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No Wi-Fi Around Huge Radio Telescope
JG0LD writes "Students at a tiny Appalachian public school can't use Wi-Fi because any such network can throw the radio equivalent of a monkey wrench into a gigantic super-sensitive radio telescope just up the road. GBT's extraordinary sensitivity means that it's very susceptible to human-generated radio interference, according to site interference protection engineer Carla Beaudet. 'If there was no dirt between us and the transmitter, a typical access point ... would have to be on the order of 1,000,000 km [more than 620,000 miles, or about two and a half times the distance from the Earth to the Moon] distant to not interfere. Fortunately, we have mountains around us which provide lots of attenuation, so we're not seeing everything from everywhere,' she said. A standard Wi-Fi access point would wipe out a significant range of usable frequencies for the observatory. 'It simply ruins the spectrum for observations from 2400-2483.5MHz and from 5725-5875MHz for observational purposes,' wrote Beaudet."
The National Radio Quiet Zone has been there since 1958. It's not like it was just discovered yesterday. People living in this zone have always had to live without radio transmitters. Not having 802.11 is just another of the services they cannot use, like wireless garage-door openers and cell phones.
NSF plans to cut the funding for the National Radio Astronomy Observatory at Green Bank. So I guess the kids will soon have WiFi and cell phones. This is a good thing, right?
If conditions are right, I can have a contact with someone on CW running 5 watts, on the other side of the globe.
Such is the sensitivity of tuned circuits. For untuned interference, like your cell phone trying to interfere with your TV, rejection is great. But when you're specifically tuned to receive a frequency, you've got such a high sensitivity to that specific frequency, (and very high rejection of any other frequencies) that a cricket fart of a signal a long ways away can sound like a lightning strike on your house, if it's on the same frequency you're straining to hear.
They're a little better off than my CW example, being on a high frequency that's mainly line-of-sight, for which surrounding mountains would be a pretty effective shield, but still their receivers are just incredibly sensitive at their design frequencies. They just can't have anything anywhere near them or you will be all they can hear. It'd be like trying to listen to someone talking to you from a table at the other end of the restaurant, while you are seated right next to a table full of loud party animals. You'd have no chance.
I work for the Department of Redundancy Department.
I'm a radio astronomer who frequently uses the Parkes radio telescope in Australia, and I really wish we had an exclusion zone around it like the one around Green Bank. It's not really something you can put in place retrospectively, though: you need to write the exclusion zone into law when you build the telescope, and fight to keep it from then on. At least we've been smart enough to put an exclusion zone in place around the new ASKAP telescope in Western Australia.
I've got to say, though, that
90% of what we know about the radio universe around us, came from Green Back, and to a certain extent, Aricebo.
is a bit of an exaggeration. Even just in the US, you've got the VLA, which is arguably a more important radio instrument than Green Bank; and then you've got Effelsberg, Lovell, LOFAR and the WSRT in Europe, the GMRT in India, Parkes and the ATCA in Australia ... None of them are quite as good as Green Bank at what it does - broad frequency coverage and excellent point-source sensitivity - but each of them has something that it can do better than any other instrument in the world. Parkes, for example, is good at high-time-resolution surveys - it's found more radio pulsars than every other telescope put together.