DSP-599zx Audio Noise Reduction Filter
March 6, 1997 6-9
Baud Rate
Baud rates vary from 45.5 baud for RTTY to 300 baud for HF packet. G-
TOR, PacTOR, and Clover have adaptive baud rates which change depend-
ing upon the quality of the channel.
For a more complete discussion of data modes, see the latest edition of the
ARRL Handbook.
QRM Operating Hint
Choosing the correct bandwidth for the baud rate and shift of a data signal
is critical to reject QRM while minimizing the bit error rate from noise. If
there is no QRM, wide bandwidths may be acceptable on a strong signal, but
could cause increased bit errors on a weak signal. The factory default set-
tings are the generally the best trade-off between bit error rate and QRM re-
jection. If necessary, change them slightly under severe band conditions. For
example, normally 250 Hz is the recommended bandwidth for RTTY; how-
ever, other bandwidths from 175 Hz to 350 Hz may improve copy under
some band conditions.
Mark Space Frequencies
The mark-space frequencies of the modem, receiver and DSP-599zx must
match. Default mark-space frequency shifts and center frequencies vary
among modem and radio manufacturers, and in different parts of the world.
Some modems have default HF Packet mark-space center frequencies dif-
ferent from their RTTY, AMTOR, and PacTOR mark-space center frequen-
cies.
The DSP-599zx mark-space center frequency factory setting is 2210 Hz for
RTTY, AMTOR, G-TOR and PacTOR data modes. The DSP-599zx HF
Packet mark-space center frequency factory setting is 1700 Hz. The mark-
space center frequencies of the modem, receiver and DSP-599zx must
match. Some modems and radios have programmable mark-space frequen-
cies. If your modem and radio default to different mark-space center fre-
quencies, you must change the modem or radio mark-space center
frequencies to match the DSP-599zx, or change the DSP-599zx mark-space
center frequencies to match the modem and radio mark-space center fre-
quencies. See your radio or modem instruction manual.
Note that some receivers do not have specific provisions to use their narrow
(200 - 600 Hz wide) filters for data. Operate these radios in their SSB voice
filter bandwidth. Other receivers may have fixed or variable mark-space fre-
quencies - check your operating instructions carefully!
The Kantronics KAM+ usually has the HF Packet mark-space center fre-
quency set to 1700 Hz (1600-1800 Hz mark-space frequencies). See the
KAM+ manual for the procedure to change the KAM+ mark-space center
frequency setting via software.
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