Medium-Power Transmitters for Terrestrial Digital and Analog TV

UHF Transmitter Family NH/NV7001 Medium-power transmitters for terrestrial digital and analog TV

After the very positive response to Air-cooled, modular design They support the digital standards DVB-T (ETS300744) and ATSC (A54) as well as the liquid-cooled, high-power trans- The transmitters of the NH/NV7001 the analog standards B/G, D/K, M/N family use the new Exciters and I. mitters of the NH/NV6000/7000 SV/SH/SC700 for high-quality modulation of digital (DVB) or analog (ATV) The TV exciters comprise an encoder, family [1] on the world market, TV signals. The Broadband Amplifiers equalizer, modulator, synthesizer and a VH650A2 with state-of-the-art LDMOS CCU for transmitter control. Due to their Rohde & Schwarz now presents the technology are used for amplification. uniform structure and design they can be easily adapted to analog and digital compact, air-cooled Transmitter The NV7001 digital TV transmitters cover TV standards. The exciters used for the a power range from 200 W to 800 W various applications differ only in the Family NH/NV7001 for medium (DVB-T) or from 250 W to 1 kW (ATSC). encoder which processes the input sig- The transmitters of the NH7001 family nals and generates digital quadrature power classes (FIG 1). provide 500 W to 2000 W of power for baseband signals in all cases. Subse- analog TV. The two transmitter families quent signal processing is basically the use identical components in the racks same in all models and is carried out by (FIG 2): a common hardware platform, which is • One or two digital exciters (dual-drive optimally adapted to the individual appli- option) cations. Thus, three types of TV exciters • Up to four broadband amplifier mod- are available: ules, each with an output power of • SH700: used in analog high-power 200 W for DVB-T or 500 W for ATV TV transmitter systems with separate combined video and audio amplification (split • Up to four 2 kW switching power mode); NH7000 family supply units • SC700: used in analog TV transmitter • Output filter (for ATV) systems with a common path for video and audio signals (combined mode); NH7001 medium-power transmitters Exciters for digital and analog • SV700: for digital TV TV standards

The new Exciters SC/SH/SV700 used Analog TV with SC700 in analog and digital TV systems are notable for their compact design, flex- The Exciters SC700 contain an encoder ibility and future-proofness. Optionally, for analog TV signals. The video input two compact exciters can be accom- signal is digitally processed irrespective modated in a 19" frame to implement of the selected TV standard. Signal modern redundancy concepts with con- processing including vestigial sideband siderably reduced space requirements. filtering is therefore perfectly stable and not subject to aging. Switching to other TV standards is handled via soft- ware so that no exchange of hardware FIG 1 2 kW transmitter of the NH7001 family is required. The analog audio signals Photo 43702/1 for analog TV are also converted into digital signals

39 News from Rohde&Schwarz Number 171 (2001/II) BROADCASTING TV transmitters

and processed by a digital signal pro- An automatic switchover unit supports The baseband signals are subsequently cessor (DSP), e.g. dual-sound coding. the implementation of redundant feeder converted into analog signals and mixed One or two high-quality sound subcarri- networks. to the RF by direct modulation. The mixer ers are generated by subsequent digital frequency is supplied by a synthesizer frequency modulation. Various encoder For use in single frequency networks which can be synchronized to external modules are available for the different (SFN), an SFN adapter integrated in the references or the optional internal GPS audio standards: encoder accepts time reference pulses receiver. • The NICAM add-on module processes from an external or optionally integrated analog audio signals when acting as GPS receiver. a coder modulator and processes a Operation from display or PC digital data stream when acting as a For ATSC/8VSB signals, the ATSC NICAM modulator. encoder operates according to the ATSC The transmitter is operated from the cen- • The BTSC add-on module with a band- standard A54. Its input section also tral control unit (CCU) via the menu- width of 120 kHz for the N/M TV stan- accepts ASI signals in addition to the supported graphical display. All param- dards provides an audio input for rout- commonly used SMPTE310 signals. eters can additionally be controlled from ing the BTSC sound multiplex signal. a PC via an RS-232-C interface. Further- more, the exciter can also be remote- Digital signal processing controlled and monitored via an RS-485 Digital TV with SV700 interface, a modem or TCP/IP/SNMP The digital baseband signals from the interface (option NetLink [2]). The Exciter SV700 is used in digital TV encoder are routed to the subsequent systems. For DVB-T, data processing of digital precorrector. The digital precorrec- the DVB encoder is in line with the DVB tor comprises a group-delay equalizer for High-efficiency power amplifiers standard ETS300744. The encoder com- correcting linear filter effects and a lin- prises an asynchronous serial interface earity equalizer for correcting nonlineari- Due to the lateral diffused metal oxide (ASI) the data buffer and flexible clock ties of the power amplifiers. Both stages silicon (LDMOS) power transistors featur- processing of which enable the network operate completely digitally so that the ing high gain and linearity, a high effi- operator to use standardized feed paths. set signal parameters are maintained. ciency, compact design and a continuous broadband characteristic is achieved for the Power Amplifiers VH650A2 between 470 MHz and 862 MHz. A control system prevents the other mod- FIG 2 Power Amplifier VH650A2 Block diagram of ules from being overdriven if one ampli- 800 W DVB-T trans- fier fails, thus ensuring that all amplifi- mitter or 2 kW ATV ers remain at the same level and operat- transmitter ing point. The amplifier plug-in (FIG 3) comprises guard circuits protecting it against reflection and overtemperature. The main components such as preampli- Exciter A ATV I I fiers and output amplifiers with current DVB-T Digital I/Q RF Q Q encoder equalizer modulator sensors are installed on an extremely RS-485 LO effective, patented heat sink. With this heat sink, the heat produced by the

= = Control Synthesizer Channel Unit CCU filter amplifiers can be effectively dissipated optional RS-485 with relatively little air. Exciter B (optional) ATV I I DVB-T Digital I/Q Fan Transistor currents and various internal Q Q encoder equalizer modulator 3 = 3 = 3 = 3 = voltages can be measured via a service LO connector on the front panel. The output = = = = = Synthesizer 3 3 3 3 power is set with the aid of a reference voltage generated by the CCU.

40 News from Rohde&Schwarz Number 171 (2001/II) FIG 3 Plug-in Amplifier VH650A2 with side cover open Photo 43705

“On air” also during Two fans with long life are installed in power failure the rack for cooling the amplifiers by More information and data sheet at two parallel air streams. A fan can there- www.rohde-schwarz.com (search for NV7001) Every amplifier is provided with a 2 kW fore be replaced during operation with- switching power supply. This redundant out leading to a program failure. unit ensures continuous transmission even if a power supply unit or an ampli- The required output filter can be accom- fier fails. A special feature of each modated in the upper half of the rack UHF Transmitter Family NH/NV7001 Air-cooled transmitters for analog and digital TV (DVB-T or AATTSC)

250 W to 2 kW output power for Ambient-air or forced-air cooling Optional second exciter for passive switching power supply is that it con- where the output directional coupler and analog TV High redundancy standby confif iguration 100 W to 800 W output power for Highly service-friendly due to modular Exciter, amplifi ier technology and DVB--T design and plug-ins transmitter control unit identical to 125 W to 1000 W output power for Digital exciter liquid-cooled Transmitters ATSC Integrated OFDM coder or 8VSB NH/NV7000 Compact standardized coder (with NV7001) 19“ rack with integrated fans Advanced LDMOS technology for sists of two separate 1 kW power sup- an optional relay remote-control inter- power amplififiers plies, which together feed the preampli- face are also installed. fier and separately feed each half of the Cornelius Heinemann; Hans Seeberger;

output amplifier. If a 1 kW power supply Rainer Steen REFERENCES fails, the respective amplifier plug-in con- [1] UHF Transmitter Family NV/NH7000 – Liq- tinues to operate with a quarter of uid-cooled TV transmitters for terrestrial digital TV. News from Rohde & Schwarz (1999) its output power. Switching power sup- No. 165, pp 11–13 plies are primary-switched, short-circuit- [2] NetLink – Remote control and monitoring proof, 3-phase regulators with internal of transmitters on the Internet. News from Rohde & Schwarz (2001) No. 170, pp 27–29 cooling. Power supplies and amplifiers can be replaced during transmitter operation without causing a program failure. Condensed data of NV/NH7001 Frequency range 470 MHz to 862 MHz Flexible cooling RF output power 200 W to 800 W (DVB-T) 250 W to 1 kW (ATSC) 500 W to 2 kW (analog TV) The cooling air for the transmitter can be TV standards digital: DVB-T ETS300744, ATSC/8VSB A54) taken in at the bottom or the top of the analog: B/G, D/K, M/N, I Colour transmission PAL, SECAM, NTSC 19" standard rack, or air can be taken Sound transmission dual-sound coding to IRT or from the room at the rear of the rack. In FM single sound and NICAM 728 (–13 dB/–20 dB) or the latter case, the rear panel acts as an FM single sound (–10 dB) or BTSC multiplex signal (–10 dB) air filter. The outgoing air is expelled at Interfaces RS-232-C, RS-485, modem, TCP/IP/SNMP the top. (NetLink) Transmitter dimensions (W x H x D) 570 mm x 2004 mm x 800 mm

41 News from Rohde&Schwarz Number 171 (2001/II)