HW V4 / © 2005 – 2013 Aaronia AG, DE-54597 Strickscheid
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Manual Spectran V4
Correct measurement
7. Correct measurement
Note that when measuring high frequency radiation, you will encounter some „strange
characteristics“ 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
radiation. 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 become “contaminated” again just due to a trivial mains cable. To avoid this, shielded
rooms must be equipped with so called mains filters.
Especially, however, the utilization of usual power cables for data transmission (e. g. Internet,
signal, video and audio transmission) is a serious source of interference and radiation.
7.1.
Noise floor
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 statically
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 lower
frequencies – for example, the noise floor at 100MHz is
significantly higher than it is at 5GHz. However, skilled users
can usually still “tease out” useful readings and distinguish
between noise and even very weak, real signals.
Determining 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.
Noise floor (below this imaginary line)
