Aaronia SPECTRAN HF-2025, Руководство пользователя

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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
etc.),
massive selective concentration (so-called “Hot Spots” ) is often noti-
ceable, 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
like antennas and cause the corresponding “concentration” or forwarding of high
frequency radiation. Thus, electrical cables are another medium for high-fre-
quency radiation and can “catch” it and “release” it again at a totally different
location. Hence, even well screened rooms can become “contaminated” again
just due to a trivial mains cable. To avoid this, screened rooms must be equip-
ped 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 inter-
ference and radiation.
8.1 Noise floor
The so-called noise floor indicates the limit below which real measurements
become
impossible . Here, only interference will be detected. Visually, SPEC-
TRAN 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).
Depen-
ding on frequency, though, the noise floor may get extremely varied . Usual-
ly, it increases with higher frequencies. The noise floor for the GSM1800 hotkey
(key 8), for example, is at around -70dBm. However, professionals with a lot of
experience can still “tease out” a lot - they can still well differentiate between the
usual noise and genuine signals. You can detect the level of the noise floor by
“measuring” WITHOUT antenna or signal.
8.0 Correct measurement
31
Noise floor
(below the imaginary line)
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