Sids Whispers and Pings – 25th November 2007

Alan Bell’s talk Sids, Whispers and Pings explored some of the effects of astronomical phenomena on radio communication. He began by giving us a short list of the scientists who laid the foundations, and then explained a little about the ways radio signals can travel round the Earth. Long-range radio communication is greatly affected by astronomical phenomena, most of which are caused by the Sun. Sunspots affect the strength of the reflective layers in the Earth’s ionosphere, and solar flares can affect them dramatically. The charged particles from solar flares can both help and hinder, and Alan played some recordings of long-range communications made using reflections off an auroral curtain to illustrate the distortions introduced by the particles’ spiralling paths. Meteors also produce ionisation trails, and these have been used as reflectors for long-range radio. Conversely, over-the-horizon transmitters can be used to count meteors. The Moon can also be used as a reflector for radio transmissions, but its distance and low albedo make it an extremely tricky intermediary to use. Alan concluded his talk by describing some of the natural forms of interference produced by astronomical sources like the Sun, Jupiter, the Milky Way’s core, the Cosmic Microwave Background, and pulsars. He mentioned the Crab Pulsar specifically, because its frequency and occasional outbursts make it a particularly bizarre source of occasional interference for 60Hz TV signals.

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