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C. These two output signals are selected (by SW-B): the 1/8 frequency divided output (from terminal 8) for the
LW, MW band and SW:~SWSs bands, and the 1/80 frequency divided output (from terminal 9) for the FM band
are applied to the input terminal (terminal 2) of the counter circuit (IC902).
D. These frequencies are converted, by !C902, into the original local oscillator frequencies. Moreover,
depending upon the signal applied to the preset terminals, the necessary frequency for each band is
subtracted from the derived local oscillator frequencies and the resulting frequency is supplied to the display.
V. Signal Selector Circuitry
Figure 8 shows the signal selector circuitry for the counter.
A. For the FM band, since the band selector (S1-9) is in the ''FM"' position, the base of each transistor (Q904,
Q905 and Q906) becomes an ''L"' level, consenquently, Q904 and Q905 turn on, and Q906 turns off.
As a result, the signal from the FM band local oscillator flows as shown below, and is counted at the counter
circuitry.
FM Local osc + C902 — Q901 —» Q902 -» C908 — IC901(3) — IC901(9) + C914—» Q907 — IC902(2)
In this case instance, the local oscillator circuitry for the LW, MW and SW bands does not function (refer to
figures 3, 4 and the +B selector).
The signal (AM) from the 1/8 frequency divider is output from terminal 8 of |C901.
However, because Q905 is turned on thus shorting its collector to emitter junction, the base to emitter junction
of Q908 is also shorted, therefore, the signal current can not flow to the counter circuit.
R908
DRIVER
CIRCUIT
—>
Q904
1c901
/8
R901
COUNTER
CIRCUIT
Ic902
FM
BAND
C902
Q901
Q902
LOCAL OSC
i)
(Sh
CIRCUIT
ss
el
c303
AM BAND
LOCAL Osc].
CIRCUIT
R907
(2) INPUT
Fig. 8
B. For the LW, MW and SW:~SWs bands, Si-9 is open, the base (Q904, Q905 and Q906) become an ''H" level,
consenquently Q904 and Q905 turn off, and Q906 turns on.
As a result, transistor Q907 turns off (base to emitter junction shorted by Q906) which results in Q901 turning
off. Therefore, the signal from the AM local oscillator circuit flows as shown below, and is supplied to the
counter circuitry (IC902).
AM local osc — C903 — Q902 — C908 — 1C901(3) — 1C901(8) — C912 —. Q908 —. IC902(2)
In this case, the local oscillator circuitry for the FM band does not function.
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