Dear Mr. Cormier,
Mike Violette of Washington Labs took the liberty of
forwarding to me your recent EMC-PSTC LISTSERV posting on
the topic of the use of biconlog antenna in ANSI
C63.4-2009. (I do not normally follow the EMC-PSTC
LISTSERV).
In order for you to judge the validity of my answer
to the question that you raised in your recent LISTSERV
posting, I first will tell you a bit about the Accredited
Standards Committee C63® and then about myself
and my relationship to the Accredited Standards Committee
C63®.
The
Accredited Standards Committee C63® is a
major United States-based EMC standards developers
focused on many aspects of emission and immunity
measurements, instrumentation, and resources for test
lab competency and quality control. Its standards
development activities are highly diversified. One of
the most important aspects
of the Accredited Standards Committee C63® is
the acceptance of its standards by US
regulatory agencies including the Federal
Communications Commission (FCC). The FCC explicitly
references several Accredited Standards Committee C63®
standards (including the EMC Emissions Testing
Standard ANSI C63.4 and EMC Antenna Calibration
Standard ANSI C63.5) in its Rules (i.e., in 47 CFR).
I have worked as an EMC Engineer for 33 years, and
for the last 15 of those years I have either co-owned or
individually owned Independent Third party EMC Test Labs
that were ISO/IEC 17025-accredited for a Scope of
Accreditation that included ANSI C63.4. I am the American
Council of Independent Laboratories [ACIL] Conformity
Assessment Section [CAS] Vice-chairman, and I am the Chief
of the Editorial Board of the ACIL's EMC Standards Alert
Newsletter. Also, I am the ACIL CAS's Alternate Voting
Member of the Accredited Standards Committee C63®.
For
the last few years, I have been a member of the Subcommitte
1 (SC1) Working Groups that are actually responsible for the
detailed technical writing and maintenance tasks for the
ANSI C63.4 and ANSI C63.5 Standards. I was active in the
many-months-long SC1 review process that ultimately resulted
in the publication of ANSI C63.4-2009. I am a current and
very active member of the SC1 Working Group Maintenance
Teams that are preparing the texts of the upcoming versions
of both ANSI C63.4 and ANSI C63.5 - both of which will be
published this year.
In other words, I was there and awake each
time the issue raised in your LISTSERV posting has come up
over the last 3 years!
Now, for my reply to your question:
First, Table 1 of ANSI C63.4-2009 is Normative.
That means that its application is mandatory as writen - it
is NOT a list of suggestions. In other words,
the ONLY antennas that are allowed to be used for making
(final compliance) Radiated Emissions Measurements per ANSI
C63.4-2009 are those antenna types explicitly listed in
Table 1. Additionally, the antenna types listed in Table 1
are ONLY to be used over the frequency range(s) given for
those antenna types in Table 1.
In the frequency range 30 MHz to 1000 MHz, Table 1 of
ANSI C63.4-2009 specifically lists:
- Dipole (passive) antennas (which are required to
be tuned - i.e., are narrowband antennas). [Note: per ANSI
C63.5, only Roberts-type tuned dipoles are allowed to be
used].
- Biconical Dipole antennas (which are center-fed
dipole "fat" antennas having multi-octave broadband
performance). Such antenna have either a 50 Ohm balun or a
200 Ohm balun and are fitted
with two "birdcage" elements).
- Log Periodic Dipole Array antennas (which have
doubly-stacked dipole elements spaced logarithmically apart,
so that the antenna is multi-octave broadband).
[Note that Log Periodic Dipole Array Antennas are
NOT Yagi Antennas - a Yagi antenna has linearly-spaced
elements that yield quite high power gain and very narrow
directivity and have
bandwidths on the order of 10% to 20% of an octave of
frequency. In contrast, Log Periodic Dipole
Array Antennas are multi-octive broadbanded antennas with
better directivity than a tuned
dipole and only slightly higher gain
than a tuned dipole].
- Double-ridged Guide Horn antennas (which are
exactly what their name says they are).
Second, despite what you stated in your
LISTSERV posting, Table 1 of ANSI C63.4-2009 does NOT in
any way mention or list "bilogs". EMC Antenna terminology
is often confusing, so let me say that the term "bilog" is
actually a trade name for one specific brand of hybrid
antenna. (The term "hybrid" should always be used unless
one is referering to a specific Make and Model of antenna
whose trade-name is "Bilog").
Third, I must state that it was NEVER the
intent of the writers of ANSI C63.4-2009 to allow the use
of hybrid antennas for making (final compliance) Radiated
Emissions Measurements per ANSI C63.4-2009. Additionally,
(although you did not raise this point) it was NEVER the
intent of the writers of ANSI C63.4-2009 to allow the use
of hybrid antennas for making Site Validation Measurements
(i.e., standard or volumetric Normalized Site Attenuation
measurements) per ANSI C63.4-2009.
The intention of the writers of ANSI C63.4-2009
to prohibit the use of hybrid antennas for making final
compliance measurements is clearly stated in the NORMATIVE
interpretation that can be found (along with all of the
other NORMATIVE interpretions issued for ANSI C63
Standards) at the following URL: http://www.c63.org/documents/misc/posting/new_interpretations.htm
Please note that the interpretation to which I
am referring is entitled "Use of hybrid antenna above
1 GHz". That said, if your read that
interpretation, the same logic applies regarding the use
of hybrid antennas from 30 MHz to 1 GHz.
Fourth, the ASC 63 have a series of annual
meetings with the lab assessors of each of the US EMC Lab
accrediting bodies. At these sessions, the ASC 63
representative (typically Don Heirman, who just ended his
term as Chair of ASC 63), has made a considerable effort
to educate the assessors that the must
cite a deficiency against any EMC Lab that uses
hybrid antennas for making final compliance measurements
(and/or site validation measurements) per ANSI C63.4-2009.
All that said, you might well ask why every
EMC Test Lab that uses hybrid antennas (for
making (final compliance) Radiated Emissions
Measurements and/or Site Validation Measurements per
ANSI C63.4-2009) has not been given a
"hard time" during an Accreditation audit?
The answer to that question is
complex. However, if we confine ourseves strictly to what
is stated explictly in the standard, we can see the
following problem:
In ANSI C63.4-2009 it is stated in clause 4.5:
Table 1 provides a summary listing of antennas and
typical frequency ranges. This wording clearly
indicates that the antenna type for a specific frequency
range is really mandatory since the table states "yes"
or "no", indicating that the antenna type is (or is not)
to be used in the identified frequency range.
However, in ANSI C63.4-2009 clause 4.5.3 the
following is stated: Linearly polarized antennas as
specified in ANSI C63.2 shall be used to measure
electric fields in the frequency range of 30 MHz to 1000
MHz (see also CISPR 16-1-4:2007). Since
ANSI C63.2 is referenced without a date in clause 2 of
ANSI C63.4-2009, the latest revision of ANSI C63.2 is to
be looked at - i.e., ANSI C63.2-2009. Now,
in CISPR 16-1-4:2007 clause 4.5.1 it is stated that: The
antenna shall be a dipole-like antenna designed to
measure the E-field, and the free-space antenna factor
shall be used. The antenna types include:
a) tuned dipole antennas, whose element pairs are either
straight rods or conical in shape;
b) dipole arrays such as the log-periodic dipole array
(LPDA) antennas, comprising a series of staggered sets
of straight rod elements;
c) and hybrid antennas. [emphasis added].
As a result of the above, some (but by no means all)
auditors take the position that due to
the reference to ANSI C63.2, the exclusion of
hybrid antennas cannot necessarily be assumed - notwithstanding
the clear direction stated in the interpretation
mentioned above.
This is because there is at least the
appearance of a conflict in the applicable standards.
Specifically, ANSI C63.4-2009 Table 1 calls out a
specific antenna type for the identified frequency range,
but, clause 4.5.3 of ANSI C63.4-2009 refers to ANSI C63.2
which in turn refers to CISPR 16-1-4:2007, which
specifically ALLOWS the use of hybrid antennas. This
reference cannot just be "argued away" because the
(undated) ANSI C63.2 reference is stated explicitly in the
normative text of ANSI C63.4-2009 clause 4.5.3, and, is a
normative reference in clause 2 of ANSI C63.4-2009. For
this reason, some auditors are very reluctant to disallow
the use of hybrid antennas from 30 MHz to 1000 MHz for the
making of final compliance measurements.
I am sorry that this answer is so long and so
complex. This is a topic that has generated a great deal
of controvery over the last three years.
Looking to the future, it is possible (but is
by no means certain) that the use of some types
of hybrid antennas may be allowed in in the next
edition of ANSI C63.4. If this does happen, the use of
such hybrid antennas will be subject to a series of strict
dimensional and technical performance criteria (which will
likely include in-house qualification testing) that will
be stated in the next edition of ANSI C63.5.
As for what you should do in your EMC Test Lab,
it is not my place to say.
If I were your accreditation auditor, I certainly
would cite a deficiency if you used a hybrid antenna for
making final compliance radiated emissions measurements
per ANSI C63.4-2009.
Yours sincerely,
Harry. H. Hodes
Principal EMC Engineer
President & CEO
Acme Testing Co.
Hi Harry,
Care to comment back to M. Cormier?
Mike
Mike Violette
Washington Laboratories &
American Certification Body
[email protected]
+1 240 401 1388
Begin forwarded message:
Date: January 13, 2012 8:13:53
AM EST
Subject: [PSES] Biconilog
antennas and ANSI C63.4:2009
Hello everyone,
I am relatively new to this mailing list, so
this question may have been
posted before. I did not find it when
searching the archive.
It has come to my attention yesterday that
some accreditors may give a
lab a hard time if it tries to get ANSI
C63.4:2009 accreditation when
using biconilog broadband antennas for
measurements from 30MHz to 1GHz.
Table 1 does not explicitely list combination
antennas as allowed, but
both biconicals and bilogs are listed as OK
for this frequency range.
Has anyone here been subjected to
accreditation issues for using biconilogs?
Thanks,
Martin
(Sorry if my English is bad, second language
for me)
-
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