[RFI] Filtering 220VAC

[Jim Brown]

On 10/19/2023 3:45 PM, nlsa at 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.