Some of you had requested I update the group a I work through my
NStar has now added grounds to the poles that were not up to spec,
unfortunately the noise is still there.
Based on the various comments you have supplied and suggestions to
look for here when the utility returns here is the situation
1. The noise disappears when it rains or snows, sometimes completely,
other times so low it could be atmospheric.
2. Often when it is cold and dry the noise rises in the AM, fairly
regularly, one comment indicated the noise could increase with the
load on the line.
3. Nothing located with the ultrsound gear. Noise very evident with
the Radar Engineering analyzer, but NStar did not think they could
identify the source. I now have the 7 element 440MHz yagi some of you
indicated good results with. Hope to have the utility try this antenna.
4. With the 7 element yagi and an Icom R20, I hear noise at a cluster
of poles within 100 Ft or so, but not very strong. No noise once I
move away from these poles.
My question is, what level of a peak should we see at the fault vs.
the noise that is radiating up and down the line for a quarter mile
or less? The NStar tech thinks it should be a very big making the
fault totally obvious.
On Feb 13, 2010, at 3:53 PM, Alan Robinson wrote:
> 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
> 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
> Boston area.
> 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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