Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S24CIRCUIT DESCRIPTIONSSB/FMat Slope Tune [Hz]SSB/PSK*2at VBT [Hz] AM [Hz] CW [Hz] FSK [Hz] FSKtoneFSKshiftCenterfrequencyLOW CUT HI CUT WIDTH SHIFT IFBW LOW CUT HI CUT IFBW WIDTH IFBW SHIFT(L) SHIFT(H) WIDTH IFBW1275Hz170Hz 1360HzzH5731zH0020050520008-00505k6k5.2000500010500010zH52400500305057-00508k6k0.3001005001108002105 1487.5Hz100 1400 100 1200 500 200 4.0k 15k 100 500 -700 100 400 500 850Hz 1700Hz200 1600 150 1300 500 300 5.0k 15k 150 500 -650 150 500 5002125Hz170Hz 2210Hz300 1800 200 1400 500 200 500 -600 200 1000 2.7k 200Hz 2225Hz400 2000 250 1500 500 250 500 -550 250 1500 2.7k 425Hz 2337.5Hz500 2200 300 1600 500 300 500 -500 300 850Hz 2550Hz600 2400 400 1700 500 400 500 -450 350700 2600 500*3 1800 500 500*1 500 -400 400800 2800 600 1900 2.7k 600 2.7k -350 450900 3000 1000 2000 2.7k 1000 2.7k -300 5001000 3400 1500 2100 2.7k 1500 2.7k -250 5504000 2000 2210 2.7k 2000 2.7k -200 6005000 2200 2.7k 2500 2.7k -150 6502400 2.7k -100 7002600*4 2.7k -50 7502800 6k 8003000 6k Initial value*1 In CW mode, the DSP filter width is displayed as 500Hz; however, the DSP filter width is actually 600Hz.*2 LOW CUT: Low-cut frequency; HI CUT: High-cut frequency; WIDTH: Bandwidth; SHIFT: Center frequency (SSB);SHIFT (L/H): Amount of change from the center frequency (CW); IFBW: Bandwidth with the roofing filter set to AUTO (default value).*3 The initial value of PSK mode is 500 Hz.*4 The initial value of SSB (WIDTH/SHIFT) mode is 2600 Hz.Table 16 RX IF filter settings4-8. Noise Blanker (NB) CircuitNoise Detector CircuitThe Noise detector circuit generates the blanking signal,depending on the short cycle pulse noise.The 10.695MHz or 11.374MHz IF signal passes throughthe buffer (Q881) in the TX-RX unit (X57-827 A/2), and issent from CN900 to the NB unit (X57-827 B/2) CN950 (SN-BIF) through a coaxial cable.The signal input into the NB unit is amplified by the 4stage amplifier (Q882, Q883/Q884, Q886/Q887 and Q890),passes through the buffer (Q893), and is then noise de-tected by D881. This noise-detected voltage switches Q892,turns Q894 ON, attenuates the IF signal in the blanking cir-cuit (D481 to D484) depending on the noise, and removesthe pulse noise.When a long cycle signal is applied, the AGC works andthe gains of the NB amplifier 2 (Q883/Q884), NB amplifier 3(Q886/Q887), and NB amplifier 4 (Q890) fall, which resultsin a low detecting voltage, and Q894 is not turned ON. Thus,the IF signal is not attenuated. The AGC time constant islong and as a result, the AGC does not work for short pulsesto drop the detecting voltage. Therefore, Q894 is turned ONand the noise blanker operates.When the NB function is turned ON, the threshold vari-able direct current “SNBL” is added to the Q892 emitter fromthe D/A converter (IC55). By changing the emitter’s voltage,the NB effect can be adjusted. Also, when the IF signal is10.695MHz, Q885, Q888 and Q891 become ON and the NBamplifier 2, NB amplifier 3, and NB amplifier 4’s tuning pointschange.Fig. 24 Noise detector circuitQ881BufferIF input(10.695M/11.374M)Q882NB AMP1Q883/Q884NB AMP2Q886/Q887NB AMP3Q890NB AMP4Q893BufferAGCQ889NB AGC AMPD881DetectionSNBL(Sub noise blankerthreshold level)Q892SwitchingQ894SwitchingSBLNK signal(Sub NB blank control)SIBKTX-RX unit (X57-827 A/2) NB unit (X57-827 B/2)