Yaesu FFT-1 

FFT-1 Unit provides the following additional features: 

1. AF-FFT (Audio Frequency Fast Fourier Transform) scope. 
This AF-FFT function was first demonstrated in the FT DX 9000 series. With this Scope, the audio characteristics of the received signals; the effect of adjusting the RX IF filter performance; and utilizing the QRM rejection features, may be visually observed. It is also possible to observe the TX audio characteristics of your own signal while using the Monitor function. This is very effective for tuning the parametric equalizer for voice characteristics and the microphone audio. 

2. RTTY/PSK31 Encode Decode 

3. CW Decode 

4. CW Auto Zero-in