ESP32-C3FN4 - Custom board, no WiFi

[Aeronautic]

Hi everyone,

I'm working on a custom PCB board based on ESP32-C3FH4 chip.
HF part doesn't seem to work correctly: softAP is not created until I reduce the TX power to 28 or less (WiFi.setTxPower(WIFI_POWER_7dBm)).

It appears that there is a critical problem with the impedance of the antenna path.

It is 2-layers board (1.6mm thickness, 1oz copper weight) from JLC PCB.
I used typical PIFA antenna (TRACE_ANTENNA_2.4GHZ_15.2MM from SparkFun-RF) and general matching PI filter 2pF - 2.7nH - 2.7pF in 0402 packages. Trace is as short as possible, 16millis and 10millis at chip pin.

When designing I knew that these values are for 4 layer board, but I didn't thought it would be so much critical.

All 5 boards that I have, have the same issue.

I looking for ideas to fix this issue. I could have access to network analyzers but I have no idea how to connect network analyzer to such a small traces.

Best regards,
Michal

Schematic

Zrzut ekranu 2023-09-11 o 16.50.14.png (215.88 KiB) Viewed 11332 times

PCB

Zrzut ekranu 2023-09-11 o 16.51.29.png (728.57 KiB) Viewed 11332 times

[Aeronautic]

I created an arduino sketch for changing channel and TX power.
I fixed position of a board and fixed position of my USB dongle used as receiver.

I am attaching the measured RSSI for various TX power and channel:

Zrzut ekranu 2023-09-11 o 19.38.42.png (75.44 KiB) Viewed 11306 times

Zrzut ekranu 2023-09-11 o 19.38.32.png (47.68 KiB) Viewed 11306 times

Code: Select all

#include <WiFi.h>
#include <WiFiClient.h>
#include <WiFiAP.h>
#include <iostream>
#include <string>

const char *ssid = "TEST";
const char *password = "TESTTEST";
int channel = -1;

void setup() {
  Serial.begin(115200);
  while (!Serial);
  
  WiFi.mode(WIFI_AP);
  //WiFi.setTxPower(WIFI_POWER_7dBm);
  WiFi.setTxPower(WIFI_POWER_5dBm);
  updateAccessPoint();
}

void loop() {
  static String inputBuffer = "";
  
  if (Serial.available() > 0) {
    char c = Serial.read();
    if (c == '\n' || c == '\r') {
      processInput(inputBuffer);
      inputBuffer = "";
    } else {
      inputBuffer += c;
    }
  }
}

void processInput(String input) {
  if (input[0] < 0x20) return;
  if (input[0] == 'C' || input[0] == 'c') { // Change channel
    int value = input.substring(1).toInt();
    if (value < 1 || value > 13) {
      Serial.println("Invalid channel number. Please enter a value between 1 and 13.");
      return;
    }
    channel = value;
    
  } else if (input[0] == 'P' || input[0] == 'p') { // Change power
    int value = input.substring(1).toInt();
    WiFi.setTxPower((wifi_power_t)value);
    
  } else {
    Serial.println("Invalid input format. Use C[0-13], P[0-99]");
    return;
  }
  
  updateAccessPoint();
  return;
}

void updateAccessPoint() {
  if (WiFi.softAPdisconnect(true)) {
    Serial.println("Access Point disconnected");
    delay(100);
  }

  WiFi.softAP(ssid, password, channel);
  
  int txPower = WiFi.getTxPower();
  Serial.print("TX power: ");
  Serial.print(txPower);
  Serial.print(", channel: ");
  Serial.println(channel);
}

[Aeronautic]

I removed whole PI filter and it started working fairly good. Still looking for approach to match it correctly

[ESP_Sprite]

Wrt VNA matching etc: you'd generally use the ESP RF Test Tool for that, iirc it comes with documentation as well. https://www.espressif.com/en/support/do ... ther-tools . From looking at the RF teams desks here, connecting the VNA to the PCB comes down to very thin coax pigtails and good soldering skills, I'm afraid.