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Chasing Background Noise

06 Oct

This weekend presented me with a new wrinkle in the fight against background noise.  A new continuous source of buzzy 30 meter background noise appeared out of no where. Naturally, since I had no changes to appliances in my home I assumed it was an external source. Now keep in mind, neutral wires run as a contiguous run all the way back to the distribution transformer and so that means that your home is connected by the neutral run to all other homes serviced off of the same transformer. Also worth remembering, a neutral wire as well as safety ground run all through your attic and crawl spaces unswitched.  Think of your home as a wire frame surrounding your radio with neutral and safety ground acting as a large cage antenna with your radio inside- all of which is connected to all other homes in your power distribution transformer service area. So when your neighbor buys a cheap switching battery charger and plugs it in, essentially he is plugging in to your wire frame cage surrounding your radio. Not being able to predict my neighbors actions I had to rescan my own home. All was clean save my utility closet. In this closet lives a air conditioning unit as well as a heating unit and various natural gas pipes and electrical conduits. My friend and I used a sniffing loop and a radio tuned to 30M to sniff the area. What was strange here is that the air conditioning copper piping seemed hot rf wise.

A day went by while I thought about this issue. I went back to the closet yesterday to sniff again and also sniffed my water heater closet just adjacent to the heater closet. The natural gas lines to the water heater were harsh and loud at 10 Mhz. I took a chance and loaded up all the interior gas pipes (flexi piping) with ferrite and also added ferrites to the ac copper plumbing for the air conditioner. Listening to 30 M again proved no changes. Well those pipes had to get RF hot from someplace so I went outdoors to the ac unit and sniffed some more. No joy. Today it was quiet while it was hot yesterday. On a lark I went to my gas meter and sniffed it as well. It was RF hot and very noisy. While at the gas meter I noticed a ground wire loose and laying on the ground. I could not tell if this was a displaced ground from the old and now out of service telephone entry or was intended to be attached to the gas meter. I took a leap and tied the ground to the gas meter and listened again on 30 M at my radio. Now it was almost quiet! I am not sure if I bumped a rusty piece of hardware, unconnected a piece of plumbing that was excited by rf from a local radio station or just what happened. The point here is that nothing that conducts should be assumed to be RF free when looking for a RFI source. That was an interesting exercise. Today my 14 Mhz background noise level (measured with preamp on, AM mode and wide bandwidth [9khz]) is around S3-4. That is lower than I have ever had it in three or four years.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on October 6, 2010 in Radio, Stuff

 

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