Sigma transmitters
Yuriy Grachev

Moscow Technical University of Communications and Informatics (MTUSI) is one of the leading Russian institutes of higher education in the field of telecommunications. Television is of the most important among the priority directions of the university's activity. The university conducts development and manufacturing of TV transmitters, transposers, measuring TV devices, antennas, and other units, necessary for TV center equipment. All transmitters are manufactured under the Sigma name. In the last 6 years more than 1,000 TV transmitters have been manufactured in the university. The transmitters have power of up to 2 kW, however the university's main direction is manufacturing transmitters of low and middle power (1...200 W).

All the manufactured devices are developed with the use of modern know-how solutions and designed on the basis of modern elemental base of such manufacturers as Motorola, Philips, Analog Devices, Hewlett Packard, Elantec, etc. All the transmitters' blocks are designed with the use of surface-mounting technology.

Transmitters of 1...25 W are designed in one NADEL-75 frame of 480x480x120 dimension. Transmitters use usual parametric power feeders (switched power feeders are supplied only at the customer option). Output of any transmitter is protected by a faucet, the transmitter of 1 W having a 20 W power faucet.

Transmitters of more than 25 W employ modulator, designed as a separate 480x480x80 block, having:

• video automatic leveler system and white level limiter;
• ive-link corrector of envelope delay and frequency response function;
• three-stage gamma corrector;
• synchro clock corrector;
• output power automatic leveler system;
• visual control and regulating of sound and video signal;
• visual output signal control.

Modulator has advanced diagnostics and automatics systems, and it is managed with the help of micro controllers.

Amplifier contains:

• output power automatic leveler system;
• overload protection;
• load break or short circuit protection;
• load power control;
• visual overheating, break, short circuit and power in load control.

Amplifier's output is protected with the help of a circulator.

Transmitters of more than 50 W have a separate display and sound amplification channel and operate in AB class suspend mode, which allows designing reliable transmitting devices, with low energy consumption, and operating under light thermal conditions.

One of the main tasks of any TV- and radio-transmitting center is organization of continuous broadcasting. However lack of financing does not always allow employing reserve transmitters. To solve the problem of reserve transmitters, MTUSI has begun serial manufacturing of all-channel TV modulators and transmitters of 1...100 W based on these modulators. Modulator of this transmitter performs formation of broadcasting television radio channel during the injection on its input of a full color TV signal and an ambient sound signal in one of the channels within the metric waves bands on TV band (48,5...230 MHz) I, II, III carrier frequencies or decimetric IV...V bands on 470...860 MHz carrier frequencies. Modulator operates in PAL, SECAM, NTSC systems, B/D/G/H/I/K/M/N standard and may be supplied in the version with common and separate display and sound amplification channel. Modulator can be programmed from the PC, connected by RS-232 serial interface port or directly from the modulator's front panel. Channel number, carrier frequency shift, broadcasting standard, output level, and other parameters are programmable in the modulator. The modulator is designed in one frame of 450 x 450 x 90 mm dimension.

All-channel TV transmitter contains three blocks:

• all-channel exciter;
• power amplifier of metric frequency band (1...12 channels) with a built-in power feeder;
• power amplifier of decimetric frequency band (21...60 channels) with a built-in power feeder.

Provided by MTUSI.

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