197ConceptsTime Gating ConceptsTime Gating ConceptsIntroduction: Using Time Gating on a Simplified Digital Radio SignalThis section shows you the concepts of using time gating on a simplified digitalradio signal. The section on Making Time-Gated Measurements demonstrates timegating examples.Figure 15-3 shows a signal with two radios, radio 1 and radio 2, that aretime-sharing a single frequency channel. Radio 1 transmits for 1 ms then radio 2transmits for 1 ms.Figure 15-3 Simplified Digital Mobile-Radio Signal in Time DomainWe want to measure the unique frequency spectrum of each transmitter.A signal analyzer without time gating cannot do this. By the time the signal analyzerhas completed its measurement sweep, which lasts about 50 ms, the radiotransmissions switch back and forth 25 times. Because the radios are bothtransmitting at the same frequency, their frequency spectra overlap, as shown inFigure 15-4 The signal analyzer shows the combined spectrum; you cannot tellwhich part of the spectrum results from which signal.Figure 15-4 Frequency Spectra of the Combined Radio Signals
