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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.
"here is a technological solution to the problem in the pipeline -802.11ad, a next-gen wireless standard that uses 60GHz frequencies to send and receive information, instead of the usual 2.4GHz and 5GHz bands. At 60GHz, according to Beaudet, radio energy essentially just bounces off the atmosphere -meaning that the frequency is useless to the Green Bank Telescope in the first place. Signals to and from 802.11ad access points, then, would have no effect on the work taking place at the GBT, allowing for the best of both worlds. Unfortunately, 802.11ad is very much a technology of the future, not of the present -experts at an Interop New York panel last year predicted that devices using the standard wouldn't hit the market until 2014."
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.
This is why the proposal to build a radio telescope array on the far side of the Moon has been around for so long. Having the moon between us and it is one helluva lot of dirt for blocking stray signals. Plus no atmosphere to get in the way. All you have to worry about then is reflection of Earthly signals off of other bodies in the solar system.
Too bad about the expense...
If they really need to use the frequencies that a technologically developed society uses all the time, then they should build their instruments in a remote enough location that regular use of technology would not be likely to interfere with them, instead of building it near enough to a town or city that a school could reasonably pose a threat just by using wifi.
Well now, aren't we the social experts all of a sudden? The National Radio Astronomy Quiet Zone, aka the NRAQZ, was setup in the 1950's as someone has already pointed out, and it is a natural bowl with 3 to 5 miles of real estate that is shielded from a lot of earthy interference because of the surrounding hills.
In 1950, there may have been some daytime AM radio in the area, which is not much of a problem because they don't listen to much below 300 mhz, 300 times the frequency of a Ma & Pa radio station. Its (the ma & pa radio) still there too.
Interesting side effect was that distant tv stations were forced to either be low band vhf, or if high band, more limited in power output. WTDV, on channel 5, about 80 Mhz, built their original facility on Fisher Hill, which was actually about 2 miles inside this designated areas borders, and was put there by the FCC's rules & regs when it was built in the later 50's because it was the highest point, and could not be moved more than 2 or 3 miles from where it a was at without being short-spaced to some other station. But was allowed to use the full 100kw sync tip peak power that any low band vhf can us as a maximum ERP.
WBOY, 17 miles north in Clarksburg and assigned to channel 12, was not allowed the high band vhf's max power of 330 kw ERP. but was limited to 100kw because of the slightly above 200Mhz frequency.
So, in the run up to the digital conversion, they wanted to recover all the low band stuff for use by Law Enforcement & because their assignment program was written by an idiot that wasn't aware of the NRAQZ, and proceeded to assign both stations new channels in the 56-58 range. That's in the high middle of the 700Mhz range. So I called the enforcement/compliance officer at Green Bank and asked him how much noise I could make on channel 58. 58 don't mean nothing so I had to translate to the actual frequency, which he plugged into his program and which said that the maximum power I (WDTV, I was the C.E. at the time) could send from 270 degrees true to Green Bank was 4.78 watts. Anything more than that he would have us shut down. I said send me a letter to that effect, and he did.
So I went to the NAB a couple months later and had a ball going around to the various transmitter makers showing that letter and asking for bids on a 4.78 watt transmitter. IOW, I had a ball poking fun at the commishes obvious stupidity.
Eventually, along with some heavy duty prompting by our Washington legal people, they saw fit to let us stay on our low band frequency. Quite a few of the tv broadcasters in the more mountainous areas have also stayed on our original channels.
As for de-funding or de-protecting the area from interference from the broadcasters, no way. 90% of what we know about the radio universe around us, came from Green Back, and to a certain extent, Aricebo. But while Aricebo can hear farther, it isn't nearly so steerable, nor as sharply focused as Green Bank's big dish. The new dish they built to replace the 300 meter that fell from rust & corrosion way back when, is performing at a level the old dish only dreamed about. It can move faster too in the event of a gamma ray burst, it can slew and be looking at the source of that burst in just a couple minutes. That facility is IMO a national treasure. FWIW, you have to take the bus into the place is your car has spark plugs. So everything that moves in that valley moves in a diesel bus, or by muscle powered bicycles.
Like Paul Harvey would say, and that's the rest of the story.
Cheers, Gene