Jim,
You're right of course. Thank you for correcting.
On page 23 of your tutorial, you write, "Commercial AC power line filters
(Fig 29) are generally a waste of money, because they provide only
differential mode filtering." Why are they manufactured? Or, why aren't
common-mode AC power filters more common?
Thank you,
Michael, W9IP
-----Original Message-----
From: RFI <rfi-bounces+nlsa=nlsa.com@contesting.com> On Behalf Of Jim Brown
Sent: Thursday, October 19, 2023 11:43 PM
To: 'Rfi List' <rfi@contesting.com>
Subject: Re: [RFI] Filtering 220VAC
On 10/19/2023 3:45 PM, nlsa@nlsa.com wrote:
> Thanks to everyone for their responses on- and off-net. It has been
unanimous that the neutral wire should not be excluded in add-on filters.
It is NOT unanimous. The neutral is NOT run to a 240V outlet, only the two
phase (hot) conductors and green. The neutral should be present ONLY at 120V
outlets, which MAY be fed between one phase and neutral. If 240V equipment
also needs 120V (for example, some power amps use a 120V blower), it must
either be fed that way, OR between one side and center-tap of the primary of
a power transformer integral to the equipment.
Finally, the choke should ALWAYS be as close as practical to the noise
source. AND all wiring connected to the noise source should be choked.
(control wiring, for example).
Another common failing in equipment -- make sure that the green wire is
bonded to the equipment's shielding enclosure AT THE POINT OF ENTRY.
It's not uncommon for it to be insulated by paint. When this happens, noise
is usually on the green wire.
Products like those motors SHOULD have an proper line filter, bonded to
their shielding enclosure. In addition to low-passing the power conductors,
it also bypasses them to the shielding enclosure, which is required to
maintain shielding. A connection to EARTH is not part of solutions to this
sort of noise (although there are other important reasons for it); what
matters for noise is shielding, which must be continuous.
Also, if you're doing EME, filter designs for HF are totally wrong. See
these recommendations for VHF and UHF chokes on cables like RG400 and
RG8/213. http://k9yc.com/ChokesVHF.pdf For mains power cables, follow
recommendations for cables sized comparable to those coax cables.
There is a LOT of tutorial material on my website about RFI and chokes.
k9yc.com/publish.htm
73, Jim K9YC
>
> My question was an product of an RFI problem that I'm currently hunting
and which has so far eluded capture. It is coming from the Variable
Frequency Drive for the elevation mechanism of my EME antenna
(https://www.qrz.com/db/W9IP ). When the elevation VFD is powered on (but
not running) it raises my noise floor by about 0.6 dB (HFers, don't laugh).
I spent all day adding chokes and bypassing the 220VAC input, but recent
posts tell me that I wound the common mode chokes improperly. No
perceptible noise is being emitted through the output of the VFD, its LAN
connection, or other related control lines... just the AC power. Tomorrow I
will re-wind the chokes.
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