PSK31 Operation
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With thanks to RICHARD B. GRIFFIN, NB6Z

PSK31 Basics
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.

Transceiver Settings
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:

Power: Because of the narrow bandwidth, PSK31 transmit power should be kept to a minimum. PSK31 is an excellent mode for QRP operations.

MixW Settings

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.

Receiving PSK31
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 Window.

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.

Transmitting PSK31
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.

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.