Tagged: plutosdr

Understanding PLLs and their Importance when Receiving/Transmitting on QO-100

Over on YouTube Andreas Speiss has uploaded a video that explains what the geostationary QO-100 satellite is, and explains about the parts needed to receive and transmit to it. In particular Andreas goes into depth explaining the low noise block (LNB), and the PLL inside it. A PLL or phase locked loop is a common design used in RF electronics as it allows us to increase the frequency of crystal oscillators.

This PLL explanation ties into the fact that most commercial LNBs available do not have a stable enough crystal oscillator to properly receive or transmit the narrowband amateur radio signals used on QO-100. A PLL can increase the frequency of a crystal, but it will also increase the frequency drift and jitter/phase noise of the crystal. He notes that in later videos he'll show how to modify the LNB to improve these factors. We note that a commercially available stable LNB is the Bullseye LNB which we have posted about previously.

QO-100 Satellite Receiving Technology. And Explanation of a PLL

TechMinds: Performing the Frequency Expansion and CPU Core Mod on the PlutoSDR

The PlutoSDR is a low cost RX/TX capable SDR with up to 56 MHz of bandwidth and 70 MHz to 6 GHz frequency range. It is typically priced at US$149. By default the PlutoSDR ships with a tuning range of  325 – 3800 MHz and bandwidth of 20 MHz. However a simple software hack allows you to expand this tuning range to 70 MHz to 6 GHz with a maximum bandwidth of 56 MHz.

The reason this is possible is possibly because the AD9363 SDR transceiver chip used in the PlutoSDR is nearly identical to more expensive AD9364 which has the higher specs. The software hack tricks the PlutoSDR firmware into believing that the AD9393 is a AD9364. Mileage may vary as we speculate that the AD9363 might be produced on lower grade silicon or could be failed AD9364 chips with lower performance at the edge frequencies. But so far most users have reported acceptable performance.

TechMinds' video shows how to apply the hack, which is a simple matter of opening a terminal connection to the SDR and running a few commands. He also shows how to enable an extra CPU core on the processor. Finally he demonstrates that it's possible to transmit in the extended tuning range via SDRangel.

ADALM PLUTO Frequency Expansion Modification Plus CPU Cores

TechMinds: Taking a look at the ADALM Pluto

Over on his YouTube channel Tech Minds has uploaded a video where he overviews and demonstrates the ADALM PLUTO (aka PlutoSDR).  The PlutoSDR is a low cost RX/TX full duplex capable SDR with up to 56 MHz of bandwidth and 70 MHz to 6 GHz frequency range. It is typically priced anywhere between US$99 - US$149 depending on sales.

In the video Tech Minds explains the specs and features of the PlutoSDR, analyzes the included antennas, shows how to connect to the PlutoSDR via USB/Ethernet/WiFi and finally demonstrates the unit running on SDR-Console V3 receiving and transmitting signals.

He also notes how he modified his unit and installed a more stable TCXO. This is required as he intends to use the unit for QO-100 SSB satellite operation which requires a very stable signal. In addition to the TCXO mod he also performed a mod to improve the grounding on the unit which reportedly prevents the unit from locking up when using long long network cables and a USB to Ethernet adapter.

ADALM PLUTO Full Duplex Software Defined Radio

 

PiSDR Ready to use SDR Raspbian Image Updated to V4.0

It's been a good time for ready to use SDR Linux OS images recently, as we've seen the release of two new images, DragonOS and gorizont-rtlsdr over this lock down period. And now the already popular and mature PiSDR image has also been updated. 

PiSDR is a ready to use Raspbian based operating system for Raspberry Pi's which comes pre-loaded with many programs for software defined radios. It currently supports the RTL-SDR, LimeSDR, PlutoSDR, Airspy, and Airspy HF+ and has preinstalled software such as SDR Angel, Soapy Remote, GQRX, GNURadio, LimeUtil, and LimeVNA.

The latest update includes various bug fixes as well the following new features:

  • Three times smaller.
  • HackRF Support.
  • Verified Compilation on GitHub Actions.
  • New Software: Quisk, CygnusRFI, rpitx, rtl_433, acarsdec, gpredict, multimon-ng, and leansdr
PiSDR Running a SDRAngel with a LimeSDR
PiSDR Running a SDRAngel with a LimeSDR

A Comprehensive Lab Comparison between Multiple Software Defined Radios

Librespace, who are the people behind the open hardware/source SatNOGS satellite ground station project have recently released a comprehensive paper (pdf) that compares multiple software defined radios available on the market in a realistic laboratory based signal environment. The testing was performed by Alexandru Csete (@csete) who is the programmer behind GQRX and Gpredict and Sheila Christiansen (@astro_sheila) who is a Space Systems Engineer at Alexandru's company AC Satcom. Their goal was to evaluate multiple SDRs for use in SatNOGS ground stations and other satellite receiving applications. 

The SDRs tested include the RTL-SDR Blog V3, Airspy Mini, SDRplay RSPduo, LimeSDR Mini, BladeRF 2.0 Micro, Ettus USRP B210 and the PlutoSDR. In their tests they measure the noise figure, dynamic range, RX/TX spectral purity, TX power output and transmitter modulation error ratio of each SDR in various satellite bands from VHF to C-band.

The paper is an excellent read, however the results are summarized below. In terms of noise figure, the SDRplay RSPduo with it's built in LNA performed the best, with all other SDRs apart from the LimeSDR being similar. The LimeSDR had the worst noise figure by a large margin.

In terms of dynamic range, the graphs below show the maximum input power of a blocking signal that the receivers can tolerate vs. different noise figures at 437 MHz. They write that this gives a good indication of which devices have the highest dynamic range at any given noise figure. The results show that when the blocking signal is at the smallest 5 kHz spacing the RSPduo has poorest dynamic range by a significant margin, but improves significantly at the 100 kHz and 1 MHz spacings. The other SDRs all varied in performance between the different blocking signal separation spacings.

Overall the PlutoSDR seems to perform quite well, with the LimeSDR performing rather poorly in most tests among other problems like the NF being sensitive to touching the enclosure, and the matching network suspected as being broken on both their test units. The owner of Airspy noted that performance may look poor in these tests as the testers used non-optimized Linux drivers, instead of the optimized Windows drivers and software, so there is no oversampling, HDR or IF Filtering enabled. The RSPduo performs very well in most tests, but very poorly in the 5 kHz spacing test.

The rest of the paper covers the TX parameters, and we highly recommend going through and comparing the individual result graphs from each SDR test if you want more information and results from tests at different frequencies. The code and recorded data can also be found on the projects Gitlab page at https://gitlab.com/librespacefoundation/sdrmakerspace/sdreval.

SATSAGEN: Software to use a PlutoSDR as a Tracking Spectrum Analyzer

Thank you to Frank, HB9FXQ for submitting news about a new Windows program called SATSAGEN which allows you to use a PlutoSDR as a wideband spectrum analyzer. SATSAGEN was created by Alberto IU1KVL and is entirely free to use. This makes it possible to get wideband scans of RF components like filters and attenuators. Together with a directional coupler it could also be used to measure the SWR of antennas as HB9FXQ demonstrates in his Twitter post.

The PlutoSDR is a low cost RX/TX capable SDR with up to 56 MHz of bandwidth and 70 MHz to 6 GHz frequency range. It is typically priced anywhere between US$99 - US$149 depending on sales.

In the video below Alberto demonstrates SATSAGEN performing some wideband scans, and he shows the various features of the software. He writes that the system has a scan range from 70 MHz to 6 GHz and can show results in dBm. The spectrum analyzer works with the TX part of the PlutoSDR to provide a tracking generator with resolution of up to 1024 points. The software can also use the PlutoSDR as a frequency generator with 1 kHz of resolution.

There is also a support group available at groups.io/g/satsagen.

SATSAGEN Screenshot
SATSAGEN Screenshot

SATSAGEN BASICS

PiSDR Updated to Version 3.0: Now Supports the Airspy HF+

PiSDR is a Raspberry Pi distribution that is pre-loaded with multiple programs for various software defined radios. It currently supports RTL-SDR, LimeSDR, PlutoSDR, Airspy, and as of the most recent update the Airspy HF+. The currently pre-installed software packages include SDR Angel, Soapy Remote, GQRX, GNURadio, LimeUtil, and LimeVNA.

Recently version 3.0 was released, and this new version adds a few new features like Desktop shortcuts, Raspberry Pi 4 support, Airspy HF+ support and documentation.

The latest image can be downloaded from the PiSDR website at https://pisdr.luigifreitas.me. It can be burned to an SD card in the same way that you would with a standard Raspbian installation. This is a great image to start from if you're experimenting with RTL-SDRs on a Raspberry Pi, as it means that you don't need to go through all the steps of installing the drivers and software like GQRX and GNU Radio which can take a long time to install.

PiSDR Running a SDRAngel with a LimeSDR
PiSDR Running a SDRAngel with a LimeSDR

Using a PlutoSDR to compare FreeDV Digital Voice with other Modes

Over on YouTube user Adrian M has uploaded a video where he compares the HF amateur radio digital voice mode known as FreeDV against other common voice modes such as USB, AM, FM and QPSK. To perform the test he uses a PlutoSDR, a GNU Radio program and a GUI called qradiolink.

FreeDV is an open source amateur radio digital voice mode that uses Codec2 compression. It's designed to compress human voice and works with narrow bandwidths and with weak signal power.

In the demonstration Adrian reduces the TX power slowly for each mode, so you can see what the voice sounds like at high and low signal power. The FreeDV mode is not high fidelity in terms of audio quality, but the voice remains able to be copied at low power when the other modes could not.

Transmit and receive FreeDV 1600 and 700C with SDR hardware