Tagged: coherent radio

Dragon Labs CR-8: An 8-Channel Coherent SDR Crowdfunding Soon

Dragon Labs have recently announced that the CR-8 model is getting ready for crowdfunding on CrowdSupply. The CR-8 is an 8-channel coherent software-defined radio with a 12-bit ADC, a tuning range of 25 MHz to 1750 MHz, and 8 MHz of bandwidth per channel. A coherent SDR unlocks various applications such as radio direction finding, beamforming, and antenna diversity.

The CR-8 was originally designed for a Master's thesis by Alexandre Rouma, who is also the creator of the popular SDR++ software, which is commonly used by RTL-SDR enthusiasts.

The core of the build appears to consist of R860 tuners for each channel and an MCP3721-200 analog-to-digital converter (ADC). The MCP3721-200 is a chip commonly used for radar, imaging, and cellular base station applications, as it naturally provides aligned samples with built-in fractional delay recovery, making it ideal for coherent applications. A seperate signal source on the PCB provides the needed signal for the phase calibration of the tuners. 

SDR++ and SatDump will natively support the CR-8, and there is also a GNU Radio source block. While the C API is open source, they note that the firmware will be closed source.

Pricing has yet to be announced, but we found a recent comment from the team indicating a target price of US$500 - $600 for the bare PCB, with a CNC-milled enclosure available as an optional add-on.

Dragon Labs CR-8
Dragon Labs CR-8

KerberosSDR with DF-Aggregator Direction Finding Attempt

Back in October we first posted about the release of DF-Aggregator, a program by Corey (ckoval7) which can be used to receive and plot data from multiple KerberosSDR direction finding units. 

If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.

In one of his latest DragonOS videos, Aaron has been testing out DF-Aggregator. In his test he had two vehicles driving around each with a KerberosSDR and antenna array, with both using a mobile data connection to send data to a remote PC running DF-Aggregator. The results were successful, with the team being able to determine the location of a broadcast FM transmitter to within a few meters after a short drive.

DragonOS Focal KerberosSDR x2 Mobile w/ DF-Aggregator Direction Finding Attempt 2 (Better Results)

A 3D Printed Automatically Adjusting Linear Antenna Array for KerberosSDR Radio Direction Finding

Over on GitLab Josh Conway has released a design for an automatically adjusting antenna array which can be used with radio direction finding capable SDRs like our KerberosSDR. KerberosSDR is a SDR consisting of four RTL-SDRs connected to the same oscillator, a USB hub, a built in noise source and calibration hardware which allows software to use the four RTL-SDRs coherently. Coherent operation of SDRs enables interesting applications such as radio direction finding, passive radar and beam forming.  

With coherent antenna array based direction finding, the optimal spacing between the antenna elements is proportional to the wavelength of the frequency being received. If you want to do RF direction finding on different frequencies, either multiple antenna arrays with different element spacings, or manually adjusting the antenna array with each frequency change is required.

Josh's design automates this problem with an antenna array that can adjust the spacing automatically. The design puts the antennas on an extending pantograph arm whose length is controlled via a threaded rod connected to a stepper motor. An Arduino microcontroller controls the stepper, thus allowing the spacing to be adjusted automatically. 

A Pantograph Antenna Array for Direction Finding

A full description of the build is provided in the document on GitLab titled "provisional_patent_application.pdf". From Twitter it appears that Josh (@CrankyLinuxUser) was unable to secure a patent for this design, so he has released the design for free under AGLP3. Most of the parts are 3D printed, and the CAD stl files all appear to be available on the GitLab. The Arduino microcontroller firmware is also available.

Thank you to Josh for releasing this design!

Pantograph Antenna Array for Direction Finding