Project to Develop and Implement the JT65 Digital Mode on a Simple LIPD Band Radio Platform

What is Amateur Radio and What are Digital Modes?

Amateur Radio (ham radio) is a popular hobby and service that brings people, electronics and communication together. People use ham radio to talk across town, around the world, or even into space, all without the Internet or cell phones. It's fun, social, educational, and can be a lifeline during times of need.

What is it?

The JT65 communications protocol was conceived and first implemented by Joe Taylor K1JT, who is both a radio ham and a Nobel Prize winnder for the discovery of the first pulsar in a binary system.

JT65 is a digital mode used in amateur radio. JT65 is designed for communications at very low SNR. A digital-mode is simple a wireless mode, including a digital protocol and an RF modulation scheme that can be used to transmit digital data

Detailed background information can be found on this webpage page which is a must read introduction to JT65 and an idea of how JT65 is used.

The Project:

In this project we aim to build a communications system based on JT65. Such a system might be useful for example for long range communications on LIPD bands.

A digital communications system consists of the following blocks.




You should already know the meanings of these blocks from your lecture courses.

Answer the following questions:

  • What is source coding?
  • What does FEC stand for? What does channel coding do?
  • What is modulation?
  • If this were a block diagram of a wireless channel, where would the antenna be?

Scope:

In this project we will cover the followng exercise:

  • We will understand how the mpeg2 transport stream works and how we can use it to send video over a wireless link.
  • Write a program in C to read an mpeg2-ts video from a file.
  • Build a JT65 codec in C
  • Implement JT65 commucaations on a real radio that can be modulated by frequency shift keying (FSK)

Procedure:

  • Learn to code in C
  • Download my simple C program which models a simple radio
  • Read up on mpeg2-ts
  • Read the document: The JT65 Communications Protocol . P.S. Use google to learn the meanings of any acronyms such as EME, QSO, VHF, OOO, ...
  • The JT65 protocol uses 65-tone frequency shift keying (FSK) with constant-amplitude waveforms and no phase discontinuities. Invetigate electronic circuits that may be used to produce such a signal. For exxample you may look at minimum shift keying (MSK) or offset QPSK (O-QPSK). Learn about the advanced linux sound architecture (ALSA) and devise a techhnique to implement a continuous FSK modulation in C on a mono output.
  • Build a low power radio frequency front (rffe) end operating on the 20dBM EIRP lipd band 39–39.7625MHz to implement FSK.
  • As an alternative approach to using the sound card and building a dedicated rffe you may also consider using the raspberry FM transmitter as both a modulator and an FM RF source. This is the same approach used in the rpidatv project

References: