RAP-TV digital measuring system

By Mikhail Leiderman

Review contents:

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RAP-TV digital measuring system produced by SOTA Company (Chelyabinsk, Russia) is the first in Russia representative of digital RF analyzers class. In 2000 RAP-TV equipment had passed certification according to ’Electrosvyaz’ system in Scientific Researched Institute of Radio certification center. In this year subsequent upgrade of RAP-TV 2002 measuring devices lineup is presented.

SOTA’s digital measuring devices lineup
Model	Type of transmitter	Documents supported (methods and error limits)
RAP-TV 2002	TV (D/K standard)	GOST 20532-83, GOST R 50890-96, TER-95/98
RAP-UKV 2002	FM (CSS, pilot tone)	GOST R 51741-2001, TER -95/98
RAP-TV 2002U	TV (D/K standard), FM (CSS, pilot tone)	GOST 20532-83, GOST R 50890-96, GOST R 51741-2001, TER-95/98
RAP-TV 2002MS	TV (D/K, B/G, M), FM (CSS, pilot tone)	ITU-T J.61, GOST 20532, GOST 50890, GOST R 51741-2001, TER-95/98

The developers traditionally place against themselves a task of creation full functional — all in one — convenient measuring tool for those who produce and align and exploit transmitting equipment. The main features of RAP-TV series devices:

• Measuring all parameters (including RF: side bands characteristics, career nonlinearity, deviation) using single device with no change of connection scheme;
• Video and audio signals digital demodulation;
• Test lines insertions into full color TV signal during transmission;
• Totally efficient and convenient tasks solving which operator faces at measuring during adjustment, alignment or continuous parameters monitoring.

RAP-UKV meter

RAP-TV meter

Measuring system consists of high frequency (HF) unit connected to personal computer via USB interface and software application package. All devices within RAP-TV 2002 lineup are designed on unified hardware platform and common software core.

Structure is shown on figure. Transmitter is being modulated by testing signals formed by ADC of HF unit. Radio signal from transmitter’s output through routing splitter is fed to tuner’s input. Tuner is a super heterodyne receiver with double frequency conversion, digital discreet auto gain control and digital-analog frequency auto tuning system. Tuner allows receiving signals of:

• TV transmitters in D/K, B/G and M standards on any channel up to 890 MHz;
• Cable TV transmitters on SK11…SK35 channels;
• IF TV — any in 30…70 MHz range with 0.1 step;
• FM transmitters in 62…110 MHz range with 0.05 MHz step.

IF signal (tuner’s output signal) is being digitized and its samples are being transferred to PC and further processing is being done by software with use of modern digital signal processing methods. Such approach provides number of advantages.

Measuring precision increase

Many key units and devices (Nyquist filter, audio rejecter, video and audio demodulators etc) are realized on software level. Characteristics of such ’virtual’ devices are closet to ideal ones and distortions caused by them are negligibly minor. Measuring errors defined by HF unit are pretty much compensated by calibration system (about 30 parameters and characteristics are being calibrated; single device calibration takes about 10…12 hours).

One of the main characteristics of any TV demodulator is nonlinearity of its own frequency response because it defines measuring error for legality characteristic, amplification difference for luminance and chrominance signals and other transmitter’s parameters. Software filter of RAP-TV demodulator (audio rejecter + Nyquist filter) has absolutely linear phase response and provides audio attenuation above 100 dB at response deviation from ideal in bandwidth of not more than ±0.001 dB. Hardware errors are being decreased by calibration system down to ±0.2 dB level. It results in that the sum nonlinearity of through frequency response of RAP-TV doesn’t exceed ±0.2 dB which conforms to the best European equipment samples. Level of self noise for software FM audio demodulator doesn’t exceed -1780 dB and frequency noise of tuner’s internal heterodynes provides measuring integral interference in audio channel for TV transmitters of V band not worse than -66 dB and for II…IV bands and FM band — not worse than — 70 dB.

Direct measuring of transmitter’s radio signal parameters

Side bands characteristics, career frequency nonlinearity, modulation coefficient (null adjustment doesn’t need), intermodulation products level, video career spurious phase modulation are being measured. There is a possibility assumed to compensate video career spurious phase modulation upon differential phase change.

At TV signal demodulation using synchronous detector the video career spurious phase modulation is being added to measured value of differential phase. Majority modulators have very minor video career spurious phase modulation value and sometimes it can reach 20…30°.

Absence of hardware relation to particular signal type

At present time RAP-TV software provides measuring parameters of TV and radio FM transmitters. Recently (in RAP-TV 2002 modification) B/G and M standards support was added. In near future one plan to realize functionality of universal panoramic specter analyzer in range of up to 1 GHz and it will be enough for users just to upgrade their software. Next it is planned to provide DVB support without sufficient hardware change.

User interface of RAP-TV at planned measures

Information displayed in a screen using RAP-TV Reglament module

RAP-TV Monitor module’s interface

Software package delivered along with system consists of three applications:

• RAP-TV Reglament for performing scheduled measures (during broadcast pauses)
• RAP-TV Monitor for measuring during transmission
• RAP-UKW Reglament for measuring FM transmitters’ parameters

All applications have similar interface avoiding operator from routine operations. Parameters’ values are calculated automatically and outputted in numerical form with error limits results. Besides, for each parameter typical waveform diagrams and histograms are shown which is traditional for operators.

Main operation modes:

• Automatic. All measures are being done with no operator’s involving and with creating and printing reports using forms according to selected normative document. For example, testing a transmitter for its compliance to second group parameters of TER-95 an operator connect RAP-TV to transmitter, sets in the application error limit category to “TER second group”, presses a button “All parameters of video channel” and in 2…3 minutes sees on a screen a protocol according to TER form which can be printed immediately. If transmitter is located at distant radio transmission center it is enough to have just compact device and CD with software;
• Alignment mode. Measures are being done by operator in random order with ability of cycle repeat. For instance aligning transmitter’s exciter operator can see on a screen continuously refreshed side bands characteristics, though frequency response (legality characteristic) etc. He also can activate ’Linear distortions; multi-test and look after measuring results for several parameters a once which characterize linear distortions simultaneously with typical waveform diagrams and specter diagrams. At alignment output blocks modes operator can activate ’Nonlinear distortions’ multi-test and simultaneously look after on a screen continuously refreshed measuring results for measuring differential amplification, differential phase, luminance channel nonlinearity and intermodulation products level;
• Measuring during TV programs transmission. Screen shows continuously refreshed values for parameters of transmitters and full color TV signal. Color indication informs about any parameter deviation.

TV waveform monitor and specter analyzer

TV measuring is very specific sphere. Creating really operable and useful tool it is necessary to keep in mind many minor at first glance details. For increasing efficiency and operator’s work convenience as well as for providing ability to work with non-standard transmitting equipment there are realized many additional features both functional and service. Majority of them had appeared upon analyzing customers’ offers and requests. In particular, there are realized:

• Ability to change modulation of image upon changing parameters of audio channel;
• Ability to form periodic test signals at the frame synch pulses background;
• Alignment multi-tests;
• Automatic setup of deviation nominal value at measuring parameters of audio channel and FM transmitter;
• Ability to define random set of parameters during automated measuring;
• Ability to deactivate Nyquist filter, video phase corrector and FM audio pre-emphasis corrector.

Material is provided by SOTA Company