KrakenSDR is a Software-Defined, Coherently Operated, Five-RX-Channel Radio Based on RTL-SDR

A coherent radio allows for very interesting applications, such as radio direction finding, and beamforming. Some use cases include:

• Physically locating an unknown transmitter of interest (e.g. illegal or interfering broadcasts, noise transmissions, or just as a curiosity)
• HAM radio experiments such as radio fox hunts or monitoring repeater abuse
• Tracking assets, wildlife, or domestic animals outside of network coverage through the use of low power beacons
• Locating emergency beacons for search-and-rescue teams
• Locating lost ships via VHF radio
• Beamforming
• Interferometry for radio astronomy

KrakenSDR is KerberosSDR++

he previous version of KrakenSDR was known as KerberosSDR, which we successfully crowdfunded on Indiegogo. KrakenSDR improves upon KerberosSDR in several important respects:

• Automatic calibration hardware. It is no longer necessary to manually disconnect antennas during calibration. It all happens automatically when you change frequency. This will allow for KrakenSDR stations to be remotely operated.
• Five channels. KrakenSDR has five channels instead of four, which greatly improves-direction finding accuracy.
• Low-noise design. KrakenSDR has a cleaner spectrum with much less internal noise than KerberosSDR.
• USB Type-C ports and rugged, CNC-milled enclosure. KrakenSDR is built for high reliability in the field.
• Interface with external devices. Bias tees on all ports allow for LNAs and other devices to be powered easily.
• Improved DAQ, DSP, and GUI software. Built on the foundation of the KerberosSDR software, the KrakenSDR software adds auto-calibration, tracking of intermittent signals, greater stability, arbitrary processing-block sizes, and a new web-based GUI.
• Software upgrades. Improvements to existing companion software and plans for new companion software.
• Custom Android app. Custom Android app that can automatically determine the location of a transmitter and provide automatic turn-by-turn navigation to the transmitter location.

Features & Specifications

• Five-channel, coherent-capable RTL-SDR, all clocked to a single local oscillator
• Built-in automatic coherence synchronization hardware
• Automatic coherence synchronization and management via provided Linux software
• 24 MHz to 1766 MHz tuning Range (standard R820T2 RTL-SDR range, and possibly higher with hacked drivers)
• 4.5 V bias tee on each port
• Core DAQ and DSP software is open source and designed to run on a Raspberry Pi 4 (see links below)
• Direction-finding software for Android (free for non-commercial use)
• Custom antenna set available

What Do You Need to Get Started?

You will need KrakenSDR, a USB Type-C cable, a 5 V / 2.4 A+ USB Type-C power supply, and antennas—such as our magnetic whip antenna set—that are appropriate for your application.

For computing we recommend a Raspberry Pi 4, for which we have a ready-to-use SD card image. To get the most out of the direction finding feautre, you will want an Android phone or tablet with mobile-hotspot capabilities, GPS, and a compass, ideally produced within the last three to four years.

How KrakenSDR Works

KrakenSDR makes use of five custom RTL-SDR circuits consisting of R820T2 and RTL2832U chips. The RTL-SDR is a well-known, low-cost software-defined radio (SDR), but throw five units together and using them on the same PC will not make them "phase coherent;" each one will receive signals at a slightly different phase offset from the others. This makes it impossible to achieve any sort of precision when measuring relationships between signals that arrive at different antennas.

To achieve phase coherence, KrakenSDR drives all five RTL-SDR radios with a single clock source, and contains internal calibration hardware to allow the phase relationship between channels to be measured precisely and corrected for in software. Additionally, the overall design of KrakenSDR works to ensure phase stability, with care taken in the areas of heat management, driver configuration, power supply, and external-interference mitigation.