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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
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
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
A DC voltage appea$ at pin no.L3 of the IF system IC
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
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
0 to 9 (with the exception of the left hand digit which employsonly 2 segmentsb and c).
o
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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
An outline of the composition of pDb009 is given in block diagram form in Fig.
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 |
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