Codan-radio MT-4E Analog and P25 Digital - User Guide Manual de usuario descargar pdf (Pagina 28)

USER GUIDE | MT-4E ANALOG & P25 DIGITAL RADIO SYSTEMS

Chapter 4: MT-4E Radio System Block DiagramsPage 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.

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Codan-radio MT-4E Analog and P25 Digital - User Guide Manual de usuario Pagina 28