by Ken Tapping
While in Washington recently I had a chance to participate in a meeting between the US Committee on Radio Frequencies and Iridium. When we last heard much about this satellite communication system it was failing financially. It was losing in the competition with cell phone companies. Since this system radiates interference into the 1610-1613 MHz radio astronomy band, which we use for OH observations, we were not regretful at the idea of Iridium's possible demise. However, Motorola has sold off Iridium to a new company, which has found a small, but stable worldwide market - emergency services. In Washington Iridium representatives said that business is now good, and they are about to pension off the existing satellites and to replace them with next generation devices. The company promised that this time technical improvements and operational changes will avoid causing interference to radio astronomy. We'll see...
Radio Quiet Zones, or Controlled Emission Zones are a key ingredient in ensuring next generation radio telescopes such as the Square Kilometre Array will enjoy a quiet environment with as much spectrum access as possible. In an era of rapidly proliferating radio devices or devices which radiate interference, such as those energy-saving light bulbs, we have to look at how we make sure existing radio observatories remain effective. The Dominion Radio Astrophysical Observatory is a typical example. A location that was once fairly isolated is now close to a valley with a rapidly growing population and the prospect of new housing developments. Increasing populations, with the infrastructure that comes with them bring two sorts of interference: narrow- band emissions from single sources, and a general degradation of the noise floor due to aggregate emission from lots of electronic devices all of which are operating legally. The national, regional and local branches of Industry Canada have now been working with DRAO for over a year testing and evaluating the DRAO interference environment and the properties of the controlled emission zone surrounding the observatory. One of the more important objectives is to provide tools to spectrum managers that can be used to provide protection to DRAO and other observatories around the world.
Thanks to the development of cheap, efficient infrared lasers, communication and radar devices are moving into the THz range. We are heavily committed to observing in every wavelength range that gets through the atmosphere without being attenuated too much. Space<->Earth links are being discussed that would also seek to use these low-loss windows. In addition there is the proposed use for deep-space tracking and inter-satellite links. We are working with other countries to make sure what we are doing and what we need for protection are taken into account in the deployment of the new systems. We got an embryonic report accepted by the International Telecommunications Union last year, and are now working on a more fleshed-out version.
A few years ago, when the 71-275 GHz band allocations were revised, we did rather well out of it, mainly because we were well-prepared. It's going to be harder to pull off as big a success in the new revisions in band allocations to 3000 GHz, but we will do better if we are prepared. We have a lot of information already, but it would be very useful if you were to pass me details of wavelength ranges or spectral lines you are really keen on, what you use them for, how often and where you observe. I do all my radio astronomy at centimetre wavelengths, so I need your help. I hope we can then prioritize and integrate this information with the help of the CASCA Radio Astronomy Committee.