FSK is pure tones of RTTY, whereas AFSK is the simulation in audio of those same tones. for FSK is needed a modem, like for example the KAM for AFSK it is but easy, since of the sound card one takes control easily. If I must choose between one of them, without a doubt I choose FSK FSK4EVER EA2RY - Roberto ex-EC2ADR FG/EA2RY CT9R http://www.ea2ry.com