MT-4R and MT-4D P25 Digital and Analog Radio Systems - Daniels ...

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22 Chapter 4: P25 System Block Diagrams BASE STATION BLOCK DIAGRAM Figure 4-2 shows a block diagram of a Daniels P25 analog controlled base station system using a CI- BC-4E base controller. The incoming FM or C4FM transmission is routed through the Front End sub-module where the RF signal is fi ltered (high selectivity multiple pole, helical resonator fi lter, 5 MHz pass band VHF, 7 MHz pass band UHF) amplifi ed through a low noise amplifi er and then passed on to the RF Board which performs the conversion to the fi rst IF, crystal fi ltering of the fi rst IF, conversion to the second IF, digital fi ltering of the fi rst IF, and demodulated to two quadrature-related baseband outputs. The baseband output is converted into a digitally sampled signal and is routed to the DSP circuitry where it is automatically detected as an analog or P25 digital signal and is then routed through either the analog or P25 digital settings programmed into the receiver. Analog signal settings may include CTCSS or DCS decoding, de-emphasis and wide or narrowband selection. P25 digital settings will include NAC and/or TGID decoding. The digitally sampled signal is then converted back to baseband and then routed out of the receiver as analog audio out the subrack / motherboard to the base controller. If a P25 digital signal is sent out as baseband analog audio, the signal must fi rst be de-vocoded before it can be converted to baseband analog audio. MT-4D Base receivers may have an optional AES or DES-OFB decryptor module. The analog audio is then routed through the base controller (CI-BC-4E Base Controller) and is sent to the auxiliary audio output for connection to an external device such as a tone remote adapter. The auxiliary audio input from the external device is routed through the base controller and is sent to the transmitter. Internal audio levels between the receiver, base controller and transmitter are typically set at -8.0 dBm for 60% of maximum modulation. Independent audio level controls in the base controller allow the auxiliary input and output levels to be adjusted separately (default is 0 dBm for 60% maximum modulation). For external control, the CI-BC-4E also has optically isolated COR and PTT inputs and outputs for connecting external equipment with high voltage control signals such as E&M. The transmitter will accept the incoming analog audio, convert it to a digitally sampled signal, and then route it through the analog or P25 digital settings programmed into the transmitter. Analog signal settings may include CTCSS or DCS encoding, pre-emphasis and wide or narrowband selection. P25 digital settings will include NAC, TGID and Unit/Source ID encoding. MT-4D Base transmitters may have an optional AES or DES-OFB encryptor module. The signal is then converted back to a baseband signal and is then modulated as either an FM or C4FM transmission based on the analog or digital software settings, or the front panel switch. The modulated carrier is then amplifi ed by the RF Power Amplifi er sub-module. User Guide UG-001 Daniels MT-4R and MT-4D Radio Systems www.danelec.com
Chapter 4: P25 System Block Diagrams 23 RF IN FM ANALOG OR C4FM DIGITAL BASE OR REPEATER RECEIVER FRONT END LOCAL OSCILLATOR IF AMP & DEMOD RF BOARD A / D CONVERTER A A / D D DETECT CTCSS / DCS DECODE NAC / TGID DECODE OPTIONAL DECRYPTION D / A CONVERTER DE-VOCODER AUDIO OUTPUT (TO SYSTEM MONITOR SPEAKER) BALANCED AUDIO OUTPUT 1 KHz TONE @ 60% MAX MOD = -8.0 dBm COR AUXILIARY COR BASE CONTROLLER OPTICAL ISOLATOR AUDIO LEVEL CONTROLS AUXILIARY BALANCED OUTPUT 1 KHz TONE @ 60% MAX MOD = 0 dBm AUXILIARY BALANCED INPUT 1 KHz TONE @ 0 dBm = 60% MAX MOD AUXILIARY PTT OPTICAL ISOLATOR PTT INPUT BASE OR REPEATER TRANSMITTER RF POWER AMPLIFIER MODULATOR CTCSS / DCS ENCODE D / A CONVERTER NAC/TGID/SID ENCODE A A / D D SELECT OPTIONAL ENCRYPTION A / D CONVERTER VOCODER BALANCED AUDIO INPUT 1 KHz TONE @ -8.0 dBm = 60% MAX. MOD. RF OUT FM ANALOG OR C4FM DIGITAL Figure 4-2: P25 Base Station Block Diagram UG-001 Daniels MT-4R and MT-4D Radio Systems www.danelec.com User Guide
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