5 Noise Test

Microchip provides a Python script for noise power analysis in the frequency band in use.

The Microchip PLC Noise test is a Python script for the analysis of the noise power per carrier in the working frequency band for the PLC communications. This PC tool requires that the PLC device runs the PHY Tester tool embedded project included in the Microchip PLC firmware package.
Figure 5-1. Microchip PLC Noise Per Carrier Tool
Typical noise sources present on PLC devices are:
  • Thermal noise inherent to the components.
  • Noise coming from AC-DC or DC-DC power supply switching frequency.
  • Noise coming from serial protocols like UART/SPI/I2C because of incorrect PCB Layout.
  • Noise coming from coupled radiated signals due to a bad isolation to interferences, signal loops.
Attention: The Total Noise value provides an idea about the performance of the design in terms of sensitivity (signal level of a frame that can be received correctly by the device under test) required. In case of the G3-PLC certification, it is established a maximum limit of 60 dBuV when communicating at ROBO BPSK modulation.
The Noise Test tool use the following PIBs to recover the information:
  • REG_VERSION_NUM, for the PLC protocol and working frequency band.
  • REG_NOISE_PER_CARRIER, for the estimation of the noise power (in dBμV) in each carrier belonging to the corresponding band for a spectrum analysis on the full frequency bands defined on the PLC standards.
Important: For more information about those PIBs, refer to the Microchip PL360 Host Controller User Guide
The process to perform the noise test is the following:
  1. Connect the board programmed with the PHY Tester Tool firmware.
  2. Runs the Python script PLCNoiseTest.py (or PLCNoiseTest.exe).
  3. Press the Refresh button to update the serial ports available.
    Figure 5-2. PLC Noise Per Carrier Tool Refresh Serial Ports
  4. Select the corresponding serial port and speed (230400 bps by default), then press the Connect button.
    Figure 5-3. PLC Noise Per Carrier Tool Connection
  5. If everything is ok, the Device Info information will be filled.
    Figure 5-4. PLC Noise Per Carrier Tool Device Info
  6. Press the Go button, then wait for results on the screen.
    Figure 5-5. PLC Noise Per Carrier Tool Screen Results
  7. Analyze the frequency of the highest peaks looking for unexpected noises at different frequencies to determine which could be the source of them. Whether the spectrum is more or less flat in the step band, the noise could be associated to thermal noise, PCB layout (RX path, ground, power supply distribution), and only the Total Noise value is important because it provides an idea about what the RX Sensitivity of the device is in terms of PLC communications. The next table shows recommended values:
    Table 5-1. PLC Noise Measurement Results
    Total Noise RANGE (dBuV)RESULT
    <= 40VERY GOOD
    40 < TotalNoise <= 47GOOD
    47< TotalNoise <= 55POOR
    >55POTENTIAL ISSUES
  8. Press the Stop button when finished. A report with the results are stored in the “report folder” on an Excel file named MCHP_BAND_TestNoise_DATE-TIME.xlsx.
    Figure 5-6. PLC Noise Per Carrier Tool Excel Results
    Figure 5-7. PLC Noise Per Carrier Tool Excel Figures