Recently GitHub user randaller released a piece of software that utilizes the RTL-SDR and neural networks for RF signal identification. An artificial neural network is an machine learning technique that is based on approximate computational models of neurons in a brain. By training the neural network on various samples of signals it can learn them just like a human brain could. A neural network trained on signal classification can then be used by anyone to identify unknown signals. Randallers neural network software can learn either from raw IQ data, FFT processed samples, slightly demodulated data, or demodulated audio data. The tensorflow machine learning library is used as the base code, and the deep learning technique is used.
At the moment the software is only really proof of concept, and the currently trained model is only able to identify WFM, TV SECAM Carriers and TETRA. It should be possible to train the network further by providing your own samples too, but a good graphics card is required for this as the software makes use of GPU processing for training. The output of the software is a percentage which shows how confident the neural network is that it is identifying a signal correctly.
Last week we posted about some interesting conference talk videos from GNU Radio Con 17. One of the videos was a talk by Sam Whiting who in conjunction with colleagues Dana Sorensen and Todd Moon from Utah State University have created an Android app that uses two coherent RTL-SDR dongles for direction finding. A coherent RTL-SDR can be created simply by removing the clock on one RTL-SDR and connecting the clock from another, so that they both share the same clock. The V3 RTL-SDR has a clock selector header which can be used to facilitate this as well.
Over on his YouTube account Sam Whiting has uploaded two videos showing the app in action. The backend GNU Radio code for direction analysis is available on GitHub, but unfortunately the Android code/apk is not available to the public as the code is owned by the funders of the project.
In the videos the app shows two arrows, one of which points towards the source of a transmission at a frequency that is being monitored. The second arrow is simply there due to the direction ambiguity produced by the methods used.
A slinky is a fun little toy that is essentially a long and loose spring. You can perform tricks with them, but the most iconic use is making them walk down stairs all by themselves. Over on Hackaday we've seen a tutorial that shows how to use a slinky as a good antenna for the 80m (3.5 MHz) band. Using a slinky as an antenna is nothing new to hams, but the original post on imgur shows some pretty clear photos and instructions on how to construct one.
The text written by the original poster on imgur notes that he uses this antenna very successfully with his RTL-SDR in direct sampling mode and this even outperforms his regular shortwave radio. He notes that slinkies aren't weather proof, so some sort of weather proofing spray coating or oil might be useful for a permanent set up.
If you are interested apart from the discussion on Hackaday there is also a comments thread on Reddit where the original poster discusses what he purchased.
Over on the SDRplay forums there has been a post by a NOAA engineer showing how they are using SDRplay RSP2 units in the field for tracking their radiosonde weather balloons. A radiosonde is a small sensor package and transmitter that is carried high into the atmosphere by a weather balloon. It gathers weather data whilst transmitting the data live back down to a base stations. You can get data such as temperature, pressure, humidity, altitude and GPS location.
Bobasaurus' coworker launching a weather balloon.
The NOAA engineer on the forum (handle 'bobasaurus') wrote SkySonde, which is the software used by NOAA to decode and plot data from the radiosondes. SkySonde is freely available for public download on the NOAA website. A PDF file showing how to use the SkySonde software with an RSP2 or RTL-SDR can be found here, and the full SkySonde manual is available here. The software consists of a client and server, with the server connecting to the RSP2 or RTL-SDR, and then sending data to the client. Both server and client can run on the same PC.
The hardware setup consists of an RSP2 (can be interchanged with an RTL-SDR), an Uputronics Radiosonde Filtered preamp and a Yagi antenna. Presumably a Yagi and LNA is not completely required, although the receivable range will be less. The RSP2 bias tee is used to power the preamp, and on a V3 RTL-SDR the bias tee should also work.
NOAA appears to use the iMet brand of radiosondes which transmit a Bell 202 signal. Bobasaurus writes that they transmit in the 401-405 MHz range. This video shows an example of such a signal. If you are in the US near an area that launches these iMet weather balloons you should be able to receive them. An alternative piece of software that supports iMet radiosondes is RS. For other radiosondes we have a tutorial that uses SondeMonitor available here.
Like the HF+ mentioned in the previous post, the RSP1A SDR was also recently released and has now had enough time in the wild to gather up a few online reviews. If you didn't already know, the $99 US SDRplay RSP1A is a revision of the RSP1. Compared to the RSP1 it significantly improves the filtering and front end design. We have our own review of the RSP1A unit here, and we mentioned some early reviews from other bloggers in this linked post. Below we post some of the new reviews that we are aware of which have come out since our last post.
Robert Nagy
In his video Robery Nagy does a full review of the RSP1A including a 15 minute primer on SDRs. This is great if you want a brief introduction to understanding how SDRs actually work, and what performance measures are important for comparing them. In the second half of the video Robert shows how to use SDRuno and shows the RSP1A in action.
SDRplay RSP 1A Review and SDR Primer
Mile Kokotov
In this video Mile Kokotov demonstrates the HF+ receiving a CW contest in his home country of Macedonia with the RSP1A and a full-size half wave resonant dipole antenna. He writes:
CQ World Wide DX Contest (CW) receiving in Macedonia with SDRplay RSP1A SDR-receiver and SDRuno software on 80m-Band with full-size half-wave (40 meters long) resonant dipole antenna.
Contest conditions are always big challenge to any receiver dynamics. Here you can see only 60 kHz wide frequency spectrum fulfilled with many competitor stations "fighting each other". In addition, there are local radio-station (only 1 km from my place) with huge signal...
RSP1A SDR receiver and SDRuno software - CQ World Wide DX Contest (CW) 2017
The Radio Hobbyist
In The Radio Hobbyist's video on YouTube Rick (VE3CNU) unboxes his RSP1A and shows the setup and download of SDRuno. He then goes are demonstrates reception on various signals.
Introducing the RSP1A
icholakov
In icholakov's video on YouTube he compares the older RSP1 with the newer RSP1A on medium wave and shortwave reception using a dipole in a noisy suburban RF setting. Differences are hard to detect as the signals he tests with are not likely to cause any overloading issues, but the RSP1A does seem to have a slightly less noise.
The new Airspy HF+ SDR receiver has now been shipped to multiple customers and reviewers, and new reviews are coming online fast. If you weren't already aware, the Airspy HF+ was a hotly anticipated low cost, but high performance HF speciality SDR receiver. The claims are that it can compete with the high end $500 US+ units. We have our own review of an early model here. Below are some new reviews that we are aware of.
Nils DK8OK's photo of the Airspy HF+.
Nils Schiffhauer - DK8OK
On his blog Nils presents us with a comprehensive set of audio recordings comparing the $525 US Elad FDM-S2 with the $199 US Airspy HF+. He compares the two receivers on various shortwave broadcast stations, time stations, and an airport VOLMET. The recordings are identical, with the two radios recording the same signals simultaneously via a splitter.
Both receivers produce excellent results so you will probably need headphones and keen ears to be able to tell the difference.
Mile Kokotov
In this review YouTube video Mile Kokotov presents a comparison of the Airspy HF+ vs. the ColibriNANO, a similarly specced SDR dongle. He writes:
In this video I am comparing two high quality SDR Receivers: Airspy HF+ and ColibriNANO. They both have 16 bit Analog-to-Digital Converter. Comparison was made with the same overall conditions.
For example, both receivers was set with equal size spectrum windows, with the same amount of decibels in their scale, and the same high of the spectrum windows. ColibriNANO has LNA gain slider which was set to maximum SNR.
Airspy HF+, on the other hand, has no LNA gain control. The SV2HQL/Beacon was chosen as a test signal on 3579.32 kHz (on 80m band)
Antenna is half-wave resonant Dipole (40 meters long) for 80m band.
In the second part of the video I was inserted 27 dB external Attenuator on both receivers. ColibriNANO automatically increased the LNA gain and sets itself to maximum SNR. With this amount of attenuation, The Airspy HF+ noise floor level was at about the same place in spectrum window like ColibriNANO, Unlike in the first part of the video, when no external attenuator was used.
Both SDR-receivers are very good! Which is better? I leave on you to judge...
Airspy HF+ vs ColibriNANO Comparison on 3.579 MHz
Mile also does a second test with his HF+ and an active Mini-Whip antenna. He writes:
Airspy HF+ is superb High-Dynamic HF and VHF SDR-receiver and I am impressed with it. In order to minimize possible negative effect on signal path from antenna connector to tuner input, Airspy HF+ has no internal attenuator. Developers takes in account that this SDR-receiver has enough dynamic range that is very difficult to overload it. Actually it is true for most cases. But, if we want to use some type of active antenna (with internal amplification) like Mini-Whip Active Antenna for example, it is good idea to add an external attenuator between antenna and receiver HF-input connector, in order to have opportunity to lower the signal level from the active antenna, and to avoid possible overload issues. In this video I am presented some scenario (receiving MW AM band) when my homemade external step-attenuator is more than welcome! By the way, the external step-attenuator is very easy to made in almost no money. All you need is 9 resistors, three switches and one metal box) I have 5.5 dB switch, 10.5 dB switch and 22 dB switch. It can be set for 8 various combinations: 0, -5.5 dB, -10.5 dB, -16 dB, -22 dB, -27.5 dB, -32.5 dB and -38 dB.
You can see on this video that the AM Broadcast signal from Macedonian Radio on 810 kHz is very strong. The Antenna is about 30 km from my house. It is self standing huge 185 meters high vertical antenna, radiating enormous RF-power, so I have to use my homemade attenuator I mentioned it before.
Airspy HF+ SDR Receiver with Mini-Whip Active Antenna and External Attenuator
The SWLing Post Blog
Here Thomas of the SWLing post blog has posted a brief review of his HF+ unit. He notes how the HF+ is very compact, with a durable enclosure and how easy it was to set up with it being completely plug and play. So far Thomas hasn't fully evaluated the performance, but his first impressions are good.
Adam 9A4QV
In his two videos Adam doesn't directly review the Airspy HF+, but he does show some pretty impressive reception with his Skyloop antenna.
CQWW-2017 the end of the contest AirspyHF+
CQWW-2017 using AirSPY HF+ and 250 feet long skyloop antenna
GRCon17 is the yearly convention all about GNU Radio and the talks are generally all about technical cutting edge developments in the software area of the SDR world. If you didn't already know, GNU Radio is an open source tool that makes implementing digital signal processing code significantly easier by providing a framework and several ready to use DSP blocks. It is an advanced tool used a lot in industry and research, but the visual nature of the blocks means that the basics can be easily learned in a few days. See Micheal Ossmans video tutorials for an excellent introduction.
This year at GRCon17 there were multiple interesting talks, and over the last few days videos of them have been released on YouTube. Slides for each presentation are also available in the YouTube description boxes. The full list of presentations can also be found on the Technical Processing page at GNURadio. A selection of our favorites videos are presented below, with several talks utilizing low cost RTL-SDRs as the core radio in the research.
GPS Beamforming with Low-Cost RTL-SDRs - Wil Myrick
In this talk Wil Myrick discusses how he's been using low cost RTL-SDR dongles to perform beamforming experiments with GPS signals.
GRCon17 - GPS Beamforming with Low-Cost RTL-SDRs - Wil Myrick
Real-Time Direction Finding Using Two Antennas on an Android Phone - Sam Whiting
In this talk Sam Whiting shows how he used two coherent RTL-SDR dongles running on on an Android phone for direction finding. At the end of the video he demonstrates his results.
GRCon17 - Real-Time Direction Finding Using Two Antennas on an Android Phone - Sam Whiting
Hacking the Wireless World 4.0 - Balint Seeber
In this video Balint Seeber continues with his popular Hacking the Wireless World series of talks and this time talks about FMCW & Passive Radar and FPV decoding with SDRs.
GRCon17 - Hacking the Wireless World 4.0 - Balint Seeber
Over on his blog 'Radio For Everyone' Akos has been testing out our multipurpose dipole kit for ADS-B reception. He goes over each of the components in the kit and does some tests with the kit set up outside. His results show that the dipole kit when used with the smaller antennas can compete favorably with the more expensive FlightAware antenna. We note that the dipole antenna is not designed to be used outdoors for extended periods of time as Akos did as they are not weather proofed for rain. The antennas are designed to be used temporarily outside in good weather conditions. Waterproofing could potentially be achieved by oiling the metal, or potting with hot glue etc.
Akos also does a comparison of the dipole used in two configurations. In one configuration the antenna is used in the recommended vertical orientation, and in the other position in a bunny ears configuration. Antenna theory says that the vertical orientation will work best as ADS-B signals are vertically polarized, and the results confirm that that is true.
