Yaesu FT-227RB Instruction Manual page 17

(E 7- )
ti
oc
), C
''
'o(AF OUT)
(TONE (
OUT)
0523 2 5o
(AF IN)
G-0(l3.5 V )
c5( EARTH )
—
0503
2SKI9GR/
JF1033
®66
0502
NE 567
0504
2SC372
47K
4. 7 K
( TONE SQ SWITCH)
TONE SQUELCH
(PB-1555A)
OPTION
( Sw
777
7. 4 7-
POWER SUPPLY
A 13.8 volt DC supply, is used for the audio power
amplifier,
Q116 ,
as well as the relay and lamps. The
supply voltage for the final amplifier is fed through
voltage regulator Q i (2SD235D), which is con-
trolled by the automatic final protection unit.
Voltage regulator
Q605
(RC14305) regulates the
supply voltage at 5 volts, to supply
Q308
and the
display unit.
Q313
(2SC372Y) and
D301(RD6„8EB)
regulates the supply voltage at 6 volts for the VCO
and phase comparator. The 5 volt supply for the
PLL control unit is regulated by zener diode
D3
(WZ050), and is connected directly (not via the
power switch) for memory backup purposes.
A regulated 8 volt circuit using
Q117
(RC14308)
is used for all other circuits.
When the transceiver is used in the memory mode,
D4
and
D 5
(WZ050) supply 5 volts to the receiver
and transmitter, respectively.
* * *
C 516 R 516 R 513 R 514 R 524
21 *
70Hz
t
0.15pF 39Kn 15Kn 470Kn 15Kfl
160Hz
160Hz
/ 0.1uF 33Kn 8.2Kn 270K0 8.2Kn
250Hz
TONE SQUELCH UNIT (OPTION)
The tone squelch circuit disables the audio circuit
of the receiver until a preset, subaudible tone is
received. On transmit, a subaudible tone is super-
imposed on the output audio signal. The frequency
of this tone can be set to any frequency between
70 Hz and 250 Hz.
The tone signal is generated by
Q 5 02
(NE567), and
its frequency is set by
R516 , VR 502 ,
and
C516 .
The
level of the tone signal is set by VR 504 , and the
signal is subsequently fed through buffer amplifier
Q503
(2SK19GR) to a low pass filter on unit "d"
of operational amplifier
Q 501
(MC3403). The tone
signal is then superimposed on the speech signal at
Q202.
The constants for setting the subaudible
tone frequency are shown in Table 2.
The audio output signal from the receiver dis-
criminator is fed to unit "a" of
Q501 .
Unit "a" of
Q501
acts as a high-pass filter, while unit "b" acts
as a T-notch filter. These filters remove the sub-
audible tone from the audio signal, which is -then
fed through audio amplifier
Q505
(2SC372Y) to
amplifier Q113
•
The subaudible tone then passes through a low-pass
filter at unit "c" of
Q501 ,
and is fed to
Q50 2 .
When
the tone frequency is the same as that preset for
transmission, the voltage at pin 8 of
Q502
becomes
low, causing
Q504
(2SC372Y) to turn off. In turn,
proper bias voltage is applied to
Q119 ,
allowing
normal operation.
When the proper tone signal is not present,
Q504
conducts, removing the bias from
Q119 ,
thus dis-
abling the audio circuit.
As the conventional carrier-controlled squelch is
still in operation, irrespective of the condition of
the tone squelch, the BUSY lamp will light up
when any carrier is received. This feature alerts
the operator that the channel is occupied, though
no signal may be heard.
Table 2