248M 15kXF1Noise blankerBlankingD26~D29To IF filtersFrom BlankingIF filters