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CIRCUIT DESCRIPTION
30
6. Antenna (ANT) Switching Circuit
The ANT switch sub-unit provides the function of the
Transmit-Receive
(TX-RX) antenna switching and the
Internal-External (INT/EXT) antenna switching as shown
in the figure 7. The TX-RX antenna switching is per-
formed by D1 (MI808), D2 (HSK277} and L2. In the
receive mode, D1 and D2 are turned off, causing an in-
coming signal from the ANT to be routed to the RX front
end through L2. D1 and D2 are turned on during the
transmit mode, and L2 is shunted to GND through D2.
L2 is electronically equivalent to a 1/4 wave length which
isolates the RX front end from the transmitter. The TX
signal is, therefore, supplied to the ANT. The INT/EXT
antenna switching is done by D3 (MI808), D4 (MI808)
and D5 (HSK277). When the INT antenna is in use, D3,
D4 and D5 are turned off, causing the RF signal goes
through L3 to the INT ANT. If the EXT ANT is connect-
ed, D3, D4 and D5 are turned on. In this condition, the
EXT ANT is connected through D3 and the INT ANT cir-
cuit is isolated since L3 and C6 form a parallel resonant
circuit through D4 and DS.
3.CONTROL
UNIT
The Control Unit has the following functions that are
mostly processed in the Main MPU, IC1 (H37450M4-
235FP) (Figure 8).
Sending the RX/TX PLL DATA according to the stored
Channel (CH)/Group (GR) information
Power save control
Various RX audio circuit switching
INT/EXT switching of the SP/MIC
QT/DOT Encode/Decode
Data exchange between the signaling unit and MPU
-
Radio programming function (with KDM-4 and KCT-1
or KCT-2)
Control functions such as, SCAN
BUSY LOCK OUT,
PTT LOCK OUT, etc.
A voltage corresponding to the frequency is supplied
to the varactor diode in the receiver.
SUB
UNIT
(ANT
SW)
9
fete)
=r '3 r=
TES
=
By?
fe) @
OH
H
° Age
oO
nN
B
29
LO
Nor
[OG
a
Te
So 8a
TX OUT
RX IN
H
APC
UNIT
Fig.
7 ANT switching
TOP FPC
EEPROM
EEPROM
CH
GROUP TX BUSY,
Sw
Sw
LEDLED
f
ob
Fey fey
|
// lead
|
OT TG
CH
GR
Swsw
SW
Sw
| —
j
— |
PTT
Sw
———+]
> PLL DATA
MONI
SW
-~———-]
$<»
KEY
UL
———»
» PS
MAIN
p~
COM
1c}
i»
PA ON
Rx AF CONTROL
f—»
MUTE
-———
MIC MUTE
+H»
SPON
INT/EXT
SW
r——
IMS
{INT MIC ON)
Swi
TUNE VOLTAGE
t-——_
Sw2
U
KEY
p- COM
SIGNALING
UNIT
Fig. 8 Control unit
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