A cell phone on Mars - NRC Publications Archive

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A cell phone on Mars
Tapping, Ken
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Skygazing: Astronomy through the seasons, 2014-09-09
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A CELL PHONE ON MARS
Ken Tapping, 9th September, 2014
”That radio telescope could pick up a cell phone if
it were on Mars”. This is one of the things we say
to visitors to the site when showing them our 26m
radio telescope. That “dish” is now quite elderly
and not very big by modern standards, although
the equipment on it is certainly state-of-the-art.
The big challenge for radio astronomy is due to
cell phones, and the multitude of other radio
devices we use, being much closer to us than
Mars. Considering the sea of manmade radio
emissions we live in today it is remarkable that
radio astronomical observations are still possible.
The cosmic radio emissions we study may have
taken thousands, millions or even billions of years
to reach us, and are incredibly weak compared
with any of the signals we produce, deliberately or
accidentally. What can we do to see those cosmic
whispers amid the roar of the radio noise we
produce? How do we cope with a situation that
gets more challenging by the day?
The first level of protection is through legislation.
Canada, as a member of the United Nations,
participates in the work of a UN agency called the
International Telecommunication Union. Through
that organization we agree internationally what
radio frequencies will be used for TV, radio, radar,
emergency services and so on, and of course
radio astronomy. We also agree on the protection
mechanisms to ensure that legitimate users of the
radio spectrum don’t get interfered with by others,
or by poorly designed electronics. For example,
put a portable FM radio alongside a computer,
tune the radio between stations and listen to the
changing noises as you do things with the
computer, like saving files, accessing the internet
and so on. Computers are pretty good
transmitters, but without firm rules setting how
much emission they can produce, the situation
would be far worse. However, because Mother
Nature sets the power of cosmic radio emissions,
we have to deal with them as they are, which is
very weak. That makes radio astronomy the most
vulnerable activity involving radio. On the positive
side it sets an immovable benchmark for clean
radio and electronic devices. These days we live
surrounded by radio signals, phone signals, wi-fi,
blue-tooth emissions and all the other familiar
radio services. Collision avoidance radars and
other electronic devices are going into cars, and
we walk around with one or more radio devices on
our persons. The individual signals might be weak,
but together they add up. This growing roar of
millions of devices all whispering at legal levels is
getting to be a problem. What we can do is not
clear. We, along with our partners in Industry
Canada are working on it. On the upside we are
getting better at identifying and evaluating potential
problems. At our observatory we have devices we
use to check interference levels, and we are
working on means to locate interference sources.
One new tool in identifying interference sources
has come through the new technology of
“software-defined radio”. Instead of processing the
signals from the antenna using conventional
electronics, the signals are digitized and fed to a
fairly powerful computer. This technology means
we can detect many different types of signal and
with the click of a mouse button we decode them.
This information may then be passed to Industry
Canada. Of course such high-speed digital
electronics is kept in a screened, metal box
because of the interference it would otherwise
cause. Doing the science of radio astronomy is
challenging enough; we do not need the additional
challenge of dealing with radio interference.
However, when forced to face such problems, we
can come up with some really innovative stuff.
Unfortunately though you can never get back to
where you would have been with no interference.
Venus lies very low in the predawn sky; Jupiter is
higher. Saturn and Mars lie close together in the
sunset twilight. Saturn is now the one on the right.
The Moon reaches Last Quarter on the 15th.
Ken Tapping is an astronomer with the National
Research Council's Dominion Radio Astrophysical
Observatory, Penticton, BC, V2A 6J9.
Tel (250) 497-2300, Fax (250) 497-2355
E-mail: [email protected]