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Chapter 9 195
9 Two-Tone Waveform Generator
In the following sections, this chapter describes the two-tone mode, which is available only in
E8267D PSG vector signal generators with Option 601 or 602:
• “Overview” on page 195
• “Creating, Viewing, and Modifying Two-Tone Waveforms” on page 195
See also: “Arbitrary (ARB) Waveform File Headers” on page 72
Overview
The two-tone mode builds a waveform that has two equal-powered CW signals, or tones. The default
waveform has two tones that are symmetrically spaced from the center carrier frequency, and have
user-defined amplitude, carrier frequency, and frequency separation settings. The user can also align
the tones left or right, relative to the carrier frequency.
The two-tone waveform generator is designed for testing the intermodulation distortion
characteristics of non-linear devices, such as mixers or amplifiers. Intermodulation distortion (IMD)
occurs when non-linear devices with multiple input frequencies interfere with adjacent channels or
cause unwanted outputs at other frequencies. The two-tone waveform generator supplies a signal
whose IMD products can be measured using a spectrum analyzer and used as a reference when
measuring the IMD generated by a device-under-test.
Two-tone waveforms are created using the internal I/Q baseband generator and stored in ARB
memory for playback. Although the two-tone mode generates a high-quality waveform, a small
amount of IMD occurs. In addition to IMD, a small amount of carrier feedthrough and
feedthrough-related IMD may be present when the spacing between the tones is centered on the
carrier frequency. To minimize carrier feedthrough for a two-tone signal, you must manually adjust
the I and Q offsets while observing the center carrier frequency with a spectrum analyzer. For
measurements that require the absence of IMD and carrier feedthrough, you can create distortion-free
multitone signals using Agilent Technologies’ Signal Studio software Option 408.
NOTE For more information about two-tone waveform characteristics and the E8257D/67D PSG
Vector Signal Generator two-tone format, download Application Note 1410 from our website
by going to http://www.agilent.com and searching for “AN 1410” in Test & Measurement.
Creating, Viewing, and Modifying Two-Tone Waveforms
This section describes how to set up, generate, and modify a two-tone waveform while viewing it
with a spectrum analyzer. Although you can view a generated two-tone signal using any spectrum
analyzer that has sufficient frequency range, an Agilent Technologies PSA Series High-Performance
Spectrum Analyzer was used for this demonstration. Before generating your signal, connect the
spectrum analyzer to the signal generator as shown in Figure 9-1.