Over on YouTube radio content creator Techminds has recently started a series that shows how to decode various signals using an SDR such as the SDRplay RSP1A. The first video explains what FT-8 is and shows how to decode it using the WSJT-X software. FT-8 is a modern digital HF ham mode that is designed to be receivable even in weak signal reception. However, the amount of information sent in a FT-8 message is small, so it is not possible to have a full conversation, and you can only make contacts.
In his second video Tech Minds explains RTTY and also shows how to decode it. RTTY is another much older mode that is used by the military as well as hams. To decode it he uses Digital Master 780 which is a program included in the Ham Radio Deluxe software.
Decoding FT-8 With WSJT-X And A SDRplay RSP1A SDR Receiver
Decoding RTTY With Digital Master And A SDRplay RSP1A SDR Receiver
Akos, author of his blog 'Radio for Everyone' has recently reviewed our new RTL-SDR.com Triple Filtered ADS-B LNA. In the review he compares our ADS-B LNA against another external ADS-B LNA by Uputronics and against the FlightAware Prostick and Prostick+. The tests use the external LNA's plugged directly into the dongle in order to more fairly compare against the FlightAware dongles which have LNA's built in to the dongles themselves. From his results the RTL-SDR.com ADS-B LNA appears to have near identical results with the Uputronics LNA, and slightly better results compared to the FlightAware dongles. Akos has not yet tested the main use-case of the LNA, which is to use it at the end of a run of coax cable, however he plans to do this in a future test. Also in his second post Akos shows how to build a simple amplified Coketenna using our ADS-B LNA.
On the subject of ADS-B performance we note that there are two ways to set up a system for optimal reception (apart from the antenna). The first is to place the computing and radio devices (such as a Raspberry Pi and RTL-SDR) as close to the antenna as possible (leaving a ~1m coax run to avoid local interference from the Pi). For this type of setup it is cheaper to use a FlightAware Prostick Plus RTL-SDR dongle since this has an ADS-B LNA built into it. However, the disadvantage is that you may need to set up a Power over Ethernet system, or find a remote power source, and possibly place the Pi in a difficult to service location such as in an attic or up a mast.
The second option is to use an external ADS-B LNA close to the antenna, and run coax down to the computing device which is positioned in a more accessible location. The LNA will negate any losses in the coax cable, and with high enough gain on the LNA, using quality coax is not such a high requirement since those losses are negated by sufficient LNA gain. Both methods will yield similar excellent performance.
Radio manufacturer Uniden have just released news about their latest product called the SDS100 which is a handheld software defined radio scanner specifically for digital voice and trunking modes. The scanner will retail for USD699, and aims to be released in the 2nd quarter of 2018 pending FCC approval. Note that certain software decoders will require paid upgrades, but it will be capable of all the major digital voice modes such as P25 Phase I and II, DMR, NXDN and trunking modes. It doesn't seem to support TETRA since it's marketed at the American consumer, however, it seems plausible that simple software update could enable this feature in the future.
As far as we know this is the first handheld scanner to incorporate SDR and is probably one of the bigger leaps in scanner technology to date. Compared to hardware based scanners, the SDS100 should provide significantly better decoding capabilities, even in weak signal and simulcast conditions. Simulcast is when multiple overlapping base stations transmit a signal at the same frequency. This can cause multi-path distortion problems, but an IQ based radio like an SDR is able to overcome these issues.
Uniden creates another first with the SDS100 True I/Q Scanner, the first scanner to incorporate Software Defined Radio technology to provide incredible digital performance in even the most challenging RF environments. The SDS100’s digital performance is better than any other scanner in both simulcast and weak-signal environments.
The SDS100 is also the first scanner that allows you to decide what to display, where, and in what color. Custom fields put the information important to you right where you need it.
And, one more first, the SDS100 meets JIS4 (IPX4) standards for water resistance.
The LA Times recently ran a story that discussed how vulnerable GPS is to malicious spoofing. This has been well known for a number of years now with researchers having been successful at diverting a 80-million dollar yacht off it's intended course 5 years ago. We've also seen GPS spoofing performed with low cost TX capable SDRs like the HackRF. For example we've seen researchers use GPS spoofing to cheat at "Pokemon Go" an augmented reality smartphone game and to bypass drone no-fly restrictions.
The article in the LA times also discusses how a group of researchers at Aerospace Corp. are testing GPS alternatives and/or augmentations, that improve resilience against spoofing. The system being developed is called 'Sextant', and it's basic idea is to use other sources of information to help in determining a location.
Other sources of information include signals sources like radio, TV and cell tower signals. It also includes taking data from other localization signals like LORAN (a long range HF based hyperbolic navigation system), and GPS augmentation satellites such as the Japanese QZSS which is a system used to improve GPS operation in areas with dense tall buildings, such as in many of Japans cities. More advanced Sextant algorithms will possibly also incorporate accelerometer/inertial data, and even a visual sensor that uses scenery to determine location.
Most likely a key component of Sextant will be the use of a software defined radio and from the photos in the article the team appear to be testing Sextant with a simple HackRF SDR. While we're unsure of the commercial/military nature of the software, and although probably unlikely, hopefully in the future we'll see some open source software released which will allow anyone to test Sextants localization features with a HackRF or similar SDR.
Thanks to Alex for submitting news about his new SDR# plugin called "SDRSharp.GpredictConnector". This plugin allows SDR# to interface with GPredict which is a tool used for tracking the orbit of satellites. Just like with the DDE Tracking plugin and the Orbitron satellite tracking program this plugin could be used to automatically tune SDR# to the frequency of a passing satellite using GPredict. It should also be able to compensate for any doppler shift frequency offset.
To use with SDR# simply download the zip file and move the .dll file into the SDR# folder. Then add the 'magicline' to the plugins.xml file using a text editor. In GPredict you can then add a radio interface from the preferences, and then use the 'Radio Connect' interface to connect to the plugin.
Connecting to GPredict using the GPredictConnector SDR# Plugin
To begin with Nexmon SDR you'll need a development environment set up on a Nexus 5 smartphone. Then it's a matter of downloading the dependencies, installing the Android NDK, and compiling Nexmon. IQ data can then be transmitted in code using from special system commands.
The Nexmon team have indicated on Twitter that they plan to present a paper with more information on Nexmon SDR at the MobiSys 2018 conference which will be held in June.
RTL-SDR dongles and other SDRs are often used on single board computers. These small credit sized computers are powerful enough to run multiple dongles, and run various decoding programs. Currently, the most popular of these small computers is the Raspberry Pi 3.
Just recently the Raspberry Pi 3 B+ was released at the usual US$35 price. It is an iterative upgrade over the now older Raspberry Pi 3 B. The 3B+ has an improved thermal design for the CPU, which allows the frequency to be boosted by 200 MHz. WiFi and Ethernet connectivity has also been improved, both sporting up to 3x faster upload and download speeds.
The Raspberry Pi 3 B+ Power over Ethernet Hat
The 3B+ also implements new Ethernet headers which allows for a cleaner Power over Ethernet (PoE) implementation via a hat. Previous PoE hats required that you connect the Ethernet ports together, whereas the new design does not. PoE allows you to power the Raspberry Pi over an Ethernet cable. The official PoE hat is not released yet, but they expect it to be out soon.
The faster processing speed should allow more processing intensive graphical apps like GQRX to run smoother, whilst the improved WiFi connectivity speeds should improve performance with bandwidth hungry applications like running a remote rtl_tcp server. PoE is also a welcome improvement as it allows you to easily power a remote Raspberry Pi + RTL-SDR combination that is placed in a difficult to access area, such as in an attic close to an antenna. Placing the Pi and RTL-SDR near to the antenna eliminates the need for long runs of lossy coax cable. If the Pi runs rtl_tcp, SpyServer or a similar server, then the RTL-SDR can then be accessed by a networked connected PC anywhere in your house, or even remotely over the internet from anywhere in the world.
Hydrogen tends to emit radio signals in the 21cm (1.4 GHz) region of the frequency spectrum. An emission from a single Hydrogen atom is very rare, but since there is so much Hydrogen in space a bump at 1.4 GHz can be observed on the frequency spectrum if a sensitive radio is used with a directional antenna pointing up at the sky. This is a moderate difficulty experiment that can be performed by amateur radio astronomers today with cheap RTL-SDRs or other SDRs together with some LNAs.
The astronomers in this experiment focus on a distortion in the 21cm line signal that is expected to have been created when the first stars formed. The their paper they write:
After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz.
The results show a successful detection of the expected phenomena at 78 MHz, confirming the age at when the first stars have been predicted to have begun forming. The phenomena is detected at 78 MHz instead of 1.4 GHz because the wavelength of a Hydrogren line signal gets stretched the further the source is from us, due to the redshift doppler effect from the expansion of the Universe. This detection is from some of the furthest (and thus oldest) stars in the Universe, so a big stretch is expected.
The experiment consisted of a broadband blade dipole which was set up in the Australian outback. Since the cosmic signal is expected to be detected right in the middle of the broadcast FM band, a dedicated radio-quiet location is required to stand any chance of detection. The receiving SDR hardware consists of an LNA, line amp, filtering and a 14-bit ADC that is connected to a PC.
It seems possible that this experiment could be repeated by amateur radio astronomers with commercial SDR hardware, but the biggest challenge would probably be finding a very radio-quiet location without broadcast FM radio signals.
The 78 MHz Cosmic Signal SDR Detection SetupDipole antenna with 30mx30m ground plane
