diff --git a/owrx/config.py b/owrx/config.py
index 3424a41..14780fb 100644
--- a/owrx/config.py
+++ b/owrx/config.py
@@ -7,6 +7,8 @@ class Property(object):
     def getValue(self):
         return self.value
     def setValue(self, value):
+        if (self.value == value):
+            return self
         self.value = value
         for c in self.callbacks:
             try:
diff --git a/owrx/controllers.py b/owrx/controllers.py
index 239ee72..d033b2a 100644
--- a/owrx/controllers.py
+++ b/owrx/controllers.py
@@ -1,7 +1,7 @@
 import mimetypes
 from owrx.websocket import WebSocketConnection
 from owrx.config import PropertyManager
-from owrx.source import SpectrumThread, DspManager, CpuUsageThread, SdrService
+from owrx.source import DspManager, CpuUsageThread, SdrService
 import json
 import os
 from datetime import datetime
diff --git a/owrx/source.py b/owrx/source.py
index 650c15b..9475f67 100644
--- a/owrx/source.py
+++ b/owrx/source.py
@@ -6,6 +6,7 @@ import time
 import os
 import signal
 import sys
+import socket
 
 class SdrService(object):
     sdrProps = None
@@ -76,12 +77,8 @@ class SdrSource(object):
 
         def restart(name, value):
             print("restarting sdr source due to property change: {0} changed to {1}".format(name, value))
-            for c in self.clients:
-                c.onSdrPause()
             self.stop()
             self.start()
-            for c in self.clients:
-                c.onSdrResume()
         self.rtlProps.wire(restart)
         self.port = port
         self.monitor = None
@@ -148,6 +145,16 @@ class SdrSource(object):
         self.process = subprocess.Popen(cmd, shell=True, preexec_fn=os.setpgrp)
         print("[RtlNmuxSource] Started rtl source: " + cmd)
 
+        while True:
+            testsock = socket.socket()
+            try:
+                testsock.connect(("127.0.0.1", self.getPort()))
+                testsock.close()
+                break
+            except:
+                time.sleep(0.1)
+
+
         def wait_for_process_to_end():
             rc = self.process.wait()
             print("[RtlNmuxSource] shut down with RC={0}".format(rc))
@@ -158,12 +165,21 @@ class SdrSource(object):
 
         self.modificationLock.release()
 
+        for c in self.clients:
+            c.onSdrAvailable()
+
+    def isAvailable(self):
+        return self.monitor is not None
+
     def getSpectrumThread(self):
         if self.spectrumThread is None:
             self.spectrumThread = SpectrumThread(self)
         return self.spectrumThread
 
     def stop(self):
+        for c in self.clients:
+            c.onSdrUnavailable()
+
         self.modificationLock.acquire()
         try:
             os.killpg(os.getpgid(self.process.pid), signal.SIGTERM)
@@ -214,12 +230,12 @@ class SpectrumThread(object):
         self.clients = []
         self.doRun = False
         self.sdrSource = sdrSource
+        self.sdrSource.addClient(self)
 
     def start(self):
         threading.Thread(target = self.run).start()
 
     def run(self):
-        self.sdrSource.addClient(self)
         props = self.sdrSource.props.collect(
             "samp_rate", "fft_size", "fft_fps", "fft_voverlap_factor", "fft_compression",
             "csdr_dynamic_bufsize", "csdr_print_bufsizes", "csdr_through"
@@ -262,13 +278,12 @@ class SpectrumThread(object):
                     c.write_spectrum_data(data)
 
         dsp.stop()
-        self.sdrSource.removeClient(self)
         print("spectrum thread shut down")
 
     def add_client(self, c):
         self.clients.append(c)
-        if not self.doRun:
-            self.doRun = True
+        self.doRun = self.sdrSource.isAvailable()
+        if self.doRun:
             self.start()
 
     def remove_client(self, c):
@@ -277,24 +292,28 @@ class SpectrumThread(object):
         except ValueError:
             pass
         if not self.clients:
-            self.shutdown()
+            self.stop()
 
-    def shutdown(self):
-        print("shutting down spectrum thread")
+    def stop(self):
+        print("stopping spectrum thread")
         self.doRun = False
 
-    def onSdrPause(self):
-        if self.dsp is not None:
-            self.dsp.stop()
-    def onSdrResume(self):
-        if self.dsp is not None:
-            self.dsp.start()
+    def onSdrAvailable(self):
+        print("Spectrum Thread: onSdrAvailable")
+        self.doRun = bool(self.clients)
+        if self.doRun:
+            self.start()
+
+    def onSdrUnavailable(self):
+        print("Spectrum Thread: onSdrUnavailable")
+        self.stop()
 
 class DspManager(object):
     def __init__(self, handler, sdrSource):
-        self.doRun = True
+        self.doRun = False
         self.handler = handler
         self.sdrSource = sdrSource
+        self.dsp = None
         self.sdrSource.addClient(self)
 
         self.localProps = self.sdrSource.getProps().collect(
@@ -360,9 +379,11 @@ class DspManager(object):
         super().__init__()
 
     def start(self):
-        self.dsp.start()
-        threading.Thread(target = self.readDspOutput).start()
-        threading.Thread(target = self.readSMeterOutput).start()
+        self.doRun = self.sdrSource.isAvailable()
+        if self.doRun:
+            self.dsp.start()
+            threading.Thread(target = self.readDspOutput).start()
+            threading.Thread(target = self.readSMeterOutput).start()
 
     def startSecondaryThreads(self):
         self.runSecondary = True
@@ -408,14 +429,18 @@ class DspManager(object):
     def setProperty(self, prop, value):
         self.localProps.getProperty(prop).setValue(value)
 
-    def onSdrPause(self):
+    def onSdrAvailable(self):
+        if not self.doRun:
+            self.doRun = True
+            if self.dsp is not None:
+                self.dsp.start()
+                threading.Thread(target = self.readDspOutput).start()
+                threading.Thread(target = self.readSMeterOutput).start()
+
+    def onSdrUnavailable(self):
         if self.dsp is not None:
             self.dsp.stop()
 
-    def onSdrResume(self):
-        if self.dsp is not None:
-            self.dsp.start()
-
 class CpuUsageThread(threading.Thread):
     sharedInstance = None
     @staticmethod