YDI AMP2440 Installation And Operation Manual
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de.edis-orteanderge,NPage 10APPENDIX A: Calculating PowerThis appendix explains how to calculate the input power to the amplifier for your configuration.1. Using Table A, convert the output power of the radio modem from Watts (or milliWatts) todBm. The Model 2440 amplifier works with input powers between 3.2 mW, +5 dBm, and100 mW (+20 dBm).2. Calculate the cable attenuation for your installation.First, determine the attenuation for the length of your cable at 2.4 GHz. Use the cablemanufacturer’s specifications, or for convenience you may refer to Table B for typical values.(For example, Table B shows that typical attenuation for LMR-400 is about 6.9 dB per 100 footat 2.4 GHz.) Then add 0.6 dB to that figure for connector, adaptor cable, and DC injectorlosses.3. Calculate the maximum power that can be expected at the amp on the pole:Radio output (dB) - Cable loss (dB) - Connector Loss = Signal level at the amp’s input (dBm)For example, a radio with 40mW (+16 dBm) output and 75 feet of LMR400 (about 3.4 dB ofloss) would have the following input level to the amplifier:+16 dBm - 3.4 dB - 0.6dB = +10 dBmUsing a standard amplifier with 14 dB of linear transmit power gain, the output power iscalculated as follows:+10 dBm + 14 dB gain = +24 dBm output power (250 mW)If the input to the amplifier will exceed +20 dB (100 mW) by your calculations, an attenuatorpad will be necessary between the modem and the DC injector. Or you can order a specialversion of the amplifier from YDI that will accept higher transmit input power.Note: Never put attenuator pads between in the cable the DC injector and the amplifier sincethere is a +12V DC voltage on the cable. Doing this would prevent DC power fromreaching the amp and will also damage the attenuator. However, a longer cable orone with higher loss could be used.Effective Radiated Power (ERP)ERP is defined as the sum of the power feeding an antenna and the gain (in dBi) of thatantenna. For example, with 250 mW (+24 dBm) of power into a 24 dBi gain grid dish antenna(like the YDI PT2424), the ERP would be:+24 dBm + 24 dB = 48 dBm or 64 watts EIRP |
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