Phoenix Contact RAD IFS Series - System Calculation in Free Space; Figure 8-17 Free Space Attenuation

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PHOENIX CONTACT 105542_en_05
8.15 System calculation in free space
Figure 8-17 Free space attenuation
– Antenna gain per antenna: 8 dBi
– Transmission power per wireless module: 14 dBm
– Cable attenuation per cable (3 m EF 142): 2.85 dB
– Free space attenuation, 400 m: 92 dB
Example calculation for 2.4 GHz with optimum free space:
– Length of the wireless path: 400 m
– Device transmission power + antenna gain - cable attenuation (EIRP): ≤20 dBm
EIRP [dBm] =
transmitter power [dBm]
+ gain of transmitting antennas [dBi]
- loss of the transmitter cable [dB]
Incoming power for the receiver [dBm] =
transmitter power [dBm]
- loss of the transmitter cable [dB]
+ gain of the transmitting antenna [dBi]
- free space attenuation [dB]
+ gain of the receiving antenna [dBi]
- attenuation of the antenna cable at the receiver [dBm]
System reserve =
receiver sensitivity [dBm]
- incoming power for the receiver [dBm]
(recommended system reserve >10 dB)
– EIRP = 19.15 dBm
– Free space attenuation, D
L
[dB]:
D
L
= 32.4 + 20log(R[km]) + 20log(f[MHz]) = 32.4 + 20log(0.4 km) + 20 log(2400 MHz)
= -92 dB
– Incoming power at the receiver = -67.7 dBm
– Receiver sensitivity = -96 dB (with a data rate of 125 kbps)
– System reserve = |-96 dB| - |-67.7 dB| = 28.3 dB
28.3 dB > 10 dB
Conclusion: The loss of -67.7 dB is significantly lower than the receiver sensitivity of -96 dB.
The desired wireless connection is therefore possible in mathematical terms.
RAD-2400-IFS
RAD-ID
Reset
+24 V
0 V
RSSI- RSSI+
ANT
SPORT
0 1
Pwr
Dat
Err
RXTX
D(A) D(B)
GND
RX
CO
1
NC
1
CO
2
TX
RAD-2400-IFS
RAD-ID
Reset
+24 V
0 V
RSSI- RSSI+
ANT
SPORT
0 1
Pwr
Dat
Err
RXTX
D(A) D(B)
GND
RX
CO
1
NC
1
CO
2
TX