18 News from Rohde& Schwarz Number 163 (1999/III)

A principle proves its success

The new DAB L band and band IIItransmitters from Rohde&Schwarz arebased on the company's more than40 years of experience in developingradio and TV transmitters. The result isa plug& play transmitter concept thatsets standards in terms of signal qual-ity, standardization and ease of ser-vicing (FIG 1). The flexible, modulartransmitter design has won inter-national recognition.

Details of the circuitry and technicaldata were presented in an earlier issueof the journal [1]. This article focuseson the plug& play concept and thewell-thought-out modular design, twoprinciples that form the basis for theexceptionally high economy of thetransmitters and have proven the keyto their success.

Modularity throughout

Standard 19-inch racks of identicalbasic design for all transmittersStandard 19-inch racks of identicalbasic design are used throughout thetransmitter family – for all powerclasses and frequency bands. Thisensures fast and easy installation andsimplifies servicing. The mechanicaldesign is so transparent and user-friendly that operators can set up thetransmitters on their own (plug& play).

Power supplies exchangeable duringoperationThe base of the transmitter rack cantake up to four power supplies, fittedas necessary for the required outputpower. Each power supply is madeup of one or two 1 kW modulesmounted on a slide. The power sup-plies are designed as plug-in units andcan be replaced during transmission.Each power supply feeds one ampli-fier, thus yielding maximum availa-bility.

Cost cutting through modularity andplug & playDAB transmitters are mainly used in single-frequency networks in which manytransmitters of a similar type are combined. So the costs of purchasing andoperating such transmitters can be drastically reduced by standardized logisticsand servicing concepts. Redundancy and the possibility of replacing importantcomponents during operation make for a high degree of availability andfrequently do away with elaborate reserve concepts. The precondition for thesecost-reducing effects is an optimized and completely modular transmitter concept.

DAB Transmitters NA 6… and NL 6…

Articles

FIG 1DAB transmitters ofthe NA 6…/NL 6…series are asophisticatedconcept for cuttingcosts in largebroadcast networks

Photo 43 212/3

News from Rohde& Schwarz Number 163 (1999/III) 19

Power amplifier B

Power amplifier

A

RS 485(I20X)

PC RS-232-C(TNPP)

RS-232-C(TNPP)

BITBUS-Gateway(option)

RS 485

(BITBUS toIEC 864-2)

RS 485

(GB2)CO

M 2

TAE

(TNPP)

RS 485

(TNPP)CO

M 3 Modem

(option)

I / O

BExciter

CO

M 1A

Exciter

Encoder I/Q modulator

CO

M 1

CO

M 2

COM 1 COM 4

Ventilation concept: open allroundThe racks feature redundant air cool-ing with two blowers operating simul-taneously. The blowers are so power-ful that one of them alone can provideadequate cooling for an extendedperiod of time. The intelligent conceptallows for air intake from above,below or behind, as well as from theambient air or via air ducts. The outletair is expelled from the top.

Plug-in power amplifiersThe 19-inch transmitter racks canaccommodate four amplifier modules,likewise designed as plug-in units. Thismodularity offers decisive advantages:• transmit power selectable in steps,• replacement during operation,• no cabling required,• plug-in power couplers, no

cabling required.

Each amplifier plug-in comprises twounits: a band III module with four 50 Wamplifiers and an L band module withfour 40 W amplifiers. The poweramplifiers feature high linearity, excel-lent efficiency and compact design.

Power couplers with minimum lossFor higher transmit powers, severalamplifiers are combined via powercouplers. Two different couplers areavailable, which are simply pluggedonto the amplifier modules. So neithercables nor alignment are required. Thenew power couplers minimize powerloss in the event of amplifier failure.This considerably enhances transmit-ter availability, and in many casescomplex reserve concepts can be dis-pensed with.

Control and operating concept:cost cuts by remote control

Exciters synchronous withGPS signalThe exciter too is identical for all trans-mitters. For applications in single-fre-quency networks it incorporates a GPSreceiver that supplies a time reference(1 pps) as well as a frequency reference

(10 MHz). By means of the secondspulse, the NA/NI converter evaluatesthe time stamps included in the ensem-ble transport interface (ETI) signal andautomatically compensates the delay.The reference frequency synchronizesthe synthesizer and ensures an exactcenter frequency of the DAB signal. Evenin the event of loss of the GPS signal,the output signals of the GPS receiverremain so stable that the transmitter cancontinue to operate for another twelvehours.

The control unit (FIG 2) is used for cen-tral transmitter control. It communicateswith all components of the transmittervia internal data lines, allows local andremote control, provides completesystem status indication and reacts tofaults by automatically activatingstandby circuits depending on thechosen reserve concept.

All setting parameters are stored innonvolatile memory. Administration ofup to four complete parameter setsmakes the exciter ideal for use also in(n+1) systems.

Remote monitoring via modemThe optional modem makes it easy tointegrate the transmitter into the tele-phone network for central monitoring.The system can be configured forautomatic link setup to a central stationin the event of a failure or warning.This concept does away with costlycyclic polling of the system by the cen-tral monitoring station. An authoriza-tion algorithm is used to preventunauthorized access via the publictelephone network.

Reinhard Scheide; CorneliusHeinemann; Manfred Reitmeier

Articles

REFERENCES

[1] Frank, P.; Heinemann, C.; Steen, R.: Digitalaudio broadcasting – reliable and econom-ical. News from Rohde& Schwarz (1998)No. 158, pp 13 –15

Reader service card 163/06

FIG 2 One Control Unit SDB600 for all trans-mitter types