A phase-coherent software-defined radio with five RTL-SDRs

Oct 29, 2021

Manufacturing News, Beacon-Tracking Experiments, Antenna Details, and a FAQ Update

by KrakenRF Inc

Thanks to everyone who’s following along with this project. We’ve now sold well over half of the initial 1,000-unit batch we are planning to produce immediately following the campaign. It’s looking like we’ll sell out that entire production run before the end of the campaign, at which point shipping estimates for subsequent orders will shift back to late September. So please do order early if you want to get your KrakenSDR by the date currently shown on the campaign page!

Manufacturing Update

We are due to begin production of our final confirmation prototype next week. Our new prototype enclosures are due to be CNC milled early next week as well, so we should have some nice photos to show off soon!

Beacon-Tracking Experiment

As mentioned in our previous update, we’ve been experimenting with tracking low-power (legal maximum -16 dBW EIRP), 433 MHz CW beacons. In our recent tests, we swapped out the ESP32 beacon for a portable ERASynth Micro signal generator so we could experiment with very short beacon pulses, which are not supported by the ESP32 LoraFox software. With good reception, the system was able to detect and direction find pulses as short as 1 ms. It’s possible that even shorter pulses will work, but the signal needs to be strong, and shorter pulses have less information for the DSP DFing code to work with, which can negatively affect results.

The video below shows a quick test in which we drove around a neighborhood with a 433 MHz beacon emitting a -16 dBW EIRP, 100 ms pulse every second. We positioned a fixed KrakenSDR, with an Arrow five-element dipole antenna array, at a high altitude within the neighborhood. The test shows that we were able to track the beacon up to about 1 km (0.6 mi) away. (Please ignore the grid, the dark blue line, and the green octagon, as they are not to this experiment.)

As expected, results are less impressive when the target vehicle goes into a valley or is blocked by buildings or other vehicles, but they improve quickly when line of sight is restored. In an environment with few obstructions, we believe it should be possible to locate a 433 MHz, -16 dBW EIRP signal at a range of 2 - 3 km (1.2 - 1.9 mi) or more. Furthermore, our DSP dev is currently working on improving the squelch-detection code for very narrowband, low-power CW signals, which should allow KrakenSDR to locate a beacon like this at even greater distances.

Magnetic-Whip Antenna Information

We’ve had a few questions about the specifications of our magnetic-whip antenna sets. While the exact details are still being finalized, we can say that, in addition to 800 MHz stubs, the antenna set will also include telescopic whips that should allow for tuning between 100 MHz and 1 GHz. These are magnetic whips, so the gain could be expected to be around 2 - 3 dBi. The coax will likely be 2 m of low-loss LMR200 or similar.

The most important thing about these antennas is that we are specifying very tight tolerances for cable-length variance between the five units. In a phase-coherent system, it is important that antenna coax lengths are identical, as even a few centimeters of difference can cause a phase offset, which will result in skewed bearings. The higher your frequency, the more strictly you must adhere to this precision requirement.


We have also updated our FAQ with questions that were sent our way this week.

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