A variety of measurement problems have been pointed out in the literature in the last 10 years, like inconsistencies and gross errors, chiefly related to low-noise oscillators. Such warnings come in large part from NIST (Boulder site) and from LNE-LTFB (FEMTO-ST Institute). This indicates that the current knowledge in the assessment of type B uncertainty and zero uncertainty (VIM terms) is insufficient. No traceability chain has been implemented yet, and no international comparison of phase noise has ever been made in the EURAMET community.
The proposed comparison
- A set of traveling oscillators (tentatively 4-5, from HF (10 MHz) to SHF (20 GHz)) is prepared by the French team, and installed in a rugged case.
- All participant NMIs are welcome to technical and organisational discussions:
- Choice of oscillator types and frequencies
- Choice of Fourier (analysis) frequency span
- Choice of the comparison scheme (polygonal, star or hybrid)
- Agree on experimental procedures
- Option to invite 1-2 experts to review our procedures
- How to exchange data
- Data analysis
- Propose guest participants, and rules which apply (see below)
- Use of the results, and future actions
- Each participant does all the proposed measurements or a subset of, depending on the available equipment. For example, some instruments may not be able to measure microwave oscillators, or have a limited span of analysis frequency.
- At the end of the measurements, each participant shares the results and sends the oscillator set back (or forward, in a polygonal scheme), at its expenses.
- The French team takes most of the burden of analysis, but all contributions are welcome.
Rather restricting ourselves to the EURAMET NMIs, we should invite qualified guests to join the comparison. Typical guests should be the manufacturers of phase noise analysers and of low-noise oscillators and some research institutions, but we may identify other cases. Because metrology and research must be kept free from the pressure of other interests, guest participants may be subject to restrictions.
- Agree on the identification of experimental difficulties, and on the identification of common inconsistencies and errors.
- Progress in the assessment of type B uncertainty, zero uncertainty, and reproducibility.
- Pave the way to the implementation of national traceability chains. European traceability may be considered too.
Depending on the knowledge acquired and on the results
- An article in Metrologia.
- A more detailed report on methods and results (supplemental material of the above, or standalone).
- A EURAMET Technical Guide on good practice.
Side targets – subject to redefinition at the issue of the comparison
- Promote the dialogue between the parties: NMIs and research institutions, manufacturers of oscillators and instruments, system integrators, and more generally users of phase noise.
- Promote a discussion about the right place of phase noise in the context of metrology. In fact, while phase noise is with Electricity and Magnetism, the bulk of scientific knowledge is with Time and Frequency (together with the Allan variances).
- Stimulate the NMIs to publish their own CMCs.
- Educate users and manufacturers to good practices and to the adoption of SI units.
The project coordination is in the campus of Besançon, where the LNE-LTFB and the FEMTO-ST Institute are located. The FEMTO-ST Institute is a laboratory affiliated to CNRS and to the local universities. The LNE-LTFB is a French DI for time and frequency, including phase noise. The activity related to the phase noise measurements of LNE-LTFB is carried out in the premises of FEMTO-ST.
Phase noise measurements are part of a research project funded by LNE, which allows LNE-LTFB, with the support of FEMTO-ST, to coordinate and pilot the TC-TF comparison project as well as to provide the traveling oscillators in order to characterise them in the framework of this project, in terms of phase noise.