6 – Data Mode
6-8
March 6, 1997
Data Operating Hints
Data Primer
RTTY, AMTOR, SITOR, PacTOR, G-TOR and HF Packet all use Frequen-
cy Shift Keying (FSK). FSK is also called AFSK Audio Frequency Shift
Keying when frequency shifted audio tones are used to modulate a transmit-
ter.
A FSK signal is produced when the frequency shift audio is generated by cir-
cuitry within the radio. AFSK signals are generated when the audio contain-
ing the shifting frequency comes from outside the radio. A common example
of this is a TNC connected to a radio through the microphone input. Our
RTTY modem supports both forms. See your transceiver owners manual for
specific information.
There are three important parameters used to describe an FSK or AFSK sig-
nal -- the frequency shift, the center frequency, and the keying or baud rate.
The combination of frequency shift and baud rate determine the spectrum of
the FSK signal. The goal of a filter is to reject everything in the spectrum
except the desired signal while minimizing the degradation of the desired
signal.
Frequency shift
You may specify the frequency shift in one of two ways. The most common
specification in amateur radio is total shift or the difference between the low
(Mark) and high (Space) tones. In the technical literature, the shift from a
center frequency is more commonly specified. For example, a 170 Hz shift
RTTY signal is the same as a +/- 85 Hz shift. Note the frequency shift re-
mains the same whether it is shifting an RF signal or an audio frequency sig-
nal. In amateur radio, there are only two common frequency shifts - 170 Hz
and 200 Hz. Other radio services use 425 Hz and 850 Hz shifts. 170 Hz is
the standard RTTY and G-TOR frequency shift, while 200 Hz is the stan-
dard for AMTOR, SITOR and PacTOR. Unfortunately, some data convert-
ers use 200 Hz shift for RTTY, which adds to the problem of properly
filtering data signals.
Center Frequency
The center frequency of a FSK signal is independent of the frequency shift
or the baud rate. In the audio spectrum, either before an AFSK signal mod-
ulates a RF signal or after the RF FSK signal is demodulated, there are sev-
eral common center frequencies. In the North America, 2210 Hz is the
standard center frequency for RTTY, PacTOR, AMTOR, SITOR, and G-
TOR, while both 1700 Hz and 2210 Hz share the standard for HF packet. In
Europe and some other parts of the world, lower center frequencies of 1300,
1360 and 1530 Hz are more common.
Summary of Contents for DSP-599zx
Page 1: ...DSP 599zx Audio Noise Reduction Filter Operating Manual March 6 1997 TECHNOLOGY INC ...
Page 56: ...4 Voice Mode 4 8 March 6 1997 ...
Page 62: ...5 CW Mode 5 6 March 6 1997 ...
Page 92: ...8 Troubleshooting 8 4 March 6 1997 ...
Page 96: ...Appendix B Glossary A 4 March 6 1997 ...
Page 98: ...Appendix C Product Warranty A 6 March 6 1997 ...
Page 100: ...Appendix D Electromagnetic Interference A 8 March 6 1997 ...
Page 102: ...Appendix E Schematic Diagrams A 10 March 6 1997 ...
Page 103: ...DSP 599zx Audio Noise Reduction Filter March 6 1997 A 11 ...
Page 104: ...Appendix E Schematic Diagrams A 12 March 6 1997 ...
Page 105: ...DSP 599zx Audio Noise Reduction Filter March 6 1997 A 13 ...
Page 106: ...Appendix E Schematic Diagrams A 14 March 6 1997 ...
