HackTNC

HackTNC turns a HackRF One into an AFSK1200 AX.25 packet radio TNC, accessible over KISS/TCP so any standard packet software (Direwolf, APRS clients, etc.) can connect to it like a hardware TNC.

Features

Full-duplex KISS/TCP server — connect any APRS or packet software to 127.0.0.1:8001
AFSK 1200 baud AX.25 — Bell 202 modem (1200/2200 Hz tones) on any HackRF-supported frequency
FM modulation/demodulation — proper FM discriminator with anti-aliasing decimation filter
Half-duplex PTT — RX is automatically gated off during TX and resumed after
Dark-themed WinForms GUI — frequency selector, RF gain controls, live client list, packet activity log
Console app — headless operation for servers or scripting
Configurable: frequency, KISS port, LNA/VGA/TX-VGA gain, FM deviation, TX delay/tail

Requirements

Windows 10/11 (x64)
.NET 8 Desktop Runtime (GUI) or .NET 8 Runtime (console)
HackRF One with firmware ≥ v2.0

Quick Start (GUI)

Download the latest release and extract the zip
Run HackTnc.Gui.exe
Set your frequency (default 144.3900 MHz — North American APRS)
Adjust LNA/VGA gain for your antenna (defaults: LNA 24 dB, VGA 24 dB, TX VGA 20 dB)
Click ▶ Start TNC
Connect your packet software to 127.0.0.1:8001 (KISS/TCP)

Quick Start (Console)

HackTnc.Console.exe --frequency 144.390M

Console options

Option	Default	Description
`--frequency <hz\|kHz\|MHz>`	144390000	RF center frequency. Examples: `144390000`, `144390`, `144.390M`
`--bind <address>`	127.0.0.1	KISS/TCP bind address
`--kiss-port <port>`	8001	KISS/TCP listen port
`--lna-gain <dB>`	24	RX LNA gain (0–40, step 8)
`--vga-gain <dB>`	24	RX VGA gain (0–62, step 2)
`--tx-vga-gain <dB>`	20	TX VGA gain (0–47)
`--fm-deviation <hz>`	3000	FM deviation in Hz
`--tx-delay <ms>`	300	AX.25 TX preamble flags duration
`--tx-tail <ms>`	50	AX.25 TX tail flags duration
`--rx-audio-gain <gain>`	0 (auto)	FM discriminator gain; 0 = auto-compute
`--amp`	off	Enable HackRF RF amplifier (+11 dB)
`--antenna-power`	off	Enable HackRF antenna bias tee
`--serial <suffix>`	—	Select HackRF by serial suffix
`--hackrf-dll <path>`	—	Explicit path to `hackrf.dll`

Connecting packet software

HackTNC exposes a standard KISS over TCP interface. Configure your software as:

Setting	Value
TNC type	KISS/TCP
Host	`127.0.0.1`
Port	`8001` (or `--kiss-port` value)

Works with: Direwolf, APRSIS32, Xastir, UiView32, YAAC, APRSdroid (via TCP bridge), and any other KISS/TCP-capable software.

Frequency notes

North American APRS: 144.390 MHz
European APRS: 144.800 MHz
UK APRS: 144.800 MHz
Bare integers < 10,000,000 are treated as kHz (e.g. 145050 → 145.050 MHz)

Architecture

HackRF IQ (2 Msps)
    │
    ▼
FM Discriminator  (IQ → instantaneous frequency)
    │
    ▼
Boxcar anti-alias LPF  (decimation factor ~41)
    │
    ▼
Linear interpolation resampler  (→ 48 kHz)
    │
    ▼
AFSK1200 Demodulator  (Bell 202 correlator, NRZI decode)
    │
    ▼
AX.25 frame → KISS/TCP → client software

──────────────────────────────────────────────

Client software → KISS/TCP → AX.25 frame
    │
    ▼
AFSK1200 Modulator  (Bell 202, NRZI, bit-stuffing)
    │
    ▼
FM IQ Encoder  (audio → FM modulated IQ at 2 Msps)
    │
    ▼
HackRF TX  (drain-buffer completion, no flush callback)

Building from source

git clone https://github.com/SarahRoseLives/HackTNC.git
cd HackTNC
dotnet build -c Release

Requires .NET 8 SDK. The native hackrf.dll, libusb-1.0.dll, and pthreadVC2.dll are included in the repo root and are automatically copied to the output directory.

Third-party components

AFSK1200 modem DSP — vendored from dkxce/AFSK1200Modem (MIT)
libhackrf — Great Scott Gadgets (GPL-2.0)
libusb — LGPL-2.1

See THIRD-PARTY-NOTICES.txt for full details.