You made my points.
In the end a commercial equipment manufacturers can only design and test to a
standardized test setup. This is exactly what's described in CISPR 11, CISPR
22, ANSI/IEEE C63 and national derivatives of those standards. It is up to the
final equipment manufacturer to use these filters in such a way as to take good
advantage of them. Companies like Corcom, Schaffner, Cosel, TE Connectivity
and others cannot have official knowledge of how these filters are finally used
in every application. If a Ham wishes to use a catalog part, they are pretty
much on their own to identify a suitable model. Unfortunately, simply looking
at data sheet specs is not going to reveal all the answers needed. Case by case
experimental data is almost always needed.
That said, there are some generalities that may be applied as a result of past
experience. It is instructive and a bit of fun to look at Henry Ott's tongue
in cheek article on maximizing your emissions.
http://www.hottconsultants.com/techtips/maxemission.html.
Thanks, Doug
Original Message
From: Jim Brown
Sent: Monday, August 15, 2016 9:09 PM
To: rfi@contesting.com
Reply To: jim@audiosystemsgroup.com
Subject: Re: [RFI] ebay line filters
Hi Doug,
You're talking about 1) properly built equipment and 2) measurements in
a lab.
The problem is that much (most?) equipment is NOT properly built -- the
green wire SHOULD go to the shielding enclosure, the shielding enclosure
of a filter integral to a product SHOULD be bonded to the shielding
enclosure, a filter external to a product must have it's shielding
enclosure bonded to the shielding enclosure of the product, and for that
external filter, all three leads (phase, neutral, and green) must be
"zero length" (that is, very short). What happens far too often is that
the green wire goes to a trace on a circuit board that may or may not
every see the shielding enclosure, and there is impedance between that
connection to the circuit board and the shielding enclosure. There's
also equipment where the green wire is insulated from the shielding
enclosure by paint. All of these conditions put the green wire above the
chassis by some amount, so if the product is noisy, that noise ends up
on the green wire, which causes current on the green wire, which causes
the noise to radiate.
Second, real world conditions are not like that test lab setup. The
green wire can be pretty long, which makes it a more efficient radiator
at RF. And those lab conditions aren't looking for radiation, they're
looking for voltage between Phase and Neutral (which they call
differential) and between Neutral and Ground (which they call Common Mode).
73, Jim K9YC
on Mon,8/15/2016 4:26 PM, Doug Powell wrote:
> Good points,
>
> It is indeed true that common mode noise is with reference to the green wire
> ground, but back at the measurement point and not the case of the filter. In
> the case if Mil Std filters this may be on a grounded sheet metal table. In
> the case of European approvals this measurement point is on the floor of the
> semi-anechoic chamber and the test sample is 80 cm above on an insulated
> table. Establishing an RF ground up there is extremely difficult and gets
> worse as you go up in frequency. So, if you buy a filter approved to IEC,
> CISPR, or EN standards you are likely to get better results than one that is
> compliant with Mil Std.
>
> All the best, Doug
>
>
> Original Message
> From: Jim Brown
> Sent: Monday, August 15, 2016 4:24 PM
> To: rfi@contesting.com
> Reply To: jim@audiosystemsgroup.com
> Subject: Re: [RFI] ebay line filters
>
> On Mon,8/15/2016 6:49 AM, Doug Powell wrote:
>> One thing you should realize about line filters is they are optimized for
>> conducted line emissions coming from the product where they are built in.
>> This means the line / load labeling will determine your best orientation
>> for connection.
> There's another MAJOR problem with commercial line filters -- most of
> the trash conducted from equipment is on the GREEN WIRE, which goes
> right past the filter. The specs for these filters CLAIM common mode
> suppression, but what they're calling common mode is voltage between
> neutral and ground. That's NOT what WE call common mode, and what WE
> call common mode is what causes most RFI -- radiation from the power
> conductors as a long wire antenna.
>
> The most effective line filter for MF and HF radio is a common mode
> choke formed by winding multiple turns around a #31 Fair-Rite ferrite
> core, using the guidelines in k9yc.com/RFI-Ham.pdf for coax the same
> size as the power cable. See Chapter Seven the "Choke Cookbook." Also
> see http://nccc.cc/pdf/CQP-RFI2013-2.pdf
>
> 73, Jim K9YC
>
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|