Topband: Fwd: Re: Home Depot LED bulb interference.

[DAVID CUTHBERT]

---------- Forwarded message ----------
From: "DAVID CUTHBERT" <telegrapher9 at gmail.com>
Date: Apr 6, 2012 4:42 PM
Subject: Re: Topband: Home Depot LED bulb interference.
To: "GeorgeWallner" <aa7jv at atlanticbb.net>

LED lamps no doubt comply with FCC conducted emissions. The noise is almost
entirely differential mode. Think of a signal on an open wire t-line; it
does not radiate (much).

But, the asymmetry in the AC power system causes differential to
common-mode conversion. Common-mode current on an open wire feedline
radiates (a lot).

The primary asymmetry I see is the neutral wire to earth ground. I ran a
NEC sim of a simplified house AC power with feed wires to a power pole. The
signal induced into a 160 meter dipole next door is S-8 from a single LED
lamp at the FCC limit of 2 mV differential into 100 ohms.

Disconnecting the AC earth ground wire drops the signal by 40 dB. Ferrites
clamped onto the earth ground wire could help.

This is crude and preliminary but is interesting as I'm an EMC design
engineer as well as a ham.

Dave WX7G
On Apr 6, 2012 4:22 PM, "GeorgeWallner" <aa7jv at atlanticbb.net> wrote:

> On Fri, 6 Apr 2012 11:57:15 -0700 (PDT)
>  "Jim F." <j_fitton at yahoo.com> wrote:
> ...Since this bulb complies with
> > part 15 of FCC rules
>
> It is marked to comply, but it may not. (Part 15
> compliance is self-certified. It would be interesting to
> test it against Part 15 requirements.
>
> I believe that one of our potential defences against the
> worst offenders is to bring the attention of retailers to
> the pontial risks of selling non FCC comliant products.
> The more cautious they get the better off we will be.
> Returning it to the retailer is a good start in that
> direction!
>
> George
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>