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 precision 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 between the tracked and the adjusted center frequency is too large, the center frequency should be corrected. Carrier tracking only works over a range of DBPSK center frequency ± 8 Hz.
Hence adjustment of the center frequency must be accurate.
In contrast to PSK-31, this mode does not use DQPSK modulation.