Rf Tuning; Uart - Espressif Systems ESP32 Hardware Design Manuallines

Chapter 3. Schematic Checklist

3.5.2 RF Tuning

The RF matching parameters vary with the board, so the ones used in Espressif modules could not be applied directly.
Follow the instructions below to do RF tuning.
Figure ESP32 RF Tuning Diagram shows the general process of RF tuning.
Fig. 13: ESP32 RF Tuning Diagram
The initial value of the parameters in the matching network can be 0 Ω. The recommended value of S11 is 25+j0.
The recommended central frequency is 2442 MHz.
If the usage or production environment is sensitive to electrostatic discharge, it is recommended to reserve ESD
protection devices near the antenna.
Note: If RF function is not required, then the RF pin can be left floating.

3.6 UART

It is recommended to connect a 499 Ω series resistor to the U0TXD line to suppress the 80 MHz harmonics.
Usually, UART0 is used as the serial port for download and log printing. For instructions on download over UART0,
please refer to Section Download Guidelines.
Other UART interfaces can be used as serial ports for communication, which could be mapped to any available
GPIO by software configurations. For these interfaces, it is also recommended to add a series resistor to the TX line
to suppress harmonics.
When using the AT firmware, please note that the UART GPIO is already configured (refer to AT Firmware Down-
load). It is recommended to use the default configuration.
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