[RFI] Noise

Hare, Ed, W1RFI Hare, Ed, W1RFI" <w1rfi@arrl.org
Mon, 27 Dec 1999 14:52:08 -0500

An additional article can be seen at:


73 from ARRL HQ,
Ed Hare, W1RFI
225 Main St
Newington, CT  06111
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> -----Original Message-----
> From: EDWARDS, EDDIE J [mailto:eedwards@oppd.com]
> Sent: Monday, December 27, 1999 2:44 PM
> To: 'kmarch'; rfi@contesting.com
> Subject: RE: [RFI] Noise
> > -----Original Message-----
> > From:	kmarch [SMTP:kmarch@ix.netcom.com]
> > Can someone tell me how to reduce or elimate noise caused by SCR
> > controlled
> > lamps?  Tnx,  Bob
> > 
> 	[Ed-K0iL]  Those darned Touch Controlled lamps!  
> 	Here's some info from the ARRL TS info server on these "Made in
> Taiwain" lamps.  Check the RFI list archives at contesting.com for my
> personal story on how I got a new neighbor to get rid of his lamp by
> "haunting" it.  
> 	73,
> 	de ed -K0iL
> Updated: November 17, 1995
> ARRL RF Touch Lamps and Dimmers Information Package
>      RF Touch lamps are RF-operated devices that often cause, or are 
> susceptible to, EMI problems.  They have a free running oscillator 
> that is very broad and rich in harmonic energy.  This oscillator is 
> hooked up to a touch plate that changes the frequency of the 
> oscillator 
> when a hand is placed near the plate.  Unfortunately, this plate also 
> acts as an antenna, radiating some of the energy of the 
> oscillator, or 
> picking up nearby radio signals.  When the former happens, it 
> can interfere 
> with other services.  When the latter happens, the circuitry 
> inside the 
> lamp reacts the same way that it would when the plate is 
> touched -- the 
> lamp changes states from "off" to "on".
>      Although cases of moderate interference can sometimes be 
> cured by 
> using a "brute-force" type AC-line filter and/or a 
> common-mode choke (see 
> the ARRL Book,  Radio Frequency Interference -- How to Find 
> It and Fix It 
> for more information about AC-line filters and common-mode 
> chokes) most 
> cases will require internal modification to the lamp.  For a 
> number of 
> different reasons (you may be blamed if anything EVER goes wrong with 
> the lamp or house wiring) you do not want to perform this 
> modification 
> on equipment that is not your own.  Remember -- house AC 
> power is dangerous.
> These modifications must only be performed by qualified 
> service personnel!
> Here are some reprints from QST "Hints and Kinks":
> RFI and Touch-Controlled Lamps.  
>      I have found a simple cure for those touch-controlled 
> lamps that turn 
> themselves on and off during nearby radio transmissions.  In my case, 
> 40-meter operation gave the most trouble, with 75-meter 
> operation a close 
> second.  Higher frequencies presented no problem.  (I use a 
> ground-mounted 
> vertical antenna for 80, 40 and 15 meters, and the lamp is 
> approximately 
> 150 feet from the antenna.  An AC-line filter at the lamp did 
> not eliminate 
> the problem.)
>      A 1k ohm resistor (in series with the signal input lead to the 
> encapsulated circuit that operates the lamp) cured the 
> problem for me.  I 
> suppose the required resistor value would vary with the 
> RF-field intensity 
> and frequency. 
> -- John M. Adams, W7OTC, Sun City, CA
> More on RFI to Touch-Controlled Lamps.  
>      I had the same problems as W7OTC with a touch-controlled 
> lamp switched 
> on and off by my transmissions (100 W to a roof-mounted 
> vertical, with two 
> radials per band).  The problem occurred during operation on 
> the 80- through
> 15-m bands, but 10-m operation had no effect.  A 1-k ohm 
> resistor was not a 
> complete cure in my case. 
>      A 3.3k ohm resistor in series with the signal input on the lamp 
> helped on all bands except 80m (an additional 1.8k ohm 
> prevented the lamp 
> from functioning).  When the resistor was replaced with an RF choke 
> (100 uH, 139 mA), the problem abated on all bands except for  80 m. 
> On 80 m, the interfering signal was considerably attenuated 
> by the choke, 
> but the lamp still switched.  The choke alone may be enough 
> to clear up 
> the problem in some cases.
>      The final answer turned out to be both the RF choke and 
> a 1.8k ohm 
> resistor in series with the signal-input lead to the 
> touch-control circuit. 
> -- Colin Hall, G4JPZ/W6, Marina Del Rey, CA
> Touch-Lamp Transceiver.  
>      When my wife told me she had bought a three-way lamp 
> that switched on 
> and off at the touch of any of its metallic parts, I did not 
> realize she 
> had purchased a transceiver.  I found that my transmitted 
> signal would 
> cause the lamp to operate exactly as if I had touched its 
> metal parts.  
> Later I discovered a raspy, S8 signal at 1875 kHz -- it was 
> coming from 
> the lamp, which was located three rooms away on a different 
> AC circuit.  
> The lamp signal is present from 40 meters down.  At 
> frequencies from 20 
> meters up, my operation is undisturbed. 
>      A box inside the lamp contains a circuit board through which AC 
> line voltage is routed and which has a wire connected to the 
> metal base 
> of the lamp.  When the lamp is plugged in, the lamp signal is present 
> at all times, regardless of whether the lamp is on or off.  
> In my attempts 
> to eliminate the interference, I tried a commercial AC 
> filter, coiling the 
> lamp cord on some ferrite material and other such approaches without
> success.
>      To make sure the lamp my wife had was not defective, I 
> borrowed a 
> similar lamp from a neighbor to try it.  I found it to 
> perform in exactly 
> the same manner except that the frequency of oscillation was somewhat 
> different.  There is no manufacturer or distributor name on 
> the lamp or 
> packing container.  The lamp was made in Taiwan.
>      I am writing so that others who may be experiencing similar 
> difficulties may have some idea of the probable source of 
> interference.  
> After I described what I discovered to a ham friend, he realized that 
> such a unit had been causing interference to his station for 
> more than a
> month. 
> -- Cal Enix, W8EN, 209 S Kalamazoo St, White Pigeon, MI  49099
>      If these cures don't work, it may be possible to shield 
> the electronic 
> switch module, but this must be done safely!  You may also 
> want to contact 
> the manufacturer and send a report of your problem to ARRL 
> Headquarters 
> RFI Desk, 225 Main St. Newington CT 06111. 
> Light-dimmer Interference Reduction.  
>      Radio Amateurs who've have been cursed with RFI from 
> solid-state light 
> dimmers will be interested to know that at least one domestic 
> manufacturer -
> Lutron - produces light dimmers that incorporate RFI 
> suppression techniques.
> The Lutron NOVA series uses toroidal chokes that provide a 
> significant level
> of RFI suppression. 
>      I bought a Lutron model N-600, which will handle up to 
> 600 watts of 
> incandescent lighting.  Temporarily installed in my radio 
> shack, a generic 
> light dimmer produced an S9+ reading at 230 kHz (an arbitrary noisy 
> frequency).  The N-600 produced a reading of S3, a difference 
> of about 40
> dB.  
> Admittedly, this is not zero, but installing the N-600 some 
> distance away 
> provided a reduction in RFI that is very gratifying.  Indeed, 
> I new hear new
> noise sources, heretofore undetectable through the dimmer din.
>      You're not likely to find these dimmers at your local 
> discount store, 
> and they are not inexpensive.  Check for the availability of 
> these dimmers 
> at a lighting fixture store and expect to pay about $25 
> apiece for them.  
> -- Richard G. Brunner, AA1P, 10 Brookside Dr., Foxboro, MA  02035
> Lutron Electronics Co., Inc.
> Suter Rd.
> Box 205
> Coopersburg, PA  18036
> 215-282-3800
>      If you come up with a better solution for these problem, 
> please write 
> to the RFI Desk with the solution.  It sounds like it would be a good 
> candidate for Hints and Kinks!
> "73" from ARRL HQ
> --
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