HAMNET Report 21st March 2021

In a letter to the editor of the ARES weekly newsletter, Doug McCray K2QWQ notes that, with an increasing number of bad actors with EMP (electromagnetic pulse) devices these days, the disruption of a country’s electronic infrastructure is tempting. Many veteran radio amateurs have older V/UHF/HF mobile radios and handhelds, and it may be a good idea to store them in a small steel trash can, along with a roll of RG58, a mag mount or other kind of antenna, and light line to hoist the antenna into a tree. There is little or no cost involved, and this puts older gear to potential use in an EMP incident.

While not too likely, the military and other government entities do pay attention to the possibility of such an incident that could cripple the internet, power grid, twisted pair telephone line, and much of the sensitive modern lower voltage circuitry.

Many hams licensed since the end of the cold war may have little or no knowledge of what an EMP blast can do, and how difficult it is to protect against. “When all else fails” means being prepared for the unlikely.

Food for thought and an easy plan to put into action. Doug is in South Jersey.

Writing in EDN this week, John Dunn, an electronics consultant, and a graduate of the Polytechnic Institute in Brooklyn, and New York University, wonders whether the SETI project has receivers with sufficient sensitivity to do signal detections via attenuations through interstellar paths of many hundreds of decibels.

He says: “Trying to find radio signals originating from extra-terrestrial civilizations presents huge technical challenges, one of which is path loss between other stars and our home planet. Neglecting the possible effects of obstacles such as dust clouds, basic geometry creates a detection problem all on its own.

“Project SETI (the Search for Extra-Terrestrial Intelligence) is looking for extra-terrestrial radio signals coming from other star systems. If we construct cones from those star systems, each with its point at the star in question and with Earth at the centre of the circular plane of that cone, we can compare the path attenuation from that far away star to the Earth versus the normalized path attenuation from the Moon to the Earth.

“The extra-solar path from Proxima Centauri, our sun’s closest interstellar neighbour, is approximately 4.3 light years. A radio beam traveling from there to the Earth would experience approximately 160 dB more signal attenuation than the beam path to the Earth from the Moon.

“The so-called local star group consists of those stars within 50 light years from here, for which the attenuation worsens to approximately 180 dB versus the beam path from the Moon. At distances of 1000 light years to 10 billion light years, the attenuation worsens further.

“If an extra-terrestrial civilization were using radio communications as we do, their antennas would not be especially different from our own because everyone would be constrained by the same laws of physics. I’m sure they would also have phased arrays and parabolic reflectors.

“Any transmissions they would likely make would not be especially targeted to reach us here. We would be searching for radio signals that just incidentally happen to come our way and such signals would experience the inferred path attenuations mentioned above.”

Would we hear them?

John says “I honestly don’t know, but it is one tall order indeed!”

Thank you to him and EDN for these excerpts from his article.

Now, here’s something in the “did you know” department.

Visitors to Greenland often believe that the colourful houses in every town are an inspired idea to add brightness to a monochromatic arctic setting. But they would be wrong.

After Hans Egede arrived in Greenland in 1721, Scandinavian culture began to impose itself on the new colony. Prefab houses were shipped north as kits, and buildings with a certain function generally had the same colour. In an era without street names or numbers, this made some of the key municipal buildings easier to identify.

Since most Greenlanders at the time couldn’t read, the colours also served as commercial signs. If you wanted something from the store, you looked for a red building. If you needed a hospital, you headed for the yellow building. Fishermen would bring their catch to a blue structure, indicating the local fish plant.

Nowadays, many of the colours are simply decorative, although some buildings still follow the old tradition. And residents need approval before painting: Nonconformists can’t express their individuality by going for an outlandish colour that clashes with every other house in town.

And here is the key to the colour palette of Greenland houses:

Red: Churches and stores, including the houses where the priest or shop owner lived. This is the most commonly used colour.

Yellow: Hospitals, including the houses where the doctors or nurses lived.

Green: Radio communications, or later, telecommunications buildings in general.

Black: Police.

Blue: Factories, fish plants.

Hmm, my house is a peachy-apricot colour. I think mine would have been recognised as the local madhouse!

Thanks to Explorersweb for that interesting snippet.

Finally, our friends at Southgate say that the IARU Region 1 Monitoring System newsletter reports that Over the Horizon Radar (OTHR) continues to be the biggest source of interference in the HF amateur radio bands

They also say “The mysterious groups of dashes (sometimes 5 dashes, sometimes 16 dashes, sometimes continuous dashes) keep on being transmitted during long hours almost daily on 7075 kHz and its near surroundings inside the segment of the 40 m band dedicated for FT-8 transmissions. They are very difficult to locate, and we still don’t know where they come from?”

The report was in their February 2021 newsletter, and can be found at www.iarums-r1.org.

This is Dave Reece ZS1DFR reporting for HAMNET in South Africa.