Receiver; Ra-Rfm Connectors And Jumpers - Texas Instruments 2000 Series Reference Manual

High Performance RA-RFM RI-RFM-008B

1.3 Receiver

1.4 RA-RFM Connectors and Jumpers

CAUTION:
The RA-RFM must not be operated in continuous transmit
mode when operated at full power output. When using
pulse widths smaller than 50%, the RA-RFM transmitter
power stage works in a less efficient way. This leads to an
increased
temperature increase of the transmitter power stage, so
ensure that more cooling is provided.
Note:
If the RA-RFM is going to be physically located within the antenna
field, it may be necessary to shield the module by means of a metal
casing.
The signal received from the transponder is a Frequency Shift Keying (FSK) signal
with typical low and high bit frequencies of 134.2 kHz and 123.2 kHz respectively.
The signal is received from the antenna resonator, which is capacitively coupled to
the receiver.
The signal RXCK is the reference clock signal to decode the RXDT data stream.
The RXCK signal changes from low to high level during each data bit and the
RXDT signal is valid before and after this positive slope for a certain time window.
For more details refer to Table 11, Timing Characteristics.
The receiver has a built-in RF receive signal detector. The receive signal strength
is indicated by the digital output RXSS-. This signal becomes active ( = logic LOW
level) when the received RF signal strength exceeds a defined level. This threshold
level may be adjusted with a potentiometer on the RA-RFM board and is located
near connector J1 (see Figure 5).
The RXSS- output is used for detection of other transmitting reading units and thus
can be used for wireless read cycle synchronization of several reading units.
There are a number of connectors, jumpers and other components on the RA-RFM
available for use.
These are:
J1 Connector for supply voltages and interface signal lines to and from the
RA-RFM
power dissipation
12
February 2002
and thus to higher