The Distributed Ground Station Network

Over on hackaday.io there is a project blog for the “Distributed Ground Station Network”. This is essentially an idea to build a large network of distributed RF receivers which automatically receive signals from sources like cube satellites and other beacons. The project mainly uses RTL-SDR dongles at the moment for their RF receivers. In some ways it appears to be similar to the SatNOGs project which won the hackaday prize two years ago but the DGSN appears to be more focused on “reverse GPS” which allows the detection and tracking of the location of small satellite signals through distributed receivers.

They write:

The Distributed Ground Station Network (DGSN) is a novel network concept of small ground-stations and connected via the internet for performing automatic scans for cubesats and other beacon signals. By correlating the received signal with the precise, GNSS synchronized reception times of at least 5 ground stations, it enables the positioning of the signal’s origin. Thus a global tracking of small satellites becomes possible in this “reverse GPS” mode. It allows mission operators to position and track their small satellites faster after piggy-back commissioning, when the final orbit is yet undefined and could differ from the specified orbit. Furthermore it allows permanent communication in “data-dump” mode. In this mode, DGSN ground-stations relay the received data to the servers and thus to the operator.
Let’s track everything, together!

Recently they have made several interesting update posts. In one post they show a video demonstrating automatic detection of a cubesat signal.

automatic cubesat signal detection (DGSN node #0)

In another post they show a timelapse video showing one day of radio contacts via the International Space Station.

one day of radio contacts by the International Space Station

Finally in their latest post they show how to use the GRAVES radar in France to detect the ISS and meteorites showers.

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Natpos: New Linux SDR Software for the RTL-SDR

Natpos is a new Linux based SDR program similar in operation and features to other programs like GQRX, HDSDR and SDR#. At the moment Natpos only works with RTL-SDR receivers as it runs via the rtl_tcp interface. The software demodulates the standard AM/FM/SSB signals and has a frequency scanner that automatically tunes to the strongest signal. There is a discussion over on Reddit regarding the software, and there the author writes about his favorite features as follows:

The thing I like most is that I can replay past transmissions by clicking in the waterfall history. Using other SDR software, when a new transmission pops up, I feel like I’m in a race to tune to it before it ends so that I can at least hear some of it, but in my software, I don’t even have to pay attention to what’s happening now, and so I seldom do. Usually I don’t notice transmissions on new frequencies until they’ve ended, but I still get to listen to them.

I also put some effort into trying to make sure AM and FM transmissions were equal in volume, as well as at the correct volume according to how well they were modulated, in that I aimed for 100% modulation leading to audio output that’s 6 dB below the ceiling. It seemed as if it was quite random in other software, as switching from AM to FM might cause a huge jump or drop in audio volume. I don’t like to play with my volume controls, so I did my best to make it so that I don’t have to.
I’m also not at all fond of the “click the numbers” method of changing the center frequency which seems to be so common. So in mine, I just type in the MHz on the number keypad and press enter.

I’m also much more fond of my waterfall coloring scheme than any other I’ve seen. It seems much smoother and more informative, at least to me anyway. I suppose that’s rather subjective.

…but it’s rather hard to compare it to other software given that I only got to use other software for two or three days. I rather soon knew I wanted to write my own, and I wanted to use the V4L2 API (that dvb_usb_rtl28xxu module you have to blacklist to use rtl-sdr is an SDR driver, not a video driver), but I had to upgrade to Linux Mint 18 to get access to it since it’s a new API, and after doing so, I haven’t been able to get any of the existing SDR software to both compile and work after it’s compiled. So I just focused on writing my own, since I was wanting to do so anyway. (No support for that V4L2 API though, as it turns out its buggy and offers no way to control the dongle’s gain, so it’s basically unusable.)

Natpos SDR Screenshot
Natpos SDR Screenshot

The Titus II Complete SDR Solution

Recently we’ve heard news of a new portable SDR called the PantronX Titus II which is currently in development. The receiver is a full SDR solution, including the computer, speakers, antenna and SDR all in a single boombox styled enclosure. The computer appears to be based on an Android tablet, and comes with a Quad-core ARM A53 @ 1.2 GHz CPU, 1 GB RAM, 8 GB Flash memory, 7″ TFT screen, touch screen, 5 watt stereo audio, li-poly battery. HDMI output, microUSB OTG connector, WiFI/Bluetooth connectivitiy as well as having an optional camera. 

The frequency range extends from 100 kHz to 2 GHz, and the built in software is capable of decoding AM/FM/SSB and DRM. Since it is essentially an SDR with an Android tablet, it should also be capable of decoding any other signal, as long as software decoders are written for it. We are unsure what SDR is used on the inside, but judging by its frequency range we speculate that it may be the same Mirics chips that are used inside the SDRplay RSP.

Rumour currently has it from word of mouth of the developers that this unit will priced “well below $100 USD”.

The promotional PDF can be found here.

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RTLSDR4Everyone: Review of the FlightAware ADS-B RTL-SDR

Akos from the RTLSDR4Everyone blog has recently uploaded a review of the FlightAware ADS-B ProStick RTL-SDR dongle. The FlightAware (FA) dongle is a standard RTL-SDR with SMA connector, but with a very low noise figure LNA built into the front end. This low noise figure helps improve the SNR of ADS-B signals, resulting in more decodes and further range. We previously reviewed the FlightAware dongle in our own review available here.

In his post Akos reviews the FA dongle on its use as a general RTL-SDR as well as an ADS-B receiver. His review is initially critical to some of the misinformed advertising claims made by FA. He then goes on to show some noise floor scans and some ADS-B reception comparisons. Finally he shows some modifications that can be made to improve the cooling of the PCB.

He concludes that the FA ProStick works very well on improving ADS-B performance, but that overloading due to the increased gain is common.

prostickreview_akos2

Introduction to Signal Analysis Class in Baltimore-DC

A four week free class on signal analysis using SDR’s like the RTL-SDR will be taking place in the “Unallocated Space” technology community center in Baltimore-DC area. It starts on Tuesday September 20, 2016 at 7pm to 10pm. The class will help participants set up their systems, and cover locating, identifying, demodulating, and decoding common RF signal types. On the final week they will host a wireless capture the flag competition, where students will use their skills to solve problems and earn points.

You will need to bring your own SDR hardware such as an RTL-SDR, as well as an omnidirectional antenna and a PC/laptop capable of running your SDR.

RFTap: A Bridge Between GNURadio and Wireshark

Recently a new Linux based tool called RFTap has been released. RFTap acts as a bridge between GNURadio flow graphs and Wireshark. GNU Radio is a visual based programming environment for digital signal processing applications, such as RF signal decoders. GNURadio supports many different SDR’s including the RTL-SDR. Wireshark is a network packet analyzer/dissector that aides with troubleshooting and analysis of network protocols. RFTap also supports other DSP languages like Pothos, liquidsdr, LuaRadio as well as other packet analyzers like TShark, tcpdump, Scapy.

The author has already released three RFTap tutorials/demos. The first shows how to decode Radio Data System (RDS) and use RFTap and Wireshark to dissect each packet. The second shows how to use RFTap and Wireshark to detect MAC spoofing on WiFi networks. For that tutorial you will need a more advanced SDR that can tune to the 5 GHz WiFi frequencies and receive the full WiFi bandwidth of 20 MHz. The third tutorial shows how to use RFTap to analyze Zigbee packets.

RFTap acts as the glue between GNURadio and Wireshark
RFTap acts as the glue between GNURadio and Wireshark

CubicSDR Updated to Version 0.2.0

CubicSDR is a relatively new SDR program, which is similar in operation to programs like SDR#, HDSDR and SDR-Console. Recently CubicSDR has been updated to V0.2.0. This version seems to be a new stable version which incorporates many changes and improvements built up over the past months. Currently CubicSDR supports the following SDR’s:

  • SoapyRemote
  • RTL-SDR
  • AirSpy
  • SDRPlay** (only AppImage supported for Linux currently)
  • HackRF
  • BladeRF
  • Red Pitaya
  • Audio Devices
  • UHD (OSX / Windows Only)
  • RFSpace (OSX Only)

CubicSDR_Logo1

A Video Explaining LNA Noise Temperature Calculations

Over on YouTube Adam 9A4QV (creator of the LNA4ALL and other products) has uploaded a video that explains Friis formula for noise, using simple calculations and theory. These calculations explain why an LNA can significantly help reception on L-Band with an RTL-SDR. In his video he uses graphs and tables provided in this document released by the US Naval Academy. At the end of this post we attached images of the graph and table that he uses in the videos calculations for easy access.

The calculations show how the noise figure and gain of the first LNA in the system dominates the result. The final result of his video shows that using an LNA with a noise figure of 1 dB and 16 dB gain can give an improvement in SNR of about 7.8 dB over a standard RTL-SDR which has a noise figure of 6 dB. This is the improvement on L-band from simply placing the LNA by the dongle, and it does not take into account the extra improvement that could be had by placing it by the antenna, if a run of coax is used. The equations can also be adapted to other frequencies, and they show that as the frequency decreases, the effect of the noise figure of the LNA becomes less important.

ant_noiseratios