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The Marti GTX transmitter and its companion Marti GRX receiver are the core of a high quality,
synthesized studio-to-transmitter link (STL), to be used for broadcast repeaters in conjunction with
any standard FM or AM transmitter. They’re an evolution of the established Marti GTX/GRX series
STL whose main circuitry is still extensively used here with a new controller, user interface and
software and more advanced oscillators in a compatible 2RU, 19" case.
They allow the reception of mono or stereo signal and its retransmission without using any
additional stereo-coder on the receiving end: in both cases the LF output signal from the receiver
must be sent to the stereo input (linear or not pre-emphasized) of the local FM rebroadcast
transmitter.
The STL is built for several different frequency slots from VHF to the SHF range. Two main models
are built: one for the 200 - 960 MHz and the other frequencies in the SHF band. While the, controls,
basic circuitry and the performances are the same, some internal components vary or are specifically
tuned as required to cover this wide frequency band. Usually these components are the local
oscillator, the power amplifier and the input/ output filters. The factory adjusted frequency slots are
10 to 50 MHz wide and must be specified in the order. In the preset sub-range, the frequency and
power of the transmitter may be freely changed on the field. The receiver may require some more
adjustment for wider frequency displacement: in fact the adoption of narrow, low loss input filters
permitted to achieve the best possible rejection of interfering signals in the band at the expense of
some frequency agility. So nearly 8-10MHz may be used without any retouching but wider variation
up to 50-60MHz will require retuning of the input filter.
Being the apparatuses are completely digitally controlled, they are extensively on field
programmable by front panel or remotely in every respect. The alphanumeric display permits easy
and accurate metering, adjustment and continuous monitoring of modulation levels, power,
operation and internal parameters. All this information is externally available on the same RS232 I/O
port that maybe used to remotely control the transmitter. In addition to the serial I/O, some signals
and controls are available on a parallel I/O socket for easy interfacing with others analog controllers
or supervisory systems. A powerful 3-levels password management permits a very high degree of
security and privacy as may be required in different situations.
The LF input and output levels are precisely adjustable over a broad range, by means of 0.5dB
stepwise variable attenuators. The transmitter has also an auxiliary input, specifically designed for
RDS and SCA encoders. A modulation monitor output permits to control other transmitters or STL's
with the same internally processed high-quality mpx signal. Furthermore, the system is optimized to
be compatible with external digital companding encoder/decoders and to provide RDS and SCA
signals, with almost no attenuation.
Optional top-quality stereo encoder/decoder boards maybe factory installed on the transmitter/
receiver or field retrofitted with minimum required technical skill. The powerful internal software
and monitoring functions recognize their presence and enable the functions. A universal switch-
mode power supply permits operation in the extended 95-250 VAC range with no intervention and a
24 V back-up battery input is provided too.
Summary of Contents for Marti GRX
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