Column Control DTX

Solutions for Using a Frequency Counter to Measure Phase Noise Close to a Carrier Signal

Application Notes

Table of Contents

  • Overview
  • Problem
  • Solution
    • Understanding gap-free measurements
    • Getting close to the carrier
  • Results and Benefits
    • Using the MDA plot
  • Applying the Allan deviation
  • Conclusion
  • References
  • Related information

Overview

A local oscillator (LO) produces carrier signals for transmitters and reference signals for receivers—and an LO is the heart of every radar, electronic warfare (EW), or communication system. In communication systems, ever more data is being squeezed into limited bandwidths. In the evolution of radar systems, there is an ongoing need to resolve targets more accurately at greater distances.

To meet the needs of these demanding applications, high stability, and spectral quality in the LO are critical to achieving high-performance transmitter and receiver designs. When verifying stability and spectral quality, an instrument such as a signal (spectrum) analyzer provides informative wide-area views of the noise and spectral content around the LO carrier signal. Unfortunately, this type of instrument may fall short in providing a clear picture of the phase noise extremely close to the carrier. In this context, “close to the carrier” or just “close” refers to the noise within ±200 kHz of the carrier frequency on the x-axis of a frequency-domain plot.

To create a clearer picture of noise close to the carrier, instruments such as the Keysight Technologies, Inc. 53230A universal frequency counter pick up where signal analyzers leave off. The rest of this note describes how the high-resolution and gap-free measurement capabilities of the 53230A can be used to take a closer look at LO signals. It also presents example results in the form of modulation domain analysis plots and Allen deviation plots.

Problem

Until recently, fully characterizing noise less than 10 Hz from a carrier signal required a complex measurement setup such as the heterodyne method (reference 2, Riley) or an expensive measurement system such as a dedicated phase noise analyzer. Signal analyzers and frequency counters are viable alternatives, but each has limits. As noted earlier, signal analyzers provide an unmatched wide-area view of spectral content. A typical measurement will clearly show noise around the carrier, and the span and bandwidth can be adjusted to dial in various views of the noise content. However, as measurements get closer to the carrier, the noise content becomes crowded, and it becomes difficult to determine the possible causes of the noise.

A frequency counter can make close-in measurements, but care must be taken to ensure useful results. For example, when working close to the carrier it is necessary to capture a data set large enough to reveal any gradual changes caused by low-frequency noise. However, when performing a statistical analysis on a large set of timing measurements, traditional methods such as standard deviation won’t suffice because they calculate the cumulative effect of the sample. The consequence: The larger the sample set, the more the standard deviation can grow. Said another way, it can become non-convergent.

×

Please have a salesperson contact me.

*Indicates required field

Preferred method of communication? *Required Field
Preferred method of communication? Change email?
Preferred method of communication?

By clicking the button, you are providing Keysight with your personal data. See the Keysight Privacy Statement for information on how we use this data.

Thank you.

A sales representative will contact you soon.

Column Control DTX