Manual SPECTRAN V5
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34
BASICS
6.
Spectrum analysis basics
6.1. What is a frequency range?
Imagine a giant motorway, several kilometers wide, with thousands of lanes. Every imaginable
kind of vehicle can be found here: motorcycles, cars, trucks, etc. In order for them to not get
into each other’s 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
traffic caused by the individual groups, these lanes also have different widths: For example
the lane reserved for cyclists is far narrower than that reserved for trucks, etc. High frequency
ranges work the same way, here the “road users” are applications (for example, a cell phone,
a microwave oven, a radio-controlled car lock, in effect all appliances that somehow work with
radio waves).
Every application has its own frequency range for exclusive use. By assigning a separate fre-
quency range for each application, conflicts between different “road users” can be avoided, so
that e. g. a cell phone cannot be disturbed by a microwave oven.
6.2. Big difference 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 on the contrary, may speed
up to 250 km/h. Exposure limits for radio applications work similarly: Here, however, the word
“speed” is replaced by the transmitting power. E. G., a broadcast station may have an enor
-
mous transmitting power of 1 000 000W or more, in contrast, a radio-controlled car lock only a
few mW (1mW=0.001W) etc. 3 examples of exposure limits in practice.
Frequency range (MHz)
Application
Power limit (W EIRP)
1 880 – 1 900
DECT phones
0.25
2 320 – 2 450
Amateur radio (11 cm)
750
5 725 – 5 825
WLAN 802.11a
0.025
It is easily visible that each radio application may only use one exactly defined frequency
range. Also, the high differences in admissible transmitting power are noticeable.
6.3. Application of spectrum analysis
There are 2 main reasons for application of spectrum analysis:
a.
You would like to know which radio applications are active.
b.
You would like to measure the exposure caused by each of the radio applications
separately, e. g. for evaluating exceeding of exposure limits.
