Kenwood TS-820 Operating Manual

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,__.,..·•""'••~•""'"'t\ V4-t\•"""t''.l\.-..."""'"'"""'•n.,.. •~•• .. ••"""'t~.~•,..••~""..,"""'"-••e.--t•"' '4\"""••• ·••~• "'"" "'ur\lt- •UOW"'tl• .. •••-4 ••.....•111-tnn• "'••.,..,..,...,n,.~n•·«• l t ... ..,.• .. wM-t~~ .,.... • n•_..n •.. •M•-"41n..,W IIt.a ..~t SECTION 5. CIRCUIT DESCRIPTION It,..ti -..,,.II •Ullb•t iiii i• .. MI• • trlfi ~ Uifl .,. 11"1'•04tllf •IUNI •tiMit•IIIIU•tiiU....IIIt • I•Mt•lriH I•Ifllll "'lfllt•1111P •I tf . ... ll llt.. IUIIt •llttff•l•llo..t LtMl•ll11\1 "4 1flti •J1 Mtt•l lf • ._t1111..1M iti ~Mitl • lnll' ' 'tltlhJfiiU •III II ••..MI••1111tlt •111ti .. II HI I ~ ·II1•11MN•IMM !Ioottft .. ,.M IIi5.1 BLO CK DIAGRAMGENERALThe block diagrarn of TS -820 is shown on page 24.The tran scei ~e r is composed of the s ing le superheterodynereceiver and the si ngle co nversion type transmitte r w ith a fil-ter type SSB ger1erator. It uses 8 ,830 kHz IF and its focaloscillat or is equipped with a PLL (phase locked loop) circuitcontrolled by VFO. Both the receiv er and transmitter u sebalanced type m ixer circuits with dual gate MOS FET's, thu sminimrzing spurious dur ing transmission and preventing theeffects of st r ong srgn a ls and sup nous signals during recep -tion.Taking full ad~antage of PLL system. the tr ansceiv er offer sIF SHIFT fu ncti on (electronic system pass band tuning) andpermit one SS B fil ter to pro ~ ide the same effect obtain ed byUS B and LSB filters. The transceiver also includes a numberof latest accessorY circuits such as th e RF speech pro cessor.th e dig ital disp lay circuit (option), tra nsmit moni to r c ircui t .etc.TRANSMITTER SECTIONThe microphone signal is fed to th e IF unit. amplified by themicrophone amplifier an d is then fed to t he ring modu l ato rcomposed of 4 diod es. Th e DSB output from the modulatorpasses t hrough buffer amp lifier and the crystal filter . TheSSB signal t hus obt ained is fu rt her amplified and fed to th etransmit m ixer of the RF un it .The transm it mixe r is a do uble balanced type m ix er with 2MOS FET s. Th e local oscillat or is VCO type (vo ltage control -led oscillat or) whose out put is con trolled bY t he PLL circui tto minimize spurious du r ing transmission. The SSB signalconverted into the wanted transmit freque ncy is amp lif ied bythe tran sm it driver tube ( 12 BY7 A) before being fed to thetw o S200 1A power ampl ifier tubes of the fi nal stage.They operate in class AB 1 because of l ow distortion ampli fi -c at ion to SSB signal.The output signal is transmrtted through a pi- netwo rk to theantenna.RF NFB is applied from th e ou tput of final stage to the dr iv erstage to fu rther re du ce th e cross mod ulation disto rti on .RECEIVER SECTIONThe antenna signal passes th rough th e RF ATI swit ch.wh ere it is a ttenuated by about 20 dB as necessary. and isthen amp lified by the RF unit.The amp lified signal i s f ed to the b uffer amplifi er and mixedwit h VCO ou tput in th e balanced m i xe r with 2 MOS FET s toproduce 8 ,83 0 k Hz IF signal,--------- ·---Th is signal is fed to ths IF uni t . passes thro ug h the norseblanker circu it and the crys ta l filter. and is finally amp lifiedby the 3-stage IF am plifier. so that it is converted in to AFsignal by the ring detec to r.The AF signal rs applied ro the AF-AVR unit wher e it is am-plified to the level to drive the speaker The frequency ch a-racteristic of the AF amplifier is auto mat ically chan ged tosuit CW or SSB operatio n by means o f the MODE swi tch .25