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Wandel & Goltermann - SPM-19 - Level Meter
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While digital transmission systems are being used more and more at the local and regional levels, FDM systems are still the main systems for long distance traffic. Level measurements play an important part in the measurement and checking of the analog parameters of these systems and the various modules. However, modern test equipment must be available for additional measuring tasks. The selective level meter SPM-19, in which the application of modern circuit technologies and of a microcomputer provide a high degree of accuracy and ease of use, is suitable for these measuring tasks. The frequency range of the meter extends from 50 Hz to 25 MHz if the coaxial input is used, and the frequency ranges of the balanced inputs extend up to 620 kHz and 14 MHz. The characteristics of the level meter make it equally suitable for development, production, installation, and maintenance of transmission systems with a maximum of 3,600 speech channels, for measurements in the lower multiplex range of single sideband radio link systems, and of single telephone channels. Its remote control facilities also make it suitable for use in automatic measuring systems. As required by its intended application, the frequency of the SPM-19 can be tuned, over the whole range, either digitally with a keyboard or continuously, and with a resolution of 1 Hz. The frequency can be stepped either manually or automatically in preset steps, for example to step from channel to channel. Up to 100 fixed frequencies can be stored and recalled either sequentially or in any required sequence for frequent measurements at fixed frequencies. If required, further fixed frequencies can be stored in a customer-specific PROM. Regardless of the type of frequency tuning, the built- in synthesizer provides high stability and accuracy of the selected frequency. The signal to be measured is either connected to the coaxial input (input impedance 75 Ohm) or to one of the two balanced inputs with frequency ranges of 50 Hz to 520 kHz (150 Ohm, 600 Ohm) andlOkHz to 14 MHz (124 Ohm, 150 Ohm); each of these inputs can also be switched to high impedance. For high impedance, low capacitance measurements, the test probe TK-11 or any other suitable test probe can be connected as required. In selective mode, levels between -140 and +22 dB. (-130 and +32 dBm) can be measured; in wide-band mode, the limits are -60 and +22 dB (-50 and +32 dBm). The measured level is displayed either digitally with automatic range selection, with a maximum resolution 0.01 dB, or on an analog meter. In the case of analog display, the most suitable scale range of 1 dB, 20 dB or 80 dB can be selected with three pushbuttons for the current measuring task. Range switching is carried out either manually in steps of 1 or 5 dB or automatically after depression of a pushbutton. In order to obtain the maximum possible measuring accuracy, the microcomputer measures the total input level and adjusts the input attenuator and IF attenuator such that measurements are always carried out with the most favorable settings. It is thus no longer necessary to fit the changeover switch "low noise/low distortion", which has previously caused some confusion. In addition to measurement of absolute levels, the SPM- 19 permits simple measurement of relative levels. For this purpose, a level which was previously measured digitally is transferred to a memory as the reference value and the difference between the measured value and this reference value is displayed digitally or on the analog meter for all subsequent measurements. In the case of measurements in transmission systems, levels are often not specified directly, but with reference to the relative level (dBr) of a test point. In order to simplify evaluation of test results in such cases, the relative level of the test point can be preset in 0.1 dB steps and the result can then be displayed as a reduced level in dBO (dBmO). The pushbutton for the relative level is also useable for setting any required reference value (e.g. for frequency response measurements). Various bandwidths are available for the various measuring tasks. The pilot level, residual carrier signals or frequency spectra are measured with the narrow 25 Hz filter. Sensitive level measurements can be carried out with the 400 Hz bandwidth. A filter with a noise bandwidth of 1.74 can be connected for weighted noise measurements in unused or cleared speech channels at the CF level. A further posi tion of the bandwidth switch permits level measurements with a channel bandwidth of 3.1 kHz. Finally, the noise power of a 48 kHz primary group can be measured. The built-in demodulator permits demodulation of single sideband signals in the normal or inverted position. The converted signal can either be assessed with the built-in loudspeaker or extracted from the demodulator output for further external processing. The demodulator is characterized primarily by a very wide dynamic range, which is necessary, for example, for precise measurement of noises or pulse noise in converted speech channels. For assess™ ment of the transmission quality of telephone lines for data transmission, phase jitter measurements can be carried out. The weighting filter and the rectifier characteristic for measurement of the peak to peak value comply with CCITT recommendation 0.91. The phase jitter is displayed either digitally or on a logarithmic scale of the analog meter in the range 0.3 to 30 degrees. An automatic level control, which makes manual calibration superfluous, guarantees high measuring accuracy over the whole frequency range, a considerable reduction in the measuring time, and a high long-term stability. The level meter is thus also suitable for continuous monitoring applications. In addition to the above mentioned frequency settings, the microcomputer control of the SPM-19 permits various other, automatic frequency sequences. The automatic search function, together with the rapid signal detector, is a major aid in searching for interference or excessive levels. The tuning, oscillator is tuned until a signal which exceeds a preset level threshold falls within the display range of the analog meter and stops the search. At the same time, an automatic frequency control (AFC) circuit is activated and tunes the oscillator precisely to the frequency of the input signal. The search can be restarted again either manually by depressing a pushbutton or automatically after the level and frequency have been printed out. The search speed is matched to the selected bandwidth. The AFC circuit can also be switched on for normal level measurements with all bandwidths. This circuit ensures that the oscillator remains correctly tuned over the whole frequency range. For selective level measurements over a line, for example in channel gaps of the system during normal operation, an electronic circuit which is activated in the mode "track" permits automatic tuning of the level meter to the frequency of a sender with the same frequency steps. The SPM-19 (BN 829/02) can be extended to form a panoramic receiver by adding a display unit SG-2 or SG-3. Because of the phase continuity during use of the sweep mode, the frequency range can be searched completely in all chosen operating modes, which means that all frequencies present in the band can be clearly identified. The sweep facility fitted in version BN 829/02 is characterised particularly by the fact that the frequency sweep is carried out without phase discontinuities, which means that precise measurements are possible even of objects with extremely steep attenuation edges. The two limit frequencies can be entered via the keyboard to match the application. The signal generators PS-19 and PSS-19 are suitable as signal sources for the sweep measurements. The combination of PS-19/SPM-19 permits measurements with offset frequencies, e.g. the testing of channel translators. Both types of measurements are possible, either point-by-point or sweep measurements. Many measuring tasks are particularly simple to solve if the user can store complete equipment settings and recall them when required. Depression of a pushbutton (address selection) causes the unit to set up all previously selected measuring conditions for a specific measuring task. The supply voltage of the memory is buffered by a small battery to maintain the stored data if the main supply fails or is switched off. All functions of the SPM-19 can be controlled by an external computer which is compatible with the IEC bus via the optionally available interface bus (lEC 625) board. The unit can also be connected to an IEEE bus (IEEE Standard 488) with an Adaptor IEC 625/IEEE 488, S 834. With the aid further externally controllable peripheral units such as signal generator, measuring point changeover switch, or external memory systems, powerfull automatic level measuring set ups can be constructed for use in test departments or FDM monitoring systems. The measuring point changeover switch MU-3 with a switching unit MUE-31 and the IEC interface board can be used for automatic testing of FDM modules with 12 channels (channel converters). For measurements at higher frequencies, the measuring point changeover switches MU-4 and MU-7 with interface boards are available. Instead of the interface kus (lEC 625) board, a printer interface for V.24/V.28 interface can be fitted for recording the measured results in various print formats. Due to its excellent NPR value, the SPM-19 is suitable as a selective receiver for measurement of intermodulation and basic noise on FDM cable and radio link systems using the white noise measuring method. An optional white noise program is available to permit, measurement of all noise parameters such as reduced noise power (in pWOp), the reduced noise level (in dBmOp), or the noise power ratio NPR (dB). The test frequencies, in accordance with the recommendations of CCITT/CCIR and INTELSAT, can either be entered via the keyboard or stored in the 100 available fixed frequency positions of the RAM; they can also be stored to customer's specifications in a EPROM. The test modes and test frequencies are recalled from the memories by suitable address selection. The measured values and the corresponding units are shown on the digital result display. The measuring adapters RFZ-5, RFZ-14 (coaxial, above 10 kHz and 100 kHz, respectively) and RFZ-12 (coaxial and balanced up to 4.5 MHz) and SDZ-12 are available as measuring accessories for return loss or unbalance loss measurements. For apparent resistance and return loss matching loss measurements, the Impedance Measuring Attachment SFZ-1 (300 Hz to 612 kHz) is available. The Relay change-over Switch RU-3 permits digital level difference measurements of higher relative accuracy. The level meter can be switched from power level calibration (dBm) to voltage level calibration (dB). Inspite of the large number of functions, the SPM-19 is installed in a relatively flat case. The connections, controls, and displays are arranged clearly on an easy to use front panel. LED's above or alongside the pushbuttons signal the selected functions to the user. The unit is available in versions for table-top use or 19" rack mounting.

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1 Manual

User manual
Manual type:
User manual
5.4 MB
2798 GN v. 2772
June 1981
Scanned document, reading partly badly, partly not readable.
Upload date:
Jan. 22, 2017