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Re: [RFI] Vibrating Ferrite Chokes on Service Line

To: rfi@contesting.com
Subject: Re: [RFI] Vibrating Ferrite Chokes on Service Line
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 12 Jul 2015 20:22:50 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On Sun,7/12/2015 7:00 PM, Aaron Kreider wrote:
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

One pass through a core is one turn.

(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.

They should vibrate -- you're hitting them with lots of current! This is NOT a proper application of ferrite chokes.!

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.

I need to add advice not to put chokes on individual lines. :)

When all three conductors go through the chokes, the net flux is near zero. When only one goes through the choke, the flux can be HUGE, and probably saturates the core.

The chokes also became strongly magnetized, making them harder to open.

The choke on the neutral line vibrated a lot less than the others.

Yup, because it usually carries much less current.

Is it safe to have the vibrating chokes on the service lines?


73, Jim K9YC

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