GENERAL
INTEREST
18
Elektor Electronics
11/2002
(which is still used in modern
microwave ovens).
The first practical application of
this system was for
Radio Detection
And Ranging,
better known as its
acronym RADAR. The operation of
radar is based on the transmission of
a series of SHF waves at regular
intervals. When these waves hit an
object of sufficient mass then part of
them will be reflected back to the
transmitter, where an aerial can
detect them.
In the original systems the start of
the horizontal sweep in the cathode-
ray tube was synchronised with the
transmission of the signal burst and
the return signal received by the aer-
ial was fed to the vertical deflection
amplifier. When the aerial received a
return signal (the waves reflected
back by an object) a spike could be
seen further to the right of the tube,
the position depending on the dis-
tance of the object (see
Figure 1
).
This system could not only be
used to detect the presence of every
object (aeroplane) that was in its
field of ‘view’, but it could also deter-
mine the distance accurately
between the aerial and the object,
since the propagation speed of the
waves and the rate of horizontal
deflection (time base) were known.
This is how R.A.D.A.R. came about,
an acronym that soon turned into an
everyday word.
Subsequently the radar was
improved to cover all of the sur-
rounding area rather than just a
small section directly in front of the
aerial. This was done by mounting
Everything you always wanted to know about
Speed Cameras
but were afraid to ask…
By: B. Bouchez
Feared by many motorists (let those who have never driven too fast cast
the first stone), the speed camera, usually containing a radar, is an
electronic device whose workings are still a mystery to most electronics
hobbyists. In this article we take the covers of these curious devices and
describe their operation in detail, also considering a few ideas to guard
against their actions.
A little bit of history
Many, many years ago, the investigations car-
ried out on electromagnetic radiation in the
thirties revealed that RF waves appeared to
be reflected back from some objects. This
property became more discernible as the fre-
quency was increased (above 100 MHz). It
wasn’t until the end of the thirties that SHF (f
> 1 GHz) waves could be generated easily,
thanks to the introduction of the
magnetron
(Source: Applied Concepts, Inc. / Stalker Radar)
Summary of Contents for EPROM
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