Weekly Photo Challenge: Sky

Pointing To The Sky

Skywave

80M Vertical Antenna

Skywave Diagram

Skywave Diagram

My 80 metre vertical antenna stands tall against a typical English ‘will it rain or will it shine’ sky.   This antenna is used to transmit and receive on the 3.7MHz Amateur Radio short wave band.   Short distance communication – perhaps fifty miles or so – normally occurs along the ground (ground wave).   Long distance communication is possible by sky wave transmission as shown in the diagram on the right.   The distance between the transmitter and the receiving station varies with the height of the Ionosphere (a layer of ionised particles in the upper atmosphere where the radio signal is refracted back to Earth) and the angle of radiation from the antenna.   The distance between the two stations is known as the skip distance.   It is possible to have multiple skips depending upon reflection back to the ionosphere from the ground – by this means global communication is possible.   The antenna in the photo has worked stations as far afield as Canada.   I also have a wire antenna for other Amateur Radio frequencies which has worked Tasmania – literally on the opposite side of the world!

This is a simplified explanation of radio transmissions on the short wave bands.   If you are interested in taking up Amateur Radio as a hobby you will need to undergo some training and obtain a license from your national organisation – Ofcom in the UK.   Training in the UK is broken down into three levels of license and the basic foundation course should present little difficulty for the vast majority of people.

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Comments

  1. Grand photo!
    (The scientific information washed [!] right over my head, I’m afraid)

    • Thanks! – Don’t worry about the science too much, all you need to know is that radio waves ‘bounce’ back off a part of the atmosphere. A bit like a reflection from a mirror 😉

  2. thirdhandart says:

    I like your perspective! Beautiful photo!

    • Thank You – I had a bit of an argument with the weeds to get the angle 😉 – note to self, Time to clear out the garden 🙂

      • thirdhandart says:

        Clearing the garden of weeds can be an endless task! My husband, John, read your explanation of radio transmissions on the short wave bands. John said that if the sky wave transmission hits a hole in the ozone layer that it will travel out into space. Has that ever happened to you?

      • LoL Theresa! – the Ozone layer sits in the Stratosphere at about 40-50km above the Earth’s surface. The Ionosphere is significantly further out with the refractive ionised layers located between 100km and 500km above the surface. So radio waves, like visible light, go straight through the Ozone Layer whether there is a hole in it or not 🙂 Your husband has a point though. You see, the shallower the angle, the further the distance before the radio wave returns to Earth. But as the angle increases towards the vertical it reaches a point where the Ionosphere cannot refract the signal sufficiently to return it to Earth and it will pass through into outer space. The SETI project was an attempt to detect the presence of aliens on other planets by listening for their radio transmissions (which should also escape their planet’s atmosphere in the same way), but none were positively identified before the project had its funding withdrawn. you can read about it at http://en.wikipedia.org/wiki/SETI@home . Hope this reply is not over long 🙂

      • thirdhandart says:

        You’re reply isn’t too long. It’s all very interesting. Thank you!

      • Thank you too – I’m glad it was of interest!

  3. thank you for breaking the whole thing down into layman’s language. 🙂

  4. yes, there are many connections to the sky …

  5. Lovely post really enjoyed both the shot and the analysis!

  6. Love the perspective too. Beautiful sky.

  7. Love the simplicity of the picture add to that your informative expanation on radio transmission!

Trackbacks

  1. […] short distance on the 40 metre band and I would guess we were using Ground Wave – See my Weekly Photo Challenge: Sky post for an explanation – especially as it’s a wet day out there! You can check out the […]

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