Technical Manual

18
Wireless Sensor Interface A720 (addIT™)
• Check if the RSSI threshold is correct: type the command
RSSI
– the actual val-
ue must be lower than the threshold set. If this is not the case, repeat several
time the
RSSI
command, maybe a transmission just happens (a radio scanner
set on the operating frequency would help detect foreign transmissions). If the
threshold difference is marginal, then you must increase it by using the
SET
RSSI
command (it must be 20 to 30% higher than the actual value).
If the any of the above targets is not reachable, check first visually if the chip U10 is
correctly soldered and that no shorts exist between its pins (most problems usually
appear around this chip). If the S/N ratio test is positive but the last check is not, then
check U8 and the components around it.
3.3.6. Checking the Transmitter Parameters
• Check that the switch on the Testing Fixture is flipped to the
Power/Sens.
po-
sition;
• Switch the DUT to transmit mode by typing at the terminal the command
XMIT 0
;
• Switch the Service Monitor to TX TEST mode, on the appropriate frequency
(432 MHz for low band and 450 MHz for high band);
• You should see the following parameters on the Service Monitor readout:
1. Carrier: 432000000, respectively 450000000 Hz (± 500 Hz);
2. Output Power: 9 dBm (+1dBm, -2dBm);
3. Frequency Deviation: ±2.3 kHz (±0.2 kHz) for 12.5 kHz units and ±4.0 kHz
(±0.5 kHz) for 25 kHz units;
• Switch the unit in stand-by (press the enter key).
If item 1 above cannot be achieved, replace R36 with a 12 K W resistor to shift the fre-
quency up, or R35 with a 10 k W resistor to shift the frequency down. If item 2 cannot
be achieved, check the solder and components around Q1 and Q3; in addition, check
if D1 and D2 are the right components (sometimes they are replaced by other visu-
ally similar parts). Finally, if item 3 cannot be achieved, replace R17 with a lower re-
sistor to reduce the deviation, or a higher one to increase it. Note that depending on
the device type, R17 can be either 470 W (12.5 kHz) or 1 k W (25 kHz). If no modulation
is present at all, then check U1 and the parts around it.
3.3.7. Data Transfer Check
The last check is a radio data transfer. In order to perform it, at least a base station
(model A730SD) or a normal remote station (model A730MD) should be installed
and operated on the same test frequency (either 432 or 450 MHz), in the near vicinity
(no more than 30 m).
Note: The base or remote station used for this test must be operated with a fictive antenna (a 50 W
resistor).