ITC 220 Base Station, Locomotive & Wayside Radio Transceiver Field Service Guide PN 0046300120 Rev. A
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Fixed installation:
In a fixed installation, a common single element exposed folded dipole antenna without reflector
has 0 up to 2.9 dBd (2.1 to 5.0 dBi) azimuthal gain depending on the design.
Once the allowable ERP is determined by applying all power-restrictive rules from above and the antenna gain is
known, the transmitter peak envelope power output feeding the transmission line is determined by subtracting the
antenna gain in dBi from the EIRP and adding the loss from the antenna feedline and connectors plus the loss from
any external inline power sensors, combiners, filters, or lightning arresters. If the net value is greater than or equal
to 44.85 dBm, then the maximum power of the Wayside transmitter can be used. If the value is less than 44.85
dBm, then the transmitter output power must be reduced to the net value.
Example for the 50 W ERP case: Antenna gain = 2.9 dBd and feedline loss is at least 0.5 dB for 25 feet of Times
Microwave LMR -400 coax plus 0.4 dB for inline lightning arrester and three connectors. Assuming no other losses,
the transmitter power output limit = 47-2.9+0.9 dBm = 45 dBm PEP. In this case, the actual Wayside ERP is
44.85+2.9-0.9 dBm = 46.85 dBm = 48.4 W PEP and therefore the system is compliant with the 50 W ERP limit. This
installation is not allowed to transmit on FCC channels 196-200 because the maximum ERP is greater than 2 watts.