February 2023 – Daniel Estévez

Running the AD9361 at 122.88 Msps

The Analog Devices AD9361 is an RFIC that is used in several popular SDRs, such as the USRP B2xx series and E3xx series, the BladeRF 2.0 micro, the ADALM Pluto, the ANTSDR, and in many other products (some of these use the AD9363 or the AD9364, which are similar chips in the same family). This RFIC has a nominal maximum sample rate of 61.44 Msps, and an analog bandwidth of 56 MHz.

A few days ago, Nuand has published a new software version that allows running the BladeRF 2.0 at 122.88 Msps. This has attracted some interest in Twitter, specially regarding questions about how they manage to achieve this and how good the performance is. One of the changes that Nuand has done to support the 122.88 Msps mode is an 8-bit wire protocol for the USB 3.0 interface. This is required to be able to pass 122.88 Msps through the USB. This change affects the FPGA gateware and host drivers. The other change involves manually setting some registers of the AD9361 in the host drivers in order to bypass a half-band filter, effectively doubling the output sample rate. In this post I will give a short review of the AD9361 register settings that enable the 122.88 Msps mode.

Maia SDR

I’m happy to announce the release of Maia SDR, an open-source FPGA-based SDR project focusing on the ADALM Pluto. The first release provides a firmware image for the Pluto with the following functionality:

Web-based interface that can be accessed from a smartphone, PC or other device.
Real-time waterfall display supporting up to 61.44 Msps (limit given by the AD936x RFIC of the Pluto).
IQ recording in SigMF format, at up to 61.44 Msps and with a 400 MiB maximum data size (limit given by the Pluto RAM size). Recordings can be downloaded to a smartphone or other device.

More details about Orion uncoded telemetry

In a previous post I analysed the residual carrier telemetry of the Artemis I Orion capsule using some recordings done by CAMRAS with the 25 m radio telescope at Dwingeloo observatory. I noticed that, in contrast to some recordings that I had done early after launch with the Allen Telescope Array, in those recordings the telemetry was uncoded instead of using LDPC. I related that finding to some tweets from Richard Stephenson about the project switching frequenctly between residual carrier and OQPSK, and between uncoded and LDPC.

I wanted to study the situation in more detail, for example to see what combinations of residual carrier / OQPSK and uncoded / LDPC were possible. Since CAMRAS hasn’t made available on their web server all the recordings they did, due to disk space constraints, I asked them to publish a few additional recordings that seemed interesting to this end. This is a short post with my findings about those new recordings.