Installation Guide

22
Manual Field Power Calibration - FCC Readers
Caution
The following procedure involves connecting and disconnecting RF cables from the
reader. The reader should be powered down (transmitter disabled) before
disconnecting any antenna, cable, or power meter from any port to prevent damaging
the unit. Antennas (or a power meter) should be attached to all active ports prior to
transmitter power up.
To achieve optimum performance and maximum range from the SAMSys UHF
reader, each active antenna port should be set to transmit at the highest power allowed
within regulatory limits. This output level is obtained by calibrating the reader for
antenna gain and cable loss.
For FCC mode, the maximum power level is 1 W (30 dBm) at the antenna (per Code
of Federal Regulations, Title 47, Part 15). If an antenna is used that exceeds 6 dBi, the
maximum power level delivered to the antenna must be reduced by the amount of
antenna gain in excess of 6 dBi (antenna gain is specified in dBi, where i = isotropic).
For example, if a 9 dBi linear gain antenna is used, the transmitter power delivered to
the antenna should be reduced by 3 dB to 27 dBm.
If a circular polarized antenna is used, subtract 3 dB from the manufacturer specified
antenna gain to get the applicable linear gain. If the specified antenna gain is 7.5 dBi,
circular polarization (7.5 dBiC), the linear antenna gain is 4.5 dBi.
In addition to the antenna gain, the reader must also be calibrated for cable loss.
RG58 A/U cable typically has a loss of approximately 1 dB per six feet of cable.
For example, if a circular polarized antenna with a gain of 7.5 dBi (4.5 dBi linear) is
used with 15 feet of cable, the optimum output power from the UHF reader is 32.5
dBm (30 dBm + 2.5 dB cable loss). Since the linear antenna gain does not exceed 6
dBi, no further adjustment is required.