After taking a major lightning strike last summer, there were lots of repairs
to do. Both my office and shack were affected. Rigs were blown; computers
damaged; it was a mess. While rebuilding, I didn't operate the station much
until ARRL DX this year. One of the things I noticed just prior to the contests
was a lot of low-band noise [80/160]. I did some basic testing, and determined
that noise sources appeared to be coming from outside the shack. This
determination was made after powering down every item in the shack, except the
receiver - and the noise was still there. It would also seem to increase in
strength with the 80m yagi aimed away from the house, and it was also strong on
the beverages [also aimed away from the house]. So, everything seemed to point
to an external noise source. But, there was no time to track and eliminate the
problem in the few remaining hours before the contest.
We operated the contests with the noise there, and lost a lot of points as a
result. I even got an email from another contester who wanted to let me know
just how obnoxious we were on the low-bands - calling DX stations when they
were already coming back to someone. He was right - we were in bad shape, and
it showed. The day after the SSB contest, I was so frustrated with the problem
that I went out and started to track neighborhood electrical noises with the
mobile rig. Boy, did I find a lot of things. Well, after a long search, I
located a very noisy CATV power supply. It was emitting a lot of electrical
noise and it was audibly humming away up there on the pole, too. I was 99% sure
this was the problem. With a boatload of assistance from well-connected
contacts in the CATV company, the power supply was replaced. The electrical and
audible noise in the area immediately around the power supply were both
eliminated. I rushed back to the shack to see if the problem was gone, and to
my amazement, it was still there - rock solid. Although it didn't solve my
noise problem, the CATV people said the supply really did need to be replaced,
so their efforts were not in vain. I really appreciated their help. Good thing
I left that 1% chance in my mind, though.
So, I went out driving again. I found more noise sources - two street lamps
that were arcing and failing to start properly. They were generating 40-60dB
over S9 noise. That noise was being radiated from the power lines for up to 2
miles from the source. I reported them to the power company for replacement.
But, these sources were time-of-day-dependent. During daylight hours, they were
quiet. And my noise was still there - all the time - day and night.
At this point, I was completely stumped, almost ready to talk to my wife about
putting the house up for sale. Instead, I decided to just take a couple of days
away from the problem and return to it later with a fresh approach. When I
decided to attack the problem again, I had already thought about how to
approach it:
1. Start over - make no assumptions.
2. Recognize that the source will very likely be obvious, when found.
3. Question everything.
So, I started over - looking inside first. Once again, I powered down
everything but the receiver. And, there was the noise. But, this time I wasn't
going to start looking for external noises so quickly. Was there still a
possible noise source in the shack or the house? I realized that I hadn't
really powered down everything - the receiver was running off the UPS hidden
under the desk! I moved the receiver to straight ac power - and the noise was
GONE!
The UPS was installed last summer as a protective measure against lightning and
other power failures [we have them frequently in my town]. I had just finished
telling the world how great the UPS was during the power glitch we suffered on
Sunday morning in the ARRL SSB contest, so the device was fresh on my mind.
The buzzing/hash noise generated by the UPS only appeared when a device was
plugged into it. It could be anything. And it would go away sometimes when the
device power was turned on - loading the UPS output. This had the feel of a
radiated noise from the device power cord. There were a number of potential
tests to perform, but the solutions were limited. So, I went straight to the
solutions, instead of messing around with testing. I took an old line cord and
wrapped most of it around multiple ferrites. I connected the stripped end to a
series line filter, and then fed that into a highly filtered multiple-outlet
strip with surge suppression. Plugged that into the output of the UPS and
started testing for noise. Gradually, I added all the loads back to the
filtered UPS output, and determined that these measures have completely
eliminated the noise.
Lessons learned or reinforced:
1. The problem is most likely to be blatantly obvious when found.
2. Don't assume too much along the way.
3. Definitely don't be too tough on anybody - like utilities - until you can
PROVE they are the problem.
4. It ain't over 'til its over.
5. The UPS is still a GREAT thing to have in the shack/office - no change in
my previous conclusions on this subject.
I think it's over. But, will continue testing - forever.
Jim Idelson K1IR
email k1ir@designet.com
web http://www.designet.com/k1ir
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