[RFI] CFL Noise Update - Neighbor Removes Burned Out CFL

Roger (K8RI) k8ri at rogerhalstead.com
Wed Oct 10 02:15:01 EDT 2012

On 10/10/2012 12:08 AM, Tony wrote:
> On 10/9/2012 10:23 AM, qrv at kd4e.com wrote:
>> Tony, Do you have a common electrical system? Could his circuit have a
>> bad ground or neutral and
>> it is using a path through yours? David
> Hi David:
> Common in that the power comes into our homes off the same power lines.

That's true in most subdivisions. The question is, are you fed off the 
same transformer?

> I'd be interested to know if the noise could travel from one home to the
> next via the power lines because of a faulty ground.

If it's the same transformer the ground can be just fine.  You will find 
that many times the devices that use the power line in the home for 
internet and TV can talk to all the homes fed from the same transformer 
and that can be a real PITA.

Like in the old days with VCRs that ran the output on Ch 3 or Ch 2. Some 
of them could be heard a 1/4 to 1/2 mile away.
Then there were those who just wired everything together instead of 
using an A/B switch and your VCR was tied to a high gain antenna that 
put out a pretty good signal.

Which BTW there are still a lot of attic and antenna mounted preamps no 
longer used but still wired to the TV with cable. Remember that channel 
18's audio sub carrier(think it's the sub carrier) is on 145.25.  Even 
without power on them they can still receive and mix a strong 2-meter 
signal and retransmit it. Our only saving grace is that if we hear them 
they definitely will hear us.

I was able to dump the cable system for an entire town by transmitting 
on 145.25 mobile. OTOH I did this while demonstrating the problem to the 
service guy for the cable company. He insisted that they couldn't hear 
us until I keyed up out in the parking lot. Their cable system was a 
whole lot cleaner after work the next day and by the day after that I 
could no longer find any places where I could hear 145.25.


Roger (K8RI)

> Tony
>>> I recently discovered that my neighbors CFL lighting was causing RFI. I
>>> managed to get close the light with a portable HF rig and found the
>>> noise was identical to what I was hearing in the shack; same
>>> frequencies, same noise characteristics. I should mention that the bulb
>>> was burned out.
>>> The problem with pointing the finger at the light as the only RFI source
>>> was that the noise would shift in frequency when I turned a light switch
>>> on and off in my home! I recorded the frequency shift "trick" on video:
>>> http://www.youtube.com/watch?v=EYHbpLfQ1gc
>>> I shut the mains to see if the noise was coming from my home, but it was
>>> still there with the breakers off. The light switch had no effect on the
>>> noise as long as the mains remained off.
>>> Long story short:
>>> The noise went away immediately the moment my neighbor removed the
>>> burned out CFL. An identical CFL that was working emitted much less
>>> noise. He hasn't replaced the bulb yet so we'll have to see what happens
>>> with the new one.
>>> The puzzling thing about all this is how a light switch in my home could
>>> have an effect on the noise coming from a neighbors CFL? It doesn't
>>> appear coincidental because the light switch "trick" hasn't happened
>>> since my neighbor removed the CFL. It's been a while now and all is
>>> quiet.
>>> Any ideas?
>>> Tony -K2MO
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