Yaesu FT-8800R Technical Supplement

Also see for FT-8800E: Brochure & specs

Contents

8Meanwhile, a portion of the output of 11.7 MHz crystalX1003 is multiplied fourfold by Q1043 (2SC4400) to pro-vide the 46.8 MHz second local signal, then applied to theIF IC Q1047. Within the IF IC Q1047, the 46.8 MHz secondlocal signal is mixed with the 47.25 MHz “Sub” band firstlocal signal to produce the 450 kHz “Sub” band second IF.The 450 kHz “Sub” band second IF is delivered to theceramic filter CF1003 (CFWM450E) which strips away allbut the desired signal, then passed through the IF ampli-fier within Q1047 to the ceramic discriminator CD1002(CDBM450C24) which removes any amplitude variationsin the 450 kHz IF signal before detection of speech.The demodulated “Sub” band audio is passed through thede-emphasis network, audio switch D1048 (DAN222),low-pass filter network (consisting of Q1053 (NJM2902V)and associated circuitry) and the high-pass filter network(consisting of Q1054 (NJM2904V) and associated circuit-ry). The filtered audio signal is passed through the audiovolume control IC Q1063 (M511312FP), which adjusts theaudio sensitivity to compensate for audio level variations,then is delivered to the audio switch Q1066 and Q1067(both TC4W66FU).When the internal speaker is selected, the audio signal isamplified by Q1069 (TDA7233D) then applied to the in-ternal loudspeaker. When the external speaker is select-ed, the audio signal is amplified by Q1068 (LA4425A),then it passes through the EXT SP jack to the external loud-speaker.Squelch Control“Main” BandWhen no carrier is being received on the “Main” band,noise at the output of the detector stage in Q1044 is am-plified and band-pass filtered by the noise amp section ofQ1044. The resulting DC voltage is delivered to pin 5 ofmain CPU Q1104 (M38268MCL), which compares thesquelch threshold level to that which set by the front pan-el SQL knob.While no carrier is being received on the “Main” band,pin 2 of Q1105 remain “low,” to disable the audio outputfrom the speaker.“Sub” BandWhen no carrier is being received on the “Sub” band, noiseat the output of the detector stage in Q1047 is amplifiedand band-pass filtered by the noise amp section of Q1047.The resulting DC voltage is delivered to pin 2 of mainCPU Q1104, which compares the squelch threshold levelto that which set by the front panel SQL knob.While no carrier is being received on the “Right” band,pin 15 of Q1105 remain “low,” to disable the audio out-put from the speaker.Transmitter Signal PathAF SignalThe speech signal from the microphone is passed throughthe MIC jack J3003 to the AF amplifier Q3001 (NJM2904V)on the PANEL-SUB UNT. The amplified speech signal ispassed through the panel separation jacks J3001 and J1005to the MAIN Unit. On the MAIN UNIT, the speech signalis delivered to the limiting amplifier Q1074 (NJM2902V) toprevent over-modulation, then is delivered to a low-passfilter network consisting of Q1074 and associated circuitry.430 MHz SignalThe adjusted speech signal from Q1074 is passed throughtransistor switch Q1114, Q1115 (both DTC144EE) to var-actor diodes D1079 (HVC375B) and D1080 (HVC350B),which frequency modulate the transmitting VCO, madeup of UHF-VCO/B Q1116 (2SC5006) and D1081(HSC277).The modulated transmit signal is passed through bufferamplifiers Q1117, Q1118 and Q1119 (all 2SC5006) anddiode switches D1099, D1101 (both HSC277) to the pre-drive amplifier Q1132 (2SK2596).The amplified transmit signal from Q1132 is passedthrough diode switch D1106 (HSC277) and the driver am-plifier Q1134 (RD07MVS1) to the diode switch D1107(HSC277), then finally amplified by power amplifierQ1135 (RD70HVF1), providing up to 35 Watts of poweroutput. These three stages of the power amplifier’s gainare controlled by the APC circuit.The 35-Watt RF signal is passed through a high-pass fil-ter network to the antenna switch D1118, D1119, andD1120 (all UM9957F), then passed through a low-passfilter network and another high-pass filter network to theANT jack.144 MHz SignalThe adjusted speech signal from Q1074 is passed throughthe transistor switch Q1114, Q1115 (both DTC144EE) tovaractor diodes D1082 and D1085 (both HVC365), whichfrequency modulate the transmitting VCO, made up ofVHF-VCO/B Q1120 (2SC5374) and D1083 (HVC131).The modulated transmit signal is passed through bufferamplifiers Q1121 and Q1122 (both 2SC5374) and diodeswitches D1089 and D1102 (both HSC277) to the pre-driveamplifier Q1132 (2SK2596).The amplified transmit signal from Q1132 is passedthrough the diode switch D1105, D1106 (both HSC277)and the driver amplifier Q1134 (RD07MVS1) to diodeswitch D1108 (RLS135), then finally amplified by poweramplifier Q1135 (RD70HVF1) up to 50 Watts of poweroutput. These three stages of the power amplifier’s gainare controlled by the APC circuit.Circuit Description