Pioneer SX-3800 manual Sx-gaoo

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stage(C) is reduced, and the reactanceof the in- ductance stage (L) increased, resulting in AM detection by D2 which leavesthe positiveportion of tlie IF signal.If the input frequencydecreases,L stage reactanceis decreasedand C stagereactance increased,resulting in AiVldetection by D1 which leavesthe negativeportion of the IF signal.The L stageand C stagereactancesincreaseas the deglee of detuning in the respective directions is in- creased,resulting in a subsequentincreasein the detector output. By thus attaining S-curvecharac- teristics,FM detection becomespossible.Sincethe IF signal is an FIvI signal frequency deviation due to modulation will be symmetricalabout a central axis, And if the central frequency is equal to the resonancefrequency,the detector output DC level will be zero. If, however,there is any displacement in the central frequency, frequency deviation in respect to the detector will becomeasymmetrical, resulting in the generationof a DC voltage.This DC voltageis passedthrough LPF1 (IF filter) and LPF2 (AC filter) to form a correction voltage which is applied to the variablecapacitancediode in tlre iocal oscillator, thereby correcting the oscillator frequency to obtain a constant tF (i.e. a constanttuned frequency).

Since the central frequency of the crystal detec- tor is regulated by the crystal resonator,tuned fre- quenciesof extremely high stability are obtained.

r Limiting the Locking Range

If lhe quartz-lock range is too wide, it will overiap with strong adjacent broadcastingfrequen- cies and result in considerabletuning difficulties.

ADC amplifier is therelore used as a limiter (limiter action by NFB circuit zenerdiodes)which restricts the voltage applied to the variable capaci- tancediode,therebylimiting the quartz-lockrange.

A DC voltage appea$ at pin no.L3 of the IF system IC (PA3007-A) when the antenna input level drops below 5pV, or when the tuned fre- quency has been detuned by more than r100kHz.

This DC voltage (FM muting signal)is applied to the gate of Q2 (fET) via a Schmitt circuit, result- ing in the FET being turned on, and the quartz- Iock circuit beingturned off.

sx-gaoo

4 . 2 AM TUNER

The AM tuner section consists of a 2-ganged tuning capacitor plus an IC (HA119Z) which con- tains a l-stage RF amplifier, converter, 2-stageIF amplifier,detector,and AGC circuit.

The AM STEREO OUT terminal on the rear panel is for connecting to an AM stereo broadcast decoder adaptor. The signal appearing at this ter- minal is the converter output passed via a buffer (emitterf ollower) stage.

4,3 DISPLAYCIRCUIT FrequencyDisplay

Frequencies received by the SX-9800 are dis- played in digital form by fluorescent indicator tube (FL tube). Each digit employs up to ? segments (a - e) (see Fig. 4-3) to display all numeralsfrom

0 to 9 (with the exception of the left hand digit which employsonly 2 segmentsb and c).

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Fig.4-3 7-segmentdigitdisplay

The signalsourceduring both AM and FM recep- tion is the local oscillator. The signal is passedvia a buffer amplifier (FET) to the prescalar IC (M54451P) where it is subjectedto frequency divi- sion (1/8 for AM and L/80 for FM) before being rFRlied to the frequency counter IC (pDb0Og). This IC is responsiblefor the dynamic drive of the

?-segmentS-digit display (each digit being turned on accordingto time-sharedsequentialscanning).

An outline of the composition of pDb009 is given in block diagram form in Fig. 4-b. With the FL tube a - g segments(anode) for each digit con- nected in parallel, the D1 - Db time division pulse signals (see Fig. 4-6) apptied to each grid (inde- pendent grid for each digit) result in the digik being lit up in successionfrom the left hand side. Each digit is lit up for lms during each bms inter-

rc (M5445rP)

AM LOCAL osc . sr6NAL

FM LOCAL

OSC.SIGNAL

F M " a M s E L g c r r o N	F L T U B E	a
SI G N A L

Fig.4-4 Frequencydisplayblockdiagram

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