Texas Instruments 2000 series, Справочное руководство

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Noise Considerations
Noise can have a negative effect on the receive performance of the RA-RFM.
There are two different kinds of noise: radiated and conducted. Their
characteristics are shown in Table 18.
Table 18: Characteristics of Radiated and Conducted Noise
Radiated Noise Conducted Noise
Source Inductive parts for example: deflection
coils, motor coils.
Power units, for example: motors, switched
mode power supplies. Can be seen as voltage
spikes or ripple voltage.
Path Via magnetic fields. Galvanically conducted via all cables (supply
and interface) connected to the RA-RFM.
Effect Disturbs receive function by magnetic
interference with signal from transponder
at the antenna. Leads to malfunction and reduced sensitivity of
receiver circuitry due to, for example, interfered
supply voltage.
Conducted noise can also cause radiated noise.
Note:
The RA-RFM has a built-in function for suppression of common mode
noise coupled to the antenna.
Method for detecting and distinguishing between noise types:
The principle of this procedure is to eliminate any conducted noise from the supply
and all interface lines. In order to do this test the RA-RFM must be powered from a
battery (for example: 9 V, 20 mA) in order to eliminate any conducted noise from a
power supply. Conducted noise via the interface lines is eliminated for this test by
simply disconnecting all interface lines to the RA-RFM. The measurement criteria
for low noise is the amplitude of the receive signal strength detector of the RA-
RFM.
The test pin RSTP at connector J1 pin 10 carries an analog output voltage
indicating the receive signal strength. This voltage should be measured in
combination with the antenna RI-ANT-G02. The necessary set-up for this test is
shown in Figure 12. This configuration operates the RA-RFM from a battery and
has no interface line connected.
Appendix 5