diff --git a/esbo_etc/classes/ITransmissive.py b/esbo_etc/classes/ITransmissive.py
new file mode 100644
index 0000000..9758119
--- /dev/null
+++ b/esbo_etc/classes/ITransmissive.py
@@ -0,0 +1,11 @@
+from abc import ABC, abstractmethod
+
+
+class ITransmissive(ABC):
+    @abstractmethod
+    def calcSignal(self):
+        pass
+
+    @abstractmethod
+    def calcNoise(self):
+        pass
diff --git a/esbo_etc/classes/__init__.py b/esbo_etc/classes/__init__.py
index b08b7a2..ba60602 100644
--- a/esbo_etc/classes/__init__.py
+++ b/esbo_etc/classes/__init__.py
@@ -1 +1,3 @@
 from esbo_etc.classes.config import *
+from esbo_etc.classes.ITransmissive import *
+from esbo_etc.classes.target import *
\ No newline at end of file