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If 20/30dB is 'LOW', you may decide if you attempt to use your base set by analyzing the data input
pin (53PIN) in the receiving section for a certain time. When you decide to use your base set,
perform the command of the base set by analyzing the RX Data, and if another person is using the
channel, you may change to another channel. You may check if your base set is usable through the
repeated change of channels (hereinafter referred to as a "Channel Scan").
When you press the Talk button, attempting to call, you may enter a channel that is not being used
and transmit the data required for the TX Data Pin of MICOM.
9.1.1.1 Receiving
The signal inputted through an antenna is provided to the RX AMP (Q101, Q102) via a SAW Filter
(FL101). The RF AMP compensates the level of signal, received from an antenna, reduced in the
process of passing the Filter. The received signal passed through the RX AMP is entered to the
Q100 of 1st local oscillating circuit and mixed and then it is entered to the IC151 (FM Detector IC)
after being resonated at 21.4MHz and amplified to Q104 through the X-TAL Filter (XF101, XF102).
It is demodulated through the super heterodyne process by being combined with the QUAD Coil (L-
103) and outputting the 455KHz after passing the external filter (CF151) and being mixed at IC151
internal 2
nd
Mixer.
The demodulated signal is supplied to the Speech IC by compensating the signal controlled by the
Compressor in the transmitting section through the AK2361 Internal OP-AMP and DE-EMPHASIS
and EXPANDOR for SNR compensation.
Even when any call is made, MICOM keeps checking the 30dB Pin, and if the value is less than
regulated level (out of service area), communication path is closed after certain time elapses (after 30
seconds' alarm). Also, MICOM detects and analyzes the data such as end of call and change of
channel by monitoring the RX Data in the service area.
9.1.1.2 Transmitting
Once a call is connected, an audio signal is transmitted to a Compressor through the OP-AMP in
AK2361. An audio signal and noise level pass through the PRE-EMPHASIS and LIMITER for the
prevention of over demodulation after being appropriately compensated. The signal outputted at
AK2361 through the SCF (Switched Capacitor Filter) for the elimination of high frequency element of
limited wave form demodulates the synthesized carrier by means of frequency synthesizer and VCO
through the damper, and the output is emitted at the antenna after being classified into
receiving/transmitting through the Duplexer and being amplified in power through the multiplier
(Q201) and two TR AMP (Q202, 203).
The data demodulated by the MSK Demodulator in AK2361 is outputted after being filtered, and
thereafter the path is same as the Audio Output Path.
9.1.2 LOGIC Section
9.1.2.1 MSK modulation and demodulation circuits
For the data communication between remote and base sets, 2400bps MSK Method is adopted and
used. The modulation and demodulation of this MSK are performed in the Modem IC AK2361.
For the MPU, if TDE Pin is 'LOW', AK2361 sends CLK of 2.4KHz to TCLK Pin, and the MPU on the
increasing Edge sends the data to the TDATA Pin. It is modulated to 0: 2.4KHz at AK2361 and 1:
1.2KHz at the MSK Modulator respectively and it's speed is 2400bps.
The MSK signal is sent to both the filter and buffer in AK2361 and it is outputted and then modulated
to FM, after being reduced by the damper and being inputted to the VCO of Module.
For the demodulation, when the signal received through the RF Module is inputted to the AK2361, it
is outputted to the MPU through the MSK Demodulator, and the MPU performs the corresponding
command by analyzing the inputted "I and O" signals.
Samsung Electronics Co., Ltd
SP-C501R
－36－
Service Manual
9.1.2.2 TEL-LINE Circuit
It consists of Speech IC (TEA1062T) and its surrounding circuits.
The RMT transmitting signal is supplied to the Speech IC (U500) 7Pin and transmitted to the TEL-
LINE through the internal AMP and Pin No. 10 after being amplified in the AMP. Upon receiving, the
signal is supplied to Speech IC (U500) Pin No. 1 from the TEL-LINE and transmitted to the RMT
through the internal AMP and Pin No. 10. In addition, the TEL-LINE Communication path is
controlled by the LOOP OUT and DP Port of MICOM.
9.1.2.3 BELL Detecting Circuit
BELL Signal is detected by the PC201 and transmitted to the PIN No. 30 of the MPU and sends the
BELL Signal to RMT through the RF in MICOM.
9.1.2.4 DTMF Output Circuit
The DTMF of this device is produced at the MPU, and is transmitted to the TEL-LINE. The MPU
outputs the DTMF Frequency through the PIN No. 61 by dividing the oscillation frequency of
oscillation device X3 and sends the DTMF Frequency to the TEL-LINE through the SPEECH
NETWORK IC. When the DTMF is sent to the TEL-LINE, it must be separated from the AUDIO
SIGNAL, so the MPU output the HIGH Signal to the SPEECH NETWORK IC PIN No. 12 using the
PIN No. 31 and gets only the DTMF Signal sent to the TEL-LINE.
Samsung Electronics Co., Ltd
SP-C501R
－37－
Service Manual
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