Digital and digital-analog (hybrid) TV-transmitters

By Sergey Petrov

Review contents:

Digit is on a horizon The standardization of the digital TV broadcasting transmitter features Digital and digital-analog (hybrid) TV-transmitters Transmitters for digital terrestrial TV broadcasting Low-power DVB-repeaters from ELTI Company Spot: filling gaps in DVB-T networks with digital repeaters NEC transmitters for digital TV Transmitters of Rohde & Schwarz for broadcasting Radio broadcasting transmitters of Technosystem and Screen Service Italia Transmitters of Thales Broadcast & Multimedia for digital television broadcasting Measurement of path parameter of digital TV radio transmitters

TV transmitters of DVB Millenium series produced by the “Broadcast Arsenal” group of companies are intended for organization of digital television broadcasting in DVB-T standard. The transmitters are produced jointly with Screen Service Company (Italy).

When the transport MPEG-2 stream is supplied to the transmitter input an exciter generates high-quality HF signal with OFDM modulation, which then will increase to level of the output power in the range from 0.25 W to 3 kW.

The DVB transmitters can work both in complexes of multi-frequency and single-frequency networks of synchronous broadcasting. For the last case the unit is provided by modules of precision shift of the carrying frequency with the step 1 Hz and by receiver of synchronizing GPS-signal. The availability of asynchronous serial (ASI) and synchronous parallel (SPI) input interfaces, as well as a support of hierarchical and non-hierarchical modulation provides the wider flexibility of the DVB equipment in using.

The transmitters form the COFDM signals in mode 2k or 8k with the 16QAM or 64QAM types of QPSK modulation, at input stream rates in the range from 3.73 to 31.67 Mbit/s. For ensuring of quick change of the broadcasting channel a version of the exciter with operative tuning of working frequency, which is possible to produce directly from the front panel of the unit, is provided.

The microprocessor control system realizes the continuous checking of all working parameters of a unit and their outlet on LCD display, as well as on analog or digital (RS-485) interface for realization of the remote control.

In purpose of the organization of “soft”, the gradual transition from analog to digital broadcasting, a hybrid configuration of the DVB transmitter is designed.

DVB400U digital TV transmitter

One of the version of its realization is based on supplying in the transmitter of an analog exciter, having an entry on intermediate frequency (IF) for connection of external DVB-T modulator. Thereby, a procedure of the transition to digital broadcasting format is concluded in change of the analog modulator by digital modulator only. The transmitters of Millennium series are compatible with digital modulators of the other producers provided that they are made in accordance with European standard EN 300744.

The other construction version of the of the hybrid transmitter is connected with a availability in the exciter of two modulators simultaneously, analog and digital. Herewith is possible a programmed method of the change the broadcasting format (analog on digital, and conversely) on command from personal computer. This allows realizing, for instance, cutting-ins of digital programs in determined gaps of time, at rest time saving the traditional broadcasting in SECAM standard. Such scheme does not require any change or overtuning of some modules and blocks of the unit.

DVB-T Exciter

The digital DVB transmitters of Millennium series are designed with the most leading broadcasting technology using. All components in use have been tested for reliable functioning in conditions of the high temperature and power voltage that has allowed to obtain the high level of unit reliability.

The nomenclature of produced hybrid TV-transmitter
Model	Output power in digital mode, W	Output power in analog mode, W
DVB1U	0.25	1.0
DVB2U	2.0	10.0
DVB10U	10.0	50.0
DVB20U	20.0	100.0
DVB50U	50.0	200.0
DVB100U	100.0	300.0
DVB200U	200.0	750.0
DVB400U	400.0	1500.0
DVB750U	750.0	2500.0
DVB1000U	1000.0	3000.0
DVB1500U	1500.0	5000.0
DVB3000U	3000.0	10000.0

The Standard technical features
The working frequency range	VHF (21…69 channels)
Resistance load, Ohm	50 (75)
Standard of analog broadcasting	SECAM, PAL, NTSC
Standard of digital broadcasting	DVB-T
Ambient temperature, °C	0…+45
Cooling	built-in, air, forced
Input signal	MPEG-2
Rate of the input stream, Mbit/s	From 3.73 to 31.67
Package length of the transport stream, byte	188/204
COFDM modes	2k/8k
Duration of the guard interval	1/4, 1/2, 1/16, 1/32
Relative rate of the code	1/2, 2/3, 3/4, 5/6, 7/8
Modulation type	QPSK, 16QAM, 64QAM
Width of the band of the channel, MHz	6/7/8
Error ratio	0 when processing the signal at the Reed- Solomon decoder input during 5 hours
Irregularity of AFC in band of the channel	+0,1

Material is provided by the “Broadcast Arsenal” group of companies