Ken Tapping, 22nd March, 2016
One of the familiar sights at our observatory is a four-wheeled cart, loaded with electronics and antennas. On the end of a very long power extension cord it prowls the building, pointing into offices and at the various bits of electronics that fill the building. Our engineers use it to sniff out equipment that for some reason has started to radiate levels of radio interference that could affect our ongoing radio astronomical observations. New equipment is carefully tested for interference emission and if necessary only operated in screened rooms, which are rooms completely enclosed in metal mesh or sheet, so that anything radiated inside stays inside. Office computers are enclosed in metal boxes. It is not possible to put keyboards, mice and monitors in boxes, so these are carefully selected for very small levels of radio emissions. Wireless keyboards or mice cannot be used because these use radio transmissions to pass information to the computer. The whole observatory building is screened to minimize what reaches the radio telescope antennas. Wifi is out!
Radio astronomy involves using the most sensitive radio receivers technology can provide in order to measure the incredibly weak cosmic signals. It also involves use of digital devices and computers; in fact radio telescopes are becoming more and more digital. The unfortunate thing about any digital devices is that they are horrendous producers of radio interference. Try putting a radio not tuned to a station next to your computer.
A few days ago strong interference appeared right in the middle of one of the frequency band used by our main radio telescope. Even though we go to enormous lengths to avoid creating interference issues for ourselves, we do have the difficulty that we are necessarily close to the radio telescope antennas. A good percentage of our interference problems we cause for ourselves, so we have standard procedures for tracking them down and dealing with them, like that cart. So, recently, trailing its long cables, it was prowling the building, looking for the cause of the latest problem.
As time passed, that cart, with its long, trailing cables got closer and closer to my office. Finally the engineer operating it was pointing the antennas into my office. Half-humorously the engineers scanned me – half humorously because I could have had a turned on cell phone in my pocket (I didn't) or my car key or digital watch could be causing problems (they weren't). After a lot of turning things on and off, the culprit was found. It was the mouse for my desktop computer. A new, tested mouse was produced, the old mouse removed and the problem was solved. Finding and fixing the problem took half a day.
That mouse had been carefully tested before being put on my computer – a couple of years ago. Back then it was OK, but over time its electronics had aged and eventually it started to transmit interference. That illustrates the big problem with mass-produced devices. In order to keep costs down in a highly competitive market, they are only as good as they need to be. There are strict Canadian and international standards that have to be met before devices can be used, but these often do not meet the extremely rigorous requirements of radio astronomy. So we are faced with an ongoing process of testing, monitoring and if possible fixing, otherwise replacement.
In addition to that sniffer cart, we have monitoring systems on the roof of the main building to identify interference originating elsewhere on our campus or beyond. So far we have been successful in ensuring that radio astronomy remains possible on our site. A measure of our success is the construction, here in Southern British Columbia, of the biggest single-antenna radio telescope in Canada, and probably the biggest in the world. However, the interference challenge is ongoing.
Report a problem or mistake on this page
- Date modified: