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Schaefer Associates
Werner Schaefer
2 Pepper Creek Way
Novato, CA 94947-2089

Tel.: (415) 898-1187
Fax: (415) 898-2878
e-mail: wsemc@cisco.com


                                                                        May 12, 2010


RE: Clarification of Content of RF/μwave Scopes


The following detail of scopes in the RF/μwave area is to be included in the “Comments”
column to ensure proper presentation of the technical capability:

1) If a calibration activity is performed in accordance with a published standard then the
standard is to be referenced. For example:

      antenna calibration: ANSI C63.5-2005
      calibration of LISNs: ANSI C63.4-2003
      current probes: IEC 61000-4-6 or ISO 11452-3
      EMI receivers: CISPR 16-1-1 (2006)

Some assessors are of the opinion that such standards are not to be included – or be
relegated to a foot note. This is not correct since these standards call out the exact me-
thod how to perform calibrations. Different methods of these activities result in different
correction factors!

2) If a laboratory measures the Reflection and/or Transmission coefficient (e.g., with a
Vector Network Analyzer) the characteristics of the EUT that is actually calibrated has a
direct impact on the test result. Therefore, the relevant EUT parameter must be included
on the scope for the uncertainty estimate to be meaningful. For example:

      A highly reflective device will cause a larger measurement uncertainty for a
       transmission measurement
      A low loss device will cause a larger measurement uncertainty for a reflection
       coefficient.

There are two ways (in my opinion) to exactly state the situation:

   a) It can be stated that the relevant EUT parameter is assumed to be ideal (e.g., the
      mismatch uncertainty is assumed to be zero for a transmission measurement).


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       This does not indicate a practical measurement uncertainty number – but is the
       (theoretically) achievable uncertainty with a given measurement system.

   b) Stating the uncertainty as an “equation”. For example: 0.15 + M with a foot note
      on the scope explaining the meaning of M and how to combine it with the stated
      uncertainty value. This approach has the advantage that the clients of the cali-
      bration laboratory can actually determine the expected uncertainty for any device
      that undergoes calibration.

   3) the achievable uncertainty is very much dependent on the test equipment used.
       For example, there are vast differences between network analyzers as far as the
       achievable uncertainty is concerned. Furthermore, specially for network analyz-
       ers the connector interface(e.g., Type N, APC7, APC 3.5 or K) is crucial to the
       achievable accuracy, and so is the calibration kit for network analyzers. The
       stated uncertainty on a scope is to be supported by the information about the test
       equipment used in order to be meaningful and to describe the technical ability of
       a calibration laboratory.

   4) Specific installations like for example a (50 x 80) square meter ground plane,
      used for antenna calibrations. is also to be included to explain relatively low best
      uncertainty values. Such installations are not common and, if not stated on the
      scope, will immediately call the uncertainty estimate into question.




Werner Schaefer                         Page 2 of 2                               5/12/2010