Interference Testing with Handheld Spectrum Analyzers Manual

Interference Testing with Handheld Spectrum Analyzers Manual
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Interference Testing with Handheld Spectrum Analyzers Manual

  • 8The reason for the breaks in the measured response for the left channel, centered at 870.0 MHz, is that this radio is not transmitting all the time and the spectrum analyzer is measuring the rapid changes in the signal amplitude as the analyzer sweeps across the display. As the analyzer was configured with a total sweep time of 159.32 milliseconds, each horizontal box is approximately 15.9 milliseconds long. It was previously mentioned that a NA GSM 850 signal has a 4.615 millisecond frame time containing 8 time slots; therefore each box on the analyzer display contains approximately 3.5 frames of user data. As some time slots do not always contain user data, the transmitter is switched off dur-ing these empty slots resulting in an uneven spectrum response as the analyzer sweeps. Later in this application note, there is a discussion on techniques to confirm that the signal has time slots rather than just a series of closely spaced narrowband signals which may have been the first impression when examining the display shown in Figure 3.Radio Duplexing (continued)