The cable layout is required to be the 'worst case' attainable, isn't it?
Michael Sundstrom
NOKIA
TCC Dallas / EMC
ofc: (972) 374-1462
cell: (817) 917-5021
amateur call: KB5UKT
-----Original Message-----
From: ext robert.s...@flextronics.com
[mailto:robert.s...@flextronics.com]
Sent: Tuesday, August 20, 2002 1:05 PM
To: alex.mcn...@ingenicofortronic.com; emc-p...@majordomo.ieee.org
Subject: RE: Radiated Emissions setup
Neil,
I would like to see the pictures of your audit board.
Without seeing the pictures I have the following comments.
1. I think this is a very good idea from a repeatability standpoint and I
would like to consider adopting it.
2. It may be more trouble than simply draping the cables over the table
edge, but less than bundling them properly.
3. Some of our customers bring their products in already attached to such a
board with their cables all fastened securely in configurations accepted by
their customers. This also lessens the setup time and gets them in and out
quicker.
4. I believe that Note 1 of Figure 10 in EN 55022 refers to cables which
connect one piece of gear on the table to another. If the cables were cut,
it would require splicing or installing connectors. If a shorter cable were
used, it may not represent actual use. I feel that generally customers
having a two meter cable which is longer than needed would either drape it
to the floor (which is not normally a metal ground plane), or bundle it
neatly to keep it out of the way. On the other hand, since we as testers
never know how equipment will be configured, the demand for repeatability
requires that a system such as that described in Figure 10 be used.
Robert Seay
-----Original Message-----
From: Alex McNeil [mailto:alex.mcn...@ingenicofortronic.com]
Sent: Tuesday, August 20, 2002 12:00 PM
To: 'emc-p...@majordomo.ieee.org'
Subject: Radiated Emissions setup
Hi Forum,
As we all know test setups are absolutely critical to EMC results. I have
the good fortune of having a good pre-compliance radiated emissions site (3m
OATS, Fully or Semi Anechoic Chamber). From using this site I see all sorts
of "funnies" but still the most annoying is how much you can change the
emission results just by changing cable positions. I carry out regular EMC
audits and could never quite get the same results as 6 months previous, when
that particular product was last tested (I keep the master product and was
still getting different results due to setup).
I now use an "Audit" board where I bundle the cables (30-40cm) in a
particular "figure of 8" fashion via fixed wooden pegs. Thru' time I have
convinced myself that this not only gives me worst case emissions but also
that much sought after REPEATABILITY! I believe the setup is as per EN55022.
I have a photograph* of this Audit board to allow this forum to comment on
the good and the bad points of using such a system. Also, is there any
reason I cannot take this Audit board to a Test House for Product Compliance
testing and at the same time get correlation between a Compliance site and
my own site?
Photograph details (EUT with 3 X Serial Ports, PSTN and DC SELV power
connection)
1. The 1M, 2M and 3M indicate the Horizontal bundling of cables from
RS232 ports which would go to a tabletop EUT peripheral (or leave open
circuit). The 3 lengths are connected to similar ports. This covers the
different lengths issues.
2. The P is the inline power supply O/P cable going to the EUT. This is
bundled vertically as it represents the power supply sitting on a customers
floor.
3. The T is the PSTN telecomms cable. Again bundled vertically as it
represents the cable going from the EUT to the wall socket.
Finally,
I have never understood the EN55022 figure 10 note 1 "If cables which hang
closer than 40cm to the horizontal ground plane cannot be shortened to
appropriate length, the excess shall be folded back and forth forming a
bundle 30cm to 40cm long". Does this mean you can cut the cable to 1m or ?
even though you will be shipping say 2m cables with the product?
*I have not attached the photograph, 212Kb. This will be sent to those
requesting it i.e. to those people who are thinking of commenting on this
email.
I look forward with interest to this forums comments.
Kind Regards
Alex McNeil
Principal Engineer
Tel: +44 (0)131 479 8375
Fax: +44 (0)131 479 8321
email: alex.mcn...@ingenicofortronic.com
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