The COMMON-BASE DETECTOR is an amplifying detector that is used in portable receivers.
The SLOPE DETECTOR is the simplest form of frequency detector. It is essentially a tank circuit
tuned slightly away from the desired fm carrier.
The FOSTER-SEELEY DISCRIMINATOR uses a double tuned rf transformer to convert
frequency changes of the received fm signal into amplitude variations of the rf wave.
The RATIO DETECTOR uses a double-tuned transformer connected so that the instantaneous
frequency variations of the fm input signal are converted into instantaneous amplitude variations.