Codan Radio MT-3 - Manual (Page 32)

USER GUIDE | MT-3 ANALOG RADIO SYSTEMS
Chapter 4: Analog System Block Diagrams Page 24
PAGING TRANSMITTER BLOCK DIAGRAM
Figure 4-3 shows a block diagram of a Codan digital or analog paging transmitter using a CI-PM-3
Paging Modulator Card.
The paging encoder can be connected to the CI-PM-3 through auxiliary connections on the subrack /
motherboard or through a front panel DB-15 located on the front panel of the paging modulator card.
The analog / digital select control line of the paging encoder is fed to the transmitter and is used to
control the signal path in the audio processor.
Analog audio is fed directly through the paging card to the balanced audio input of the transmitter.
The incoming paging data from the paging encoder is connected to the appropriate 2 or 4 level input.
These signals are fed to control circuits that will turn on or off the appropriate pre-set control voltages,
which are then routed to the modulation input of a high stability reference oscillator (OCXO). The
modulated 10 MHz signal is fed to the reference in put of the transmitter’s synthesizer. A component
of the digital page is also sent to the modulation input of the transmitter synthesizer through the direct
modulation input of the transmitter’s audio processor.
If the system requires a great amount of frequency stability, as required in simulcast transmissions, an
external high stability reference can be connected to the external reference input of the paging card.
The reference signal in combination with the paging cards phase lock loop (PLL) circuit will condition
the OCXO to +/-0.002ppm.