Specifications

58 Chapter 8
Making Time-Gated Measurements
Generating a Pulsed-RF FM Signal
Making Time-Gated Measurements
Generating a Pulsed-RF FM Signal
Traditional frequency-domain spectrum analysis provides only limited
information for certain signals. Examples of these difficult-to-analyze
signal include the following:
• Pulsed-RF
• Time multiplexed
• Interleaved or intermittent
• Time domain multiple access (TDMA) radio formats
• Modulated burst
The time gating measurement examples use a simple
frequency-modulated, pulsed-RF signal. The goal is to eliminate the
pulse spectrum and then view the spectrum of the FM carrier as if it
were continually on, rather than pulsed. This reveals low-level
modulation components that are hidden by the pulse spectrum.
Refer back to these first three steps to setup the pulse signal, the
pulsed-RF FM signal and the oscilloscope settings when performing the
gated LO procedure (page 62), the gated video procedure (page 64) and
gated FFT procedure (page 66).
For an instrument block diagram and instrument connections see
“Connecting the Instruments to Make Time-Gated Measurements” on
page 61.
Step 1. Setup the pulse signal with a period of 5 ms and a width of 4 ms:
There are many ways to create a pulse signal. This example
demonstrates how to create a pulse signal using a pulse generator or by
using the internal function generator in the ESG. See Table 8-1 for
setup information of a pulse generator and Table 8-2 for setup
information of the internal generator of the ESG. Select either the pulse
generator or a second ESG to create the pulse signal. You need two
ESGs if you want to use the ESG internal function generator to create a
pulse signal.
Table 8-1 81100 Family Pulse Generator Settings
Period 5 ms (or pulse frequency equal to 200 Hz)
Pulse width 4 ms
High output level 2.5 V
Waveform pulse
Low output level -2.5 V
Delay 0 or minimum