Skip to main content
U.S. flag

An official website of the United States government

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Time and Frequency Metrology

NIST's Time and Frequency Metrology Group has the world's most advanced measurement and calibration facilities for characterizing noise components in oscillators and frequency synthesizers. It engages in many activities to determine the cause of various kinds of noise for the purpose of isolating and reducing it, ultimately leading to improved components, instruments and techniques that are often necessary for new applications.

Noise, present everywhere, causes a signal source to deviate from its ideal performance. It introduces time-dependent, random fluctuations in the frequency, phase and amplitude of a signal. These fluctuations due to noise manifest themselves as frequency modulation (FM), phase modulation (PM) and amplitude modulation (AM) of the ideal carrier. The spectral purity and frequency stability of a signal are characterized in terms of these modulation noise types. 

The goals of NIST’s Time and Frequency Metrology Group are to: (1) support high-precision noise measurements, (2) contribute to fundamental improvements in spectral purity of oscillators and frequency synthesizers, and (3) provide certified state-of-the-art PM and AM noise measurement capabilities to National Measurement Institutes (NMIs), US military, industrial and commercial organizations.

Projects and Programs

Noise Metrology

We provide state-of-the-art phase and amplitude noise measurements for signals from RF to optical frequencies.

FPGA Design

Our group is developing FPGA based digital phase noise measurement and control systems.


Multipath Mitigation from FM-AM Correlation

Archita Hati, Craig W. Nelson
Multipath is one of the limiting factors for an accurate outdoor and indoor localization. We proposed an approach that uses a multipath mitigation derived from


  1. V. Gerginov, Two-Photon Optical Frequency Reference with Active AC Stark Shift Cancellation, Provisional Patent Application # 62,629,800
  2. A. Hati, C.W. Nelson, D.A. Howe, Phase Modulation Noise Reducer, United States, Patent # 10,050,608.
  3. D.A. Howe, A. Sen Gupta, C.W. Nelson, and F.L. Walls, High Spectral Purity Microwave Oscillator Using Air-Dielectric Cavity, United States Patent # 7,075,378
  4. F.L. Walls, Calibration System for Determining the Accuracy of Phase Modulation and Amplitude Modulation Noise Measurement Apparatus, United States Patent # 5,172,064
  5. F.L. Walls, Frequency Calibration Standard Using a Wide Band Phase Modulator, United States Patent # 5,101,506
  6. F.L. Walls, Method and Apparatus for Wide Band Phase Modulation, United States Patent # 4,968,908
  7. F.L. Walls and J.R. Vig, Acceleration Insensitive Oscillator, United States Patent # 4,575,690


2018 IEEE Fellow - David A. Howe

The IEEE Grade of Fellow is conferred by the IEEE Board of Directors upon a person with an outstanding record of accomplishments in any of...

2013 W. G. Cady Award - David Howe

The W. G. Cady Award is to recognize outstanding contributions related to the fields of piezoelectric or other classical frequency control...

1995 Rabi Award - Fred Walls

The Rabi Award is to recognize outstanding contributions related to the fields of atomic and molecular frequency standards, and time...

Job Openings

Our group has periodic openings for Postdoctoral Fellows, Visiting Scientists, and Graduate Students. Please contact us for more information.


Group Leader

Calibration Leader