Appendix 3: Threshold Level Adjustment - Texas Instruments 2000 Series Reference Manual

Threshold Level Adjustment
The RA-RFM has a built-in receive signal field strength detector with the output
signal RXSS- and an on-board potentiometer (R409) to adjust the threshold level of
field strength detection. The digital output RXSS- is used for wireless
synchronization of two or more reading units. This is necessary to ensure that if
more than one reading unit is in an area, they do not interfere with each other.
The Control Module software monitors the RXSS- signal to detect whether other
reading units are transmitting. The Control Module can operate the transmitter of
the RA-RFM such that the reading units either transmit simultaneously or
alternately. In this way the read cycles of each of the reading units occur at the
same time or at secure different times. Depending on the antenna type used and
the local noise level, the RXSS- threshold level has to be adjusted. This needs to
be done after the antenna has been tuned to resonance. It is recommended to use
a small screwdriver to adjust the RXSS- threshold level. The R409 potentiometer is
located on the upper side of the RA-RFM board near connector switch SW1.
Turning the potentiometer all the way clockwise (right-hand stop), results in
minimum threshold sensitivity, i.e. the RXSS- signal will be activated at high
receive field strength. This is the default position and can be used for standard
gate antennas. It may be necessary to increase the sensitivity when using ferrite
core antennas. If there is high noise level in the area, it is necessary to adjust the
RXSS- threshold level.
Adjust the RXSS- threshold level as follows:
1. Turn the RXSS- threshold level potentiometer fully counter-clockwise (left-hand
stop).
2. Deactivate the transmitter by connecting pin 1 to pin 3 of connector J2 (using a
jumper).
3. Ensure that no other reading units are transmitting, by connecting pin 1 to pin 3
of connector J2 (jumper) of all other RA-RFMs in the area.
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Appendix 3