1 hour and $35 to build, here's how:

  1. Order the parts
    • DRA818V $11 (also available on eBay)
      • A community member confirmed that SA818S-V is identical to DRA818V, so it's an alternative if you can't find a DRA818V.
    • ESP-WROOM-32 Development Board Type-C USB $5 (1 from 5-pack)
    • SMA male antenna of your choice. If you're not sure, either of these works:
    • USB C 180 degree OTG male-to-male $8
      • Alternative (cable): Short USB-C Cable [5 inch]. The 180 degree connector usually only works without a phone case. If you want to use it with a phone case, consider a very short male-to-male cable.
    • SMA female 90 degree connector $1 (1 from 12-pack)
    • Sticky gel pads $1 (1 from 10-pack)
    • PCB $3
      • NOTE 10/8/24: My spectrum analysis of the v1.5 PCB confirmed compliance with FCC harmonic suppression requirements, but it was too marginal for my liking. The new v1.6 PCB design should significantly improve filtering, if you want to be an early adopter of v1.6 use "Intermediate" below. I'm awaiting my prototype PCBs to be delivered (ETA about 7 days) so I can verify the better harmonic suppression. It's up to you if you want to wait for this revision with better filtering, but I recommend it.
      • Easy: Takes ~4 weeks, order "PCB+Assembly" from kv4p HT v1.5 PCBWay project
      • Intermediate: Takes ~1 week, custom order from JLCPCB, get v1.6 design files here
  2. 3D print the case, and optionally the stand
  3. Solder the DRA818V, ESP32, and SMA connector to the PCB
    • Once the ESP32 is soldered, trim all of its legs as short as possible (so they don't contact your phone)
  4. Insert the PCB into the case until it snaps in
  5. Flash the ESP32 firmware
    • Plug USB C cable from kv4p HT to your computer (your phone's browser won't work)
    • Use this online flash tool to install the latest firmware, which requires Chrome or Edge. Select the device "CP2102 USB to UART Bridge Controller":
    • Device not showing up? You might need to install the CP210x device driver.
  6. Attach kv4p HT to your phone with a piece of sticky gel pad
    • Cut a strip of sticky gel pad to attach the kv4p HT to the back of your phone
    • Tip: insert the USB C 180 degree connector before pressing the kv4p HT to your phone, to help you align it properly
    • It will stay put, but can be easily removed with no residue
  7. Screw on the antenna
  8. Install the Android app
    • While the app is in beta, email kv4pht@gmail.com and ask to be added. You need a Google account (such as Gmail) to join the beta.
    • Once in the beta, you can install the Android app from your phone or from a computer
  9. Get on the air, and have fun!

Need some help?

Visit the kv4p HT Discord general channel and ask for advice.