hardie (01/16/83)
With help from various people, I have managed to track down a source of noise which has plagued me ever since I got my first rig seven months ago. The noise has got worse over those seven months to the point that it will obliterate all useful HF bands on my rig for a period of as much as a week. I looked at the rig's audio output with a scope and the noise is basically a 120Hz spike with some ringing. I won't bore you with all the blind alleys I followed! The problem turned out to be one of two transformers in the substation which feeds this whole residential area. One of the beams that supports some lightning arrestors and insulators has a ground wire running along the underside and this wire is stapled to the wood. Neither the staples nor the wire are insulated. The problem was one of those staples! According to the DOC inspector who accompanied me to the substation (and who has the expensive ultrasound gadget that detected the problem) said this is a common cause of noise. It seems that there are so many high-tension wires around there that sometimes a path to ground can occur through the wood. He says that in some substations there is so much juice around that the power crews won't even touch supporting guy wires unless they know it is safe. I thought I would pass along the basics of how the problem was ultimately tracked down. 1. First of all prove that the noise is not in your rig, not due to faulty house wiring and NOT due to a light dimmer. The first thing DOC asked me when I first complained to them was ' have you got any light dimmers'. They can be a dreadful source of interference. 2. Once you are satisfied that the noise is power line related but coming from outside then all you have to do is locate the fault. Our area has overhead wiring. If your power is distributed underground then about the only thing you can check is the transformers. If your power is above ground then the noise can be detected by using essentially the same technique as the DOC. Find the highest frequency at which you can just hear the noise and walk (or drive) around the neighbourhood to find out which direction gives you the strongest signal. (If you have a beam antenna then you are a long way towards solving it. If you also have a nearby friend with a beam you can triangulate and its done!). Then walk in the direction of the noise and increase your listening frequency as the signal gets louder. At some point you should locate the noise. I was almost certain the noise was coming from the transformers anyway so we checked it first and the 2 meter rig confirmed it. Those rigs are really useful because the two transformers are only about 15 feet apart and because of the fence around the substation you cant get closer than about 15 feet. Even so, the mobile rig indicated, and the handheld 100% confirmed, that the noise was coming from only one of the transformers. The reason for this is, of course, that most of the energy caused by the arc goes into the lower frequencies so that you have to be close to the source of the noise for it to interfere with VHF rigs. The arc is also the reason why there is a 120Hz spike - one for each half cycle of the 60Hz power wave. Another cause of interference is arcing insulators or lightning arrestors. With overhead wiring the fault could be one of those two or simply a loose connection somewhere and finding out where the noise is NOT, is sometimes as valuable as knowing where it IS. In my case I found that the noise also occurred in my daughter's piano teacher's house which is about 10 blocks away and which is also fed from a different phase than our house. BUT we are both on the same transformer. If you suffer from power line noise the fault could be much closer to home. For example, the local transformer that supplies power to your block. If anyone has questions about this I will be glad to answer mail but I should stress that I am NOT an expert in this sort of thing. If necessary, I will summarize to the net. I am also interested in hearing of any noise problems ( no matter what source ... e.g. cordless phones etc.) you may have had for which you have a solution - post them to the group or mail to me. I should mention that the ultrasound device that the DOC uses looks like a bullhorn but it has a parabolic dish and a pair of headphones. I presume that it uses the doppler effect to convert the motion of an abject into sound. Anyway, the DOC inspector let me try it and there was no doubt that it was the staple. You could point the thing at the staple and hear it vibrating like crazy and only an inch or so away there was silence! 73 pete ve5bel