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9.2 REMOTE SET
9.2.1. RF Circuit
This phone is operated in FULL DUPLEX Method that transmits the TX Signal and receives the RX
Signal by an antenna. In addition, it is operated in a MCA (Multi Channel Access) Method of 40
channels.
9.2.1.1 Antenna
This phone uses an antenna in order to send a high frequency signal.
9.2.1.2 DUPLEXER
The Duplex consists of BPF (FL101, FL201), L and C Matching devices, which play the roles of
separating the transmitting and receiving, and it plays a role of band filter as to the RF Signal of
different frequency band.
9.2.1.3 RECEIVER
(1) Low Noise Amplifier
LAN, Q101 (TR:2SC4784), DC BIAS Circuit, coil and condenser, consists of input and output impedance
circuits. In addition, it amplifies the little high radio frequency signal received from an antenna.
(2) Band-Pass Filter (FL102)
It eliminates the unnecessary signal inputted from the receiver and limits the local signal received
from an antenna.
(3) 1
st
Mixer
It is a Dual Gate FET Type Amplifier. The received high radio frequency signal and high local
oscillation frequency operate in the non-linear area after entering the FET (Q103, 3SK29) Gate and
output numbers of modulation signals and one of them is the 1
(4) MCF (Monolithic Crystal Filter)
The MCF, Band Pass Filter with narrow bandwidth of
couple (XF 101:21.7MHz), selects the IF Signal out of signals generated in the first mixing process,
and limits the other unnecessary signals.
(5) Amplify the first IF Signal.
(6) FM Detector
The FM Detector consists of FM IF IC (TA31136FN) and some surrounding devices, and it includes FM detectors
and SQUELCH Circuit in the TA31136FN 2
nd
Mixer. The local signal (21.25MHz) oscillated by the Crystal
(XT351) and Load capacitor is mixed with the first IF Signal (21.7MHz), and the 2
generated by the 2
nd
mixture of IC.
The second IF Signal is demodulated in the method of Quadratic detection by the internal FM detection circuit
after being filtered by the BPF (CF151).
The Quadratic signal produces the signal with the Quadratic Coil (L103), and SQUEL CH Circuit consisting of a
filter or noise amplifier is adversely proportioned to the input of IF signal.
9.2.1.4 Transmitting
(1) TX VCO
TX VCO generates the signals of 407.00625MHz ~ 407.4937MHz. The transmitting and data signals
are supplied to the MOD Terminal from the remote set of LOGIC B'D and these signals are
modulated by the TX VCO Terminal.
(2) DOUBLER (Q201: 2SC4784)
The signals, 407.0062MHz ~ 407.4937MHz, of TX VCO become the TX Frequency, 2
frequency, which is 814.0125MHz ~ 814.9875MHz.
(3) Power Amplification (Q202, Q203:2SC4784)
Samsung Electronics Co., Ltd
SP-C501R
st
intermediate frequency (1
st
7.5KHz and high selectivity, consists of a
nd
IF Signal (450KHz), is
nd
high radio
－38－
Service Manual
You may appropriately adjust the TX Signal with two amplifiers of Q202 and Q203.
(4) Band Pass Filter (FL201)
The Band Pass Filter reduces unnecessary signals generated from the TX AMP and TX VCO to
prevent the emission through an antenna and impact to the other components.
9.2.2 LOGIC Circuit
LOGIC B'D of remote set controls the RF and TX & RX Audio signals, modulates, and demodulates
the MSK Data in order to communicate with the base set, and also, it controls the buttons and
microphone.
9.2.2.1 Buttons of Remote Set
Buttons of remote set consist of 4*6 Matrix and recognize the corresponding key by detecting the H/L
Value according to DIODE (D3, D4) direction in the column when any key is pressed with the pulse
oscillated in the row.
When MPU detects the key, the data corresponding to the pressed key is sent to the Base through
the RF Module after the data is modulated through the AK2361 (U2).
9.2.2.2 EEPROM
The EEPROM memorizes the initial data and phone number.
9.2.2.3 MSK Modem Circuit
For the data communication between remote and base sets, 2400bps MSK Method is adopted and
used. The modulation and demodulation of this data are performed in the Modem IC AK2361E. The
clock used at this time is 3.58MHz. When CPU designates the TDE port as the Low, AK2361E sends
2.4KHz to the TCLK port and AK2361E allows the clock to read the Ring Edge. CPU sends a Low
IF) signal.
signal to TDATA Port at this time. The signals, 2.4KHz and 1.2KHz MSK, are produced in the
AK2361E, and the speed is 2400bps. The CPU analyzes the MSK Data sent to the MOD of RF B'D
through an internal Splatter filter and RX Signal of 2400bps inputted from the DEMOD Terminal.
9.2.2.4 C/S Circuit
When carrier is judged as high by the DC Level detection in the IF IC (1A31136FN), the channel is
free, and when it is judged as high, the channel is busy, so it is a reference to judge if the channel is
used.
9.2.2.5 Power Supply Circuit
The power source used for the remote set is a rechargeable battery (3.6V DC).
9.2.2.6 TX and RX Audio Circuits
The audio signal is connected from the condenser microphone to the Compressor, and the
Compressor circuit has the characteristic of S/N: 2:1 and is used to compensate the Expander.
If the difference between input and reference level is 10dBm, the difference between reference and
output levels is 5dBm. This signal passes through the internal limiter circuit to limit the level of above
-8dBm. The limiter output whose element of above 3KHz is eliminated in the Splatter Filter (LPF) is
inputted in the MOD of RF B'D. The RX Audio signal outputted from the DEMOD of RF B'D passes
through the AMP2 of AK2361E IC. This signal passes through the Expander with the reference
voltage of -10dBm.
The Expander has the characteristic of 1:2 and compensates the signal compressed by the
Compressor.
The signal passing through the RX AFSW is transmitted to the SPK Unit through the buffers, AMP3
and AMP4, of AK2361E at this time.
Samsung Electronics Co., Ltd
SP-C501R
－39－
Service Manual
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