In opening the March 2013 issue of QST which arrived on valentines day (How am I supposed to read it?) a couple of articles looked interesting. So as I was thumbing through the magazine to get to an article when another article caught my eye. It was about HF Noise problems.
The article appeared under technical correspondence and was written by Larry Parker, VE3EDY. It appeared on page 59 and was titled “Noise Problems for Broadcast and MF/HF Receivers” the subtext was titled “New Electromagnetic Interference (EMI) Troubles”
Larry details his quest to find the source of his HF noise problems after moving to a new house. So “new” refers to new to him. I had exactly the same problem over a decade ago and it appeared in a short, four paragraph, Hints and Kinks article that appeared QST in May of 2001.
HF Noise Problems – Finding
I had it slightly easier in finding my identical source of noise. I had done a retrofit adding the lights under the cabinet myself. Unfortunately, I’m not as active on the radio as I would like to be so it went unnoticed for quite a while. I too found the noise to correlate with time of day. To find my HF noise problem I was able to take a slightly more brute force approach to finding it. Since my shack is in the garage it was across the way from the circuit breaker panel. I checked several of the usual suspects by turning off and UNPLUGGING them, no Joy!
Being relatively impatient, I took a more aggressive approach to finding my HF noise problem. My “shack” is the garage, the operating position taking up one end of my workbench. Since the circuit breaker panel is in the garage, I simply turned up the volume on my TS-930 and started opening and closing breakers.
Actually, I opened them one at a time noting the noise went away on #7 -the Kitchen. At that point, I shut all the others, still no noise. I shut the one to the kitchen and bam!! HF noise problem reappears instantly, no warm-up, no nothing, just noise.
I put the wall-wart on my scope to see what the waveform looked like and it was a square wave at about 25kHz, the same interval as my noise spikes. Photos added here: http://w6lsn.com/blog/viewing-the-noise/
I installed another set of lights inside of a cabinet that has a glass front and we store/display some of our crystal in. When I put the lights in the top of that I also had a glazier make me two shelves of glass. Now the lights can illuminate the entire cabinet.
HF Noise problem – Solution
My H&K article details a couple other findings in my quest to find and solve my noise source. My solution was to install a transformer physically MUCH larger than the wall warts and used it to power up the original string and a second one that I added at the same time as the transformer.
The lights in the cabinet remain powered by the original power supply. Why if it causes HF noise problems you ask? Well, if those lights are on, I’m not allowed to be on the radio. 😉
HF Noise Problems – thanks
I received a couple of thank you emails from other hams at the time, one was about the solution as he had tried returning the power supply several times to no avail.
Let me know if this helps or if you have questions.