Path Calculation - Cal Amp Phantom II Operating Manual

7.0 Installation
FCC regulations allow for up to
36dBi effective isotropic
radiated power (EIRP). The sum
(in dBm) of the transmitted
power, the cabling loss, and the
antenna gain cannot exceed
36dBm.
© CalAmp

7.1 Path Calculation

Assuming adequate antenna heights, a basic formula to determine if
an adequate radio signal path exists (i.e. there is a reasonable fade
margin to ensure reliability) is:
Fade Margin = System Gain - Path Loss
where all values are expressed in dB.
As discussed on the previous page, a desired fade margin is 20dB.
System gain is calculated as follows:
System Gain = Transmitter Power + (Transmitter Antenna
Gain - Transmitter Cable and Connector
Losses) + (Receiver Antenna Gain -
Receiver Cable and Connector Losses) +
| Receiver Sensitivity |.
where all values are expressed in dB, dBi, or dBm, as applicable.
Assuming a path loss of 110dB for this example, the fade margin =
140-110 = 30dB.
30dB exceeds the desired fade margin of 20dB, therefore this radio
communications link would be very reliable and robust.
Example 7.1.1:
Tx power = 30dBm
Tx antenna gain = 6dBi
Tx cable/connector loss = 2dB
Rx antenna gain = 3dBi
Rx cable/connector loss = 2dB
Rx sensitivity = -105dBm
Phantom II
System Gain = 30+(6-2)+(3-2)
+105
= 30+4+1+105
= 140dB.
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