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About PSK31

PSK31 is a digital communication mode for amateur radio. It is one of the most common and easy-to-use digital modes as a PSK31 station needs only to consist of an SSB transceiver, an antenna, and a soundcard equipped PC.

Brief history of PSK31

PSK31 was created by Peter Martinez, G3PLX, in the mid-’90s. In the early stages, PSK31 signals were sent using specialized DSP platforms. However, in 1999, Peter released software that allowed PSK31 to be sent and received using a computer soundcard. Due in part to the widespread availability of such a setup, PSK31 has become one of the most popular digital modes in amateur radio.

How PSK31 Works

PSK31 signals consist of changing audio tones to convey the transmission content. Individual characters are represented by a binary sequence of 1′s and 0′s, the sequence being determined by a system called Varicode. The number of bits per character varies based on how commonly the letter is used, an “e” being represented by 11, thus achieving greater transmission speed.

The bits, 1′s and 0′s, are transmitted my phase-shifting an audio tone, hence the name Phase Shift Keying (PSK). The 31 in PSK31 refers to the speed at which data is sent; in this mode, at about 31 bits-per-second.

PSK31 archives its weak-signal performance as a result of two factors. First, a PSK31 signal is narrow, being about 31 Hz wide. Second, the structure of Varicode allows the receiving computer to anticipate the times for each data bit. These factors combine to make PSK31 one of the most popular and high performance digital modes.

What’s the “b” in BPSK31?

The “b” in BSPK31 stands for binary. This refers to the most common form of PSK31, which sends two channels of data with a transmission. There is also another flavor, QPSK31, which adds two additional channels for error correction, but it is far less popular than BSPK31.
PSK31 is a digital communication mode for amateur radio. It is one of the most common and easy-to-use digital modes as a PSK31 station needs only to consist of an SSB transceiver, an antenna, and a soundcard equipped PC.

PSK31 Station Setup

A basic PSK31 station should consist of the following components:

• HF SSB Transceiver
• Soundcard-equipped PC
• Antenna
• PSK31 Software
• (optional) Soundcard Interface

Transceiver / Antenna

Virtually any SSB transceiver will do. The same is true of the antenna, as PSk31 will function with a few watts and a wire antenna. Obviously, the better the transceiver and antenna, the better performance will be achieved, however PSK31 performance is often virtually the same on both low-end and high-end equipment.

PC / Software

The only major requirement for the computer used to send and receive the PSK31 signals is that it contain a soundcard. As a rule, a faster CPU and more memory are desired, however PSK31 will work on virtually any PC equipped with an internal or external soundcard.

Software for PSK31 is abundant, so the choice of software packages depends largely on personal preference, as will as system requirements. All PSK31 software has the basic ability to send and receive PSK31 signals. Many more features exist. Be sure to check our Software Reviews section to see some of the available packages.

Soundcard Interface

PSK31 software will output audio to the PC’s soundcard to send a transmission, however a mechanism must exits for keying the radio to transmit an RF signal, as well as link the audio tone to the radio’s audio input. Therefore some form of soundcard interface may be used. It might simply be an audio cable with a radio with VOX capabilities, or it might be a specialized external interface. These interfaces connect to the computer and key the transmitter whenever an audio tone is present. Some interfaces contain external soundcards themselves, allowing extra flexibility in soundcard setup. My personal favorite is the SignaLink USB from TigerTronics. This device is an external soundcard that connects to the computer via USB and to my Yaesu FT-857D radio via its data port. It is plug-and-play compatible with minimal setup required.

Another option lies in software based keying. The software suite, Ham Radio Deluxe, can utilize this approach. If the radio’s CAT port is already connected to the computer, Ham Radio Deluxe and its multimode software, Digital Master 780, will send the keying command via the CAT connection.

Setup Steps

1. Setup / Install Soundcard Interface or Cable
2. Install PSK31 Software
3. Read User Guide / Help for Software
4. Configure Settings as Desired
5. Operate!

PSK31 Operation

The first, and most important, step before operating any station is making sure to tune the transmitter. This will prevent damage to the transmitter and guard against messy, distorted signals. most PSK31 software packages have a testing / tuning feature for this purpose.

Another thing to watch is the ALS (automatic leveling control) meter on the radio. Adjust the audio level until the ALS meter always reads at 0. If the audio level is too high, the ALC controls in the transmitter will kick in, and the result will be a distorted PSK31 signal (splatter).

If you do contact someone with a messy signal, do not give them an automated (macro) signal report of 599 – an easy 595 will let them know to adjust their audio drive.

Next, tune your radio to a common PSK31 frequency; two are 7.070 MHz and 14.070 MHz (see a full list of PSK31 Frequencies). Make sure your radio is set to SSB mode on the upper sideband (USB). Your will not have to change frequencies after that, since PSK31 signals are so narrow (31 Hz), all the transmissions will be picked up by the receiver without changing frequencies. It is then up to the software, not the radio, what signal(s) to decode.

Fire up your favorite your favorite PSK31 software. Most packages will have a “waterfall” display where you will see all the signals from the receiver. If all station setup is correct, you will see something like this:

In most software packages, you can click on or move a marker to a signal to begin decoding the transmission.

Conversation

The first transmission is usually a CQ call. This is similar to CW, like this:

CQ CQ CQ de KD5TEN KD5TEN KD5TEN
CQ CQ CQ de KD5TEN KD5TEN KD5TEN K

This basically means that KD5TEN (myself) is calling for someone to contact. The “K” a the end of the transmission means “over,” signifing that the other station may begin transmission. Typically, the next transmission would be something like this:

KD5TEN KD5TEN KD5TEN de OTHERCALL OTHERCALL OTHERCALL
KD5TEN KD5TEN KD5TEN de OTHERCALL OTHERCALL OTHERCALL pse K

After that, the conversation proceeds with the station transmitting back and forth following this format:

OTHERCALL de MYCALL Hi there! (rest of message) BTU OTHERCALL de MYCALL k

The “BTU” stands for “back to you” and is optional.

Finally, at the end of the conversation, both stations end their last with “sk” instead of “k” to signify the end (“sk” stands for silent key).

Further Reading

ARRL’s HF Digital Handbook
ARRL’s VHF Digital Handbook
Nifty E-Z Guide To Psk31 Operation
Signal Reports and IMD
PSK31 without a Computer