Kenwood TH-77A Service Manual page 15

IA-/7A/E
CIRCUIT DESCRIPTION
7-4 Remote Control Microphone Circuit
The remote control microphone circuit has two internal audio
amplifiers. The external speaker is directly connected to IC5 via
the AFO pin. The speaker microphone and speaker plug con-
nections are detected using the REM and MDT signals. The
ICS(CONTROL UNIT) AFO sp
MIC AMP
REM and MDT signals are made high when the speaker micro-
phone and speaker plug are not connected. The REM and MDT
signals are then output from IC6 to the internal speaker. An au-
dio signal is output to the external speaker when the MDT or
REM signal is set low.
EXTERNAL
SPEAKER
EXTERNAL
MIC
tOpF (32)
(*1) Voltage appears from the internal M5 line (5 V) via R2.
(*2) In the next case, the capacitor is not required.
Make the connection directly.
@ |n the case when a capacitor to cut DC voltage is con-
nected to the external device
@ In the case when a two-terminal condenser micro-
phone is used as the external microphone
Fig. 13 Speaker, Microphone, Remote circuit
7-5 CTCSS Operation
The CTCSS in the main band and sub-band is checked by the
CTCSS timing unit. Only the main band is checked when a
single band is used. The band carrying a BUSY signal is
checked when a dual bandis used with the main band and sub-
band CTCSS set on. The main band and sub-band are checked
every 500 ms when they carry a BUSY signal. During full-du-
CTCSS CHECK TIMING (MAIN, SUB CTCSS ON)
plex operation, the CTCSS in the main band outputs a subtone
when the TONE and CTCSS signals are on. Turns the CTCSS in
the subband cannot be checked. In that case, the squelch in
the subband is opened or closed using only the BUSY signal.
For the band in which the CTCSS cannot be checked, the "CT"
display disappears only during transmission.
i OFF | | | | (iT
(CLOSE)
ON | | | | | |
S. BUSY
OFF
ctcss MAIN
UNIT yp
— L_Y U
J
500ms
Fig. 14 CTCSS timing chart
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