[Elecraft] CFL lamp noise

[Jim Wiley]

What you are hearing is almost certainly a "touch control" lamp dimmer. 
  Either in your home or nearby.  If you do not have any of these 
devices, check around your neighbor's home (with their permission of 
course), starting with the electric meter.  It will be fairly strong 
there if you have the right house.  Your observation that it peaks on 40 
meters is a typical artifact of resonances in the house wiring.   The 
signals actually start in the 50 to 200 kHz range, depending on the 
controller, and have a "comb" of harmonics that diminish in strength and 
get wider in frequency as the order of the harmonic increases.

Once you find the right house, if it is not your own, the issue can 
become more complex.  There are good texts on the subject to be found on 
the Internet.

Occasionally such noises  come from other devices such as battery 
chargers for laptop computers and games, but the "drifts slowly up and 
down the band" is a tell-tale characteristic of lamp dimmer RFI.   The 
controller can emit interference whether or not the lamp is on.  It will 
exhibit sudden jumps in frequency when the lamp is turned on or off, or 
set to different levels of brightness.

Occasionally the interference effect goes both ways - as you key your 
rig, the lamp will change state from off to on to various brightness 
levels.  I got one neighbor to take his lamps out of service (they were 
in his living room) because when I keyed my KW rig on 40 meters, the 
lamps would go nuts.  Quite distracting when trying to watch TV!. I 
discovered it because I could see his home from the shack, and made the 
correlation quickly.  He was very grateful that I could tell him what 
was going on.  I think he thought the lamps were possessed.   He took 
them back to the store where he purchased them and got a refund.

  One way to check for this effect, even if you cannot see the lamps 
directly is to use a high a power as you can manage  on various bands, 
then key just single "dits", listening to the interference each time. 
If you are causing the lamps to change state, you will hear jumps in the 
frequency of the interference. This may not always work, but it works 
often enough that it's worth a try.


- Jim, KL7CC





ab2tc wrote
>
> I do have a recent noise problem that affect mostly 40m and vicinity. On the
> panadapter it shows as "humps" 10-15kHz wide and spaced about 40kHz apart.
> It sounds like a scratchy noise and it drifts slowly. Folks on the LP-Pan
> Yahoo forum have suggested it's a washer or drier, but who is washing and
> drying 24 hours a day? If it is a motor control, it must be some motor that
> is running more or less continuously. Unfortunately I have a difficult time
> arranging an antenna on the car with reasonable efficiency on 40m, so I
> haven't been able to sniff around the neighborhood.
>
>