Last Chance To See: Sporadic E TV
I'd like everyone in Britain to take a few minutes this summer, for your last chance to see a very dear friend of mine, Sporadic E Propogation.

During a hot, damp, muggy day, take a moment to retune your old analogue TV and see if you can find some foreign TV stations!

Propagation is the term us radio geeks use to describe a radio signal that, due to the Earth's athmosphere, manages to travel a very long distance that it otherwise normally wouldn't. The classic example is skywave propogation, the way that AM-MW band on your radio allows you to hear foreign radio stations overnight. These often interfere with other AM-MW stations such as Talk Sport, Absolute Radio (Virgin 1215) or local independent "Classic Gold" stations. By day, the signal travels in a straight line, and what with the Earth being round, it disappears into space at the horizon, so you can't hear distant stations. By night, as the atmosphere cools, the ionosphere is at a lower altitude and reflects distant radio signals back to the surface. Radio Luxembourg, an overnight English station which ran from 1933-1992, is probably the best known example. As with all propogation, these signals tend to fade in and out, seeming to become quiet, loud then quiet again.

Sporadic E propogation is different. The heat and humidity allows radio signals to be reflected, or bent, by a higher ionospheric layer than would normally be the case, and affects much higher frequencies. This is not fully understood, but the end result is that FM-VHF radio and UHF TV channels can be received five hundred miles or further away from their normal reception area.

Although FM-VHF radio is going to be with us for several years to come (although not as long as you might think if Labour stay in power), analogue TV is not. Starting later this year, old analogue TV signals will be switched off in many areas. Digital TV cannot be manually retuned, you won't be able to simply turn a knob or press some +/- keys to retune your TV, it will tune itself automatically from the digital signal. Once the ability to manually tune analogue TV goes, you'll also lose the ability to witness Sporadic E Propogation and its ghostly images of fuzzy foreign TV channels from overseas. With most European countries starting to shut down their analogue TV output, 2009 may be your last good chance to receive long-distance terrestrial TV; digital signals aren't suited to being received in short bursts.

So, what are you looking for? Well, first learn how to manually retune your analogue TV. Typically you go into a setup menu and select something like "tuning", "frequency" or "UHF channel". The UHF channel numbers will be between 22 and 68. Don't use "auto tune", you need to manually check each channel yourself for the weak signal. You are most likely to see Sporadic E examples on the lower UHF channels during hot, muggy, humid days, particularly in the afternoons and early evenings. You're looking for a ghostly image, probably black and while (many but not all European countries use an incompatible colour system) with, most importantly, foreign language audio. It will fade in and out, and will probably last no longer than 20 seconds or a couple of minutes before disappearing completely.

If you're in the West of England, Welsh doesn't count, it's too close for Sporadic E, neither does French if you're on the eastern English Channel coastline. Having a TV aerial that faces the European continent (ie. south or east) will generally give you a better chance of success, although due to the bouncy nature of Sporadic E, you never know.

Here's some screenshot examples to get you in the mood.