In a CTCSS controlled FM receiver, the CTCSS tone is filtered out after the:

In a CTCSS (Continuous Tone-Coded Squelch System) controlled FM receiver, the CTCSS tone is filtered out after the discriminator but before the audio section. The discriminator is a crucial component in an FM receiver that converts the frequency variations of the incoming FM signal into amplitude variations, which represent the audio information.

Once the FM signal has been demodulated by the discriminator, it may still contain the CTCSS tone, which serves as an access code for the receiver to ensure that it only opens the audio path for transmissions that include the correct tone. In this stage, the receiver processes the demodulated output — which includes any audio and the CTCSS tone — by using a low-pass filter, specifically designed to eliminate the CTCSS tone. This allows the audio section, where the human-intelligible audio signal is amplified and made audible, to receive only the desired audio content without interference from the CTCSS tone.

This filtering step is important as it ensures that the audio output to the speaker is clear and free from the sub-audible tone used for squelch control, allowing the user to hear only the intended communication. Interpretations of the signal occur after this step, and the audio amplification can