Manual SPECTRAN V5
© Aaronia AG 2016 | www.aaronia.com
30
CORRECT MEASUREMENT
5.
Correct measurement
Note that when measuring high frequency radiation, you will encounter some „strange charac-
teristics“ which can be pretty irritating particularly for novices.
In practice, high frequency radiation rarely constantly fades with distance from the source: due
to reflections, diffusion and diffraction (by houses, trees, walls, furniture etc.) massive selective
concentration (so called “Hot Spots”) is often noticeable, especially inside rooms. Here, the
difference in measured signal strength can easily vary by a factor of 10 or 100 in a range of
just a few cm. Thus, it is sometimes pretty difficult to find the actual source or the maximum
strength of RF radiation.
High-frequency fields are often also measurable on metal objects, as these act as antennas
and cause the corresponding „concentration“, reflection or forwarding of high frequency radia
-
tion. Thus, electrical cables are another medium for high-frequency radiation and can “catch”
it and “release” it again at a totally different location. Hence, even well shielded rooms can be
-
come “contaminated” again, just because of a trivial mains cable. To avoid this, shielded rooms
must be equipped with so called mains filters.
However, the utilization of normal power cables for data transmission (e. g. Internet, signal,
video and audio transmission) also is a serious source of interference and radiation.
5.1. Noise floor
Noise floor (below the red line)
The so-called noise floor indicates the limit below which real
measurements become impossible. Here, only interference
will be detected. Visually, Spectran would display this as a
collection of small “points” or bars which either stay statical
-
ly at the same place or change with every sweep (noise).
However, depending on frequency and selected settings, the
noise floor can be vastly different and must be determined
before starting a measurement.
In the case of Spectran, the noise floor increases with low
-
er frequencies – for example, the noise floor at 100MHz is
significantly higher than it is at 5GHz. However, skilled us
-
ers can usually still “tease out” useful readings and distin
-
guish between noise and even very weak, real signals. De-
termining the noise floor is relatively straightforward: Simply
conduct a “measurement” without an antenna and/or signal
source or by connecting a 50 Ohms terminator. Any signals
then possibly shown are the noise floor of your instrument.
