Codan Radio MT-3 - Manual (Page 10)

USER GUIDE | MT-3 ANALOG RADIO SYSTEMS
Chapter 1: Introduction Page 2
MT-4
The MT-4 series of radio modules entered production during 2001. This radio series is the P25
compliant digital narrowband radio system, capable of analog (wideband and narrowband) or P25
digital operation. For more information on the MT-4 series of radios, see the MT-4R and MT-4D P25
Digital and Analog Radio Systems User Guide or Codan MT-4E Analog and P25 Digital Radio Systems
User Guide.
DIFFERENCES BETWEEN MT-3 SERIES MODULES
The MT-3 series of modules were designed and manufactured with three different oscillators in the
transmitter and receiver modules.
CRYSTAL
Crystal modules use a fundamental crystal in an oscillator circuit to determine the operating frequency
of the oscillator. To maintain high frequency stability, the crystal oscillator has an on-board digital circuit
board which provides temperature compensation information for each individual crystal element. To
change the transmitter or receiver operating frequency, a new crystal oscillator assembly must be
purchased. The crystal module was discontinued in the transmitter modules in 1995 and in the receiver
modules in 2005. The crystal receiver had a current draw of less than 50 mA.
LOW CURRENT SYNTHESIZED
The Low Current Synthesized modules select the operating frequency in standard channel increments
that are programmed into the synthesizer. The synthesizer uses a Voltage Controlled Oscillator (VCO)
to generate RF frequencies. To maintain high frequency stability, the VCO is locked to a frequency
reference (either an internal TCXO, or an external reference) by use of a Phase Locked Loop (PLL)
circuit. The VHF (150 MHz) and UHF (400 MHz) low current synthesized transmitter module was
discontinued in 1995. The 800 MHz and 900 MHz transmitter use the low current synthesizer. The
low current synthesized receiver module had a current draw of less than 100 mA and was typically
recommended for solar sites. The low current synthesizer was discontinued in 2006.
ENHANCED SYNTHESIZED
The Enhanced Synthesized modules operate with higher performance specifi cations and higher
current draw than the Low Current Synthesized modules. The enhanced synthesizer circuitry is
distributed between two printed circuit boards which are physically isolated from each other. This
eliminates the electrical noise between the digital and analog circuitry in the oscillator. The boards
are interconnected via photo-logic optical transceivers. The VHF (40 MHz), VHF (150 MHz) and UHF
(400 MHz) transmitters all operate with enhanced synthesizers. The enhanced receiver has a current
draw of approximately 400 mA and is typically recommended for AC powered sites. The enhanced
synthesized receiver module is manufactured with an accompanied enhanced front end that has a
higher L.O. injection than the standard low current front end.
The local oscillators that are used in the MT-3 receiver and transmitter modules can be determined by
the frequency bands of those modules.