What is a frequency range?
Imagine a giant motorway, several kilometres wide, with thousands of individual
lanes. On this motorway, all imaginable kinds of vehicles can be found: pede-
strians, motorcycles, cars, trucks etc.. To not let them go into one others way,
every lane is reserved for only a single group of road users: e.g., lane 1 ONLY
for cyclists, lane 3 ONLY for pedestrians, lane 40 ONLY for trucks etc..
Depending on the density of the individual kinds of traffic, these lanes also have
corresponding widths. For example, the lane reserved for cyclists is much nar-
rower than the one for trucks and so on. Electromagnetic fields work exactly like
this, just that the lanes are called
frequency ranges
and the vehicles are called
applications
(for example, a traction power line, mains cable or a TV are all
applications - just as
every
appliance that somehow makes use of electricity,
including their cables).
Every
application
utilizes its very own, reserved, exclusive
frequency range
.
By assigning a seperate
frequency range
for each
application
, conflicts bet-
ween individual applications can be avoided (just as with the different vehicles
on the motorway) - so that for instance, a cellphone cannot disrupted by a high-
voltage line.
Big differences between exposure limits
Back to our motorway: Of course, all road users also have their own specific
speed limits. For our example, a pedestrian may only walk at up to 5 km/h., cars
might go at up to 300km/h.
Exposure limits for
applications
work similarly, just that the word “speed“ is
replaced with
field strength
: a traction power line operating at 16.7Hz for
instance, may only emit a
field strength
of 7,500V/m, while a 50Hz power line’s
limit is 5,000V/m, an energy saving lamp’s maximum is only a few V/m, and so
on. As a practical example, following are three official exposure limits:
Frequency [Hz]
Application
Limit [V/m]
16,7
Traction power
8.500
50
Mains power
5.000
40.000
Energy saving lamp
87
It is easily noticable that each
application
may only operate in EXACTLY ONE
frequency range
. The significant differences between the individual limits are
also clearly visible.
Why spectrum analysis?
There are two principal reasons:
1.) You would like to know WHICH EXACT applications are operating,
Firmware V 1.0 / © 2005-2013 by Aaronia AG, D-54597 Euscheid, www.aaronia.com
57
19.0 Spectrum analysis basics
