Texas Instruments 2000 series, Reference Manual

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High Performance RA-RFM RI-RFM-008B February 2002
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4. Monitor the voltage at RXSS- output pin with a voltmeter or an oscilloscope.
5. Turn the RXSS- threshold level adjustment potentiometer on the RA-RFM
clockwise, until the RXSS- output is just statically inactive. "Statically" means
no voltage spikes present on the RXSS- signal. 'Inactive' means that the
receive signal strength is below the RXSS- threshold level and not triggering
RXSS- (the RXSS- output voltage remains > 4 V).
6. Remove all jumpers connected to J2
Note:
Reducing the RXSS- threshold level sensitivity (turning the
potentiometer clockwise), reduces the sensitivity of the built-in receive
signal strength detector. This has the effect that the distance for
wireless detection of other transmitting reading units is decreased,
leading to reduction of wireless synchronization distance. The wireless
synchronization distance between two reading units is normally about
15 meters for two aligned stick antennas (RI-ANT-S02) with maximum
receive field strength detection sensitivity.
When the RXSS- threshold level is adjusted such that it is too
sensitive, then the RXSS- output is constantly active (i.e. low RXSS-
output level). Therefore a Control Module assumes that another
reading unit is transmitting and continually tries to synchronise to this
other reading unit. As a result, the reading repetition rate decreases
from approximately 10 down to 5 readings per second. This reading
unit can additionally no longer synchronise to other reading units,
causing interference with other reading units and reading at all
reading units becomes impossible.
The RXSS- threshold level must be adjusted individually for every
RA-RFM and reading system antenna. In addition, the RXSS-
threshold level must be individually adjusted to the local noise level in
the application area where the antenna is used.
As high noise levels mean that the RXSS- threshold level must be
adjusted to a less sensitive value, it is recommended to reduce the
local noise level in order to have high synchronization sensitivity and a
long reading distance.
The RXSS- threshold level must be adjusted so that no spikes occur
on the RXSS- signal output since these lead to an incorrect
synchronization function. An oscilloscope should therefore be used
when adjusting the threshold level.
The Antenna Tuning Indicator (RI-ACC-ATI2) accessory can be used
to adjust the RXSS- threshold level, since this device automatically
switches the transmitter off and has an internal spike extension circuit,
causing the RXSS- threshold level to be adjusted such that no spikes
occur on the RXSS- output.