Performance testing and troubleshooting in digital communication. You can only determine the real performance of your device under test by using the right analysis tools. RF transmitters and receivers, for example, can be tested with a high-performance test system consisting of a signal generator and spectrum analyzer. Find out here how an optimum test system can support your measurement tasks during development.
During the development of transmitter and receiver systems for high-frequency applications, a signal generator can simulate the local oscillator (LO) and clocking subsystems. Ideally, the signal generator should have the lowest possible phase noise and only minimum interference signals so that you can correctly assess the system performance before the corresponding subsystems are added.
Before an amplifier is integrated into a design, its performance should be carefully checked. Corresponding measurements are typically carried out with a signal generator and an RF power sensor. Here, the input to the amplifier, i.e. the output from the signal generator, is varied and the power is measured with the power sensor. The results can be read off directly from the signal generator.
During the actual use of a device, interference signals often appear in the spectrum. These may impair the ability of a receiver to receive signals correctly. To check the device performance in the presence of an interference signal, the output of two signal generators can be combined and applied to the device under test.
A spectrum analyzer (signal analyzer) is used to test RF or modulated signals. An oscilloscope, on the other hand, is used for baseband signals. Spectrum analyzers are narrowband analyzers, so to speak, that can fully meet your measurement requirements when testing RF transmitters. When characterizing RF components, frequency and power measurement are among the primary test parameters.
Wireless communication designers need to monitor unwanted spurious emissions such as second and third harmonics or TOI (third order intermodulation) as such distortions can affect the performance of other system components. Almost every electronic device on the market today is tested for its emission values in accordance with the CISPR standards. It is also necessary to ensure compliance with the prescribed frequencies and bandwidths.
In many cases, the target signal is a low-level signal. However, every active circuit also generates noise signals that are superimposed on the useful signal. Tests to determine noise factor, signal-to-noise ratio (SNR), etc. are essential to characterize the performance of a device and assess the impact of noise signals on the overall system.
A modulated signal may have to be demodulated in order to match the power of an RF transceiver with its target specifications. The N5166B CXG signal generator offers you an I/Q modulator to emulate and transmit digital signals. This means it meets all measurement requirements in the areas of IoT, WiFi, etc.
Passive intermodulation (PIM) occurs when two or more radio frequency signals meet non-linear transmission components such as connectors, screw connections, etc., e.g. the RF transmission frequencies of a mobile phone base station. This results in signal mixing, which generates new signals. If these PIM signals enter the receive band (Rx) of the mobile radio base station, the background noise increases. This leads to increased breakdowns in connections and lower data rates. PIM measurements are required to optimize the quality and performance of a radio transmission.
Develop and test transmitters and receivers with a high-performance test system from Keysight: Analyze the performance of your design with the N5166B CXG signal generator and the N9000B CXA spectrum analyzer.
The specified frequency range of the signal generator indicates which frequencies can generally be generated. Frequency and amplitude accuracy are also part of the general specifications of a signal generator. It describes how close the real output is to the set target value. The frequency and amplitude switching speed defines how quickly the signal generator can switch from one value to the next. These specifications determine whether a signal generator is suitable for your applications.
Spectral purity describes the inherent stability of a signal. Stabilities can be short-term or long-term, whereby the greater interest is in short-term stability or frequency changes in less than one second. Spectral purity is important for mobile radio tests, selectivity tests of RF receivers or for oscillator substitution applications. Common specifications for spectral purity are shown in the following figure.
Spectrum analyzers are narrowband analyzers, but they are flexible in their settings. They can therefore cover a wider frequency range than oscilloscopes.
The frequency and amplitude accuracy influence the measurement (un)reliability. The frequency accuracy is determined by various factors: Frequency reference accuracy, measurement span, resolution bandwidth (RBW) and horizontal resolution.
The amplitude accuracy also depends on various factors: Input connection (mismatch), RF input attenuator, mixer and input filter ripple, IF gain/attenuation (reference level), RBW filter, display scale fidelity and calibrator accuracy (absolute accuracy).
IF filter: A wide range of variable setting options for the analysis bandwidth (Resolution Bandwidth, RBW) allows the signal analyzer to be optimally adapted to the sweep and signal conditions. This allows you to achieve the ideal balance between frequency selectivity (i.e. the ability to resolve signals), the signal-to-noise ratio (SNR) and the measurement speed.
The narrower the RBW, the better the spectrum analyzer can distinguish signals that are close together.
The displayed average noise level (DANL) is an indicator of how well the spectrum analyzer can also measure small signals. The sensitivity indicates the smallest measurable signal. The displayed noise is a function of the IF filter bandwidth; it decreases as the RBW decreases. The sensitivity of your signal analyzer increases with the setting of the smallest possible analysis bandwidth.
The dynamic range (unit in dB) is the ratio of the highest measured signal strength to the lowest signal strength measured at the same time. The lower limit of the measurable range is due, among other things, to the background noise that overlays the smallest useful signals. The maximum signal that can be generated by the DUT used limits the dynamic range upwards.
EAn in-channel test measures the sensitivity of the HF receiver. The sensitivity indicates the minimum signal level for a certain percentage of errors in the demodulated information.
The co-channel immunity test is similar to a sensitivity test. The level of signal distortion is monitored in the presence of an interference signal on the same RF channel. Immunity describes the ability of an RF receiver to respond selectively to the desired useful signal while the receiver is exposed to an interference signal.
Out-of-channel tests verify the correct functioning of an RF receiver in the presence of signals from outside the channel and monitor its susceptibility to internally generated spurious responses. The performance of an RF receiver can essentially be checked via the interference immunity, the intermodulation immunity and the adjacent channel selectivity.
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