Codan Radio MT-3 - Manual (Page 17)

MT-3 ANALOG RADIO SYSTEMS | USER GUIDE
Chapter 2: Technical Information Page 9
Crystal
The MT-3 crystal controlled receiver and transmitter modules operating frequency is selected by the
control module’s fundamental crystal frequency. The channel select lines and internal BCD rotary
switches are not used by the crystal control module.
Crystal modules use a fundamental crystal in an oscillator circuit to determine the operating frequency
of the oscillator. The output frequency of a VHF crystal module is three times the frequency of the
fundamental crystal oscillator circuit. Output frequency of a UHF crystal module is nine times that of
the fundamental crystal oscillator circuit.
To maintain ± 1 ppm frequency tolerance the crystal oscillator circuitboard has an on-board digital board
which provides temperature compensation information for each individual crystal element. To change
the transmitter or receiver operating frequency, a new crystal oscillator board must be purchased.
Frequency Switching Range
Although the receiver or transmitter channels can be programmed for any frequency in their band,
the Maximum Frequency Switching Range of the module must not be exceeded or the module will
require hardware re-tuning. The maximum frequency switching range of the modules are listed in the
Technical Notes, and are typically shown as +/- 0.5 MHz +/- 1 MHz, +/- 2 MHz or Full Band, based on
the individual specifi cations of the module. For example, a VHF receiver may be programmed for any
frequency between 136 to 174 MHz, but the front end helical fi lter has a typical pass band of 5 MHz,
requiring re-tuning if any frequencies are used that are outside of that pass band.