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RFI with a twist - noisy air condx switch

Jul 26th 2011, 19:14

N1GY

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I recently and almost accidentaly discovered the source of the RFI that has plagued me for several months. The RFI caused noise on my transmitted signal when using several different types of headsets. It was not noticable with the stock hand mic on my 706. Coincidentally, about 2 months ago, when rainy season started here in FL, we began to suffer electrical blackouts,but only at our house, no one elses. Since the blackouts always seemed to trip both main breakers and the air conditioner breaker, we called the AC company. When they came out the technician found that the T-handle shutoff for the AC had an arcing problem between one of the two main wires feeding power to the shutoff and the ground wire. In dry conditions the arcing was not bad enough to cause the breaker to pop, only when the rains made the area wet would it increase the amperage enough to pop the breakers. As soon as the arcing was fixed, my RFI disappeared as well. Obviously, the arcing was acting like an old time spark gap transmitter and since the shutoff is right outside my radio room, it was being transmitted along with my signal. Apparently the stock HM-103 hand mic had enough filtering to get rid of it, but the other headset mics did not. I had never heard of this problem before so I thought I should pass it along.
Jul 27th 2011, 22:25

w1rfi

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
What an interesting story. I am surprised that the arcing didn't seriously imact your ability to receive. Generally, arcing noise is much worse on HF than VHF, so you operate only VHF, especially if you operate only FM, which has noise limiting inherently, you may not have noticed the noise. Seeing as you are using an IC-706, though, it is likely that you at least listen on HF from time time.

Still, I bet that on HF and VHF, your station is more sensitive now.

73, Ed Hare, W1RFI
ARRL Lab
Technical forums moderator

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