Nice write up Scott.
Once the pandemic winds down I have to have JCP&L (just crummy power and light)
come back out. I am 99% sure it is the insulator on the pole in front of my
house. It is the end of a high voltage run. I have videos using an RS390
receiver and tapping on the pole with a small sledge hammer (I did not hit it
hard enough to dent wood). With my Flex 6700 I can listen and watch the
panadapter noise floor from my iPhone (SmartSDR for IOS). So it is easy to
listen to the 390 and watch the SDR noise floor at the same time.
My noise is the same. Wide band looks like whole noise floor rises. 10 to 20 dB
jump and most pronounced on dry breezy days. Goes away with rain.
Dave wo2x
Sent from my waxed string and tin cans.
> On Jun 22, 2020, 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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