NarrowBeam

HackRF NTSC transmitter with webcam capture

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NarrowBeam

NarrowBeam is a Windows desktop application for amateur television work with HackRF. It currently includes a transmitter mode for generating NTSC video and a receiver mode in the application shell.

Features

  • DirectShow webcam enumeration through ffmpeg
  • NTSC composite generation for HackRF transmit
  • Test pattern transmit mode
  • Callsign overlay in the lower-left corner of transmitted video
  • Amateur TV preset channels for US 70cm, 33cm, and 23cm allocations
  • Live transmitter monitor preview
  • Persistent transmitter settings stored in narrowbeam.ini
  • RTL-SDR Receiver mode with AM video demodulator
  • Real-time video display of received signal
  • Manual gain control and frequency tuning

Requirements

  • Windows
  • .NET 8 SDK or .NET 8 Desktop Runtime
  • HackRF with the required native DLLs (for Transmitter)
  • RTL-SDR with rtlsdr.dll (for Receiver)
  • ffmpeg.exe available beside the built executable, or in the repository root during development

The repository already includes the native files expected by the project:

  • ffmpeg.exe
  • hackrf.dll
  • rtlsdr.dll
  • libusb-1.0.dll
  • pthreadVC2.dll

Build

From the repository root:

dotnet build .\NarrowBeam\NarrowBeam.csproj -c Release

Release output:

NarrowBeam\bin\Release\net8.0-windows\

Run

After building, launch:

.\NarrowBeam\bin\Release\net8.0-windows\NarrowBeam.exe

On startup, choose either transmitter or receiver mode.

Transmitter usage

  1. Select a webcam, or enable the test pattern option.
  2. Pick an ATV preset or enter a custom frequency.
  3. Set transmit bandwidth, gain, amp state, and optional callsign.
  4. Press Start.
  5. Watch the Live Monitor pane to confirm what is being transmitted.

Saved transmitter values are restored from narrowbeam.ini in the application directory.

Receiver usage

  1. Select an RTL-SDR device from the dropdown.
  2. Choose an ATV preset or set a custom frequency.
  3. Note: The receiver tunes 500kHz below the target frequency to avoid the DC spike.
  4. Adjust RX Gain manually for best picture quality (start around 30-40dB).
  5. Press Start.
  6. The received video will display in the Live Video pane.
  7. Sync: The receiver uses a simple "hard sync" detector. It is robust but may unlock if the signal is very weak.

Notes

  • Webcam capture uses ffmpeg with DirectShow.
  • The transmitted preview reflects the frame being encoded for NTSC output.
  • If no camera appears, verify the device is visible to:
ffmpeg.exe -hide_banner -list_devices true -f dshow -i dummy