When visiting our observatory, you may well not notice a small antenna mounted on a mast on the roof of the original observatory building. It looks rather like one of those TV antennas for use by homes a long distance from the transmitter. That antenna is not used for TV or anything like that. It is being used to study one of the most critical issues in radio astronomy today, and is a joint project between our observatory and Industry Canada.
The fact that radio astronomers or any other user of the radio spectrum can operate without being jammed by other users comes from a process called “spectrum management”. Canada does this nationally, but applies internationally agreed policies set up through an agency of the United Nations. Taxis are allocated different parts of the radio spectrum from, say, radio stations, which means you can listen to the music and not the taxis. This is also how we can do radio astronomy in a world filled with radio transmitters. Every different application of radio is allocated its own part of the spectrum. Moreover, because there is no such thing as a radio device that doesnít radiate electromagnetic pollution into parts of the spectrum used by others, there are regulated limits to the intensity of these “unwanted emissions”.
This scheme worked very well until somewhere in the 1990’s, when things got a lot more complicated. That is when we started to make the transition from a world with relatively few transmitters, usually at fixed locations, to countless transmitters for many home, business and personal applications, all moving around. In addition we are using more devices that although not designed to be radio transmitters, are radiating radio signals. Two prime examples are computers and energy-saving, fluorescent light bulbs.
Cell phones and other personal communication devices are allocated their own part of the radio spectrum. However, they also radiate a small amount of “unwanted emission”. After they have been dropped, had coffee spilled on them and so on, they probably radiate a rather larger amount.
Every device might be producing less than the limit for unwanted emissions, but when there are enough of them, the total power produced by all of them together can be a serious problem for radio astronomy and other high-sensitivity uses of the radio spectrum. Consider a library. We are obviously not supposed to go in there and talk loudly. However, if you have enough people whispering quietly, the result could be the same, or worse. Similarly, the whispering of unwanted emissions from millions of radio devices is adding up to a rising level of background hiss that is blanketing large amounts of the radio spectrum.
That brings us back to that antenna on the roof. We are monitoring the total amount of unwanted emission coming from local communities as the usage of energy-saving light bulbs and other radio devices grows. This study will hopefully help ensure we can all enjoy the benefits of new radio devices without their unwanted whispering deafening us.
Saturn rises about 7pm. The Moon will be New on the 2nd.
Ken Tapping is an astronomer with the National Research Council’s Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton.