PSK31 and PSK63 are digital modulation schemes used in amateur radio to transmit text messages. Both protocols are based on phase modulation, but have different bandwidths and speeds. They are particularly suitable for use on short wave, where efficient use of the frequency spectrum and good performance with weak signals are required.

 

PSK31 (Phase Shift Keying 31 Baud)

Features of PSK31

• Baud rate: PSK31 operates at a symbol rate of 31.25 baud, which means that 31.25 symbols are transmitted per second. This low baud rate allows a very narrow bandwidth of approximately 31 Hz.
• Bandwidth: The narrow bandwidth of approximately 31 Hz makes PSK31 efficient and ideal for narrowband transmissions, especially on the shortwave band.
• Modulation: PSK31 uses Binary Phase Shift Keying (BPSK), in which the phase of the carrier signal alternates between two states (0° and 180°) to represent the digital data ('0' and '1'). Quadrature Phase Shift Keying (QPSK) can also be used to provide additional error correction.
• Coding: PSK31 uses Varicode, a special character encoding in which common characters have shorter codes. This makes transmission more efficient as fewer bits are needed for common characters.
• Low signal sensitivity: PSK31 is very robust to noise and can decode signals well below the noise level.

 

Typical use of PSK31

• Shortwave operation: PSK31 is often used on shortwave bands (e.g. the 20 metre band on 14.070 MHz), where it is used for DX (long distance) communications and text communications under difficult conditions.
• QRP operation: Due to the low transmit power required, PSK31 is ideal for QRP operation (low power operation, e.g. 5 watts or less).

 

PSK63 (Phase Shift Keying 63 Baud)

PSK63 is a faster variant of PSK31 and uses a higher baud rate, which increases the data rate.

Properties of PSK63

• Baud rate: PSK63 operates at 62.5 baud, twice the speed of PSK31.
• Bandwidth: The higher baud rate results in a wider bandwidth of about 125 Hz, making it less efficient in busy frequency bands.
• Modulation: Like PSK31, PSK63 uses BPSK or QPSK, with the higher symbol rates allowing faster data transmission.
• Weak signal sensitivity: PSK63 is less sensitive to weak signals than PSK31 because it uses a wider bandwidth and is therefore less robust to interference.

 

Typical use of PSK63

• Shortwave and VHF operation: PSK63 is better suited to situations where faster data transfer is possible and signal conditions are good, such as on the VHF band or with strong shortwave signals.
• Higher speed data exchange: PSK63 is used when a higher transmission rate is required for text or simple data.

 

Differences between PSK31 and PSK63

1. Baud rate and speed: PSK31 has a baud rate of 31.25 baud, while PSK63 operates at 62.5 baud, making PSK63 faster.

2. Bandwidth: PSK31 uses a bandwidth of about 31 Hz, while PSK63 uses about 125 Hz. This makes PSK31 narrower and more suitable for limited frequency ranges.
3. sensitivity to weak signals: PSK31 is more sensitive and better suited to weak signals. PSK63 is faster but less robust to noise and interference.
4. application area: PSK31 is preferred for slow and robust communications on shortwave, while PSK63 is used for faster data transmission under better signal conditions.

 

Conclusion

PSK31 is a popular modulation method for radio amateurs operating on short wave with weak signals and low noise. PSK63 offers a faster transmission rate, but is less sensitive to weak signals and requires more bandwidth. Both protocols complement each other well and offer various options for digital communications in amateur radio, depending on requirements and conditions.