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Re: [RFI] RFI from Astron power supply

To: <rfi@contesting.com>
Subject: Re: [RFI] RFI from Astron power supply
From: "Andrew Ingraham" <ingraham.ma.ultranet@rcn.com>
Reply-to: Andrew Ingraham <ingraham.ma.ultranet@rcn.com>
Date: Mon, 4 Jun 2007 09:37:48 -0400
List-post: <mailto:rfi@contesting.com>
> I was told by the City Manager that they are going to have the ballasts in the
> fluorescent lights in the radio room replaced with electronic ones. Not sure
> what he meant by electronic.

Here is my crude understanding.

Fluorescent lights require a somewhat large voltage to fire, but the voltage
then drops way down.  The ballast I think allowed that to happen, and was
basically a large inductor inside a box in the fixture.

Some modern fluorescent lights (in particular the compact fluorescents that
screw into conventional lamp sockets) use an electronic circuit of some
sort, instead of the big inductor.  What they actually do, I don't know, but
I believe they are more than merely an active inductor or a current source.

The inductor itself probably doesn't cause RFI (unless it's got a bad
contact), but the combination of inductor and the fluorescent tube, which
snaps into and out of conduction, tends to generate large voltage spikes
which might be responsible for the RFI.  Perhaps the electronic ballasts
do this in a more graceful way without the large spikes.

Past experience with fluorescents and "carrier-current" radio says that the
RFI may be conducted over rather large distances so replacing only the ones
in the radio room may not totally fix it.

Regards,
Andy

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