Thanks for the knowledge and details.
On Tue, Jun 23, 2020, 06:46 Michael Martin, RFI Services <
mike@rfiservices.com> wrote:
> Great job Scott
>
> RFI Services
> Michael Martin
> 240-508-3760
> rfiservices.com
>
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>
> On Jun 22, 2020, 11:53 PM, at 11:53 PM, K9MA <k9ma@sdellington.us> wrote:
> >For many months, I've been plagued by line noise, often 25 dB above my
> >"normal" urban noise level. I tracked it down to a 60+ year old power
> >pole about a quarter mile (350 m) from my QTH. I tracked it down
> >initially with the MFJ-856, a 135 MHz receiver with a 3 element yagi. I
> >
> >have two shorting straps on it to act as attenuators, one across the
> >antenna and another across the receiver input. The noise nearly pegged
> >the meter with both straps in place. To verify it was the correct
> >source, I relayed the HF noise from my station receiver, so I could
> >listen to both simultaneously. There are usually fluctuations in the
> >noise; when they match, I know I have the right one. Unfortunately,
> >when
> >it was active, this source was often very steady. It frequently went
> >silent in wet weather, so I made numerous trips over there. It was
> >always silent at 135 MHz when it was silent on HF, and vice versa.
> >Finally one day it was erratic, so I walked over there and indeed heard
> >
> >matching patterns. Later I took the MFJ-5008 ultrasonic receiver over
> >when it was active, and heard noise from a specific area near some
> >insulators on the pole.
> >
> >MFJ-856 Shunts <http://sdellington.us/hr/MGE/shunt1.jpg>
> >
> >The pandemic gave my local utility an excuse to be even more
> >intransigent than usual, but after a couple months a crew actually
> >showed up. Four guys, two trucks. One guy in the bucket truck did all
> >the work. To make matters worse, the streets in the area were all torn
> >up for utility work, and there was a constant stream of dump trucks,
> >front end loaders, and excavators going by. The pole in question was a
> >rat's next of HV wires, coming from several directions. Working on it
> >was clearly very dangerous. Although the crew called me when they
> >arrived, they had very little interest in communicating when I got
> >there. (All the noise didn't help.) I could have saved them a lot of
> >trouble if the lineman had just poked around with a pole until I heard
> >the noise change. Instead, he just started replacing insulators,
> >starting on the opposite side from where I heard the ultrasonic noise.
> >Sure enough, changing the first 4 insulators had no effect. As soon as
> >he started working on the other side, it affected the noise. I couldn't
> >
> >tell which of the 3 insulators it was, but after they were replaced,
> >the
> >noise was almost entirely gone. I could hear just a little at 135 MHz
> >with both shorting straps open, much, much weaker than earlier. Because
> >
> >of that residual noise, and the fact that I couldn't identify the
> >specific component that caused it, I wasn't entirely sure the problem
> >had been solved.
> >
> >Nearly a week of monitoring, in both wet and dry weather, makes it
> >pretty clear the this particular problem has been solved. Here are the
> >"Before" and "After" spectra:
> >
> >Before <http://sdellington.us/hr/MGE/Before.jpg>
> >
> >After <http://sdellington.us/hr/MGE/After.jpg>
> >
> >Note that the signal in the "After" plot would have been completely
> >inaudible "Before". That signal was about S5. Now I can again hear all
> >the routers and switching supplies in the neighborhood. And sometimes
> >DX, too.
> >
> >The method I used to track down this source is the same one I've been
> >using here for about 30 years. (It's a constant battle; such is the lot
> >
> >of the urban ham.) I've only been using the ultrasonic receiver for a
> >few years, but it's been very useful. In every case of a strong line
> >noise source, I've been able to hear acoustic noise. It can localize
> >the
> >source within a foot or so at a range of 50 feet. The ultrasonic noise
> >fluctuations usually match the HF ones, another sure sign it's the
> >correct source. Conversely, when I point that thing at other utility
> >poles, I never hear anything. It's a useful tool.
> >
> >Hopefully, this experience will help other surrounded by overhead power
> >
> >lines.
> >
> >
> >73,
> >
> >Scott K9MA
> >
> >--
> >Scott K9MA
> >
> >k9ma@sdellington.us
> >
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