WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0
Transmission Modes
227
Parameter
Value
Input format(s)
AF, IF
Additional Info
3.580 MHz, 7.035 MHz, 14.070 MHz
The baud rate is fixed at 31.25 Bd. The speed of transmission is about 30 words per minute compared to
CW.
Each bit is repeated 13 bits later for forward error correction using the same principle as used in AMTOR
FEC or PSK-AM, except that this type of FEC is bit related instead of character related.
To separate the transferred characters, a “011” sequence is inserted between each character guaranteeing
separation as long as this sequence does not appear in the character itself.
PSK-31-FEC uses the same varicode alphabet as PSK-10 having a maximum length of seven bits per char-
acter.
PSK-63F, PSK-125F, PSK-220F
PSK-63F and PSK-125F, are very narrow-band and reliable modes. The performance against disturbances
is achieved by the use of DPSK modulation.
Parameter
Value
Frequency range
HF
Operation modes
Simplex FEC
Modulation
DBPSK
Symbol rate
62.5, 125 and 220 Bd
Receiver settings
DATA, CW, LSB or USB
Input format(s)
AF, IF
Additional Info
Varicode, 3.580 MHz, 7.035 MHz, 14.070 MHz
Compared to PSK-31 an improvement was made, concerning the error rate and ionosphere effects such as
doppler, fading and multi-path. The result was a mode, which uses forward error correction (FEC) and also
has a higher baud rate.
In contrast to PSK-31, only DBPSK modulation is used. The baud rate is optimized to the data rate, which
an operator can input on a keyboard by hand.
To recover bit stream after demodulation, a Viterbi decoder with K = 7 and code rate ½ is used. Because
of the use of DBPSK only, the mode is insensitive against a confusion of LSB and USB.
To optimize the data throughput rate of the system, the alphabet uses a variable character length. For
frequently used characters a symbol is used, which has a short word length (as is done with the Huffman
compression).
Note:
In contrast to PSK-31 these modes do not use DQPSK modulation.
Tuning a PSK-63F and PSK-125F Signal
After launching the mode, the first step is to look for a valid PSK-63F or PSK-125F signal in the spectrum.
It is possible that within a bandwidth of 4 kHz more than on station is working.
The bandwidth of the spectrum can be switched between 500 Hz, 1000 Hz, 4000 Hz and 24000 Hz. After
that with the left cursor the lower limit and with the right cursor the upper boundary of the signal may be
selected. Using the center cursor, the center frequency may be more precisely set.
The adjustment pre-
cision of the center frequency is very important and directly influences the performance of the
decoding.
To ensure, that the system can handle drifting signals or a coarsely adjusted center frequency,
AFC
may
be enabled in the
Demodulator
menu. The carrier tracking function is now activated. If the deviation be-
tween the tracked and the adjusted center frequency is too large, the center frequency should be correct-
ed. Carrier tracking only works over a range of DBPSK center frequency ± 8 Hz.
