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Radio Communication

Radio Communication. Geoff Partridge. The Radio Spectrum. Radio Spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies -. Radio Bands and Channels.

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Radio Communication

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  1. Radio Communication Geoff Partridge

  2. The Radio Spectrum Radio Spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies -

  3. Radio Bands and Channels The radio spectrum is divided into ‘bands’. A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose. Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers.

  4. Radio Bands (1)

  5. Radio Bands (2)

  6. Radio Bands (3)

  7. Personal Experience • HF radio communications control in Hong Kong (part of the Defence Communication Network) – 27 Sig Regt. • Mainly Telegraphic communication over HF radio (Long Haul) • Connections to Singapore, Gan (Indian Ocean), Cyprus, Brunei • Role was to monitor received signal quality and to request frequency changes to ensure a high availability of the communication links. • Transmitters and Receivers located on Stonecutters Island and The Peak (maintained by RN and C&W) • 24/7 operation but great views of the harbour and Kowloon.

  8. HF CommunicationsPropagation characteristics Shortwave radio frequency energy is capable of reaching any location on the Earth as it can be refracted back to the earth by the ionosphere, (a phenomenon known as "skywave propagation").

  9. HF CommunicationsPropagation characteristics

  10. HF CommunicationsPropagation characteristics • A typical phenomenon of shortwave propagation is the occurrence of a skip zone where reception fails. With a fixed working frequency, large changes in ionospheric conditions may create skip zones at night.

  11. Skip Zone

  12. The Ionosphere • The ionosphere is a part of the upper atmosphere, from about 85 km to 600 km altitude. It is ionized by solar radiation. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth

  13. The Ionosphere

  14. Effect of Ionosphere Changes As a result of the multi-layer structure of the ionosphere, propagation often simultaneously occurs on different paths, scattered by the E or F region and with different numbers of hops. Particularly for lower frequencies of the shortwave band, absorption of radio frequency energy in the lowest ionospheric layer, the D layer, may impose a serious limit due to collisions of electrons with neutral molecules, absorbing some of a radio frequency's energy and converting it to heat.Predictions of skywave propagation depend on: • The distance from the transmitter to the target receiver. • Time of day. During the day, frequencies higher than approximately 12 MHz can travel longer distances than lower ones. At night, this property is reversed. • With lower frequencies the dependence on the time of the day is mainly due to the lowest ionospheric layer, the D Layer, forming only during the day when photons from the sun break up atoms into ions and free electrons. • Season. During the winter months of the Northern or Southern hemispheres, the AM broadcast band tends to be more favorable because of longer hours of darkness. • Solar flares produce a large increase in D region ionization so high, sometimes for periods of several minutes, all skywave propagation is non-existent.

  15. Frequency Changing (QSY) Communication quality and reliability on HF is dependant on the frequency in use. Methods used to determine when to change frequency were – • Distortion Monitoring • Forecasting using frequency prediction charts (these were useful for choosing a frequency but not reliable for timing when to change frequency) • Over a period of several days an HF path may be expected to fail at roughly the same time. With a number of other ‘new boys’ changed the culture from re-active to pro-active frequency changes leading to fewer and shorter outages.

  16. Frequency Prediction Chart

  17. Further Study • The field of radio communication is so vast that this talk only covers a fragment. • There is a wealth of information on Wikipedia and the internet. • The research for this talk resulted in me finding a number of documents that added to my memory of my work in Hong Kong

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