Also known as: KrakenSDR, Kraken SDR
KrakenSDR is a five-channel, phase-coherent RTL-SDR receiver from KrakenRF, built so that all five tuners share a single clock and can be phase-synchronised — the property that makes radio direction finding and passive radar possible from cheap hardware.1 It is the productised successor to the earlier four-channel KerberosSDR, and its headline application is estimating the direction of arrival of a signal using array-processing algorithms.
Overview
KrakenSDR packages five RTL2832U receivers, each with an R820T2 tuner, onto one board. The critical engineering is that they run from a single shared reference clock and include a built-in noise source that can be switched into all inputs to calibrate out the relative phase offsets between channels. Ordinary RTL-SDR dongles cannot do direction finding because their independent clocks drift apart; coherence is what turns five receivers into a usable antenna array. The device covers roughly 24 MHz – 1.766 GHz (the R820T2’s range) and, like every RTL-SDR, is receive-only with 8-bit converters.
What it is for
The whole point of a coherent array is to exploit the phase differences of one signal arriving at antennas spaced apart. KrakenSDR’s open-source software feeds those phase measurements to the MUSIC algorithm (MUltiple SIgnal Classification), a super-resolution method that estimates the direction of arrival far more sharply than the array’s raw aperture would suggest. Driving around while logging bearings lets the software triangulate a transmitter’s location — a mobile form of multilateration. The same coherent hardware also supports passive radar, where a broadcast tower serves as the illuminator and reflections off aircraft or vehicles are detected in the cross-channel correlation.
The array’s geometry sets the mode: antennas in a circle (a uniform circular array) give 360° coverage, while a straight line gives higher accuracy over a limited arc. KrakenSDR does not do beamforming in the transmit sense — it has no transmit path — but the receive-side array math is the same family of techniques used in phased-array systems.
In practice
Because it is five RTL-SDRs, KrakenSDR inherits their limits: an 8-bit ADC per channel, easy front-end overload near strong transmitters, and modest per-channel bandwidth. It also draws real power (a powered USB hub or dedicated supply is usual) and runs warm. At $450–$600 it is priced for its niche — direction finding, transmitter hunting, and passive-radar experimentation — rather than as a general scanner, where a single good dongle is cheaper and simpler.
Relevance to GopherTrunk
GopherTrunk is a trunking decoder, not a direction-finding platform, so it does not use KrakenSDR’s coherent array or DoA features. In principle any one of its five channels is an ordinary R820T2 RTL-SDR that GopherTrunk could treat as a plain IQ source, but there is no reason to buy a KrakenSDR for decoding — a standard RTL-SDR or an Airspy is the right tool. KrakenSDR is worth knowing as the canonical example of how cheap coherent receivers bring array signal processing — direction finding, MUSIC, passive radar — within hobbyist reach.