So I finally got around to putting monster chokes on the service line
that feeds my house and several neighbors. 3 chokes on each line
(positive, negative, and neutral) with zero turns (as the wire is too
thick). It decreased my noise on 492 khz from 50 uV to 42 uV (*probably
- there is some uncertainity as the level of noise varies presumably due
to electricity usage -- currently it is at 62 uV*).
The 492 khz is a 9th harmonic of the 49.5 khz fundamental rfi source.
The unexpected thing was that the chokes vibrated and made a loud
buzzing noise that can be heard 40 feet away (even over modest street
noise). This was very concerning at first, until I looked it up online
and found that this is normal behavior.
Jim Brown - you might want to include information about choke vibration
in your very informative guide. I searched it for "vibrat" and didn't
find any mention of this phenomena.
Anyways, I removed the chokes - because I'm concerned that the vibration
would damage the insulation on the service lines.
The chokes also became strongly magnetized, making them harder to open.
The choke on the neutral line vibrated a lot less than the others.
Is it safe to have the vibrating chokes on the service lines? I took a
video, but it was low-resolution and I wasn't able to find out what part
of them is vibrating. I'm guessing that it is the small gap between the
two pieces of ferrite - in which case the ferrite might eventually
break, but it won't cause problems with the service line. It sounds
like it might be a 60 hz vibration.
It could also be that the ferrite is vibrating against the service line,
or the metal is vibrating against the plastic shell on the choke.
I could reduce the vibration with foam or another method.
I might also try putting chokes on the service line on the other side of
my house, as I'm not sure if the original noise is from the main power
lines or one of my neighbors (and there are multiple noises - so
probably at least one of them is from the neighbors). Unfortunately
access to this other side of the service lines is very difficult.
Aaron
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|