I sometimes want to operate using the JT65/9 modes from local hills, as my home QTH is close to sea-level. However, doing so is not so easy, due to the quantity of kit I’d have to take:

  • Battery
  • Laptop
  • Phone (for Internet access and NTP sync of laptop)
  • HF Transceiver
  • USB external sound card / rig interface
  • Antenna and associated matching unit
  • Antenna mast/fibreglass pole/guy lines

This does not all fit in a single rucksack, as a CW QRP system might. So, I’m thinking about what a self-contained JT-modes transceiver might look like, so that I just take:

  • Battery
  • Self-contained JT-modes transceiver
  • Phone
  • Antenna and associated matching unit
  • Antenna mast/fibreglass pole/guy lines

So what would be in the box? I think this could be developed in two phases.

  • Phase 1: Merge the transceiver and USB interface.
  • Phase 2: Add the computer.

So for phase 1:

  • Arduino Micro (my board of choice) presenting multiple devices via its USB connector: a 16 bit 8000kHz mono sound card; a serial interface for CAT commands (to change operating frequency); a serial interface for diagnostics/control via a terminal emulator.
  • The Arduino would be connected to a 16-bit digital-to-analogue converter, which, when transmitting, would provide the analogue signal to the transmitter (as sent from the main computer).
  • Also, an analogue-to-digital converter which passes the received audio in receive mode back through the USB sound card to the main computer.
  • The USB CAT interface would control the output frequency of a direct digital synthesis (DDS) unit, for precise generation of the correct frequency for the JT-modes section of the band.
  • Transmitter/PA and receiver system suitable for the transmission and reception of JT-mode signals.
  • Possibly monitoring of SWR forward/reverse measurement, and PA transistor temperature; triggering of a cooling fan.

This phase 1 system could be connected to my existing OSX laptop and appear as a CAT-controllable USB sound card, with decode/generation of the JT-mode signals being done by the ‘proper’ WSJT-X software.

Phase 2 could extend phase 1 by adding:

  • A touch screen, connected to…
  • A Raspberry Pi Zero W, running a cut-down/embedded Linux, a customised version of WSJT-X optimised for the touch screen, and WiFi/Bluetooth connection to an optional Bluetooth keyboard and phone (for NTP sync). USB connection to the phase 1 ‘sound card/CAT’ transceiver.

Risks/things I don’t yet know:

  • How to make an Arduino provide multiple devices; It provides a single serial interface ‘out of the box’ – I require two discrete ones, and a sound card.
  • How to provide a USB sound card interface.
  • The design of the transceiver capable of digital modes, in much more detail than a basic SSB transceiver block diagram.
  • How easy it’ll be to customise WSJT-X for the phase 2 system.

So to address the first two, it should be possible to provide the two serial interfaces wired ‘back to back’, so that anything you send on one, gets received by the other, and vice versa.

The sound card could just send a varying-pitch sine wave (simulating the ‘receiver output’), or send back what it has been receiving (on its ‘microphone’ when ‘transmitting’).

The transceiver itself could be based on existing SSB DDS-driven systems, possibly the BIT-X, or the QRPver (replacing the VFO with DDS). This is the riskiest part of the entire endeavour, as I’m a very amateur amateur, and something of a beginner at RF electronics design.

To be continued….

 

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