fix dial frequencies

csdr/chain/demodulator.py

@@ -1,13 +1,9 @@
-from pycsdr.modules import Reader
 from csdr.chain import Chain
 from abc import ABC, abstractmethod
 
 
 class BaseDemodulatorChain(Chain):
-    def getFixedIfSampleRate(self):
-        return None
-
-    def supportsSquelch(self):
+    def supportsSquelch(self) -> bool:
         return True
 
 
@@ -17,14 +13,20 @@ class SecondaryDemodulator(Chain):
 
 class FixedAudioRateChain(ABC):
     @abstractmethod
-    def getFixedAudioRate(self):
+    def getFixedAudioRate(self) -> int:
         pass
 
 
 class FixedIfSampleRateChain(ABC):
     @abstractmethod
-    def getFixedIfSampleRate(self):
-        return self.fixedIfSampleRate
+    def getFixedIfSampleRate(self) -> int:
+        pass
+
+
+class DialFrequencyReceiver(ABC):
+    @abstractmethod
+    def setDialFrequency(self, frequency: int) -> None:
+        pass
 
 
 # marker interface