Codan Radio MT-4R - Manual (Page 28)

UG-001 Daniels MT-4R and MT-4D Radio Systems
www.danelec.com
Chapter 4: P25 System Block Diagrams 20
User
Guide
REPEATER BLOCK DIAGRAM
Figure 4-1 shows a block diagram of a Daniels P25 mixed mode repeater system using a CI-RC-4L or
CI-RC-4M repeater 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 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 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 may include CTCSS or DCS encoding,
pre-emphasis and wide or narrowband selection. P25 digital settings will 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.