TECHNICAL DESCRIPTION AND OPERATING MANUAL ST131 <PIRANHA II> and ST131N
42
4.1.4.1.1.1 Determination of frequency range
Frequency range contraction is possible when additional information available. In case
of absence of additional information all possible frequency range on given channel is selected.
“Popular” ranges of STM are 110-500MHz and GSM frequencies (see 4.1.4.4)
4.1.4.1.1.2 Determination of necessary sensitivity
Sensitivity of the device depends on the band (see section Annex 2) and is defined by the
displayed noise level.
In future, we will accept detection of signal exceeding its level above the noise at 10dB.
In FULL RANGE mode noise level is no worse than –88 dBm (about 10 µV).
When selecting the BAND mode and the minimum bandwidth - 0.5 KHz noise value will be about
–150 dBm (about 0.01 µV). Clearly, this noise level can be seen only without signal observed in the
measurement bandwidth.
Thus, range of changing sensitivity due to changes in the frequency band is up to 60 dB (1000
times). Before starting work, you must decide what level of radiation is to be detected. All possible levels
of radiation for modern STM is greatly wide. In very general case, we can talk about radiation levels
from a few watts up to tenths of microwatts. For example, the radiated power of the "classic" STM with
FM modulation with a range of several hundred meters - is the tens of milliwatts.
Maximum power of GSM transmitter is 1W (at a maximum distance from the base station).
Minimum real power of 3G and 4G transmitters are decimals of microwatts (with minimum
distance from the base station).
In “usual” practice it is about milliWatts.
Let’s define, which sight band it is necessary to use and on which distance from examined
interior UHF converter antenna should be settled.
Figure 45 shows an example on the dependence of level of the received signal on the distance
from the source (for a frequency of 2 GHz). Based on threshold sensitivity of the ST131, depending on
the analyzing frequency band (red lines) are determined the maximum distance at which the signal can
be detected with a given power.
Figure 45