Second Edition, 2002-08 - Radio disturbance characteristics for the protection
of receivers used on board vehicles, boats, and on devices – Limits and
methods of measurement
The 1995 edition of CISPR-25
is a widely regarded standard, adopted by many automotive OEMs and used as the
basis for other standards, both OEM and ISO standards.
The LISN defined in CISPR-25 is used in virtually all automotive
component test standards and often referred to as the CISPR-25 LISN, hence
CISPR-25 is potentially the most important single standard for automotive
component EMC testing.
The 1995 standard has some
idiosyncrasies that plague both test services and equipment designers, some are
due to the frequency bands which are non-contiguous, some are due to the
undefined classifications in the standard, some are due to modern technology
exceeding the frequency limit. There
is also a lack of correlation of the test set-up with the EU legislative
directive 95/54/EC due to minor set-up differences for radiated emissions
testing. Despite these
idiosyncrasies CIPSR-25 is the de-facto global standard for conducted emissions
and the prime global standard for radiated emissions.
The standards was up-issued
and published in 2002, this article examines the changes from the 1995 edition
and discusses which, if any, of the previous editions idiosyncrasies have been
The first things to note are
the lack of changes to most of the test conditions; scan times, resolution
bandwidth (RBW), use of peak, average and quasi-peak (QP) detectors remains the
same as with the 1995 edition. The
definitions of frequency classes (LW, MW, SW, FM, VHF and mobile services) is
consistent between the older and newer revision, the test methods both
on-vehicle and of components remains the same as do the test set-ups, this
includes the use of TEM cell testing that some commentators expected to be
removed from the revision.
Power supply regulation for
component testing is the same as the previous edition, however the 2002 revision
include regulation specification for the supply during on-vehicle testing (12V
+2/-0V and 24V +4/-0V). Many will
be disappointed with the lack of contiguity in the standard, the standard still
has non-contiguous frequency bands (non joined-up frequency ranges), the
previous standards bands remain intact apart from a few minor changes given
The lower limit of the high
VHF band has reduced by 2MHz from 70MHz to 68MHz; the upper span is now 68MHz to
108MHz. The note that used to be at
the bottom of table 6 (broadband peak and QP detector limits) specifying the 6dB
addition to the limits for short duration disturbances is removed, this
clarifies the situation significantly and does not cause the previous confusion
on short duration versus narrowband signals.
The note on table 7 (narrowband, peak detector limits) specifying a
similar 6dB addition for the 76MHz to 108MHz band has been removed and the table
explicitly lists 68MHz to 87MHz as a mobile services band with the previous
limits intact and 76MHz to 108MHz as a broadcast band with the 6dB addition
The artificial network (AN
or LISN) is maintained, the component tolerances are still not specified, but a
lower limit of attenuation is provided for signal line AN's as well as the typical curve used in the
1995 edition. The lower limit curve
starts at 10dB at 1MHz, rising to 40dB at 30MHz, then continues at 40dB
up to cut-off frequency of the measurement (400MHz in the provided example where
attenuation drops to 20dB up to 1GHz). The specifying of the minimum attenuation across the range 1MHz
to 1GHz is a welcome improvement and should help with repeatability of results
from different AN makes for signal line results (not normally a problem for conducted emissions as these
were within the previously specified frequency band (100kHz-100MHz). As the
same AN is used for radiated emissions this limited attenuation could have an effect
on these results as the harness termination will have a defined impedance over the
complete measurement frequency band. Not applying this lower limit of
attenuation to the power line AN is a serious omission in this revised standard.
Not applying this lower limit of attenuation to the power line AN is a serious omission in this revised standard.
Another addition to the
specification that makes measurements easier for fixed harness length
installations is the ability to use a harness length other than 0.2m, although
this is still specified as the standard length for conducted emissions.
If using a harness other than the standard 0.2m the upper measurement
frequency (fc) is limited by the equation;
fc = 30 / lp
Where lp is the length of
the harness in metres.
Although most testing will
still be performed with 0.2m harnesses, if a component has integral fixed power
leads these could be used and result obtained at the terminal end.
This may be more useful for testing after market products that come with
a fixed cable and accessory socket plug.
The same 2MHz frequency
change has been implemented in the radiated emissions testing, for both
on-vehicle and component test methods, increasing the mobile services VHF band
from 70MHz-108MHz to 68MHz-108MHz.
Other upper frequency bands for mobile services have had their spans
increased. VHF band 4 spans
142MHz-175MHz (-2MHz and +3MHz from first edition), UHF band 1 spans
380MHz-512MHz (-40MHz and +0MHz from first edition) and UHF band 2 is unchanged.
On-vehicle tests have
unchanged limit levels for radiated emissions testing.
The frequency bands below 54MHz have unchanged limit levels for both peak
and quasi peak detector (table 10) and for narrowband signals (table 11) for
component tests. However, above 70MHz in the first edition of CISPR-25 all
bands had the same limits set for each CISPR-25 class for components, the second
editions separates out these upper bands and applies different levels above
175MHz. Above 175MHz the limit
levels for radiated emissions are raised by 7dB in the band 380MHz to 512MHz and
by 13dB for the band 820MHz to 960MHz, for all detectors and broad and
One of the more
forward looking changes implemented, that is new to the second edition, is a
flow chart to determine the applicability of CISPR-25 (Annex A). What is interesting and forward looking is not just the
inclusion of such an applicability flowchart, but the implication that both
compression engine vehicles (diesel) and electric vehicles are covered by the
standard (and therefore hybrid and fuel cell vehicles).
There are several very
disappointing aspects of this revision of CISPR-25, the main being the minute
level of changes that may clarify some of the minor idiosyncrasies, but do
nothing to significantly improve this test standard. There is virtually no need to buy this new edition since the
changes are so minor as to question the need for a revision at all.
The one caveat for this is if you have a product that is showing failure
at frequencies above 175MHz where the increased limits may help a non-compliant
to CISPR-25: 1995 product pass the revised standard CISPR-25: 2002.
The main missed opportunity
has been the lack of extension of the upper test frequency for radiated
emissions to encompass mobile telephony services at 1800MHz and 1900MHz and
bluetooth technology at 2.4GHz. Many
OEM's have already increased their radiated emissions upper frequency limit to
between 2GHz and 3GHz using the CISPR-25 set-up, to have this encompassed in the
generic standard alone would have made the revision worthwhile.
Another missed opportunity was to specify limits in the out-of-band
regions of the frequency scales for both conducted and radiated emissions.
Even the simple step of joining the end points of the existing bands to
produce a ramped limit set would have been a step forward, this revision adds no
significant change to the frequency bands or the limit lines.
Other more minor changes
that would have made some improvement would have been the increase of the test
table height to 1m. Increasing the
test table height by 10cm would not only align this standard with 95/54/EC, but
increasing the antenna height from the chamber floor does improve signal
reception for large log-periodic and biconical antennae, making the
repeatability better for 1m antenna calibrations in the vertical polarisation.
a wasted opportunity to significantly improve the CISPR-25 standard, the
revision is nothing more than a minor clarification of the existing document,
that after 7 years was well understood anyway, and a reduction of the radiated
emission limits above 175MHz.
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