diff --git a/hosts/radiobert/sbs2json.rb b/hosts/radiobert/sbs2json.rb
index d61d7c0b..57cf37df 100644
--- a/hosts/radiobert/sbs2json.rb
+++ b/hosts/radiobert/sbs2json.rb
@@ -5,6 +5,7 @@ require 'webrick'
 require 'json'
 
 TIMEOUT = 60
+last_purge = Time.now.to_i
 data = {}
 
 Thread.new do
@@ -21,17 +22,18 @@ sock = TCPSocket.new "radiobert.serv.zentralwerk.org", 30003
 while line = sock.gets
   begin
     fields = line.chomp.split(/,/)
-    msg_type = fields[1].to_i
+    msg_type = fields[1]
+    hex = fields[4].downcase
     values = {
-      :hex => fields[4].downcase,
+      :hex => hex,
       :last => Time.now.to_i
     }
 
     case msg_type
-    when 1
+    when "1"
       values[:flight] = fields[10]
 
-    when 3
+    when "3"
       unless fields[14].empty? or fields[15].empty?
         values[:lat] = fields[14].to_f
         values[:lon] = fields[15].to_f
@@ -40,7 +42,7 @@ while line = sock.gets
         values[:altitude] = fields[11].to_i
       end
 
-    when 4
+    when "4"
       unless fields[12].empty?
         values[:speed] = fields[12].to_i
       end
@@ -49,16 +51,20 @@ while line = sock.gets
       end
     end
 
-    old_value = data[values[:hex]]
+    old_value = data[hex]
     if old_value
       old_value.merge! values
     else
-      data[values[:hex]] = values
+      data[hex] = values
     end
 
-    data.delete_if { |hex, values|
-      Time.now.to_i >= values[:last] + TIMEOUT
-    }
+    now = Time.now.to_i
+    if now >= last_purge + TIMEOUT / 10
+      data.delete_if { |hex, values|
+        now >= values[:last] + TIMEOUT
+      }
+      last_purge = now
+    end
 
   rescue
     STDERR.puts $!