Installation Guide

24
Manual Field Power Calibration - ETSI 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 ETSI mode, the maximum power level is 500 mW ERP (27 dBm) at the antenna
(per EN300 220--3 V1.1.1). This is equvalent to 820 mW (29 dBm) EIRP (equvalent
isotropic radiated power). An EIRP of 29 dBm is used for the following example.
If a circular polarized antenna is used, subtract 3 dBi 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 has typically has a loss of approximately 0.5 dB per meter of cable.
For example, if a circular polarized antenna with a gain of 7.5 dBi (4.5 dBi linear) is
used with 5 meters of cable, the optimum output power from the UHF reader is 27
dBm (29 dBm - 4.5 dB antenna gain + 2.5 dB cable loss).