Regular readers will likely recall my early January blog describing the sudden and very unwelcome appearance of a severe noise problem badly affecting my LF reception. I had spent an afternoon D/F'ing the noise source (which was being radiated via the local power lines), only to discover that the residence in question was not occupied ... and has been vacant for the past seven weeks as the noise continued.
Yesterday I noticed that the home was once again occupied and this morning, with radio in hand, I paid visit. It seems that the part-time residents had been spending the past several weeks in Hawaii and had just returned to the house to check up on things. I explained to the owner what I believed to be the problem and, as suspected, it was a CFL light ... a particularly noisy one. Turning the light on and off quickly verified the culprit light and swapping the bulb out for a different one produced no observable noise, as was the case for one that had been left switched-on in the living room.
Whether the offending bulb was just a poorly designed one, a very early manufactured model or one that was about to fail, I do not know ... but I am amazed at the strength of the QRN (and QRM) that the bulb was able to produce at such a distance, about ten properties away!
|CFL Crud on LF|
The owner was very concerned that he had unknowingly caused a problem and was very apologetic, as I have found with similar situations in the past.
One of the worst was also a CFL bulb that had actually burned-out and was located in a nearby (three properties away) crawl space. When finally traced, the bulb was heavily charred and had partially melted at the base, yet was still producing an ear-shattering level of crud right into the HF spectrum.
In cases like these, it is often difficult to get an accurate D/F on the signal through normal means since the signal is being propagated via the overhead powerlines. Attempts to D/F the signal almost always point to the closest powerline and not to the signal source. Usually such a noise generator will be confined to your local power grid ... that is, the homes that are powered between the two large power distribution transformers in your local neighborhood. In my case, this limits the search to about 15 homes.
I have found that the best way to tackle this is to make a 'noise map' and to try and measure the noise intensity at a similar point for each property - ie. directly beneath the powerline as it enters the property. This will usually put you at the same vertical distance from the line and will give you a better noise sample that is directly (or not) associated with that property. After mapping this out, if the culprit property is not obvious, then you will at least have narrowed it down to a very few choices. Other types of noise, that can be detected into the VHF range, are probably best detected using normal D/F methods.
After bringing the offending bulb home, I Google-searched the product name and number and came up with a 'product recall' for this particular model.
"According to a Health Canada and Electrical Safety report, the lamp may overheat and melt the enclosure exposing live parts, posing a risk of fire and/or electric shock."
Apparently they were indeed manufactured incorrectly and it's just as well that it was found and removed before causing serious damage!
Once again LF sounds as it should. Hopefully it can remain this way for a long time but with the proliferation on noise-making appliances and 'improvements', I have my doubts.