Sunday, January 21, 2018

Sound of Silence: QRN Eliminated

Back in December I mentioned (and showed a picture) of power line noise I have been experiencing at times throughout 2017. Now it's gone. To refresh our memories here is the noise on 6 meters with the yagi pointed directly at the noise source.

That's bad, real bad. As the frequency is decreased the noise gradually declines in signal strength with increasing loss of pulse definition. On 6 meters through 15 meters the noise could be mostly removed with the noise blanker, at the expense of inter-modulation distortion (IMD) products. This gets particularly ugly when faced with contest and pile up conditions.

Interestingly there was no impact on 80 or 160 meters. On 40 meters the yagi saw the noise as an deterioration of the noise floor, but not whten using the inverted vee.

Now the noise is gone. From the discussion I had with the utility crew I suspect it will not be back.

This is an exceedingly uninteresting picture, and it's just how I like it.

I have to say that the local electrical utility, Hydro One, was very responsive and helpful. This is welcome since we have among the highest electricity prices in the country. On top of that we face high distribution fees in our "rural, low density" township.

As a general rule utilities like to find and fix problems like this one. What they don't like is wasted labour costs spent searching for and not finding the source of the problem. This is why it is helpful to first localize the problem before calling them out. The intermittent nature of so many power line equipment problems can then be eliminated as a time waster. The crew lead told me that there is quite a lot of old and problematic equipment out here that they would in any case like to replace. My call had the effect of giving them a reason to do so.

I did not localize the problem since I am not equipped to easily go out with portable equipment that can find problems like this one. What I could do was accurately determine the direction from my house. In our low density neighbourhood this was enough since there is very little distribution equipment compared to towns and cities. In fact I could point them directly at the most likely culprit.

Although the noise was not present when the crew arrived with their bucket truck they went right to work. They found and replaced two cracked insulators, isolated the lines from rotting wood posts and replaced old switches just in case they were contributing to the problem. As they worked the noise appeared, disappeared, came back in spurts and then disappeared for good. I could listen as they worked since the power wasn't disconnected on my segment of the distribution network.

Then they switched off my power and went north to replace suspect switches at two other transformers. I have had weak power line QRN in that direction a few times so perhaps that will also disappear. Time will tell. Is there still some power line QRN? Yes, but just weak source or sources that are not serious problems. At least not at present. As equipment ages and deteriorates the future appearance is more a matter of when not if.

Rural distribution is typically 14,400 VAC, twice that in urban areas. It can run as high as 28,800 VAC. The higher voltage is more prone to causing arcs when equipment deteriorates. I don't know the distribution voltage on my road. I ought to have asked.

Now I have one less worry when I switch on the rig. The only serious noise remaining is from the Ethernet cable drop from my terrestrial wireless ISP antenna. I may deal with that later this year. It is now a minor problem since I mostly use the antennas on the new tower which are quite a lot farther from the house. All the LED lighting I have been installing has been clean, as is the new heat pump. A year ago I replaced a dimmer switch that created a lot of QRN on the low bands.

I am getting closer to having a QRN free QTH. Listening here in the relatively empty farm and bush country is wonderfully quiet. You can't work them if you can't hear them. Now I can hear them. They don't always hear me, but that's to be expected.

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