5. Amplifier Connections and Indicators
CAUTION: Only use high quality N-type connectors. Do not use PL259 “CB” type UHF
connectors. Doing so will ruin the N-Female jacks and void your warranty.
This LED glows RED when the amp has switched to the transmit mode.
This occurs when the amp detects RF power at the jack labeled “To
DC Injector”. (See Section 9 operation for more information)
This LED glows GREEN in the receive mode when DC power is applied
to the amplifier. It is goes off when; the amp is in the transmitting
mode.
This N-type female connects to the DC Power Injector via the transmis-
sion cable. The length of this cable will determine the type of cable
that should be used. See the installation diagram and the Appendix for
more information.
Transmit LED:
Receive LED:
Antenna
Connection:
DC Injector
Connection:
6. DC Power Injector Operation
A DC Power Injector is an in-line device which “injects” the DC power necessary to operate
the amplifier onto a transmission line. This allows the coax cable to carry both RF signals and
DC power to the mast-mounted amplifier. This precludes the need to run a separate power
cable to the remote mounted amplifier.
Page 5
This N-type female connects to the antenna with a short length of
low-loss coax cable.
When grounded to a good earth ground through either the grounding stud or mounting flange,
the DC Injector will provide maximum lightning protection to your radio modem, wireless LAN
card or Access Point.
Page 10
APPENDIX A: Calculating Power
This 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) to
dBm. The Model 2440 amplifier works with input powers between 3.2 mW, +5 dBm, and
100 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 cable
manufacturer’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 foot
at 2.4 GHz.) Then add 0.6 dB to that figure for connector, adaptor cable, and DC injector
losses.
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 of
loss) would have the following input level to the amplifier:
+16 dBm - 3.4 dB - 0.6dB = +10 dBm
Using a standard amplifier with 14 dB of linear transmit power gain, the output power is
calculated as follows:
+10 dBm + 14 dB gain = +24 dBm output power (250 mW)
If the input to the amplifier will 20 dB (100 mW) by your calculations, an attenuator
pad will be necessary between the modem and the DC injector. Or you can order a special
version 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 since
there is a +12V DC voltage on the cable. Doing this would prevent DC power from
reaching the amp and will also damage the attenuator. However, a longer cable or
one 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 that
antenna. 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
