diff --git a/RX_FSK/src/json.cpp b/RX_FSK/src/json.cpp
new file mode 100644
index 0000000..0675f0c
--- /dev/null
+++ b/RX_FSK/src/json.cpp
@@ -0,0 +1,99 @@
+#include "json.h"
+#include "RS41.h"
+
+extern const char *sondeTypeStrSH[];
+extern const char *dfmSubtypeStrSH[];
+
+static char typestr[11];
+
+const char *getType(SondeInfo *si) {
+    if( si->type == STYPE_RS41 ) {
+        if ( RS41::getSubtype(typestr, 11, si) == 0 ) return typestr;
+    } else if ( TYPE_IS_DFM(si->type) && si->d.subtype > 0 && si->d.subtype < 16 ) {
+        const char *t = dfmSubtypeStrSH[si->d.subtype];
+        if(t) return t;
+        sprintf(typestr, "DFMx%X", si->d.subtype);
+        return typestr;
+    }
+    return sondeTypeStrSH[sonde.realType(si)];
+}
+
+// To be used by
+// - MQTT
+// - rdzJSON (for Android app)
+// - Web map
+int sonde2json(char *buf, int maxlen, SondeInfo *si)
+{
+    SondeData *s = &(si->d);
+    int n = snprintf(buf, maxlen, 
+        "\"type\":\"%s\","
+        "\"id\": \"%s\","       // TODO: maybe remove in the future, ser is enough, client can calculate APRS id if needed
+        "\"ser\": \"%s\","
+        "\"frame\": %u,"	// raw frame, from sonde, can be 0. (TODO: add virtual frame # as in sondehub?)
+        "\"time\": %u,"
+        "\"lat\": %.5f,"
+        "\"lon\": %.5f,"
+        "\"alt\": %.1f,"
+        "\"vs\": %.1f,"
+        "\"hs\": %.1f," 
+        "\"climb\": %.1f,"	// used by HTML map, to be removed (-> vs)
+        "\"speed\": %.1f,"	// used by HTML map, to be removed (-> hs)
+        "\"dir\": %.1f,"
+        "\"sats\": %d,"
+        "\"freq\": %.2f,"
+        "\"rssi\": %d,"
+        "\"afc\": %d,"
+        "\"launchKT\": %d,"
+        "\"burstKT\": %d,"
+        "\"countKT\": %d,"
+        "\"crefKT\": %d",
+        getType(si),
+        s->id,
+        s->ser,
+        s->frame,
+        s->time,
+        s->lat,
+        s->lon,
+        s->alt,
+        s->vs,
+        s->hs,
+        s->vs,
+        s->hs,
+        s->dir,
+        s->sats,
+        si->freq,
+        si->rssi,
+        si->afc,
+        s->launchKT,
+        s->burstKT,
+        s->countKT,
+        s->crefKT
+    );
+    if(n>=maxlen) return -1;
+    buf += n; maxlen -= n;
+
+    // add only if available
+    if(s->batteryVoltage > 0) {
+	n = snprintf(buf, maxlen, "\"bat\": %.1f,", s->batteryVoltage);
+	if(n>=maxlen) return -1;
+	buf += n; maxlen -= n;
+    }
+    if ( !isnan( s->temperature ) ) {
+        n = snprintf(buf, maxlen, ",\"temp\": %.1f", s->temperature );
+	if(n>=maxlen) return -1;
+	buf += n; maxlen -=n;
+    }
+    if ( !isnan( s->relativeHumidity) ) {
+        n = snprintf(buf, maxlen, ",\"humidity\": %.1f", s->relativeHumidity);
+	if(n>=maxlen) return -1;
+	buf += n; maxlen -=n;
+    }
+    if ( !isnan( s->pressure) ) {
+        n = snprintf(buf, maxlen, ",\"pressure\": %.1f", s->pressure );
+	if(n>=maxlen) return -1;
+	buf += n; maxlen -=n;
+    }
+    return 0;
+}
+
+
diff --git a/RX_FSK/src/json.h b/RX_FSK/src/json.h
new file mode 100644
index 0000000..608e924
--- /dev/null
+++ b/RX_FSK/src/json.h
@@ -0,0 +1,8 @@
+#ifndef _JSON_H
+#define _JSON_H
+
+#include "Sonde.h"
+
+int sonde2json(char *buf, int maxlen, SondeInfo *si);
+
+#endif
diff --git a/RX_FSK/src/mqtt.cpp b/RX_FSK/src/mqtt.cpp
index fd40760..3e0b463 100644
--- a/RX_FSK/src/mqtt.cpp
+++ b/RX_FSK/src/mqtt.cpp
@@ -4,6 +4,7 @@
 #include <AsyncMqttClient.h>
 #include <ESPmDNS.h>
 #include "RS41.h"
+#include "json.h"
 
 TimerHandle_t mqttReconnectTimer;
 
@@ -59,6 +60,14 @@ void MQTT::publishPacket(SondeInfo *si)
     mqttClient.connect(); // ensure we've got connection
 
     char payload[1024];
+    payload[0] = '{';
+    int n = sonde2json(payload+1, 1023, si);
+    if(n<0) {
+	// ERROR
+        Serial.println("publishPacket: sonde2json failed, string too long");
+    }
+
+#if 0
     snprintf(payload, 1024, "{"
         "\"active\": %d,"
         "\"freq\": %.2f,"
@@ -134,6 +143,8 @@ void MQTT::publishPacket(SondeInfo *si)
         snprintf(payload, 1024, "%s%s%s%s", payload, ",\"subtype\": \"", subtype, "\"" );
     }
     snprintf(payload, 1024, "%s%s", payload, "}" ); // terminate payload string
+#endif
+    strcat(payload, "}");   // terminate payload string
 
     char topic[128];
     snprintf(topic, 128, "%s%s", this->prefix, "packet");