Codan Radio MT-4E Analog and P25 Digital - User Guide - Manual (Page 28)

USER GUIDE | MT-4E ANALOG & P25 DIGITAL RADIO SYSTEMS
Chapter 4: MT-4E Radio System Block Diagrams Page 20
REPEATER BLOCK DIAGRAM
Figure 4-1 shows a block diagram of an MT-4E mixed mode repeater system using a CI-RC-4L or CI-
RC-4M-G2 repeater controller.
The incoming FM or C4FM transmission is routed through the RF Preselector where the RF signal:
• is fi ltered with a high selectivity multiple pole, helical resonator or ceramic fi lter
• is amplifi ed through a low noise amplifi er
• is filtered again by a low pass, high pass or band pass filter
• is mixed, with a local oscillator supplied by the synthesizer
• produces an IF frequency of 21.4 MHz (136 - 520 MHz) or 73.35 MHz (768 - 960 MHz) that is output
to the Receiver Mainboard.
The Receiver Mainboard processes the low level 21.4 MHz or 73.35 MHz IF signal from the RF
Preselector through selective crystal fi ltering and IF amplifi cation. The signal is then passed through the
IQ Demodulator and Digitizing Stage for demodulation to two quadrature-related baseband outputs.
These outputs are represented in a digital stream which is passed to the UDB Board, where DSP
techniques are used to further process the incoming sampled signal to detect and extract P25 digital
voice signals and analog voice signals and is then routed through either the analog or P25 digital
settings programmed into the receiver.
Analog signal settings include:
• CTCSS or DCS decoding
• de-emphasis or fl at audio selection
• wide or narrowband selection
P25 digital settings include NAC and/or TGID decoding.
The digitally sampled analog or P25 digital signal is then split and routed out of the receiver as both
LVDS serial data out the front panel and analog audio out the subrack / motherboard. If a P25 digital
signal is sent out as analog audio, the signal must fi rst be de-vocoded before it can be converted to
analog audio. An analog or digital COR signal is also routed out the front panel.
The analog and digital COR signals and LVDS serial data are then routed through the repeater controller
(CI-RC-4L Repeater Controller or CI-RC-4M-G2 Multiple Link Controller) and are sent to the transmitter
as analog and digital PTT signals and LVDS serial data.
The transmitter will accept the incoming LVDS serial data and route it through the analog or P25 digital
settings programmed into the transmitter. Analog signal settings include:
• CTCSS or DCS encoding
• pre-emphasis or fl at audio selection
• wide or narrowband selection
P25 digital settings include NAC encoding (unless the receiver is set to a NAC of $F7F to pass the NAC
through the repeater).
The digitally sampled analog or P25 digital 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 PTT input. The
modulated carrier is then amplifi ed by the RF Power Amplifi er sub-module.
The analog audio input to the transmitter is not used in a repeater confi guration.