MT-MR PLATINUM. POINT TO POINT AURAL RADIO RELAY SYSTEM
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MT-MR PLATINUM
POINT TO POINT AURAL RADIO RELAY SYSTEM
chapter III
THE MT PLATINUM LINK TRANSMITTER
3.1.- Description.
MT Platinum Transmitter is a device used to transmit multiple audio information through the UHF frequency
spectrum (
for aural links, generally are used the medium-upper UHF band upto 960 MHz, or the lower microwaves
range in
the 2 GHz band, depending on Country standards
). Originally designed for 400 MHz band, it is being
developed also for the 220, 300,470 or 960 MHz bands, according to the particular needs specified by Customer.
This transmitter is used together with the MR Platinum receiver to form the MT-MR Platinum aural point-to-point
Radio link system.
MT Platinum is an wideband FM Transmitter having 10 watts p.e.p. output in all versions (each version is built for a
particular frequency band) having a transmission baseband comprising one main program audio channel and three
subsidiary (SCA) auxiliary channels, also used to transmit low speed data (RDS) through system. These channels
can also be used to receive information from different stations (telemetry) or to control equipments at these stations
(telecontrol). LT DIG is built around independent modules joined together to integrate equipment within a solid and
sturdy duraluminum closed cabinet. Dimensions of this cabinet are reduced; only a low height of 2U, and 44 cm.
depth, with a standard 19" width for rack mounting. Modules are easily replaceable in event of a failure.
Fundamental control & supervision elements are all located in the Equipment's Front Panel. All connectors are
located in the Rear Panel, thus avoiding the audio or RF cables to drop in the Equipment's front, obstructing the
reading of the supervision elements.
Main transmitter oscillator generating directly the RF carrier frequency is a VCO device (voltage-controlled
oscillator) whose frequency is kept locked into its value by a PLL (Phase-Locked Loop). This control loop gets a
sample of the RF output of the oscillator, frequency-dividing it and making a phase-comparison with another
reference signal of the same frequency, this signal obtained from a reference thermally-stabilized oscillator (TCXO)
whose output signal is also frequency-divided before being phase-compared with the RF sample. Phase
comparison is made at the lowest possible frequencies in order to minimize the frequency error or phase "jitter" at
phase comparator circuit. Output of phase comparator is a DC error voltage who sets the exact value of oscillator's
center frequency. Frequency divider circuits of reference oscillator are externally programmable within tuned
frequency band. This fact allows a complete programming of selected operating frequency, since comparison
between almost any desired frequency and the reference frequency is allowable, once both are divided. Conditions
are only 1) desired frequency must follow the programming order given by the frequency setting steps of PLL
synthesizer, that is, 25 KHz apart. and 2) Selected frequency must be situated into the synthesizer's programmable
band. This Equipment uses a Microcontroller unit (specialized Microprocessor) fitted with a Digital Display to
control the programmable dividers setting. Microcontroller can be internally programmed with a broad set of
frequencies covering practically all assigned Equipment's tuning sub-band. Another security element has been
introduced in this circuit: carrier operating frequency can not be altered or changed unless a certain password is
entered into Microcontroller Unit.
