This week, I am still in Green Bank, West Virginia, the heart of the National Radio Quiet Zone and the largest fully steerable radio telescope in the world. I've written a bit about the radio astronomer's version of "light pollution," called RFI (radio frequency interference) and how we have to live a different way out here to avoid destroying our own observations. However, cell phones and microwaves aren't the only devices to give off radio waves. The electronics in the telescopes themselves can hamper observations if you are not careful.
So how do you know what is giving off interfering radio light? We can't see with "radio eyes," but we can build a device to act like them. We can use radio antennas to seek out "noisy" equipment. You can do this on your own using just a walkie talkie! In Green Bank, they do this testing in style, as can be seen in the picture above.
This is the anechoic chamber in Green Bank. It looks like some kind of weird torture chamber with a mad scientist's death ray, but I promise you, no electronics were hurt. The spiky walls are made of foam that absorbs radio waves, both due to the type of material and the shape of the spikes. The "death-ray" is actually an antenna that measures how much radio interference a device is emitting.
The anechoic chamber seals the device to be tested from any outside interference and ensures that, while under testing, the device does not interfere with telescope observations. Any receivers, computers, or other scientific instruments to go on the telescope or on site are tested to make sure they emit at low enough levels for radio astronomers to tolerate.
How do you get a "noisy" computer to "quiet" down? (Yes, I'm abusing terminology about sound to talk about light, but the lingo is hard to shake.) Like the microwave in the cafeteria, you can shield it in a big, heavy metal box. The metal is opaque to radio light, trapping the radiation inside. However, those can be clunky, and will heat up very quickly inside.
Copper mesh is also an excellent way to block radio waves, so protective boxes can be built out of that as well. Much of the electronics for the project I work for (PAPER) are shielded in such a structure. In fact, the control room for the Green Bank Telescope, though over a mile away from it, is wrapped in copper mesh as well!
The United States is not the only country with a mandated "quiet zone." Similar sites have more recently been set up in South Africa and Australia. Both of these countries are bidding to host the Square Kilometer Array, an incredibly large, multi-wavelength telescope that is in the planning stages. There is even talk of sending radio telescopes to the quietest place imaginable... the far side of the Moon.
As technology improves our lives, and even our astronomical instrumentation, radio astronomers have to jump through bigger hoops to do better astronomy. Whether this involves proper shielding, better algorithms to remove RFI from data, or finding new places in which to build big telescopes, maintaining "quiet skies" is a constant, but rewarding, challenge.
Images: Top: By Erin Benoit, with permission and help from Wes Sizemore and Carla Beaudet. Bottom: View from inside a copper-mesh box at Erin connecting cables!
Tags: Astronomy, Telescopes
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