[RFI] Noise changes when room lights turn on / off

[Pete Smith N4ZR]

This may be in the category of "you should never say never, when it 
comes to RFI".  Back in the 80s, when I lived in a townhouse, I was 
focusing on 80 meters to finish 5BDXCC. I became aware of local RFI 
covering two segments of about 10 KHZ at (wouldn't you know?) 3500-3510 
and 3790-3800.  It was there some of the time, and not others, tending 
to come on in the morning just before dawn.

I walked the neighborhood with a portable radio, and localized the 
racket to a neighbor's townhouse.  Though I barely knew him, this very 
nice guy invited me in to try to find the source.  We looked at 
instant-on TV sets and other, similar sources, to no avail. Then, just 
as I was leaving in defeat, he switched off a bathroom light fixture 
(ordinary 110v bulbs, spst switch).  The noise started.  Switch on, 
noise off.  Too weird.  He confirmed that he was in the habit of leaving 
the bathroom light on at night and turning it off before leaving for work.

Carrying niceness further, he allowed me to replace the light switch, 
and though we didn't expect much, that cured the noise! Both the 
original switch and the replacement were ordinary 72-cent "silent" types 
from the local big box store.

Subsequently, I found another source in yet another neighbor's house, on 
two *different* frequencies in 80 meters.  They too let me in, and we 
isolated it to one of two switches controlling the ceiling light in the 
kitchen, again with the noise happening only when the light was off.  
Again, I replaced the switch, and again, the noise disappeared.

All these years later, nobody has offered a specific explanation of how 
this could have happened.  I still have the switches, and have often 
toyed with the idea of setting up a test bench to see if they still make 
noise when switched off, but never got around to it.

73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000

On 9/14/2012 4:31 PM, Tony wrote:
> On 9/13/2012 11:52 PM, Jim Brown wrote:
>> On 9/13/2012 5:19 PM, Tony wrote:
>>> Assuming it is a house wiring problem and not an appliance, what 
>>> would cause it to come on in the evening and stay on till morning? 
>>> Would temperature and humidity cause this?
>>
>> I suspect a combination of things -- a wiring problem that is making 
>> the noise source radiate (or conduct) more effectively. The thing 
>> that makes me suspect house wiring is that you said you switch a 
>> light and the noise changes.  THAT'S why I said you should check your 
>> wiring very carefully, and all of us should anyway. The law of 
>> averages says that whoever did your house wiring made at least one 
>> mistake.  Some mistakes are a nuisance, some are very dangerous.
>
> Good advice Jim. I checked the switch and the socket today and they 
> appear to be wired correctly. Wiring is also in good condition. I 
> shook the outlet and switch to see if noise changed, but nothing 
> happened.
>>
>> The only lights that could GENERATE noise are fluorescents or those 
>> that have a DC power supply.  It's become quite common for most track 
>> lighting to use a DC power supply, and they are virtually all 
>> switching power supplies. 73, Jim K9YC
>
> Understand. In this case it's a simple incandescent bulb. I'll have 
> the 12 volt battery in hand this weekend so I can run the rig with the 
> mains turned off.
>
> Tony -K2MO
>
>
>
>>
>>
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