We've decided to ask the community what sort of radio would be more popular for a ~$30 RX-only SDR. Note that thus far this is only a hypothetical SDR that does not yet have any designs. We are just feeling for what's most interesting to people and exploring for future ideas which may not even be feasible at this time.
As always with engineering, there is always a trade off. It is likely that any low cost SDR can only be wide band, with basic RF performance, narrowband with good RF performance, or expensive.
Wider bandwidth: Currently the RTL-SDR allows you to see up to 3.2 MHz of spectrum live. Higher bandwidth (10 MHz or more) would mean seeing more of the spectrum at once without needing to retune, faster whole spectrum scans and the ability to receive wideband signals.
RF Performance: The RTL-SDR has an 8-bit ADC. While sufficient for many applications, in the presence of strong signals the ADC will saturate resulting in poor reception and signal overload. Higher end SDRs like the SDRplay, Airspy, LimeSDR etc use 12-bit or higher ADCs.
Frequency Range: The RTL-SDR V3 can tune from 500 kHz to 1.75 GHz. An expanded SDR could potentially tune up to 4 GHz or even higher.
If you're interested in other things, please comment on this post!
On this episode of SignalsEverywhere on YouTube Corrosive shows off several antennas that can be used for Inmarsat and Iridium satcom reception. His video shows off a commercial Inmarsat branded satlink antenna which is designed to be used on moving ships, a grid dish antenna, a custom QFH iridium antenna made from a repurposed Vaisala radiosonde, a commercial Iridium patch, an older Outernet/Othernet Iridium patch and a custom Iridium patch that Corrosive built himself.
Satcom Antennas for L-Band Reception via RTL SDR
A few days prior Corrosive also released a new episode of his podcast. In this episode he interviewed Derek a student from The University of Michigan who is working on the MiTee CubeSat. The MiTee cubesat is a small experimental satellite that will explore the use of miniaturized electrodynamic tethers for satellite propulsion.
The Software Defined Radio Academy YouTube channel recently uploaded an interesting talk by Alex Csete (creator of the popular GQRX and GPredict applications), and Sheila Christiansen. Their presentation discusses their work with the European Space Agency (ESA), Libre Space Foundation and how they are running SDR Makerspace's that are helping students create and track cubesats. During the talk Alex and Sheila also describe various SDR hardware, and how they test them for their purposes.
SDR Makerspace (https://sdrmaker.space) is a collaboration between the European Space Agency and Libre Space Foundation, with the objective of bringing innovative open-source SDR technologies to space communications.
Space is a complex environment. Attempting to incorporate SDRs into complex subsystems of space missions without sufficient understanding of the technology can add unnecessary risks and uncertainties to the mission. SDR Makerspace aims to bring open-source SDR technology to the space industry, focusing on the practical aspects of satellite communications, so as to reduce such risks.
Makers, open-source hackers, SDR enthusiasts, and researchers are collaborating on SDR hardware and software activities, focusing on rapid prototyping and development of reusable, open-source SDR components for future CubeSat missions.
The collaboration consists of many activities, which are organized into three main elements: development of reusable GNU Radio components, research and development in cutting edge technologies like AI/ML, and testing of SDR hardware and software.
Current activities are presented with a focus on the testing of the hardware and software. An overview of the investigation into the characteristics, such as, performance under realistic conditions, damage by radiation to essential parts, functionality of FPGA toolchains, the SDR-system’s complexity, and accessibility to the open-source community will also be covered.
Alex Csete, OZ9AEC: SDR-Makerspace: Evaluation of SDR boards and toolchains
Back in April 2018 we posted how the NOAA-15 APT weather satellite that many RTL-SDR users enjoy receiving images from was having problems with it's scan motor resulting in image errors. The satellite recovered from that problem, but today the problem appears to be back and in a much worse way now.
NASA have put out a statement indicating that yet again it is a problem with the scan motor, and the problem could be permanent.
The NOAA-15 AVHRR Scan Motor current began showing signs of instability at approximately 0400Z on July 23, 2019. At about 0435Z the current rose sharply to about 302mA where it has remained. Scan motor temperature began rising about the same time and is currently steady at ~26M-0C. Black body temperatures dropped sharply at about the same time. The instrument appears to no longer be producing data. This behavior is consistent with a scan motor stall, but requires further investigation. Options for recovery are limited.
Having been launched in 1998 with a minimum spec of 2 years operation, NOAA-15 has already well outlived it's time and may finally be failing for real. We hope it will recover, but if not we should be thankful that Russian weather satellite Meteor M2-2 is now fully operational and transmitting beautiful high resolution images.
Reports from Reddit and Twitter are in that the recently launched Meteor M2-2 weather satellite is now functional and broadcasting images at 137.9 MHz. A few people have noted that the reception quality appears to be better than the older satellite.
Thank you to Happysat whose also provided the following information that can be used to receive the images. It appears that a slightly modified version of LRPTDecoder is required:
This version of LRPTDecoder was used to test/debug OQPSK with Meteor M-N2-1 in 2014, it will work on Meteor M-N2-2. The ini file attached in the archive is processed manually from s files. Buttons 72K and 80K respectively for the modes “without interleaving” and “with interleaving”. Also in the archive there are examples for other modes.
Transmissions on LRPT with a OQPSK Modulation are expected tomorrow on most probably 137.900MHz.
PICTOR is an open source and open hardware radio telescope that aims to promote radio astronomy on a budget. It consists of a 1.5 meter parabolic dish antenna, 1420 MHz feedhorn, a two stage low noise amplifier (LNA), high pass filter, and from what we gather, an RTL-SDR. Future designs may also use higher bandwidth SDRs. Currently there doesn't seem to be much information about the build and exact components used in their design, but we're hoping that those details will come in time.
The radio telescope allows a user to measure hydrogen line emissions from our galaxy. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). The emissions themselves are very rare, but since our galaxy is full of hydrogen atoms the aggregate effect is that a radio telescope can detect a power spike at 21cm. If the telescope points to within the plane of our galaxy (the milky way), the spike becomes significantly more powerful since our galaxy contains more hydrogen than the space between galaxies. Radio astronomers are able to use this information to determine the shape and rotational speed of our own galaxy.
PICTOR also has a very interesting web based interface which can be used to let users from anywhere in the world access the telescope and log an observation. The first PICTOR telescope is currently online and observations can be created simply by going to their website, and clicking on the "Observe" link. Users can then enter the frequency and other parameters for their observation, and the resulting graph will be emailed to you after the observation. The software source is available on their GitHub page, and is based on a GNU Radio flowgraph and Python plot script.
For more information about PICTOR, logging an observation, and radio astronomy in general, we recommend checking out their PDF guide. We test ran a short observation at the hydrogen line frequency, and we received a graph with the hydrogen line peak clearly visible (spliced in to the photo below). We note that the wavy shape is due the to shape of the filters they used.
Over on GitHub Ian Wraith has released his design and microcontroller code for a low cost 2.4 GHz downconverter circuit. A downconverter is a hardware device that shifts the signals that it receives into a lower frequency band. This is useful in the case of RTL-SDRs and Airspy SDRs, as their maximum frequency range is only 1.7 GHz. Ian's 2.4 GHz downconverter reduces those 2.4 GHz signals down to 1 GHz, which can then be received with his Airspy.
Rather than designing a circuit from scratch, Ian's design makes use of several very cheap Chinese evaluation/development boards that he found on eBay. It costs of a mixer board, oscillator board, and an STM32 development board for controlling the oscillator board via SPI. The whole set of hardware cost him less than £30 (~37 USD).
After spending some time working through the difficulties in programming the SPI interface on the STM32 board, he was able to get the downconverter circuit fully working. He notes that he's been able to receive WiFi, Zigbee, Bluetooth and ISM band signals at 2.4 GHz, as well as 3G and 4G cellular signals at 2.6 GHz.
This week on the SignalsEverywhere YouTube channel host Corrosive explores why impedance matching matters when trying to obtain the best reception possible. To do this he reviews the NooElec 1:9 Balun, which is designed to convert the (roughly) 450 Ohm impedance of a long wire antenna or ladder line dipole back down to 50 Ohms, which is the standard impedance that an SDR expects. Small amounts of impedance mismatch are negligible for RX, but larger mismatches can result in poor reception.
SDR Nooelec 1:9 Balun | Why Impedance Matters in Radio