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54 E L EC TR I C AL CONNEC T I ON
AU T UMN 20 1 6
TASTY DISHES
C
onstruction workers of all types
are severely affected when the
economic climate is uncertain
and demand for new building blows hot
and cold.
Electricians seem to survive
downturns fairly well. One coping
mechanism is to reach out into closely
related fields such as refrigeration and
data networking. Electricians have
tools and knowhow that are applicable
wherever electrons or photons are being
moved about.
Communications circuitry is one area
that has a lot in common with power
and light. Design, installation and repair
concepts are simple, but task-specific
demands have a way of becoming
complex and detailed. Of course,
electricians are used to that.
Many homes in the developed world
have TV and an internet connection
using cable or a satellite dish.
Audio, video and data transmission
operate at much higher frequency than
the 50Hz or 60Hz we are accustomed to
in power and lighting. For home owners
it’s a mysterious world of bandwidth,
harmonics and duty cycles.
For an electrician it’s not a very big
step beyond Ohm’s law and familiar
notions of capacitance and inductance.
There is abundant information available
in textbooks and on the internet.
Otherwise you could find some
malfunctioning equipment and dive right
in. You may not have an oscilloscope or
spectrum analyser just yet, but bring
along your multimeter.
If a TV is completely dead – dark
screen, no sound, no illuminated
LEDs on the front panel – it probably
means the internal power supply is
defective. (Occasionally the problem is
as simple as a defective power cord or
tripped breaker.)
If the set shows signs of life but the
video and/or audio quality is poor or
the video has difficulty staying in synch,
there will be a range of possible faults.
The way to proceed is to examine the
transmission line, including modem,
cable box and antenna. (A satellite dish
is technically a type of antenna.)
A good tool in this endeavour is a
field strength meter. It can measure the
transmitted signal in space or at various
points along a transmission line. This can
also be done using a small portable TV
with an RF port on the back panel that
accepts a coaxial cable connector.
Troubleshooting consists of moving
along the transmission line and watching
for an abrupt change in signal strength,
indicating the fault location.
For campus-style buildings under
single ownership, the coax is usually
mounted on power poles some distance
below the grounded conductor
associated with the high-voltage circuit.
You will need a cherry-picker.
To make this type of transmission
cable work, inline amplifiers are located
at less than 100m intervals to make
up for signal attenuation, and these
amplifiers need power to bias the
semiconductors.
The power is carried along with the
RF signal in the coax. It may be AC or
SATELLITE DISH WORK CAN BE
A PROFITABLE SIDELINE FOR
ELECTRICIANS, AS THE TOOLS
AND EXPERTISE ARE ALREADY IN
PLACE.
DAVIDHERRES
OFFERS
AN OVERVIEW.
ANTENNA SYSTEMS