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Manual-for-DDX.md

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Overview

DDX is a rugged 5W+ digital transceiver featuring manual band switching and flexible power capabilities. Designed for reliability and ease of use, it's perfect for digital modes like FT8.

Power Specifications

  • Solid 5W+ output at 13.8v

  • 10W+ ouput at higher voltages (external fan REQUIRED!)

Requirements

The following items are required for operating DDX:

  • Power Source (Choose one)

    • Traditional "12V" battery (4S LFP or 3S Li-ion or lead-acid)

    • 21v input is also fine, and produces more power

  • An antenna

    For field operations, we recommend getting / building an EFHW antenna.

    See https://github.com/kholia/HF-Balcony-Antenna-System for an example.

    https://www.kk5jy.net/three-wire-gp/ is a solid choice as well.

  • Android phone or laptop

    The laptop can run the standard WSJT-X software.

    On Android, use our FT8 Radio app from Google Play Store.

  • TX-BPF (HIGHLY RECOMMENDED for good performance and compliance, REQUIRED if you have radio interference problems)

    Sources: eBay / AliExpress

    Cost: ~45 USD

    This TX-BPF helps your other radios as well and is a one-time investment.

    TX-BPF 1

    TX-BPF 2

    If you have the budget, better TX-BPF filters are available from SurgeStop (Morgan Systems).

    While many amateur radio operators focus solely on antenna optimization, the significant benefits of TX-BPF filters are often overlooked or under-discussed in the hobby!

    Even with HOA antenna restrictions, you can still optimize your station's performance through proper TX-BPF filtering.

  • [Optional] Common-mode choke (CMC)

    Can be useful depending on your operating conditions.

Assembly Steps

  • Connect the fully assembled DDX board to a heat sink (heat sink can supplied as an option).

    Heat Sink

    The heat sink needs two holes to be made in it. A 3mm bit on a battery powered hand drill is sufficient for the job.

  • Put the DDX board into a suitable enclosure of your choice. This is optional for home usage.

  • Done!

Power-on sequence

  • First, connect the Micro-USB cable from DDX to the PC or phone

  • Next, turn on the DC power supply (using the onboard switch)

Usage (with WSJT-X)

  • Configure WSJT-X with your callsign and grid.

    WSJT-X 1

  • Select MicNode as the Soundcard Input.

    WSJT-X 2

    Tip: The Soundcard Output setting does NOT matter.

  • Ensure the following default settings are present.

    WSJT-X 3

  • Launch the wsjtx_helper/transceiver_server.exe program.

  • That's it!

Usage (with FT8 Radio app on Android)

  • Install FT8 Radio app from Google Play Store.

  • Launch the app and go to settings (gear icon).

    Configure settings and choose DDX as the radio.

    NB: Restart the app forcefully.

    FT8 Radio

  • Connect DDX to the phone using a Micro-USB cable and a reliable OTG adapter.

  • Done!

PS: See https://github.com/kholia/DigitalRadioReceiverSupport/tree/master/NewApp for more help.

Tips

For best results, we recommend syncing time on your laptop / PC using https://www.timesynctool.com/ software.

On Android, open the https://time.is/ site to see the clock delta.

Features

  • Comes as a fully assembled and fully tested-on-air board

  • Single USB connection for Audio + CAT control

    DDX has a built-in 'sound card'

  • Rock-solid PA which handles open, short, and bad SWR conditions (~10:1 SWR tested)

  • Rock-steady VFO which does NOT drift even under exposed conditions. Yes - it receives WSPR at 28 MHz just fine.

  • Reliable T/R switching based on a DPDT relay

  • No toroids to wind with the TX-BPF in use ;-)

  • The final MOSFET remains as cool as a cucumber (Class-D operation)

  • DDX has a bit-perfect, deterministic TX output

  • It works beautifully with the 'FT8 Radio' app (https://github.com/kholia/DigitalRadioReceiverSupport/). The 'FT8 Radio' app handles FT8 decoding well in real time (Native MCU decoders offer significantly reduced performance at the moment). The app can decode 35++ stations at a time, and even large screens can fill up very rapidly - such is the receiver's performance (with a BPF)!

  • No calibration is (ever) required. Just pick up DDX and it is ready to go on air. Comes with 26 MHz 0.5ppm TCXO as standard.

  • Low cost (cost-effective)

  • Stress tested by WSJT-Z for multiple days

  • DDX routinely receives FT8 traffic from 80 to 100+ countries using a simple 5m long EFHW antenna with a BPF attached

  • All this in a compact (< 100mmx100mm) size!

Firmware Upgrade

  • Disconnect all power sources

  • Unplug the Pico MCU board from the computer

  • Keep the white button on the Pico MCU board pressed, and connect Pico to the computer via a USB cable

  • Upload the supplied .uf2 firmware file to the new drive that opens up on your computer

  • Done!

Render

DDX-Commercial-1

Support Resources