Основные измерения анализатором спектра Методика измерений. - презентация

1 Основные измерения анализатором спектра Методика измерений

2 Making Basic Measurements

3 Noise Measurements The ESA Spectrum Analyzers allow you to measure the total power of noise-like signals, tones, or both. Additionally, adjustable markers can be used to set the frequency span over which power is measured. The markers allow you to easily and conveniently select any arbitrary portion of the displayed signal for measurement. However, while the analyzer does select the average (Video/RMS) display detection mode, you must set all of the other parameters. (Co+No)/No N (C+N) at 30kHz (C+N)/N C/N=lg10[Antilog[0.1*(C+N)/N] –1] Ebc/No=Co/No –10lg(m)-10lg(code)

4 SPACE SEGMENT MONITORING Monitoring of the downlink spectrum of the operational transponders. The downlink parameters measured are: 1) Carrier E.I.R.P. 2) Carrier Center frequency 3) Carrier spectral shape 4) Carrier C/N. The monitoring facilities will be used for setting the initial operating parameters for each earth station's digital carriers and thereafter for maintaining the proper operating point of each carrier while in service. However, every station should periodically monitor assigned transmit and receive carriers.

5 Carrier Line-Up Test Procedures Demodulator Performance (Intermediate Frequency (IF)Loop) Demodulator Performance (Adj Channel) Demodulator Performance (Radiofrequency (RF) Loop) Modulator Output Spectrum and Energy Dispersal Transmit E I R P and Frequency HPA Output Spectrum Link Performance: Receive (Co+No)/ No vs. Bit Error Rate (BER) Transmit E I.R.P. and Frequency Receive BER

6 Demodulator Performance Test

7 Measuring Low Level Signals The analyzer Input Attenuator and Resolution Bandwidth settings affect the sensitivity by changing the signal-to-noise ratio. The Attenuator affects the level of the signal passing through the instrument, whereas the Resolution Bandwidth affects the level of internal noise without affecting the signal. If, after adjusting the attenuation and resolution bandwidth, a signal is still near the noise, visibility can be improved by using the video bandwidth and video averaging functions. To view a -100dBm signal, as in this demonstration, take the following steps: 1) Preset the analyzer 2) Reduce the Span centered around the signal of interest 3) Reduce the Reference Level and RF Attenuation* 4) Reduce the Resolution & Video Bandwidth 5) If installed, turn On the optional built-in RF Pre-Amplifier The ability of the analyzer to measure low level signals is limited by the noise generated inside the analyzer. A signal may be masked by the noise floor so that it is not visible. This sensitivity to low level signals can be affected by the measurement setup.

8 Detector Modes Peak detection is used primarily when measuring CW signals out of the noise floor of the analyzer. Peak detection obtains the maximum video signal between the last display point and the present display point and stores the value in memory. Sample detection is used primarily to display noise or noise-like signal. This detection should not be used to make the most accurate amplitude measurement of non noise-like signals. In sample mode, the instantaneous signal value at the present display point is placed in memory. Sample detection is activated automatically for the Marker Noise and Band Power functions, when the resolution bandwidth is less than 1 kHz. Negative peak detection functions the same as peak detection, but selects the minimum video signal. Negative peak detection is used to find signals that are close to, but below the noise floor. This detection should not be used to make the most accurate amplitude measurements of signals. Average (Video/RMS) displays the average of the signal within the trace element or digital bucket. The averaging method depends upon Avg Type selection (Video or Pwr). The Average Detector and Average Type of the Pwr is what is sometimes referred to as, "RMS Detector".

9 Marker Functions Marker Formats Include: Normal Delta Delta Pair Span Pair Marker Table Marker Freq. Count Peak Functions Include: Peak Search Continuous Peak Peak Table (shown) Next Peak Functions Peak to Peak Search NdB Points Marker Functions: Band Power Marker Noise Marker Readouts: Frequency Period Time Inverse Time The ESA Spectrum Analyzers can utilize many different marker functions to obtain the information the user requires.

10 Channel Power The Channel Power measurement measures and reports the power in the channel (integration) bandwidth as well as the computed power spectral density as shown. The power calculation method used to determine the channel power is a traditional method known as the integration bandwidth (IBW) method.

11 Occupied Bandwidth The power-bandwidth routine first computes the combined power of all signal responses contained in the trace. For 99% occupied power bandwidth, markers are placed at the frequencies on either side of 99% of the power. 1% of the power is evenly distributed outside the markers. The difference between the marker frequencies is the 99% power bandwidth and is the value displayed. The Occupied Bandwidth measurement also indicates the difference between the analyzer center frequency and the center frequency of the channel. This difference is referred to as Transmit Freq Error. The Occupied Bandwidth measurement integrates the power of the displayed spectrum and puts markers at the frequencies between which the selected percentage of the power is contained. The measurement defaults to 99% of the occupied bandwidth power.

12 Adjacent Channel Power When Method is set to IBW, one sweep of the trace will be taken, and the band power for each offset will be computed. Results will be displayed relative to the total power or the power spectral density, depending on your selection after pressing Meas Setup, Meas Type. You may view the results as the current trace, bar graph, or a combination. When Method is set to RBW, the main channel and offets will be measured in zero span and the combined results reported according to the Meas Type selection. Measures the power present in adjacent transmit channels. The span is set according to the six available offsets and their associated integration bandwidths defined by you or the selected radio standard (Mode Setup, Radio Std).

13 Power spectral density mask at modulator output ISR-405

14 Spectrum Emissions Mask The spectrum emission mask measurement includes the in-band and out-of-band spurious emissions. It may also be expressed as a ratio of power spectral densities between the carrier and the specified offset frequency band.

15 Spurious Emissions The Spurious Emissions measurement identifies and determines the power level of spurious emissions in user defined frequency bands.

16 Intermod (TOI) The Intermod (TOI) measurement computes and displays the third order intercept point and places markers on the trace to indicate the measured signals and third-order products.

17 Antenna patterns The measurement of the antenna sidelobe pattern is mandatory test for access to the space segment.