[RFI] Update on the Boston area RFI
robinsah at engr.orst.edu
Sat Feb 13 12:53:25 PST 2010
A couple of thoughts............
The fact that the noise (RFI) goes away after a storm would indicate an outside source on the power line. It also means that the source is not inside an arrester. So using an ultrasonic locator, like the Radar Engineers Model 250, should be helpful in locating the source(s) after the pole is identified.
You didn't say what kind of yagi antenna they were using with the Radar Engineers RFI locator. So I will assume that it is actually the log periodic that comes with the Model 240 RFI Locator. This beam is essentially a two element beam with a wide frequency response. I would suggest using a multi-element yagi, such as the Cushcraft A4496S, a 6 element yagi for 440 to 450 MHz. It is much more directional and with higher gain. I sometimes use an 8 element 685 MHz yagi. This antenna is like a "flashlight" for RFI. The Model 240 does have an RF antenuator. So strong signals can be located.
In my experience, if you get a good DF signal at 685 MHz, you found the pole with the offending hardware. Then use the 250 Ultrasonic to pin point the part that needs replacing.
In one recent case I worked on the offending hardware turned out to be one of the new solid state lightning arresters. Naturally I couldn't get an audio signal from it. But I did have a very strong DF signal at 685 MHz. Then the local utility used a Model 247-B Hotstick Line Sniffer and found the part immediately. The arrester was replaced and that pole has been quiet ever since. It had been producing S9+ interference for more than a mile.
Good luck with you RFI locating.
----- Original Message -----
From: Ash Thornton
To: RFI List
Sent: Saturday, February 13, 2010 10:08 AM
Subject: [RFI] Update on the Boston area RFI
Some of you had requested I follow up on my findings here in the
And, thank you to all for the tips and suggestions.
NStar did come out last week with their Radar Engineering VHF/UHF
gear with a yagi for pinpointing the noise. The noise was so high
along the power lines they could not pinpoint a specific pole or spot
unfortunately. Not sure just what this means. So, their next step is
to upgrade the grounds they found that were below spec.
Interestingly, just after they were out we had a light, wet snow and
the noise quickly all but disappeared for about 15 hours and then
quickly rose back to previous level. This has happened each time we
have had a storm. This last snow was so light and the noise
disappeared with the first few flakes it is hard to believe that
helped, but there was a big rise in the humidity? I would assume this
indicates an out door fault, given the correlation with snow?
There was a very low level of noise coming from the same area, but
did not have a chance to get back to check it with the 440 Mhz RCVR,
but will be ready next time.
Stay tunedand thanks,
Was thinking about calling our volunteer fire Dept to hose the poles
down given we don't use hammers, but.......Just kidding
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