Codan Radio MT-4R - Manual (Page 30)

UG-001 Daniels MT-4R and MT-4D Radio Systems
www.danelec.com
Chapter 4: P25 System Block Diagrams 22
User
Guide
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.