Picture of RTTY QSO in the MixW display.
Picture of a PSK31 QSO in the same display.
PSK31's two modes: BPSK and QPSK
In the QPSK mode, instead of just keying by phase reversals, or 180-degree phase-shifts, an additional pair of 90 and 270-
degree phase-shifts are possible.
If you think of BPSK as reversing the polarity of the signal, then QPSK can be thought of as two BPSK signals on the same
frequency, but 90 degrees out of phase with each other, and with only half the power in each.
The extra speed in QPSK is used for error correction. This works well under most conditions. Certain noisy conditions, and
weaker signals, can benefit from the full power (single signal) of the QPSK mode.
Visit the PSK31 Official Home Page at:
Note: Because this is commercial software, Peter Martenez, G3PLX's Introduction and Theory of PSK31 cannot be included
as part of these help files, but these really should be reviewed for a better understanding of PSK and its development. Peter
Martenez's outline and theory of PSK31 can be viewed on the website of MixW beta tester and help file contributor,
RICHARD B. GRIFFIN, NB6Z at the following link: http://www.teleport.com/~nb6z/psk31.htm
MixW has full BPSK31 and QPSK31 capabilities, but Nick did not use the G3PLX source code to implement it. By using
his own source code, Nick is in keeping with Peter's guidelines for the use of PSK31 in commercial software.
The MixW team is very grateful to Peter for PSK31, a great gift to the radio art.
MixW: PSK31 Operation
With thanks to RICHARD B. GRIFFIN, NB6Z
Due to its limited bandwidth, PSK31 is perhaps the most critical mode for proper soundcard to radio configuration.
Overdriving your transceiver audio input will cause over modulation, creating multiple side bands and interfering with
adjacent QSOs. See the Basic Set Up topic in the Configuration and Set Up section for additional information.
Fine Tuning: If your transceiver is equipped with a "FINE" tuning feature, always use that for PSK31 tuning, but you will
find that most of your adjustments are made in software, and not with the transceiver's VFO. Some older rigs are not stable
enough for PSK31 operation and will drift considerably off frequency.
USB: USB is the convention for PSK31 operation in all bands. For BPSK31 either sideband can be used, but with QPSK31
the sender and receiver must be using the same sideband, or one station must be inverted (see Inversion in the Configuration
topic of the Configuration and Set Up section.
Filtering: Optimum filtering depends on your transceiver's SSB filtering options and its IF rejection characteristics. Wide
filtering will enable you to work the largest spectrum without retuning your transceiver, but can also cause problems when
there are strong adjacent signals. A narrow (CW or FSK) filter may help significantly with some radios and situations. Many
transceivers, however, do not have narrow filtering options while operating in SSB modes. Consult your manual and
experiment for the optimum configuration for your setup and conditions. The following waterfall display shows MixW's
panoramic display while using a wide filer setting on the transceiver:
Here there are 8 different QPSK31 QSOs we could copy with the simple click of the mouse in roughly 3 KHz of spectrum.
You can even see the bottom of an MFSK QSO in the far right hand side of the display.
Power: Because of the narrow bandwidth, PSK31 transmit power should be kept to a minimum. PSK31 is an excellent
mode for QRP operations.
Mode will be set to either BPSK31 or QPSK31. Most PSK31 operations are BPSK31 unless conditions will benefit from the
limited error correction offered in the QPSK31 mode.
AFC should be on to assist in tracking PSK31 signals. The one exception is when a strong adjacent signal pulls you off of a
weaker station you are working.
Lock should be off so you will be transmitting on the same frequency you're receiving. The exception here would be if
you're working a station that is drifting and want that station to always tune to your more stable "locked" transmit frequency,
or you are working split.
Squelch and Threshold can be used and adjusted to suit your operating preferences.
Inverted is grayed out for BPKS31 operation, and is never used. It may be needed while operating QPSK31 however. If you
are having difficulty copying a QPSK31 signal, try clicking Mode | Inverted and see if you start to print it. Note: This
feature works differently in MixW than most other SoundCard digital programs, so please read and understand the
information about inversion in the Configuration and Set Up Section.
PSK31 signals display as two closely spaced parallel lines in the Spectrum Window. Tune in a PSK31 signal by pointing to
it with the mouse and clicking the left mouse button. The text being sent by the station will then appear in the Receive
In this screen capture of a portion of the Spectrum Window of an actual MixW screen, the bright orange stripe with the
diamond-shaped cursor in the middle is a strong PSK31 station, the one to the left is a weak PSK31 station (yellowish
streaks), but would likely still print readable copy, and the very faint signal to the right is a PSK31 station that is too weak to
copy enough to sustain a QSO.
PSK31 is less than 40Hz in bandwidth, so it is virtually impossible to manually tune to the correct frequency with the
transceiver's VFO, or even to manually touch up the tuning because the increments are so small. However, if your Rig is
equipped with "FINE" tuning, Always use that when you're in the BPSK31 and QPSK31 modes.
To transmit to a station, first tune it as indicated above. Type outgoing text in the Transmit Window. Press the TX/RX
button, and the text in the Transmit Window will be transmitted. You can continue to type, and that text will also be
transmitted. As it is being transmitted, text in the transmit Window will also appear in the Receive Window. To stop
transmitting, press the TX/RX button again. Pressing ESC will abort transmission and return MixW to receive mode, but the
last several characters typed will not be transmitted. This process can also be automated with the use of MixW's Macros.
Note: PSK31 utilizes the full ascii character set, so normal useage is upper and lower case instead of all caps, and whatever
punctuation you want. Callsigns are either upper and lower case, or ALL CAPS. Both ways are acceptable, but an important
consideration is that the lower case letters use fewer phase changes and are less likely to be garbled in bad conditions.
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When transmitting, the waterfall will freeze and remain frozen until returning to Receive.
See the Basic Set Up topic for adjusting your sound card volume controls. PSK31 is extremely sensitive to proper
adjustment of both the volume and record level setting of your sound card.
This screen capture of a MixW screen shows several PSK31 stations. The station to the left of our QSO is idling (not typing)
and the two desired sidebands of the PSK31 signal can clearly be seen as parallel lines. Also visible are two more, fainter
parallel lines on each side of the solid parallel lines at the bottom of this signal, which are unwanted sidebands, produced by
slightly overdriving the transceiver. It looks as if this station is "setting" the soundcard output level. It was too strong at first
and produced the unwanted side bands, and it looks about right where they ended up at the top of the display. The signal
marked and circled as "over modulated station" also has the wide unwanted sidebands. Notice how close the sidebands are
to interfering with the QSO directly to the right of them.
As with most of the other digital modes, It is possible to open multiple RX windows and switch the active window (the one
you will be sending to) between them.
For these and other general operation techniques see the Operation Section.
MixW: PSK63/125 Operation
PSK63 & PSK125 Basics
BPSK63, BPSK125, QPSK63 & QPSK125 are provided as a variation of BPSK31 & QPSK31 by changing the
BAUDRATE using either a macro command or the Settings Dialog. Two macros are suggested, one for switching to
PSK63/125 and one for changing back to PSK31.
PSK63 will operate exactly like PSK31, except that the signal will be twice as wide, and you can transmit twice as fast (if
you can type that fast). By the same token, PSK125 will be 4 times as fast.
MixW will properly recognize the mode in the Log based on the baud rate.
Macro to change to BPSK63: <MODE:BPSK31><BAUDRATE:62.5>
Macro to change to BPSK125: <MODE:BPSK31><BAUDRATE:125>
Macro to change back to BPSK31: <MODE:BPSK31><BAUDRATE:31.25>
You can also change the baud rate by selecting the BPSK31 Settings Dialog
NOTE: PSK63 & 125 are normally found above the traditional PSK31operating frequencies rather than intermixed with
them since PSK63 & 125 require more bandwidth. If you change from PSK31 to PSK63/125 during a QSO you risk
expanding into another user's signal, which will not improve your image as a courteous and considerate operator.
MFSK Introduction and Theory
MFSK Image Mode
MixW: MFSK Intro and Theory
By Murray Greenman, ZL1BPU
MFSK Overview for Beginners
MFSK is a technique for transmitting digital data using multiple tones, extending
the RTTY two-tone technique to many tones, usually, but not always, one tone at a
MFSK means Multi - Frequency Shift Keying, and should not be confused with
MSK (Minimum Shift Keying). There are a number of different techniques, using
concurrent (or parallel) tones, sequential (one after another) tones, and
combinations of tones. MT-Hell can be either concurrent or sequential, DTMF
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tones used for telephone signaling are concurrent tone pairs, while Piccolo and
Coquelet, although using tone pairs, are decidedly sequential.
MFSK transmissions have a unique sound, almost musical, which is why Piccolo
and Coquelet received their names (Coquelet means rooster).
MFSK uses relatively narrow tone spacing, so remarkable data rates are achieved
for a given bandwidth - 64 bps in a signal bandwidth of 316 Hz is typical. The
following picture is a spectrogram of an MFSK16 signal (16 carriers) with a
spacing of 15.625 Hz and operating at 15.625 baud. The transmission operates at
62.5 bps (about 80 words per minute!) and occupies about 316 Hz of bandwidth.
The two black horizontal lines in the picture are at 1000 Hz and 1300 Hz, and the
horizontal scale is about 20 seconds. This short transmission contains about 120
letters. MFSK16 is always operated with FEC, so the text throughput is actually
only about 42 WPM (31.25 bps).
Fig. 1. Spectrogram of an MFSK16 Signal
MFSK has several performance advantages:
High rejection of pulse and broadband noise due to narrow receiver bandwidth
Low baud rate for sensitivity and multi-path rejection - data bit rate higher
than symbol baud rate
Constant transmitter power
Tolerance of ionospheric effects such as doppler, fading and multi-path
Most important of all, with an MFSK system, the error rate improves as the
number of tones is increased, so with as many as 32 tones the performance is
unrivalled. With PSK systems the opposite is true.
Let's be fair - there are disadvantages to MFSK! The main disadvantages are
related to the narrow spacing and narrow bandwidth of the individual tone
detectors - drift can be a problem and accurate tuning is essential. Good tuning
indicators and AFC are necessary at the slower speeds. It is important that the
radio transceiver be very stable, and also that it has very small frequency offset
between transmit and receive (preferably less than 5 Hz).
MFSK also uses more bandwidth for a given text speed than a 2FSK or PSK
system, but by the same token it is therefore more robust.
There are many ways to encode the alphabet from the keyboard for transmission.
Perhaps the most common now is ASCII (ITA-5), but ITA-2 (as used by
teleprinters) is common. MFSK16, like PSK31, is based on a Varicode, which,
unlike most such alphabets, assigns a different number of bits to different
characters, so that more frequently used characters have fewer bits and are
therefore sent faster.
The number of bits per alphabet character therefore depends on the character
frequency, just like Morse. For example:
Thus, the alphabet coding performance depends on the chosen code, and with a
Varicode, even on the text sent:
ITA-5 ASCII 10
Varicode ~ 7-8
The strength of the varicode is that the alphabet is essentially infinitely
expandable. For example, all the European accented characters are defined, and
others have been added for control purposes, that are outside the character set. The
MFSK16 varicode is not the same as the PSK31 varicode, although the technique
Another important advantage of using a varicode is that the stream of data can be
much more quickly re-synchronized in case of errors, than is possible with other
systems, and so a minimum of data is lost.
The user is most interested in the actual usable text throughput, which is specified
in characters per second (CPS) or words per minute (WPM). Both depend on the
alphabet used, and the number of words per minute depends on the average word
size. In English this is taken for convenience to be five letters plus a letter space.
So we can say that:
Text Throughput (CPS) = User Data Rate / Alphabet Bits per Character
Text Throughput (WPM) = CPS x 60 / letters per word
Say we are using an MFSK system with 16 tones (16FSK), operating at 15.625
baud with FEC Rate = 1/2, and an ASCII alphabet using 10 bits/character. Then:
Symbol Rate = 15.625 baud
Channel Data Rate = 15.625 x log216 = 15.625 x 4 = 62.5 bps
User Data Rate = 62.5 x 1/2 (FEC RATE) = 31.25 bps
Text Throughput (CPS) = 31.25 / 10 CPS = 3.125 CPS
Text Throughput (WPM) = 31.25 x 60 / (10 x 6) = 31.25 WPM
This will take place in a bandwidth little more than 16 x 15.625 = 250 Hz.
Amateur Radio RTTY operating at 45.45 baud achieves 60 WPM with no error
correction, and requires about 300 Hz bandwidth. 300 baud packet is error
corrected, but is unsuited by its design to HF conditions, and rarely delivers better
than 30 WPM, and often much less. Packet requires 1 kHz bandwidth. PSK31
operates at 31.25 baud, and in QPSK mode gives error corrected text at 31.25
WPM approximately. It has the narrowest bandwidth, less than 100 Hz.
Fig. 5. Graph showing raw data rate of various digital modes
versus approximate bandwidth.
In terms of performance, of the examples given, only MFSK16 and PSK31 are
considered practical for DX QSOs. PSK31 often performs poorly on long path, and
provides no improvement when the FEC is used, so is usually used without it.
MFSK is virtually as sensitive as PSK31 in practice and is unaffected by Doppler.
It is also less affected by interference, and offers effective FEC. These results are
supported by ionospheric simulation tests.
The new MFSK16 mode includes continuous phase tones and many other
improvements, especially to the receiver. The mode is loosely based on Piccolo,
but differs in a few important ways:
The transmitted data is bit oriented, rather than character oriented.
The fundamental signal is a single symbol, not a symbol pair.
Error reduction coding is built in.
Tone spacing and baud rates are divisions of 125.
The transmitted tones are phase synchronous CPFSK.
No symbol phase or other AM information is transmitted.
1. The system can therefore potentially transmit text and binary files, any alphabet
including varicodes, and can use error coding.
2. The tones and baud rates (15.625 Hz, 31.25 Hz etc) are chosen to allow
straightforward PC sound card sampling at 8 kHz sample rate.
3. This means the transmitter need not be linear. Using the receiver FFT, the
transmitted carrier phase can be extracted, and from it the symbol phase is
deduced. This technique is very fast and reliable.
Of course MFSK16 is computer oriented, rather than an electromechanical system,
so will be easy and inexpensive to install, and easy to operate, with no
Accurate tuning for transceive operation using "point and click" techniques
Convolutional coded FEC (Forward Error Correction) with interleaver for
FFT (Fast Fourier Transform) symbol filtering and detection
Symbol sync recovery by measuring transitions or carrier phase in the symbol
Two signaling speeds with differing numbers of tones (but the same
bandwidth) to suit conditions
The MFSK Varicode is slightly more efficient than others, since smaller codes are
available. This in turn is because the combinations "000", "0000" etc do not need
to be reserved for idle and can be used inside character bit streams. Only the
combination "001" is forbidden, as this signals the end of one character and the
start of the next. The speed on plain language text is almost 20% faster than using
the G3PLX varicode. The average number of bits per character for plain text has
been measured at 7.44, giving MFSK16 a text throughput of 42 WPM at 31.25
baud user data rate.
Note: Murray has an excellent website with much more information on MFSK16
and other related modes. This is an great resource for anyone interested in learning
more about this fascinating new mode:
MFSK, "The official MFSK website"Murray Greenman, ZL1BPU.
MixW: MFSK Operation
MFSK16 uses approximately the same bandwidth as 170Hz shift RTTY and so
your MFSK16 transceiver settings can be roughly the same as those used for
standard shift RTTY.
Fine Tuning: If your transceiver is equipped with a "FINE" tuning feature, always
use that for digital mode tuning once you have found the general area of the
signals, however, most of your adjustments can be made in software, and not with
the transceiver's VFO if you prefer. Some older rigs are really not stable enough
for MFSK operation and will drift considerably off frequency.
USB: USB is the convention for MFSK operation in all bands. Either sideband can
be used, but the sender and receiver must be using the same sideband, or one
station must be inverted ( see: Inversion in the Configuration Topic).
Filtering: Optimum filtering depends on your transceiver's SSB filtering options
and it's IF rejection characteristics. Wide filtering will enable you to work the
largest spectrum without retuning your transceiver, but can also cause problems
when there are strong adjacent signals. A narrow (RTTY or FSK) filter may help
significantly with some radios and situations. Many transceivers do not have
narrow filtering options while operating in SSB modes.
Mode: Click on the mode box in the status bar and select MFSK. Then click on
the mode box in the status bar again and select "Mode Settings". This brings up the
following dialog box:
TX and RX frequencies are set to the location of your cursor is in the spectrum
window. Keeping this around 1500 Hz, will keep your transceiver operating close
to the center of its pass band.
AFC, which should always be set to ON for MFSK operation due to the critical
nature of MFSK tuning.
Squelch and the Squelch thresholdcan be adjusted to limit garbage characters, but
you can also miss characters by using squelch as well.
The MFSK tones can also be inverted by checking the Inverted box. Note: This
feature works differently in MixW than most other SoundCard digital programs, so
please read and understand the information about inversion in the Configuration
You can easily recognize the sound of MFSK once you have heard it. It sounds a
lot like RTTY, only with multiple, rather musical tones. The following tuning
display shows the distinctive waterfall pattern of MFSK16:
Documents you may be interested
Documents you may be interested