[RFI] Re: touch lamps RFI

EDWARDS, EDDIE J EDWARDS, EDDIE J" <eedwards@oppd.com
Wed, 21 Apr 1999 08:57:04 -0500

SCAMERON [SMTP:SCAMERON@prodigy.net] wrote:
> A simple rf choke in that lead going to the lamp base will cure the
> problem.
> There's articles in past QST's that have more details.
> 3/88 p.42 (4.7mh choke in series with a 1.8k resistor), 
> 1/86 (100mh choke in series with 1.8k resistor), 
> 5/85 (1k resistor)
> I used a 4.7mh choke in series with a 1.8k resistor as suggested in the
> 3/88 article and it worked.
> Touch lamps also cause RFI in your receiver!
> Skip W5GAI
> > From: Glenn Wiebe <gswiebe@mb.sympatico.ca>
> > I'm sure I don't have to tell you about the to/from RFI problems
> > created by touch lamps. 
> > In the base of the
> > lamp is a black blob with I believe five wires in/out. The light
> > yellow wire is connected to the metal lamp base. This is where the
> > problem must be resolved. Any suggestions?
> > Glenn VE4GN

Hi Glenn: 
Which RFI problem are you dealing with?  
There are two:
1) RFI pick-up by the lamp responding to ham signals by turning ON/OFF/ON
2) RFI generated by the lamp and causing noise packets every 50-70 khz on
ham bands.

And there are two possible ways for each to occur:
1) Direct pick-up and/or radiation by the metal lamp base.
2) Conducted pick-up and/or radiation by the electrical wiring.

Sometimes replacing the Taiwanese made, non-UL listed "black blob" control
box with a UL listed version will reduce or eliminate problems.  

Skip's suggestions should correct RFI from direct pick-up/radiation via the
yellow control wire connected to the lamp's metal base.  Excellent job on
providing QST article references!  

For Conduction issues which are usually associated with RFI to the ham rcvr,
installation of ferrite cores, either clamp-on or wrap around types, on the
AC line at the base of the lamp is needed, and possibly alot of them.  The
closer to the control box the better.  It could fit inside the lamp's base
even.  43 mix ferrites will work.  73 mix might be better for noise on HF,
but I've never tried any 73s.  My noisey lamps moved away a year or so ago
before I got to try 73s on them.  Of course, they took my $12 ferrite core
with them as well as my AC line filter! RATS!

I've noticed that plugging these lamps into different AC socket locations
can change the bands affected or even eliminate the problem entirely!  It
changes the length of the "antenna" also called house wiring making the
wiring a more or less effiecient antenna depending where it's plugged in at.

I'll hafta tell ya'll about the time a new neighbor moved in next door and
plugged in they're touch lamp that picked up my 20-CW signal; I made them
think the house was haunted! ;^)  They did get rid of the lamp, and were
even good friends now.  But I never told them it was me controlling their
lamp every night! >:-}

de ed -K0iL

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