Manual-for-DDX.md

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.

DDX is brought to you by Yantra Research! We are proud to play a small part in the Made In Bharat movement.

Supported Modes

• FT8

• WSPR (via a dedicated firmware)

Other Modes

• FT4 (support can be added as per demand)

Power Specifications

• ~5W output @ 15v on 28 MHz (after strong BPF)

• ~7W output @ 20v on 28 MHz (after strong BPF)

Requirements

The following items are required for operating DDX:

• Power Source (Choose one)

  • USB PD 3.0 battery bank (portable and flight-safe option) - RECOMMENDED!

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

  20v input (typically via PD 3.0) is RECOMMENDED!

• PD Trigger Module

  Something like this module.

• 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.

  The Banggood store also sells an EFHW 49:1 transformer for a reasonable price.

• Laptop / PC / Android phone

  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)

  Update (December-2024): We have open-sourced our TX-BPF designs here. Our filters works great and can be homebrewed!

  To truly unlock the performance of CD2003, a TX-BPF filter is a MUST.

  Tip: Buy or build one filter for your favorite band and then keep adding more later on

  Sources: eBay / AliExpress

  Cost: ~45 USD

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

  

  

  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.

• [Optional] 10 meters plus of coax cable if operating an EFHW antenna.

• [Optional] Thermal compound / thermal grease - for better heat transfer

Supplied components

• DDX transceiver

• 2 x Mica insulator pads (for IRF510 and 7809 regulator)

• 2 x TO-220 bushes (for IRF510 and 7809 regulator)

• 2 x Steel screws + spring washers + regular washers + nuts

• 1 x 5.5x2.1mm DC power cable (male connector)

• 1 x On-off switch (SPST)

• [Optional] Small TO-220 + TO-3 heat sinks

• [Optional] M3 standoffs

• [Optional] SMA male to SO-239 or PL-239 pigtail cable

Assembly Steps

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

  

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

  [ALTERNATE HEAT SINKING OPTION]

  You can also use two smaller heat sinks like the following:

  • https://etstore.in/index.php/product/8087/ (Small TO-220 heatsink)

  • https://www.electronicscomp.com/heat-sink-to3-40mm (Yes - a TO-3 heatsink)

  The whole assembled PCB can then be raised on M3 standoffs.

  

  https://robu.in/product/m3-x-35mm-male-to-female-brass-hex-threaded-pillar-standoff-spacer-12-pcs/

• 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.

  

• Select MicNode as the Soundcard Input.

  

  Tip: The Soundcard Output setting does NOT matter.

• Ensure the following default settings are present.

  

• 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.

  

• 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

• It comes as a fully tested-on-air board with minimal assembly required.

• 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 external TX-BPF in use ;-)

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

• DDX has a bit-perfect, deterministic TX output

  We simply do NOT use the audio tones emitted by the PC (or phone).

  We implement the various FSK encoders on the MCU itself.

• 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)!

  Note: The FT8CN app is NOT supported.

• No calibration is usually required. Just pick up DDX and it is ready to go on air. It comes with 26 MHz 0.5ppm TCXO as a standard.

• Relatively low cost (cost-effective)

• Stress tested by WSJT-Z and WSJT-X for multiple days.

  Compatible with wsjt-x_improved as well.

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

  And we use a SMPS with RuiDeng DC-DC buck module with >= 100mV ripple in our testing work to "stress out" the receiver.

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

Limitations

• Special / complex callsigns are NOT supported yet.

• While we have a fully-functional VFO, it is locked to certain FT8 frequencies for safety reasons. You can request addition of more frequencies as needed.

Firmware Upgrade

Note: DDX comes with the firmware installed on it.

• 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

Support Resources

• The Global Communications Transceiver - Video demo of older version

• FT8 Radio App demo

• DDX contest writeup

• https://github.com/kholia/wsjtx

Pricing

Note: The profits earned are dedicated for charity purposes.

• Option 1: Kit with all components (including Pico 2 and TCXO Si5351 module) and blank PCB: 2499 INR (shipping within India included).

• Option 2: 80% assembled boards with remaining components included (including Pico 2 and TCXO Si5351 module): 3999 INR (shipping within India included).

• Option 3 (SLOW!): Fully assembled and on-air tested DDX: 4999 INR (shipping within India included). Note: Heat sink is removed prior to international shipping.

Please note that international shipping costs around 15 to 20 USD.

Note

We do NOT have the resources to provide any support at the moment. We expect our customers to be hands-on home brewers.

Note: There are NO guarantees provided.

Thanks

Image credit: https://www.freepik.com