AFSK and FSK

By convention, amateur RTTY uses the lower sideband, with the Mark frequency 170 hz higher than the Space frequency. The generation of Mark and Space frequencies required for Amateur Radio RTTY transmission is commonly accomplished in one of two ways:

• Frequency Shift Keying (FSK), in which the transmitter is directly switched between Mark and Space frequencies via it's FSK Input (sometimes referred to as the RTTY keying signal); the FSK input must be driven by an FSK connection

• Audio Frequency Shift Keying (AFSK), in which Mark and Space frequencies are generated from Mark and Space tones fed to the transceiver's audio input, typically driven by a soundcard's audio output

Also by convention, a RTTY QSO's frequency is that of its Mark frequency. Thus accurate DX spots for RTTY stations specify the station's Mark frequency.

FSK

FSK requires a transceiver support in the form of a RTTY or FSK mode in which the transmitter frequency switches between RTTY Mark and Space frequencies as dictated by the signal driving the transmitter's RTTY input. FSK's advantages include

• the transceiver displays the Mark frequency on its front panel and reports this frequency via its transceiver control (CAT) interface

• recent Icom transceivers provide a Twin Peak Filter for RTTY reception that is only available when the transceiver is in RTTY (FSK) mode

However, only a few transceivers provide RTTY output waveshaping.

AFSK

AFSK is accomplished by placing the transceiver in LSB mode (some transceivers provide an LSB DATA or PKT mode for use with AFSK) and directing the PC soundcard to generate Mark and Space tones that are fed to the transmitter's audio input to produce Mark and Space frequencies at the transmitter's output. AFSK's advantages include

• can be used with any transceiver capable of SSB transmission

• does not require an FSK connection to drive the transceiver's RTTY input

• the MMTTY engine can be configured to provide good RTTY output waveshaping

  • disable compression in the transceiver
  • configure the MMTTY engine's TX bandpass filter

    1. set WinWarbler's Operating Mode to RTTY

    2. on the RTTY tab of WinWarbler's Configuration window, click the MMTTY Setup button on the tab's right edge

    3. in the TxBPF/TxLPF panel on the Setup window's TX tab,

       1. check the Tx BPF box

       2. set the Tap selector to 512

  • set the the AFSK Audio Output Level

Setting up CW, Phone, PSK, and RTTY Operation

Getting Started with CW, Phone, PSK, and RTTY Operation

Getting Started with DXLab