However, especially at high power, a number of effects can lead to non-linearity through formation of a metal–semiconductor junction at what is supposed to be a metal-metal junction. Passive components such as cables, connectors and antennas, are generally expected to be linear and therefore not liable to generate any intermodulation. The output of the DUT is fed to a spectrum analyser where the results are observed, possibly via an attenuator to reduce the signal to a level the instrument can cope with. These harmonics could cause unexpected intermodulation products in the DUT, again giving misleading results.
TEST TONE GENERATOR ABLETON GENERATOR
Low-pass filters may also be provided at the generator outputs to remove any harmonic distortion. The circulators have one port connected to a resistive load so that they act as isolators. The circulators are there to provide even more isolation between the generators and isolation between any signal that might get reflected back from the device under test (DUT) and the generator. The resulting intermodulation products will give a false result to the test. If this happens, intermodulation can occur in the non-linear parts of the generator internal circuit. The combiner needs to have good isolation to prevent the signal from one generator being sent to the output of the other. Two signal generators, set to two different frequencies F1 and F2, are fed into a power combiner through circulators. General test setup for two-tone testing Component testing Ĭircuit components such as amplifiers can be tested using the two-tone method with a test setup like that shown in the figure. That is, the ability of the receiver to distinguish between transmissions close in frequency. Two-tone testing can also be used to determine the discrimination of a radio receiver. Intermodulation effects cannot be detected with single-tone testing, but they may be just as, or more undesirable than harmonic distortion depending on their frequency and level. The new frequencies created by intermodulation are the sum and difference of the injected frequencies and the harmonics of these. Intermodulation distortion can produce outputs at other frequencies. This kind of distortion consists of whole-number multiples of the applied signal frequency, as well as the original frequency being present at the device output. If there is any non-linearity in the device, this will cause harmonic distortion at the output. An electronic device can be tested by applying a single frequency to its input and measuring the response at its output.
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