diff --git a/RX_FSK/RX_FSK.ino b/RX_FSK/RX_FSK.ino
index 9a953bf..dcd66df 100644
--- a/RX_FSK/RX_FSK.ino
+++ b/RX_FSK/RX_FSK.ino
@@ -31,6 +31,12 @@
 #include "src/mqtt.h"
 #endif
 
+#if FEATURE_SD_CARD_LOG
+#include "FS.h"
+#include "SD.h"
+#include "src/sd_card.h"
+#endif
+
 //#define ESP_MEM_DEBUG 1
 //int e;
 
@@ -2146,6 +2152,11 @@ void setup()
   sonde.setup();
   initGPS();
 
+#if FEATURE_SD_CARD_LOG
+  sd_card_init();
+  createDir(SD, "/log");
+#endif
+
   WiFi.onEvent(WiFiEvent);
   getKeyPress();    // clear key buffer
 }
@@ -2373,6 +2384,9 @@ void loopDecoder() {
       sondehub_send_data(&shclient, s, &sonde.config.sondehub);
     }
 #endif
+#if FEATURE_SD_CARD_LOG
+  sd_card_log(s);
+#endif
 
 #if FEATURE_MQTT
     // send to MQTT if enabledson
diff --git a/RX_FSK/features.h b/RX_FSK/features.h
index 7e605b5..a401807 100644
--- a/RX_FSK/features.h
+++ b/RX_FSK/features.h
@@ -9,6 +9,7 @@
 #define FEATURE_MQTT        0
 
 #define FEATURE_RS92        0
+#define FEATURE_SD_CARD_LOG 1
 
 /* Most recent version support fonts in a dedicated flash parition "fonts".
  * This is incomabtible (in terms of code and flash layout) to previous versions.
diff --git a/RX_FSK/src/sd_card.cpp b/RX_FSK/src/sd_card.cpp
new file mode 100644
index 0000000..f25e5bf
--- /dev/null
+++ b/RX_FSK/src/sd_card.cpp
@@ -0,0 +1,123 @@
+// sd_card related functions
+// https://randomnerdtutorials.com/esp32-microsd-card-arduino/#sdcardcustompins
+
+#include <math.h>
+#include <SPI.h>
+#include "SD.h"
+#include "sonde.h"
+#include "sd_card.h"
+
+SPIClass spi_sd = SPIClass(HSPI);
+
+void createDir(fs::FS &fs, const char * path){
+  Serial.printf("Creating Dir: %s\n", path);
+  if(fs.mkdir(path)){
+    Serial.println("Dir created");
+  } else {
+    Serial.println("mkdir failed");
+  }
+}
+
+void writeFile(fs::FS &fs, const char * path, const char * message) {
+  Serial.printf("Writing file: %s\n", path);
+
+  File file = fs.open(path, FILE_WRITE);
+  if(!file){
+    Serial.println("Failed to open file for writing");
+    return;
+  }
+  if(file.print(message)){
+    Serial.println("File written");
+  } else {
+    Serial.println("Write failed");
+  }
+  file.close();
+}
+
+void appendFile(fs::FS &fs, const char * path, const char * message) {
+  Serial.printf("Appending to file: %s\n", path);
+
+  File file = fs.open(path, FILE_APPEND);
+  if(!file){
+    Serial.println("Failed to open file for appending");
+    return;
+  }
+  if(file.print(message)){
+    Serial.println("Message appended");
+  } else {
+    Serial.println("Append failed");
+  }
+  file.close();
+}
+
+void sd_card_init(void) {
+    Serial.println("sd_card_init()");
+    spi_sd.begin(14, 2, 15);
+    if(!SD.begin(13, spi_sd)){
+        Serial.println("Card Mount Failed");
+        return;
+    }
+    else {
+        Serial.println("Card Mounted");
+    }
+
+    uint8_t cardType = SD.cardType();
+
+    if(cardType == CARD_NONE){
+        Serial.println("No SD card attached");
+        return;
+    }
+
+    Serial.print("SD Card Type: ");
+    if(cardType == CARD_MMC){
+        Serial.println("MMC");
+    } else if(cardType == CARD_SD){
+        Serial.println("SDSC");
+    } else if(cardType == CARD_SDHC){
+        Serial.println("SDHC");
+    } else {
+        Serial.println("UNKNOWN");
+    }
+
+    uint64_t cardSize = SD.cardSize() / (1024 * 1024);
+    Serial.printf("SD Card Size: %lluMB\n", cardSize);
+    Serial.printf("Total space: %lluMB\n", SD.totalBytes() / (1024 * 1024));
+    Serial.printf("Used space: %lluMB\n", SD.usedBytes() / (1024 * 1024));
+}
+
+void sd_card_log(SondeInfo *s) {
+  char file[18];
+  char log_msg[150];
+  struct tm timeinfo;
+  time_t now;
+  time(&now);
+  gmtime_r(&now, &timeinfo);
+  if (timeinfo.tm_year <= (2016 - 1900)) {
+    Serial.println("Failed to obtain time");
+    return;
+  }
+
+  sprintf(file, "/log/%s.txt",s->d.ser);
+  // timestamp,serial,frame,lat,lon,alt,vel_v,vel_h,heading,temp,humidity,pressure,type,freq_mhz,snr,f_error_hz,sats,batt_v,burst_timer,aux_data
+  // 2021-10-30T00:58:41.000Z,S2250304,6826,59.48863,26.47421,9997.6,-25.5,23.0,82.6,-50.7,25.0,-1.0,RS41-SG,404.001,8.3,-187,9,2.5,08:28:27,-1
+  sprintf(log_msg, 
+    "%04d-%02d-%02dT%02d:%02d:%02d.000Z,%s,%d,%.5f,%.5f,%.1f,%.1f,%.1f,%.1f,%.1f,%.1f,%.1f,%s,%.3f,%d,-1,%d,%.1f,%d,-1\n",
+    timeinfo.tm_year + 1900, timeinfo.tm_mon + 1, timeinfo.tm_mday, timeinfo.tm_hour, timeinfo.tm_min, timeinfo.tm_sec,
+    s->d.ser, s->d.vframe, (float)s->d.lat, (float)s->d.lon, (float)s->d.alt, (float)s->d.vs, (float)s->d.hs, (float)s->d.dir,
+    (float)s->d.temperature, isnan((float)s->d.relativeHumidity) ? -1: (float)s->d.relativeHumidity, isnan((float)s->d.pressure) ? -1: (float)s->d.pressure, s->d.typestr != 0 ? s->d.typestr: " ", (float)s->freq, s->rssi, s->d.sats, 
+    s->d.batteryVoltage, s->d.burstKT
+    );
+    Serial.println(log_msg);
+
+    if (SD.exists(file)) {
+      // append data
+      Serial.println("append new file");
+      appendFile(SD, file, log_msg);
+    }
+    else {
+      // new file
+      Serial.println("new file");
+      writeFile(SD, file, "timestamp,serial,frame,lat,lon,alt,vel_v,vel_h,heading,temp,humidity,pressure,type,freq_mhz,snr,f_error_hz,sats,batt_v,burst_timer,aux_data\n");
+      appendFile(SD, file, log_msg);
+    }
+}
\ No newline at end of file
diff --git a/RX_FSK/src/sd_card.h b/RX_FSK/src/sd_card.h
new file mode 100644
index 0000000..0b2650f
--- /dev/null
+++ b/RX_FSK/src/sd_card.h
@@ -0,0 +1,11 @@
+// sd_card module header
+#ifndef _SD_CARD
+#define _SD_CARD
+
+void sd_card_init(void);
+void writeFile(fs::FS &fs, const char * path, const char * message);
+void appendFile(fs::FS &fs, const char * path, const char * message);
+void createDir(fs::FS &fs, const char * path);
+void sd_card_log(SondeInfo *s);
+
+#endif // _SD_CARD
\ No newline at end of file