Analysis of Amateur Radio Frequency Code Modulation Protocols for Transmitting Short Messages

Abstract

The article is dedicated to analyzing common short message transmission protocols in digital code used by radio amateurs in amateur radio communication. The following protocols are considered: RTTY, AMTOR, PACTOR1, ISCAT, JT4, JT9, JT65, FT4, and FT8. All of them use frequency shift keying (FSK), which provides significantly better noise resistance since information is encoded in frequency changes rather than amplitude. Because of this, FM is widely used in broadcasting. The primary purpose of the listed protocols is to prevent signal fading due to radio wave reflection from the ionospheric layer (sporadic propagation), where reflection windows can be short. Therefore, modulation must be fast, and data transmission reliability must be high to ensure successful radio exchange. The article analyzes the main characteristics of these protocols, including the maximum signal-to-noise ratio (SNR) at which digital data reception and decoding are possible, transmission speed, and the bandwidth occupied by the signal. Additionally, related characteristics are examined, such as the bit transmission time and the use of error-correcting codes for noise immunity. The main FSK modulation modes are reviewed, comparing their advantages and disadvantages. It has been established that the JT4, JT9, JT65, QRA4, WSPR, FT4, and FT8 protocols provide a SNR greater than -20 dB compared to RTTY, AMTOR, PACTOR, and ISCAT. In such protocols, the signal occupies a narrower bandwidth. All the discussed protocols ensure a higher message transmission speed compared to other modulation modes. The conclusion is made that frequency modulation, combined with the use of error correction codes, significantly improves the SNR. The application of similar signal detection and decoding methods could enable the development of a decoder with substantially higher sensitivity. The development of a new type of signal for digital information transmission can be based on modifications of the JT4, JT9, JT65, QRA4, WSPR, FT4, and FT8 protocols.