Intermec 869 RFID Reader, Инструкция по эксплуатации

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Theory of Operation Chapter
—
2
6 869 RFID Reader Service Instruction Manual
1 General Description
The 869 reader provides basic tag identifies, reads and writes at both 869
& 915 MHz. The RF board supports 4 antenna ports simultaneously. The
DSP engine supports asynchronous serial communication using RS-232 to
connect to a host. The General Purpose Input/Output (GPIO) connector
allows the 869 reader to monitor and/or control external devices. This
would allow, for instance, a conveyer position switch to activate the reader
for tag operations.
The reader has an on/off power switch and is powered from an external
DC source. Four LED status indicators are located on the serial connector
side of the reader. It operates under 2 watts, so it is capable of continuous
operation.
The reader contains the manager function that provides communication to
the host. The host must support the command strings used by the managĆ
er.
In the 869 MHz band, the 869 reader utilizes the raised cosine modulation
envelope to reduce the bandwidth of the transmissions. Raised cosine
modulation is a digital filter, which programs the DSP to form a resultant
response. In this case, it has been programmed to respond according to
the harmonic content of the output waveform. This modulation is unique
and the bandwidth can best be described by:
Bandwidth = (1+
α
)/2Ts where
a = roll-off factor
Ts = one sampling time period
The net result from the raised cosine approach is that the output envelope
has a very low harmonic content, which dramatically reduces unwanted
harmonic and spurious energy in the output waveform.
The 869 reader also utilizes a pre-distortion filter. Pre-distortion was imĆ
plemented to the base band modulation envelope to compensate for non-
linearities in the mixer and power amplifier circuits. To meet the spectral
occupancy requirements for ERC/DEC/(01)04, it is essential to keep the
up-conversion and amplification of the data very linear. To accomplish
this, the output power was reduced to 500 mW, the driver kept out of
compression, and the dynamic range of the mixer was limited to increase
its resolution.
Pre-distortion also has the effect of reducing transmit harmonics and inĆ
creasing spectral containment. The pre-distortion was implemented by
re-mapping the values outputted by the DAC, to a discrete power level at
the transmitter's output, as opposed to a base band voltage level. This efĆ
fectively compensates for a non-linear transfer between the base band data
and the transmitted power level. The entire DAC range wasn't computed,
but only the points necessary to build the raised cosine filtered data stream.