Specifications

Chapter 15 133
Concepts
Time Gating Concepts
Concepts
Time Gating Concepts
Introduction: Using Time Gating on a Simplified
Digital Radio Signal
This section shows you the concepts of using time gating on a simplified
digital radio signal. “Making Time-Gated Measurements” on page 57
demonstrates time gating examples using the ESA and PSA.
Figure 15-2 shows a signal with two radios, radio 1 and radio 2, that are
time-sharing a single frequency channel. Radio 1 transmits for 1 ms
then radio 2 transmits for 1 ms.
Figure 15-2 Simplified Digital Mobile-Radio Signal in Time Domain
We want to measure the unique frequency spectrum of each
transmitter.
A spectrum analyzer without time gating cannot do this. By the time
the spectrum analyzer has completed its measurement sweep, which
lasts about 50 ms, the radio transmissions switch back and forth 25
times. Because the radios are both transmitting at the same frequency,
their frequency spectra overlap, as shown in Figure 15-3. The spectrum
analyzer shows the combined spectrum; you cannot tell which part of
the spectrum results from which signal.