HW V4 / © 2005 – 2013 Aaronia AG, DE-54597 Strickscheid
73
Manual Spectran V4
Physical units
λ
=
"#
= 0.15 m
(For 2 GHz, the result is 0.15 m)
Further information concerning wavelength is contained in table 4.
11.5. Calculating the „close-up range“ in [m]
If you want to perform a measurement, you need to do this outside of the so-
called close-up range of the transmitter. The close-up range depends on the
transmitter frequency. According to the aforementioned formula, the close-
up-range can be determined quickly. Here, you simply need to multiply the
resulting wavelength by a factor of 10 (there are some sources which only
use a factor of 3). The result is the close-up range, i. e. the minimum
distance to the transmitter in which a realistic and sensible measurement can
be achieved.
Example: For a „900MHz cell phone“ the wavelength is:
λ
=
!
"#
= 0.33 m
Hence, the close-up range is 0.33m * 10 = 3.3m.
It is easy to see, that e. g. measurements taken directly next to the cell
phone will definitely result in wrong readings.
Inside the close-up range, E and H fields would need to be measured
separately. However, outside the close-up range, both field types are
coupled tightly to each other, so knowing the strength of one of them will be
enough to derive the other.
.
11.6. Calculating power density [W/m²] from power [dBm]
Only if you know the transmitter’s frequency you can convert from dBm to
W/m². You will also need the antenna gain of the antenna used for
measurement. The formula you need looks like this:
=
$
&'(&',*
+(
$
∗
,∗ -
, $./!²
=
,
0
$
*
$ ,.00
, !!/
= 0,00000408 W/m² = 4,08 µW/m²