diff --git a/network/api/views.py b/network/api/views.py
index 746329c..bcc2451 100644
--- a/network/api/views.py
+++ b/network/api/views.py
@@ -1,3 +1,4 @@
+from django.core.exceptions import ObjectDoesNotExist
 from django.shortcuts import get_object_or_404
 from django.utils.timezone import now
 
@@ -19,13 +20,26 @@ class ObservationView(viewsets.ModelViewSet, mixins.UpdateModelMixin):
     pagination_class = pagination.LinkedHeaderPageNumberPagination
 
     def update(self, request, *args, **kwargs):
+        instance = self.get_object()
         if request.data.get('client_version'):
-            instance = self.get_object()
             instance.ground_station.client_version = request.data.get('client_version')
             instance.ground_station.save()
         if request.data.get('demoddata'):
-            instance = self.get_object()
-            instance.demoddata.create(payload_demod=request.data.get('demoddata'))
+            try:
+                file_path = 'data_obs/{0}/{1}'.format(instance.id, request.data.get('demoddata'))
+                instance.demoddata.get(payload_demod=file_path)
+                return Response(data='This data file has already been uploaded',
+                                status=status.HTTP_403_FORBIDDEN)
+            except ObjectDoesNotExist:
+                instance.demoddata.create(payload_demod=request.data.get('demoddata'))
+        if request.data.get('waterfall'):
+            if instance.has_waterfall:
+                return Response(data='Watefall has already been uploaded',
+                                status=status.HTTP_403_FORBIDDEN)
+        if request.data.get('payload'):
+            if instance.has_audio:
+                return Response(data='Audio has already been uploaded',
+                                status=status.HTTP_403_FORBIDDEN)
 
         super(ObservationView, self).update(request, *args, **kwargs)
         return Response(status=status.HTTP_200_OK)
diff --git a/network/base/migrations/0056_unique_demoddata_payload.py b/network/base/migrations/0056_unique_demoddata_payload.py
new file mode 100644
index 0000000..f6a90a4
--- /dev/null
+++ b/network/base/migrations/0056_unique_demoddata_payload.py
@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.20 on 2019-03-07 18:17
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import network.base.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('base', '0055_add_new_antenna_type'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='demoddata',
+            name='payload_demod',
+            field=models.FileField(unique=True, upload_to=network.base.models._name_obs_demoddata),
+        ),
+    ]
diff --git a/network/base/migrations/0057_no_null_demoddata_observation_field.py b/network/base/migrations/0057_no_null_demoddata_observation_field.py
new file mode 100644
index 0000000..bcc6bf0
--- /dev/null
+++ b/network/base/migrations/0057_no_null_demoddata_observation_field.py
@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.20 on 2019-03-07 18:28
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('base', '0056_unique_demoddata_payload'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='demoddata',
+            name='observation',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='demoddata', to='base.Observation'),
+        ),
+    ]
diff --git a/network/base/models.py b/network/base/models.py
index 5f9715a..5e2847d 100644
--- a/network/base/models.py
+++ b/network/base/models.py
@@ -59,6 +59,7 @@ def _name_obs_files(instance, filename):
 
 
 def _name_obs_demoddata(instance, filename):
+    # On change of the string bellow, change it also at api/views.py
     return 'data_obs/{0}/{1}'.format(instance.observation.id, filename)
 
 
@@ -610,8 +611,8 @@ post_save.connect(_observation_post_save, sender=Observation)
 
 class DemodData(models.Model):
     observation = models.ForeignKey(Observation, related_name='demoddata',
-                                    on_delete=models.CASCADE, blank=True, null=True)
-    payload_demod = models.FileField(upload_to=_name_obs_demoddata, blank=True, null=True)
+                                    on_delete=models.CASCADE)
+    payload_demod = models.FileField(upload_to=_name_obs_demoddata, unique=True)
     copied_to_db = models.BooleanField(default=False)
 
     def is_image(self):