Technical Description

FCC ID: NS2FF905

Operational Description

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FCCID_87763

CIRCUIT DESCRIPTION Model: FF9OXCX (Southwestern Bell Freedom Phone) 1 Base a. RF Transmitter Section — RF Board Compressed audio signal is frequency modulated through the varactor diode D3. Diode D3, choke coil L2 and the external components formed the voltage controlled oscillator circuit for the transmitter part. This circuit generates the TX VCO frequency. A portion of this signal is fed back to the PLL IC‘s pinl (FIN1) for phase comparison. Once the phase of oscillation stabilized, the PLL circuit generates the error voltage necessary for the VCO to oscillate at the desired transmitter‘s RF frequency. The VCO circuit impedance is matched with the succeeding circuit through the transistor Q7 that also acts as the buffer amplifier. RF amplifier QS5 boosts the signal for transmission. This amplified RF signal is trimmed to the desired frequency band by BPF9O03 so as not to interfere with the receiver circuit. The transmitter RF signal is then propagated through the antenna. b. RF Receiver Section — RF Board The Base Unit antenna receives RF signal. Band Pass Filter BPF927 trims the signal to the desirable frequency band. Transistor Q8 is a low noise amplifier that boosts the RF signal to a specific level for mixing. PLL IC1 (TB31202) is used as a Universal Phase Lock Loop circuit. The frequency from the Voltage Controlled Oscillator (VCO) D1, L1 and Q4, is fed back to the PLL IC through pin 16 (FIN2) for phase comparison. During channel scanning or turning the unit on, once the phase of oscillation stabilized (locked), the PLL circuit generates the first local oscillator frequency for down—converting the received RF signal into the first IF frequency 10.7MHz. This process is accomplished through the IF mixer circuit Q3. Q1 is used for matching the impedance of the mixer circuit with the succeeding circuits. The resulting IF signal is kept constant by the IF Filter FL2 to 10.7MHz which is then mixed with the second local oscillator frequency 11.150MHz (derived from X1 & C47) to produced a much lower IF frequency. This lower IF frequency if further filtered by IF Filter FL4 to produce a more stable signal of 450KHz. Quadrature signal detection is accomplished internally by the Narrow—band Detector IC2 (KA3361) with the IF coil L7. The recovered audio frequency can be taken from IC2 audio output pin9. Double conversion of received signal is utilized to improve the image frequency rejection of the unit. FFI0XXX Page 1 12/02/99

c. Transmitter Audio Section — Main Board Audio Frequency signal from the telephone line is compressed through the compressor part of IC4 to minimize the transmission noise. The degree of compression depends on the external RC combinations. AGC is also utilized by IC4 to avoid shock noise caused by abrupt change of audio levels. The compressed audio is filtered and amplified for better acoustical performance. d. Receiver Audio Section — Main Board The compressed Audio Frequency signal is passed through passive RC filters for acoustic compliance. The filtered audio is then fed to the Compander IC4 for expansion thus retrieving the original Audio signal with noise filtered out. Q2 & Q9 are used as buffer circuit. Matching transformer HYBI isolates the high—voltage telephone line to the rest of the circuit. HYBI is also used as a hybrid transformer to create a two—way path for audio transmission to and reception from the telephone line. 2 Handset a. RF Transmitter Section — RF Board Refer to portion 1.a for this section. All circuit performance is exactly the same except that Band Pass Filter BPF903 be changed to BPF927 for the handset transmission. b. RF Receiver Section — RF Board Refer to portion 1.b for this section. All circuit performance is exactly the same except that Band Pass Filter BPF927 be changed to BPF903 for the handset reception. c. Transmitter Audio. Section — Main Board Audio Frequency signal from the handset or from the headset microphone is compressed through the compressor part of IC2 to minimize the transmission noise. The degree of compression depends on the external RC combinations. AGC is also utilized by IC2 to avoid shock noise caused by abrupt change of audio levels. The compressed audio is filtered and amplified for better acoustical performance. QS5 is a switching transistor that controls the power supply for the TX RF part. d. Receiver Audio Section — Main Board The compressed Audio Frequency signal is passed through passive RC filters for acoustic compliance. The filtered audio is then fed to the Compander IC2 for expansion thus retrieving the original Audio signal with noise filtered out. Q3 actas FFOOXXX ' Page 2 12/02/99

audio amplifier to sufficiently drive the handset speaker. Q1, Q6 are switching transistors that control the power supply for the RF part, the Compander part and the AF amplifier respectively. An earphone jack is provided for an optional headset unit for handsfree conversation on the handset. 3 OTHERS (Handset): a. Charging and Reset Controls Recharging the handset battery is accomplished by putting the handset on the cradle. Q200 detects this action and sends a command to the CPU for proper exchange of security code. Switching SW4 to the RING OFF mode can extend Battery life. b. Ring Detection When the handset receives the ring command from the base unit, the CPU will send buzzer signal to the ringer amplifier Q201 that drives the Buzzer. | 4 OTHERS (Base): a. Hook Switching and Dialing Hook switching and pulse dialing is accomplished by the photo—coupler IC3 which is controlled by the CPU. DTMF signal from the ladder circuit internal to the CPU is filtered and amplified by U1ID. b. Over—voltage Protection Fuse F1 and varistor Z1 act as high current and high voltage protectors for the telephone line interface. In case of presence of voltage surge across the telephone line, Z1 decreases its resistance and dumps the line voltage to a safe level. Fuse F1 opens when excessive current is present on the line thus protecting both the user and the line interface. c. Battery Charging & Code Setting Battery charging commences when transistor Q7 detects the presence of the handset on cradle. C29 and R71 form the reset circuit to command the CPU to change the security code everytime the dco supply is removed and restored. When the reset circuit is activated, the CPU will send a new security code to the handset selecting among 65536 combinations. FFI0XXX Page 3 12/02/99

d. Ring Detection Incoming ring signal is detected by the LM324 U1ID. External RC combinations set the level of signal detection. The CPU checks the frequency of the ring signal, and when valid, sends the ringing command to the speaker or to the Handset. e. Power Supplies Diode D11 ensures uniform polarity for the entire circuit. Transistor Q1 and capacitor C1 regulate the voltage to +9Vdc for the buffer amplifier circuit. 1C1 regulates the voltage to +5Vdc for the rest of the circuit. Transistor Q8 controls the power supplied to the TX part of the RF circuits. f. Squelch Detection In conjunction with the 3361 IC (IC2 of the Base RF), fixed resistor sets the level of signal detection and UIC acts as the comparator circuit whose composite output is the RSSI signal for the CPU. g. RX Data Commands from the Handset is filtered and re—constructed by the Schmitt trigger circuit UIB. The composite output is the RX Data that is input to the CPU for validation and processing. FFI0XXX | Page 4 | 12/02/99

TITLE : Model FFIOXXX {(900MHz 40—Channels) Automatic Channel Selection Mechanism AUTOMATIC CHANNEL SELECTION MECHANISM 900MHz 40—Channels Basic Cordless Telephone MODEL: FF9OXXX (SWB Freedom Phone) During the activation of Talk, the Handset receiver scans for free channel from its last linked receiver channel (about 50ms per channel). Once a free channel is found, the Handset transmits the Talk instruction to Base together with the receiver‘s free channel information for the Base to use this free channel as the Transmit channel. Likewise, the Base receiver continuously scans each channel (25ms per channel) and stores all free channels into its memory. Once the Base receiver received the instruction from its Handset, it will stop from scanning and transmits its acknowledgement data with the Base receiver free channel information. When the Handset receives this Base free channel information, it will transmit the link command to Base and both will link on the clearest channel. The Handset and Base scan and find their receiver‘s clearest channel separately. If all transmit channels of Handset and Base are occupied (all busy), Handset and Base will link on the default channel (Channel 20). BASE HANDSET BASE HANDSET CH TX RX TX RX CH TX RX TX RX 1 902. 121 926.117 926.117 902.121 21 902.722 926.717 926.717 902.722 2 902.252 926.147 926.147 902.252 22 902.752 926.747 926.747 902.752 3 902182 926.177 926.177 902.182 23 902.782 926.777 926.777 902.782 4 902.212 926.207 926.207 902.212 24 902.812 926.807 926.807 902.812 5 902.242 926.237 926.237 902.242 25 902.842 926.837 926.837 902.842 6 902.272 926.267 926.267 902.272 26 902.872 926.867 926.867 902.872 7 902.302 926.297 926.297 902.302 27 902.902 926.897 926.897 902.902 8 902.332 926.327 926.327 902.332 28 902.932 926.927 926.927 902.932 9 902.362 926.357 926.357 902.362 29 902.962 926.957 926.957 902.962 10 902.392 926.387 926.387 902.392 30 902.992 926.987 926.987 902.992 11 902.422 926.417 926.417 903.422 31 903.022 927.017 927.017 903.022 12 902.452 926.447 926.447 903.452 32 903.052 927.047 927.047 903.052 13 902.482 926.477 926.477 903.482 33 903.082 927.077 927.077 903.082 14 902512 926507 926.507 903.512 34 903.112 927107 927107 903.112 15 902.542 926.537 926.537 903.542 35 903.142 927.137 927137 903.142 16 902.572 926.567 926.567 903.572 36 903.172 927167 927167 903.172 17 902.602 926.597 926.597 903.602 37 903.202 927197 927197 903.202 18 903.632 926.627 926.627 903.632 38 903.232 927.227 927.227 903.232 19 903.662 926.657 926.657 903.662 39 903.262 927.258 927.258 903.262 20 903.692 926.687 926.687 903.692 40 903.292 927.288 927.288 903.292


Document Created: 2000-02-24 11:23:05
Document Modified: 2000-02-24 11:23:05
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