User's Manual

APPENDIX C

Calculating Input Power

The following information explains how to calculate the input power to the amplifier for your configuration.

1. Using Appendix A, Table A, convert the output power of the radio modem from Watts (or

milliWatts) to dBm. The Model AMP2440 amplifier is optimized to work with input powers

between 3.2 mW (+5 dBm), and 10 mW (+10 dBm).

2. Calculate the cable attenuation for your installation.

Determine the attenuation for the length of your cable at 2.4 GHz. Use the cable manufacturer’s

specifications or, for convenience, refer to Appendix A, Table B for typical values. For example,

Table B shows that typical attenuation for LMR-400 is about 6.9 dB per 100 foot at 2.4 GHz. Add

1.7 dB to that figure for miscellaneous losses for the connector, adaptor cable and DC injector.

Subtract total attenuation from the radio’s transmit power.

3. Calculate the maximum power that can be expected at the amplifier when mounted on the pole

as follows:

Radio output (dB) - Cable loss (dB) - Miscellaneous Loss =

Signal level at AMP2440 input (dBm)

For example, a radio with 32mW (+15 dBm) output and 50 feet of LMR400 (about 3.4 dB of loss)

would have the following input level to the amplifier:

+15 dBm – 3.4 dB – 1.7dB = +9.9 dBm approx. +10dBm (10 mW)

Using a standard amplifier with 14 dB of linear transmit power gain, the output power is calculated

as follows:

+10.0 dBm + 14 dB gain = +24 dBm output power (250 mW)

If the input to the amplifier exceeds +10 dBm (10 mW) according to your calculations, an

attenuator pad will be necessary between the modem and the DC injector. You can also order a

special version of the amplifier from YDI that will accept higher transmit input power.

NOTE: Never put attenuator pads between the cable, DC injector and amplifier since

there is a +12V DC voltage on the cable. This will prevent DC power from

reaching the amplifier and also damage the attenuator. A longer cable or one

with higher loss could be used.

Effective Isotropic Radiated Power (EIRP):

EIRP is defined as the sum of the power feeding an antenna and the gain (in dBi) of that antenna.

For example, with 250 mW (+24 dBm) of power into a 24 dBi gain grid dish antenna (such as the

YDI PT2424), the EIRP would be:

+24 dBm + 24 dB = 48 dBm or 64 watts EIRP