RTL-SDRs and the VHF+ Reverse Beacon Network

The Reverse Beacon Network is a project that monitors the amateur radio bands by using volunteer stations to continuously and autonomously collect data on what/when stations are being received, and how good the signal is. The data is made public on the internet and this allows amateur radio operators to easily determine overall propagation conditions. It is currently working mostly with CW (morse code) stations, and mostly on HF, although it is expanding to VHF+ as explained below.

During October, John Ackermann (N8UR) did a talk at the "Microwave Update 2018" conference held in Dayton, Ohio. His talk was about setting up a VHF+ reverse beacon network monitoring station, using multiple RTL-SDR dongles for monitoring. The RTL-SDR dongles run on a Raspberry Pi which runs the rtl_hpsdr software. This allows multiple RTL-SDR dongles to emulate a multi-band HPSDR receiver over Ethernet. They can then be accessed on a PC by the CW Skimmer program which decodes the received CW signals, and then logs it online on the reverse beacon network's website.

The talk slides can be found here, and the video is shown below. More talks from the conference can be found on this YouTube playlist.

Four RTL-SDR.COM V3 dongles used in a VHF+ Reverse Network Setup
Four RTL-SDR.COM V3 dongles used in a VHF+ Reverse Network Setup
John Ackermann, N8UR - The VHF+ Reverse Beacon Network

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Amazon AWS Satellite Ground Stations Now Available For Hire

Over on the AWS blog Jeff Barr has blogged about Amazon's new rentable ground station system called "AWS Ground Station". AWS, or Amazon Web Services is the server farm division of Amazon. They allow customers to rent out server capability on demand. In a similar sense, AWS Ground Station is aiming to allow customers to rent out satellite ground stations on demand.

Launching low cost micro/nano satellites has become very affordable in recent years and it's now common to see high schools, colleges, organizations and hobbyists designing, fabricating and launching their own satellites. Once launched, a ground station is required to receive the satellite's radio transmission as it passes over. Most low cost satellite owners will not have the budget to deploy ground stations all around the world for continuous monitoring of the satellite. This is where AWS Ground Station can take over, allowing a ground station on the other side of the world to be rented temporarily during a pass.

Currently the service is just starting, and only has 2 ground stations, but by 2019 they hope to have a total of 12. More information available on the official AWS Ground Station website.

Alternatively, there are other free open source services that could be utilized such as SATNOGS. SATNOGs relies on volunteer ground stations running antenna rotators that can be built with a 3D printer, some low cost motors and electronics, and an RTL-SDR. The antenna rotator carries a Yagi antenna and will automatically track, receive and upload satellite data to the internet for the public to access.

AWS Ground Station Web Site
AWS Ground Station Web Site
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Element14 Video on Setting up a Portable Raspberry Pi & RTL-SDR Based NOAA Weather Satellite Receiver

Electronics distributor element14 has uploaded a video to their 'element14 presents' YouTube channel showing presenter Matt building and setting up a portable Raspberry Pi & RTL-SDR based NOAA weather satellite receiver. More information is also available on their supplemental content page.

The build consists of a Raspberry Pi, RTL-SDR and QFH antenna as the basic components. However, it is made into a very nice portable unit by using a stripped down LCD monitor placed into a heavy duty waterproof brief case. The whole thing is powered via a PC power supply. After the build is completed, Matt leaves the case on the roof for a few days collecting images.

Emboldened by the success of his Raspberry PIrate radio, Matt indulges in some more radio hacking by building a specialized QFH antenna and a briefcase form-factor satellite receiver in an attempt to intercept "faxes" from OUTER SPAACEEE!!! Connect with Matt on the element14 community: http://bit.ly/2RiSXC5

Project TIROS is a self-contained, Raspberry Pi-based satellite signal reception system designed to automatically download images and data from NOAA's POES spacecraft as they pass overhead and display the data on an integrated LCD panel. In this video, Matt will walk through how to set up an RTL-SDR module with a Raspberry Pi for automated satellite downloads as well as how to design and build a quadrifilar helical antenna for polar-orbiting signal reception.

Raspberry Pi NOAA Satellite Receiver

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Watching DVB-T TV and Using SDR Mode at the same time with two RTL-SDRs

Normally if you want to use the RTL-SDR as an SDR on Linux you install the SDR drivers, and blacklist the Kernel's built in DVB-T drivers to prevent them from taking over the RTL-SDR. Once blacklisted, no RTL-SDR plugged into that system can be used for DVB-T watching unless the blacklist is removed. But if the blacklist is removed, SDR mode cannot be used. So it's impossible to use one RTL-SDR as an SDR, and one for DVB-T TV at the same time.

However now, Hayati A. has submitted news about his RTL-SDR driver patch which allows you to run SDR mode and DVB-T TV mode at the same time with two RTL-SDR dongles.

The idea behind allowing two dongles to operate in separate modes is that one dongle needs to have the PID code stored in its EEPROM changed to a code which was recently registered by Hayati. The dongle with this PID code won't be recognized as a DVB-T device by Linux, and so can only be used for SDR. An dongle with the stock EEPROM can then be plugged in and used for DVB-T.

The patch has been accepted into the development branch of the librtlsdr drivers and the Readme notes read:

  • A special USB vendor/product id got reserved at http://pid.codes/ : 0x1209/0x2832 
  • for such devices the linux kernel's DVB modules are not loaded automatically, thus can be used without blacklisting dvb_usb_rtl28xxu below /etc/modprobe.d/
  • this allows to use a second RTL dongle for use with DVB in parallel 
  • the IDs can be programmed with 'rtl_eeprom -n' or 'rtl_eeprom -g realtek_sdr'

Note that the DVB-T drivers in Linux should not be blacklisted if you are doing this. Also some cheaper RTL-SDR models don't come an EEPROM, and those models can not do this.

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Designing and Testing a PCB Wideband Spiral Antenna

Back in January we posted about a Vivaldi antenna project by "hexandflex". In that project he showed how he designed and manufactured the Vivaldi. A Vivaldi antenna is wideband and directional and the design works well for frequencies above 800 MHz, but becomes too physically large to handle for lower frequencies like 400 MHz. In his latest project, hexandflex has designed a PCB based spiral antenna to cover these lower frequencies.

Hexandflex's post is split into three parts. The first post introduces us to his motivation and talks about what spiral antennas are. The second post discusses the modelling and simulation of the antenna with OpenEMS. OpenEMS is a free front end for MATLAB or Octave which allows you to simulate antenna parameters such as impedance and radiation pattern. Finally in the third post the real world parameters of the antenna are determined in an anechoic chamber owned by Antenna Test Lab, a professional antenna testing agency.

Hexandflex is currently selling his spiral antennas over on Tindie. There are two versions, one smaller one costing $32 designed for 800 MHz+ and a larger one costing $42 designed for 300 MHz+. Both come with suction cups that allow for easy window mounting.

The 800 MHz+ and 300 MHz+ spiral antennas by Hexandflex
The 800 MHz+ and 300 MHz+ spiral antennas by Hexandflex
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YouTube Tutorial: Using RTL-SDR on an Android Smartphone

Over on YouTube, channel Null Byte has uploaded a video showing us how to use an RTL-SDR V3 on an Android smartphone. In the video he discusses the hardware and software required to get started on Android and demonstrates the free SDRoid Android app (based on RFAnalyzer) by tuning to several signals including a voice signal. Later in the video he also shows an ADS-B app for receiving aircraft positions. The video is intended for people new to RTL-SDR so it is a little basic, but it's a great introduction.

He notes that the next video (which will probably be released in a week) will show RPiTX being used with the RTL-SDR.

Use an RTL-SDR Software-Defined Radio Receiver with an Android Smartphone [Tutorial]

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A LimeSDR Mini Based Doppler Radar

Thanks to Luigi (aka @luigifcruz and PU2SPY) for writing in and submitting to us his LimeSDR based doppler radar blog post. The LimeSDR Mini is a low cost two port TX and RX capable SDR. Luigi's doppler based radar makes use of one TX port to transmit the radar signal, and the RX port to receive the reflection. The idea is that the if the object being measured is moving, the received reflected signal will be altered in phase due to the doppler effect.

In terms of hardware, Luigi's radar uses the LimeSDR Mini as the TX/RX radio, a Raspberry Pi 3 as the computing hardware, an SPF5189Z based LNA on the RX side, and two cantenna antennas. It transmits a continuous wave signal at 2.4 GHz.

Luigi's LimeSDR Based Doppler Radar
Luigi's LimeSDR Based Doppler Radar

On the software side it uses a GNU Radio program to transmit, receive and process the returned signal. Luigi's post goes over the DSP concepts in greater detail, but the basic idea is to measure the phase shift between the transmitted and reflected signal via a Multiply Conjugate block, and then decimate the output to increase the resolution. The result is then output on a frequency domain waterfall graph. The GNU Radio is all open source and available on Luigi's Github.

In order to test the system Luigi first set up a test to measure an electric fan's blade speed. The result was clearly visible line in the spectrogram which moved depending on the speed setting that the fan was set to.

Software Defined Radar - Continuous Wave Doppler Radar w/ LimeSDR

In his second test Luigi measures the speed of vehicles by placing the radar on the sidewalk, pointed at cars. The result was clear indication of the vehicle passes as shown by the longer vertical lines on the graph below. The smaller lines have been attributed to pedestrians passing by.

LimeSDR Vehicle Doppler Radar Results: Each long line indicates a vehicle, and shorter lines indicate pedestrians.
LimeSDR Vehicle Doppler Radar Results: Each long line indicates a vehicle, and shorter lines indicate pedestrians.

In a third test, Luigi measured vehicle speeds in tougher conditions, with the radar placed 50 meters away from the highway, at 45 degrees, and with weeds in the way. The radar still generated obvious lines indicating vehicles passes. Finally, in his fourth test, Luigi tested the speed accuracy of his radar by measuring a car driving at a known speed. The results showed excellent accuracy.

Software Defined Radar - Continuous Wave Doppler Radar w/ LimeSDR

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Black Friday SDR Sales: Airspy 15% Off, SDrplay RSP2 $20 Off, HackRF 20% Off

Airspy

Airspy is currently running a 15% Black Friday sale over on the manufacturers website iead.cc, and on their US distributor airspy.us. The coupon code is BF2018.

This results in an Airspy Mini costing only $84.15, an Airspy HF+ costing $169.15, an Airspy R2 costing $143.65 and a SpyVerter costing $41.65. This is the cheapest we've seen these products to date.  

SDRplay

Over on Ham Radio Outlet, the RSP2 is currently reduced by $20, taking it down to a price of only $149.95. The RSP2 Pro is also reduced down to $192.95. Other SDRplay products, and products on their website appear to be not discounted.

HackRF

Over on SparkFun the original HackRF is 20% off, resulting in a price of only $239.96. It's still double the price of an Aliexpress clone, but it is an original unit. In the UK ML&S are also selling it for 15% off at £219.95. This is the cheapest price we've seen an original HackRF sold for.

Elad FDM S2

At the higher end of the SDR spectrum, we see that the Elad FDM-S2 is currently reduced by $51, resulting in a sale price of $529.

Most of these sales are expected to run until Monday, or until stocks run out.

Have you found any other great SDR deals? Let us know in the comments.

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