Over on YouTube Andreas Spiess has uploaded a video titled "How does Software Defined Radio (SDR) work under the Hood?". The video is an entertaining introduction to how software defined radio works and begins from the beginning by explaining how basic analogue radios work with components such as modulators, demodulators, frequency generators, mixers and filters. After the basics he goes on to explain the digitization of radio signals that occurs in SDRs, and gives an introduction ADCs and how IQ sampling works.
Later in the video Andreas shows various applications for SDRs, discusses various SDRs on the market like RTL-SDR, HackRF, SDRplay, LimeSDR and PlutoSDR and introduces GNU Radio Companion and other SDR programs from our big list of software post.
#286 How does Software Defined Radio (SDR) work under the Hood? SDR Tutorial
Over on YouTube TechMinds has uploaded a video showing how to use the Iridium Toolkit software to receive data and audio from Iridium satellites with an Airspy. Iridium is a global satellite service that provides various services such as global paging, satellite phones, tracking and fleet management services, as well as services for emergency, aircraft, maritime and covert operations too. It consists of multiple low earth orbit satellites where there is at least one visible in the sky at any point in time, at most locations on the Earth.
The frequencies used by the older generation Iridium satellites are in the L-band, and the data is completely unencrypted. That allows anyone with an RTL-SDR or other SDR radio to decode the data with the open source Iridium Toolkit. If you're interested in how Iridium Toolkit was developed, see this previous post about Stefan "Sec" Zehl and Schneider's 2016 talk.
In the video Tech Minds shows decoding of various data, including an audio call and the satellite tracks and heat map of Iridium satellites.
We just wanted to note that this Monday the reduced preorder pricing of US$130 + shipping will end, and the price will rise to the retail price of $149.95 + shipping. So if you have been thinking about ordering a unit, now would be a good time. Ordering is currently possible through Indiegogo. On Monday we will change to our own store. EDIT: Now available to purchase on the Othernet Store.
For shipping, US orders will be sent domestically from Othernet's office in Chicago. They are still waiting on the US shipment to arrive, but it is expected to arrive by the end of next week. Once shipped locally you will receive a shipment notification.
For international orders, the packages are being labelled now, and should be going out early next week, or sooner.
KerberosSDR Inside and Outside the Enclosure
Future Updates to KerberosSDR
With the profits raised from KerberosSDR sales we are looking to continue funding development on the open source server software and visualization software being created (as well as applying updates ourselves). In future updates we will be looking at features such as:
Streamlining the sample and phase sync calibration process.
Experimenting with software notch filters for calibration (may reduce the need to disconnect the antennas during calibration).
Reworking the buffering code for improved sample ingestion performance and increased averaging.
Direction finding and passive radar algorithm improvements.
Creating a networked web application for combining data from two or more physically distributed KerberosSDRs over the internet for immediate TX localization.
Updates and bug fixes for the Android mobile direction finding app for use in vehicles.
Improving passive radar to be able to use all four RX ports for surveillance so that larger areas can be covered.
Plotting passive radar pings on a map.
Beginning experimentation with beam forming.
In the farther future we hope to eventually have even more clever software that can do things like locate multiple signals in the bandwidth at once, automatically plot them on a map, and track them via their unique RF fingerprint, or other identifiers.
Future hardware updates may see more streamlined calibration and smaller sizes.
Over on Reddit user u/isysopi201 has put up a fun post showing what an RTL-SDR Blog V3 looks like under an X-Ray machine. With the full resolution images, it is possible to see the PCB traces in internal planes, the windings on the electrolytic capacitor, inductors, USB choke and direct sampling matching transformer, as well as the bond wires on the RTL2832U and R820T2 silicon chips that connect the pins to the silicon.
Thank you to Nils Schiffhauer (DK8OK) for submitting an article documenting his tests on the Airspy HF+ Discovery (pdf mirror). Spurred on by discussions on the SDR-Console mailing list, Nils went looking for issues with spurious signals generated by the HF+ itself. In the end he finds some minor spurious signals, but notes that they have absolutely no adverse effects once an antenna is connected.
Youssef Touil (developer of the Airspy HF+ line of products) has also noted that the minimum discernible signal (MDS) of the HF+ is so low that it's become normal for very weak spurs to now be visible without an antenna connected. However, once an antenna is connected the natural atmospheric noise floor which is much higher than the MDS hides these spurs, and so the spurs have no consequence on reception.
In Nils' first test he uses a very high end Winradio W65DDC SDR to detect the spurs coming from an Airspy HF+, Airspy HF+ with preselector retrofit, and the Airspy HF+ Discovery. The results are quoted below:
[With the Airspy HF+] you indeed see a very few spurious signals, all well below -140 dBm/Hz.
With the Airspy HF+ Preselector connected, the number of spurious signal is very much reduced, as is their maximum level.
This picture still further improves with the Airspy HF+ Discovery connected: all visible seven spurious signals are measured to well below -150 dBm/Hz.
The first result is clear:
Airspy has improved also the spurious signals from model to model, landing at a stunning reduction with their matchbox-like Discovery.
The spurious signals were significantly reduced in both numbers and level.
Together with sensitivity and dynamic range, the performance of these SDRs is exceptionally good. If you see their price tag, they are a real bargain.
Overall: they deliver professional performance in every important aspect at an incredible low price.
In the second test Nils tunes to the center of a spur, then tested with a dummy load and then antenna connected. His results showed that all spurs disappeared once an antenna was connected. He summarizes below:
Yes, there are a very few and low-level spurious signals at all Airspy’s receivers – as they are found [much] worse at some competing SDRs.
By development, even this has been significantly improved from model to model with the new Discovery leading the gang.
All spurious signals disappear with an antenna connected.
There has been found no case where, in practice, any spurious signal even remotely touched or even limited reception of the most miniscule signals.To complain about “spurious signals” simply is “Much Ado about Nothing” in an Ivory Tower, far away from any practical application.
Nils also tested 7300 kHz reception and the co-existance of weak amateur radio signals with strong broadcast signals.
Thank you to Zoltan for submitting a short post about using a moRFeus to uplink WSPR to the Es'Hail-2 (QO-100) geostationary satellite with amateur radio repeater. moRFeus is a versatile US$99 signal generator and frequency mixer that can be controlled either by it's built in LCD screen, or via software on a Windows or Linux PC. It can generate a clean low phase noise tone anywhere between 85 to 5400 MHz, and can be used as a mixer for upconverting or downconverting signals. We have discussed moRFeus a few times before on this blog as we think it's a useful tool.
In his setup, Zoltan uses a QRP Labs U3S WSPR transmitter kit that was configured to transmit WSPR at 2m (144 MHz). It is not designed for transmitting the 2.4 GHz QO-100 uplink frequency. To get around that limitation, the moRFeus is used to upconvert the 144 MHz frequency into the QO-100 uplink band by mixing it with a 2,255,634.309 kHz signal. The resulting 2.4 GHz output signal from moRFeus is sent to an amplifier, 2.4 GHz band pass filter, and finally into a 5-turn LHCP helical feed mounted on a 1m parabolic dish.
Successful uplink was confirmed by a UK based WebSDR receiving the QO-100 downlink. Zoltan estimates that the total output power was only 4mW, and actually more like 1-2 mW due to losses in the coax feed.
Rodrigo's system consists of an IF tap amplifier+filter board that is connected to an internally mounted RTL-SDR. The RTL-SDR is internally connected to the FT-991A's USB hub which had to be upgraded from a 2-port hub to a 4-port hub as the 2-ports were already in use by the CAT and Audio features. This required the stock USB hub IC to be replaced with a hot air rework station.
Everything is mounted inside the radio chassis itself, and the end result is a neat solution with no external wires, hubs or dongles that has essentially turned the FT-991A into an SDR. Plugging in the single stock USB cable from the FT-991A results in the standard CAT and Audio interfaces showing up, as well as the RTL-SDR.
What's also interesting is that Rodrigo makes use of the GPIO pins on our RTL-SDR Blog V3 to enable the RX_EN, BPF and BYPASS switches on the IF tap board. This allows for a cleaner solution as no external switches need to be installed.
The entire project is open source with schematics and the BOM provided over on the GitHub, and excellent documentation is available on the project's Wiki.
FT991A Converted into an SDR.
Turning FT-991A to a REAL SDR: Embedding a SDR Panadapter INSIDE the radio, no extra wires!
This week on the SignalsEverywhere YouTube channel Harold shows us the mobile SDR and ham radio setup that he's installed on his car. On the roof of his car he's installed several antennas for various amateur radio bands including the 1.25m, 2m, 70cm, 33cm bands, a modified GPS puck antenna for Inmarsat and Iridium reception, and an antenna and GPS pick dedicated for APRS.
Inside the vehicle is a Windows tablet attached to the dashboard which is used for APRS, remotely controlling a scanner radio stored in the trunk and for running SDRSharp. There is also an Android unit installed in the center console which has an RTL-SDR connected. The Android unit runs RF Analyzer, and an ADS-B decoder. As well as SDRs, Harold also runs several standard ham radios within the vehicle.
