This page contains some information concerning PSK31, the PSK31 modem driver for Analyzer2000 and Terminal2000, the teletype terminal for Analyzer2000.
What is PSK31?
PSK31 is a new amateur radio teletype mode invented by amateur radio enthusiasts like Peter Martinez G3PLX. Like traditional RTTY, it is a kind of keyboard to keyboard communication (chat). The baudrate used is 31.25 Baud, fast enough to handle most operators manual typing capabilities. It is not suitable for transporting computer data like pictures or programs, but intended as a mean of human communication between two or more operators in a very simple and thus very robust way. It can be compared to CW (morse code radio communication), but it is more efficient than CW. It uses a bandwith of just 31 Hz with a speed of about 288 LPM or 48 WPM (words per minute). According to the small bandwidth, the system gain against a CW filter with 500 Hz is 10 * log(500/31) dB = 12 dB. That means a CW transmitter has to output 16 times more power than a PSK31 transmitter to gain the same signal to noise ratio on the receiving side. PSK31 seems to be the perfect mode for all amateur radio stations with small antennas and little power.
As the name of the new mode says, PSK (phase shift keying) modulates the carrier phase. The phase modulation has some more advantages against CW, which uses ASK (amplitude shift keying). In noisy and distorted propagation environements, the amplitude of a signal varies much more than the phase of a signal. To cope with the problem of phase shifts caused by different propagation paths (especially in HF links), the modulation is done in differential phase shift keying (DPSK). Thus only the phase differences between two bits are used, not the absolute phase.
To get some kind of online information compression (like zipping files on the computer), G3PLX introduced the use of a varying length code (varicode). In contrast to normal compression techniques where statistical analysis is used during transmission, G3PLX does something Samual Morse did many years ago. He analyzed english language ASCII textfiles and built an alphabet, where the more frequently used characters are represented by less lengthy codewords. Additionally he made the code selfsynchronizing, which means there are no codewords having two or more zero bits in them. Two zero bits are used to describe the end of a word. Thus eliminating the start and stop bits used in asynchronous codes like the ASCII or BAUDOT code.
PSK31 in Analyzer2000
Analyzer2000 is ideal suited for digital communication modes like PSK31. It delivers an easy to use Man Machine Interface with all displays needed to operate PSK31 in a fast and uncomplicated way. With the spectral overview, it offers a view over the signal scenario around the current receiving frequency. The spectrum is used to easily identify PSK31 signals, pick them out with one mouse click and bring them to the PSK demodulator. The demodulator offers a high sophisticated AFC feature, which simplifies the tuning process. No receiver finetuning is needed. All is done by the automatic search capability of the demodulator.
The transmission side offers the feature to pretype text while receiving text of the communication partner. Thus the QSO can be more fluent, even if the typing speed is far below 31 Baud.
The implementation of PSK31 is encapsulated
into a data source driver called PSK31Drv. It is a special version of the
SndblstDrv coming with the basic software of Analyzer2000.
It also uses the soundcard for input and output.
The text interface to PSK31Drv is made by sockets. Thus any telnet client application can be used to receive and send characters. Brown Bear Software offers a telnet application especially made for PSK31Drv (Terminal2000). To get the software interface details to build own telnet applications, send an email to: firstname.lastname@example.org.
Following are the restrictions in the current implementation of the PSK31 protocol:
1. QPSK is not supported
2. RX Freq and TX Freq are always coupled (NET function)
3. AFC is always on
4. CW mode is not supported
5. Telnet socket port is fixed to 5555
6. TCP/IP protocol has to be installed
A detailed explanation how to install TCP/IP protocol can be found in Terminal2000.hlp, which is installed together with PSK31Drv.
Switch your receiver to SSB and
use a BFO of 1 kHz.
Using PSK31 driver, the span changes to 1 kHz +/- 250 Hz :
To ease the tuning to psk31 signals,
has a built in AFC.
To see the result of the demodulator, Analyzer2000 has been extended by a constellation digram:
The Constellation Diagram is ideal to analyze the different propagation conditions. If the signal is coming through a ground wave, the phase is stable and a constant ellipse will be shown. If the signal is coming through the ionosphere, the ellipse will tumble up and down and is distorted through fading etc.
Another special development is Terminal2000, an external application working as a text interface for Analyzer2000:
Important : Before installing PSK31Drv, install the newest Analyzer2000 5.00 first!