Appendix 5: Noise Considerations - Texas Instruments 2000 Series Reference Manual

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
Source Inductive parts for example: deflection
coils, motor coils.
Path Via magnetic fields.
Effect Disturbs receive function by magnetic
interference with signal from transponder
at 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.
Noise Considerations
Power units, for example: motors, switched
mode power supplies. Can be seen as voltage
spikes or ripple voltage.
Galvanically conducted via all cables (supply
and interface) connected to the RA-RFM.
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.
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Appendix 5
Conducted Noise