diff --git a/README.md b/README.md
index 022bf35..8214dfe 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ Under active development, everything is subject to change without notice.
 | `MAX_DIST`  | Set this to a nonzero value to reject parsed positions that are too far away. Only applies to positions parsed from message text. | `0` |
 | `DIST_UNIT` | The unit of the value in `MAX_DIST`. One of `km`, `m`, `mi`, `nmi`, `ft`, `in`. | `nmi` |
 | `SEND_ALL`  | Set to any value to send SBS messages for messages without a position. Set to `log` to also print a log entry for each non-position message. | Unset |
+| `ACARS_FREQ_AS_SQUAWK`, `VDLM2_FREQ_AS_SQUAWK`, `HFDL_FREQ_AS_SQUAWK`  | Set to any value to send the received frequency as the squawk value, for each incoming message type. | Unset |
 
 ## Docker Compose
 
diff --git a/rootfs/scripts/acars2pos.py b/rootfs/scripts/acars2pos.py
index 43531b5..2278c89 100755
--- a/rootfs/scripts/acars2pos.py
+++ b/rootfs/scripts/acars2pos.py
@@ -122,11 +122,22 @@ def thread_wrapper(func, *args):
       continue
 
     if sbs["type"] == "acars":
-      squawk = "1111"
+      if getenv("ACARS_FREQ_AS_SQUAWK"):
+        squawk = f"{round(sbs['freq']/1000-100000):d}"
+      else:
+        squawk = "1111"
     elif sbs["type"] == "vdlm2":
-      squawk = "2222"
+      if getenv("VDLM2_FREQ_AS_SQUAWK"):
+        squawk = f"{round(sbs['freq']/1000-100000):d}"
+      elif sbs.get("xid"):
+        squawk = "2220"
+      else:
+        squawk = "2222"
     elif sbs["type"] == "hfdl":
-      squawk = "3333"
+      if getenv("HFDL_FREQ_AS_SQUAWK"):
+        squawk = f"{round(sbs['freq']/1000):d}"
+      else:
+        squawk = "3333"
     else:
       squawk = "9999"
 
diff --git a/rootfs/scripts/acars_decode/Decoder.py b/rootfs/scripts/acars_decode/Decoder.py
index 3711f9c..254c614 100644
--- a/rootfs/scripts/acars_decode/Decoder.py
+++ b/rootfs/scripts/acars_decode/Decoder.py
@@ -252,6 +252,7 @@ def decodeACARS(msg):
   dat["flight"] = msg.get("flight", "")
   dat["txt"] = msg["text"]
   dat["msgtype"] = msg["label"]
+  dat["freq"] = round(float(msg.get("freq", 0))*1000000)
   return dat
 
 def decodeVDLM2(msg):
@@ -262,12 +263,14 @@ def decodeVDLM2(msg):
   dat = {}
   dat["type"] = "vdlm2"
   dat["time"] = int(msg["t"]["sec"])
+  dat["freq"] = int(msg.get("freq", 0))
   if msg["avlc"].get("acars"):
     dat["reg"] = msg["avlc"]["acars"].get("reg", "")
     dat["flight"] = msg["avlc"]["acars"].get("flight", "")
     dat["msgtype"] = msg["avlc"]["acars"].get("label", "")
     dat["txt"] = msg["avlc"]["acars"].get("msg_text", "")
   elif not (msg["avlc"].get("xid") is None or msg["avlc"]["xid"].get("vdl_params") is None):
+    dat["xid"] = True
     dat["icao"] = msg["avlc"]["src"]["addr"]
     for p in msg["avlc"]["xid"]["vdl_params"]:
       if p["name"] == "ac_location":
@@ -292,6 +295,7 @@ def decodeHFDL(msg):
   dat["type"] = "hfdl"
   dat["time"] = int(msg["t"]["sec"])
   dat["flight"] = msg["lpdu"].get("hfnpdu", {}).get("flight_id", "")
+  dat["freq"] = int(msg.get("freq", 0))
   try:
     dat["lat"] = msg["lpdu"]["hfnpdu"]["pos"]["lat"]
     dat["lon"] = msg["lpdu"]["hfnpdu"]["pos"]["lon"]