[This is partly observations in case it helps someone else and partly a
query.]
I have an attic-mounted fan dipole for 40/30/20/17m (which I realize is
suboptimal). For a long time, 80m has been atrociously noisy and the
upper bands pretty reasonable. Last week, I noticed S9 noise on all of
20m, constantly, but 40m didn't seem any worse. I didn't think I had
any new devices that would cause trouble, and the nearest neighbor is
200m away.
Sniffing around with a portable HF receiver (powered by AA cells) and a
2m quarterwave whip, I found some noise near AC power outlets and
anything connected to them. Interestingly, signals also seemed to come
up near outlets, apparently from coupling from power lines to the whip.
After not too long, I found the source: I have about 6 batteries on
float 4, 7 and 12 Ah, connected to rigrunner. The only load is a small
computer (Soekris net5501) that pulls 0.5A at 12V, and I have a DelTran
Battery Tender connected to float charge the batteries, which normally
sit at about 13.3V. The batteries and charger have been there for at
least 5 years, and the computer for just about 2. Putting the whip in
the middle of the battery cables over the rigrunner produced the highest
noise reading I ever saw.
Unplugging the charger silenced the noise. Given that it seems coupled
to AC wiring elsewhere, it seems pretty clear that this was conducted
emissions. What isn't clear yet is if it started on the DC side and was
conducted to AC, or if it was generated in the charger.
I will try out the charger without the computer load. I wonder if this
is a sign of incipient failure. I saw another instance of this model
fail and overcharge batteries to 16V, but this one was regulating
properly.
Has anyone seen similar behavior?
73 de n1dam
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