Home » Time & Frequency Metrology: Group Leader and Quantum Subject Matter Expert

Time & Frequency Metrology: Group Leader and Quantum Subject Matter Expert


David Howe is a Senior Research Advisor at Colorado University, Physics Department. He is identified as a subject matter expert in the following areas:

  1. Quantum-physics, quantum communications, and quantum-engineering research,
  2. Complex electronic control and waveform development,
  3. Quantum-enabled time-transfer over satellites and fiber,
  4. Research, demonstration, and application of next-generation, highest-accuracy, smallest size, weight, and power, transportable atomic clocks,
  5. Ultra-high resolution cm-level resilient outdoor and indoor PNT,
  6. Environmental testing, accuracy validation, synchronization measurements, GPS and UTC time-scale algorithms, and certified calibrations.

2000 TO 2017

Since 2000 Howe has been Group Leader for NIST’s Time and Frequency Metrology Group. The Group originally measured and characterized the spectral purity of oscillators and provided calibration services that fit the overall mission of the Physics Lab and its Time and Frequency Division.  Because of his numerous ties to commercial, military, and international standards bodies, he has expanded the mission of the Group to include a significantly broader scope of specialized research and services that extend to atomic standards, photonics of ultra-stable lasers, cryogenic oscillators, mm-wave device testing, and quantum-sensors.  As Group Leader, he consistently secured annual funding with a total exceeding $20M from other-agency and commercial-companies, including the following:

  • Army Research Lab
  • Office of Naval Research, Naval Research Lab and U.S. Naval Observatory
  • AF Space Command: GPS Master and Alternate Master Control Stations
  • Raytheon Missile Systems
  • NASA-JPL, NGA, NSA, NRO, CIA, Johns-Hopkins APL
  • Symmetricom (now Microsemi), OEwaves, AOSense

While consistent funding, program oversight, and competitions are not the only measures of successful leadership, they are indicators of Howe’s skill in identifying and promoting valuable innovations as well as his ability to solve and deliver on a vast array of real-world applications.


Because of Howe’s years of innovative leadership in the diverse fields of electronics, photonics, atomic and molecular physics, optics, and materials technologies, he is recognized as a “game changer.” His wide-ranging experience with all aspects of the most-accurate atomic clocks, lowest-noise oscillators and components, as well as state-of-art global timing and synchronization networks has prepared him to meet the challenges of emerging technologies and research developments that require timing solutions.  Synchronization networks are vital to a unified coordinated system of timing, acting like gears in complex machinery that connect multiple actuators.

He is tasked with meeting the most challenging synchronization needs, often on moving, nonstationary, platforms with high precision.  This requires substantive knowledge and familiarity with a variety of complex technologies that depend on timing. His work with numerous agencies has been instrumental in developing innovative new, and often disruptive, technologies in sectors including microwave radio-frequency (rf), fiber-optic, satellite synchronization, THz and laser AM and PM spectra, hi-speed modulations with low-bandwidth, cybersecurity, commercial chip-scale integrations, and harsh military environments.

As the leader of the time and frequency metrology group he is tasked with actively leading the group to maintain research that is at the forefront of research. To meet this obligation, he has arranged the acquisition of a fiber optic time transfer modem which the group has tested on the BRAN fiber network in Boulder, CO.  Optical time and frequency transfer is gaining popularity around the world and these experiments are motivated by a high demand this technology in the United States.  Other work at the forefront of timing science include identifying and attempting to solve the issue of anti-correlation. The discovery of anti-correlation has negated the legitimacy of many past measurements and has re-directed the attention of the measurement community toward solving this problem.


As a leader in the field of timing standards, Howe has worked with a broad spectrum of government agencies and corporate organizations.  his particular strengths are in establishing global partnerships to set policy for public and government programs in diverse projects that rely on accurate standards.  From 1988-1990, he has published the governing standards used today for Two-way Satellite Time Transfer which are upheld by the annually-convened International Telecommunications Union (ITU) in Geneva.  Spring 2016, ITU delegates voted in favor of his new statistical standards called TOTAL and THEO variances that outperform the famous Allan variance for fixed-duration atomic-clock testing.

Through a consensus process, he has coordinated the development of operational policies and standards for Raytheon, Ball Aerospace, Boeing, and Northrup-Grumman, which provide the most sophisticated components and systems to a large base of customers worldwide. Over the past four decades he has initiated the development of operational policies and standards in collaboration with Agilent, and Rohde-Schwarz USA which together supply the broadest product line of instrumentation  and with Microsemi (formerly Symmetricom).  Microsemi is well known in the time and frequency community for manufacturing the world’s best-selling atomic frequency standards and related components. More recently, he has developed standards with Redstone Arsenal, a test facility for the most advanced terrestrial and space communications and radar systems and for DARPA, NSA, and CIA technical governance.

For more than 50 years Allan variance has been the accepted standard for analyzing the fractional frequency stability and noise types for stable oscillating reference frequencies. This statistic does not report variance beyond half of the measurement period. The ITU (International Telecommunications Union) has recommended acceptance of a statistic that he has developed called TheoH (Theo Hybrid) for the standards of governance in Geneva. This statistic is a hybrid statisitic that combines the overlapping version of the Allan variance in the short term with the TheoBR (Theo with Bias Removed) which provides the long term estimate of noise. Click here to review the final recommendation.

Related publications:


As Group Leader for NIST’s Metrology Group, Howe directs the AM and PM noise as well as frequency stability calibration measurements of oscillating signal sources and components for industry, military, and other national calibration labs.  Calibrations provide certified, traceable, proof-of-performance measurements, to a list of capabilities as follows (partial list only):

Single-Sideband Phase and Amplitude Noise:

  • Carrier Frequency from 5 MHz to 110 GHz and 500 – 700 GHz
  • Fourier Frequency from 0.1 Hz to 10 MHz or 10% of Carrier Frequency
  • -145 dB at 1 Hz, -190 dB at 10 kHz —  Typical Uncertainty of 1 dB

 Round-Robin Tests Using Portable Calibrated Noise Source:

  • Carrier Frequencies of 5 MHz, 10 MHz, 100 MHz, 10.6 GHz, 21.2 GHz, and  42.4 GHz
  • Calibrated Noise Levels of +/- 0.1 dB out to 3% of Carrier Frequency

 Time-domain Frequency Stability:

  • Optical reference 800 – 1570 nm, locked to H-maser or optical cavity
  • Multi-channel, ultra-low noise dual-mixer measurement system for RF to mm-wave
  • ALLAN, TOTAL, and THEO variance analysis (Howe is inventor of TOTAL and THEO variances)
  • Averaging times starting at 0.01 s

Related publications:


NIST technology is often developed to stay ahead of known or potential new scientific developments.  In a similar way, the Department of Defense (DoD) must stay ahead of U.S. adversaries and threats to national security. Howe is called upon to advise on and authenticate time and frequency requirements in restricted topics.  As a result, his expertise is sought when new research in U.S. Government (USG) agencies in the DoD, NRO, CIA, and NSA. As an expert research advisor, Howe has provided consultation to:

  • DHS: National Science and Technology Council’s Critical Infrastructure Security and Resilience (CISR) R&D Subcommittee to develop an Implementation Roadmap
  • NIST’s Communication Technology Lab’s (CTL’s) Public Safety Communications Research (PSCR) team to plan and test position, navigation, and timing (PNT) for FirstNet Location Base Services using 4G LTE

Responsibilities include creation of programs, policies,standards, performance requirements, funding approval, and technical consultation to Program Directors.  As an advisor he helped create RFPs, BAAs, recommend funding awards, review papers and reports for peer review publications.

Related publications:


Active member of the following committees, evaluation teams, and study groups:

  • PTTI GPS Frequency Standards Working Group, to analyze GPS clock performance and recommend actions
  • Member of evaluation team to eight DARPA programs in MTO and DSO
  • Member of NASA Space Advisory Board on Joint Missions
  • Member of Two-way Satellite Time and Frequency Transfer CCTF WG
  • Member of DoD PNT-PTTI Working Group
  • Delegate for U.S. critical infrastructure as an expert on timing
  • Inst. of Navigation (ION) & Joint Services Data Exchange (JSDE) Technical Program Committee,
  • Member CTL-PSCR assessment team to study PNT for FirstNet Location Base Services using 4G LTE

As a Senior Life member and Fellow of the IEEE, Howe’s participation in the time and frequency committee include:

  • IEEE International Frequency Control Symposium (IFCS), Technical Program Committee 29 years; 1 year for Group 3: Microwave Frequency Standards and Session Chair, and 28 years for Group 2: Oscillators, Synthesizers, Noise, & Circuit Techniques,
  • Joint Program Committee member for IFCS/EFTF (European Frequency and Time Forum),
  • Host, sponsor, and contributor to IEEE-UFFC student scholarships (up to 10 winners) to attend annual NIST Time and Frequency Seminar and Conference for which Howe is the General Chair,
  • Ongoing reviewer for the submitted abstracts to the IFCS and recent Evaluator for UFFC Outstanding Paper Award,
  • Judge for IFCS/EFTF Student Paper Competitions,
  • Contributor to IFCS Tutorial Sessions.


Howe has done extensive work related to making precise signal and noise measurements, particularly phase-noise measurements, for electronic signal carriers ranging from below 1 MHz to 1 THz and photonic signals from 200 – 2000 nm. This work requires expertise in many topics related to fundamental research design and electronic/photonic electromagnetic theory and measurements. He is proficient in:

  • Network and circuits analysis, and equivalent circuits
  • Pulse power measurements, pulse amplification, and pulse distribution
  • Filter design (Butterworth, Chebyshev, FIR and IIR, recursive, constant-delay, multi-tap, etc.)
  • Scattering parameter estimation, Bode plots, Smith charts
  • Fast rise-time detection and related noise uncertainty analysis
  • Wideband analog-to-digital (ADC) and digital-to-analog (DAC) conversion schemes
  • Dielectric coefficient measurements, dielectric loss, and loss tangent
  • Laplace and z transforms, Maxwell’s equations
  • Windowing and side-lobe leakage suppression
  • Digital filter design and characterization
  • Time-frequency domain, and related convolution-multiplication and scaling effects
  • Spectral aliasing
  • Frequency synthesis (using direct digital, PLL, multiplication-division, programmable array logic, etc.)
  • Noise suppression (using cross-correlation spectral analysis, negative feedback, synchronous lock-in methodologies, etc.)
  • Multiresolution signal decomposition and signal reconstruction
  • Design of all-pass equalizers, delay-line filters, and complex-conjugate matched filters
  • Impedance, reactance, and resistance transforms for matching network design
  • Analysis and reduction of media phase and frequency dispersion, standing waves, multipath, and transmission-line loss
  • Electrical-length measurements (for example, accurate phase and group velocity estimation)
  • Uncertainty analysis of volt and resistance standards
  • Most signal modulation schemes
  • Single and multi-mode optical fiber delay measurements
  • Directional couplers, bridge couplers, and circulators

Related publications:


Howe has extensive background in the research and development of key improvements for oscillator design which include:

  • Vibration and acceleration sensitivity analysis and reduction
  • Phase noise measurements for radar characterization
  • Oven control, intrinsic (dual-frequency mode) and internal temperature sensing
  • Low-noise active and passive component selection and design
  • Environmental sensitivity and its reduction
  • Estimating frequency predictability, aging, and frequency drift
  • Miniaturizing, ruggedizing and configuring oscillator hardware
  • Detecting and eliminating frequency steps
  • Phase-locked loop design, frequency-locked loop design
  • Reduction of cost and power-requirements

Howe acquired, characterized, and upgraded the longest operating Hydrogen maser from the time-scale at NIST, s/n-001. He saw the enormous value in upgrading this H-maser, made by Sigma Tau Corporation, and he was in fact part of the original technology transfer project and was very familiar with the standard.  The manufacturing team led by Dr. Harry Peters of NASA GSFC was thrilled to work with original researcher Howe.  In spite of its 25-year age, s/n-001 now performs as well as the best modern H-masers and is a huge addition to the assets held by the Time and Frequency Metrology group as both a research tool and frequency standard.  For perspective, all H-masers held by metrology labs around the world are used for timekeeping and the maintenance of local UTCs.  Since this particular H-maser is not used as a clock, it provides a rare opportunity to adapt and configure it for special measurements, such as increased H-beam density to achieve excellent short-term phase stability to measure advanced atomic clocks, eg., optical clocks.

Related publications:


High power shaker with slip-table and controller for measuring vibration sensitivity.  The controller for this shaker has the ability to test various user defined vibration profiles for simulation of real-life interactions.


Time synchronization is the foundation for most modern and all future large communications networks. Wide bandwidth, high throughput time-division multiple access (TDMA), code-division multiple-access (CDMA) and orthogonal frequency-division multiplexing (OFDM) protocols depend directly on the synchronization of a large number of oscillators which time the signals which are redirected through various nodes, base transceiver stations, routers, and switchers. Howe recently generalized the TOTAL variance approach to encompass a broader range of models and noise classes for efficiently assessing network stability using such information carriers as spread-spectrum, wireless OFDM & CDMA (cell phones), and Internet-based and specialized military networks. Using and interpreting what is called the “modified TOTAL” variance, He was able to develop quick, short-cut wavelet transform, Kalman, and auto-regressive moving-average (ARMA) predictive algorithms for steering these local network oscillators during loss-of-lock, or what is called “oscillator holdover” periods. Holdover specifications set the single most crucial limit for how long the network continues to operate during any one of a variety of loss-of-lock scenarios. He advises major cell phone and telecommunication service provider stakeholders to find ways to protect services, especially during holdover, while data traffic is projected to increase at exponential rate in some areas.  This work is coordinated through NIST’s Communications Technology Laboratory (CTL) and Public Safety Communications Research (PSCR).

Worse than a simple loss-of-lock scenario, network timing loops occur when a local oscillator loses normal synchronization to a higher stratum (when stratum 1 to 4 architecture is used), whereupon the local oscillator seeks any suitable reference timing signal, but ultimately finds itself to lock to. He advises conventional telephone service providers who must comply with standard stratum 1 to 4 frequency synchronization topologies within their networks and who must detect and eliminate timing loops without reducing bandwidth or disturbing normal communications and operations.

Related publications:


As Group Leader for NIST’s Metrology Group, Howe directed migration and expansion of the Phase Noise Metrology into the Katherine B. Gebbie laboratory at NIST.  This building was designed for for low noise measurements. Each lab module in this building was constructed on individual concrete slabs for vibration isolation.  This move required extensive planning on the group and facilities management level.  Prior to this move he organized the construction layout of the laboratory space to accommodate the future needs of the group.  This planning included the layout of the lab space for everything from the wall placement down to the layout of the 120 V electrical receptacles.


16′ X 11′ RF shielded enclosure in Katherine Gebbie Building

One of the most important capability upgrades involved with migrating over to the  new lab space was the procurement and assembly of a 176 square foot shielded room.  The shielded room enhances the measurement capabilities of the group by eliminating EMI interference in an environment where wireless communication device use increases daily.  This room is rated for an attenuation of 100 dB at 10 GHz.

With this migration he also expanded research into optics by adding a state-of-the art optics lab.  The group now has access to a Bose Einsten Condensate experimental setup, a Rubidium magneto optical trap, and a low noise optical frequency comb which is used as an optical frequency reference.

Back To Top

Log Out