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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An Overview on RF Direction Finding with RTL-SDRs

Thanks to K2GOG of the Hudson Valley Digital Network for writing in a sharing with us his latest blog post which is a useful overview of some direction finding techniques that can be used with RTL-SDR dongles. RF direction finding is the act of using a radio to determine the physical location of a signal.

In his post K2GOG mentions our successfully crowd funded KerberosSDR which will be shipping in January next year. KerberosSDR is our 4x coherent RTL-SDR, and one possible application is to use it as a four antenna phase coherent direction finder. K2GOG explains the phase coherent concept in his post quite elegantly.

While looking over KerberosSDR, K2GOG was also reminded of another direction finding technique called heat mapping which can be performed with a single RTL-SDR. This process involves driving around with an RTL-SDR and GPS logger, measuring the signal power as you drive and combining it the current GPS coordinates. From that data a heat map can be generated, which shows where the signal is the strongest, and therefore where the likely source is. The RTLSDR Scanner application by eartoearoak makes doing this easy, and in his post K2GOG provide a short tutorial on setting it up.

A heatmap generated by K2GOG with an RTL-SDR, GPS and RTLSDR Scanner.
A heatmap generated by K2GOG with an RTL-SDR, GPS and RTLSDR Scanner.
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Othernet Sale: $75 Dreamcatcher LoRa Radio, $99 moRFeus Signal Generator

Othernet (previously known as Outernet) are currently having a 50% off sale on all their products. This means that you can snag a discounted Dreamcatcher at only US$75, and a moRFeus at US$99. The sale expires midnight on the 26th.

The sale is exclusive to RTL-SDR Blog readers (although feel free to share the coupon) and the coupon code to use at checkout is rtlsdrblog83759. 

Dreamcatcher and Othernet Data Signal Information

If you weren't already aware, the Othernet project aims to bring live data such as news, weather, video, books, Wikipedia articles and audio broadcasts to the world via a free satellite service and cheap receivers. Although an internet connection provides the same data, Othernet's satellite broadcast is receivable in remote areas, will continue working in disasters, and costs nothing to continually receive roughly 200MB of data a day. The trade off is that the service is downlink only, so the data that you get is only what is curated by the Othernet team.

Othernet can provide this service for free because they are funded by private customers whom they provide private data/audio satellite channels to. One such private customer is attempting to implement an Othernet based Tsunami early warning system in Vanuatu which would work even when the cell phone system fails in a disaster. Each siren is equipped with an Othernet receiver and LNB that receives the Othernet signal. The goal is to allow for any village to be able to set up their own low cost warning system. At the same time the Othernet Tsunami warning receiver is made use of in normal circumstances as it receives a satellite radio broadcast which is then re-transmitted to the village over regular FM radio.

Currently the public service is in a test period and is only available in North America, but public service for the EU and possibly Oceania is planned to begin in Q1 2019. The rest of the world should eventually follow after. Some more information about the data service can be found on our previous post.

Alternatively, if you have no interest in the data service then your Dreamcatcher could also be used as a TX/RX capable LoRa radio. In a previous post we had some fun with two Dreamcatchers and a LoRa chat application.

Outernet Dreamcatcher - Precursor to the Lantern
Othernet Dreamcatcher

moRFeus Information

The moRFeus is a low cost signal generator. It's capable of generating a tone anywhere from 85 MHz to 5400 MHz, and it can also be used as a frequency mixer component for implementing things like homebrew upconverters and downconverters.

In the past we've seen it be used as a tracking generator for measuring filters and VSWR, and users from the Othernet community have implemented custom GUIs to control it. Recently @sam210723 released a new very slick looking GUI too.

moRFeus Signal Generator
moRFeus Signal Generator
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An Open Source VOR Receiver for Airspy and RTL-SDR

Thank you to Thierry Leconte (TLeconte) for writing in and submitting his new command line based open source software called vortrack. Vortrack is a simple VOR decoder which calculates the angle towards the VOR. It is compatible with both RTL-SDR and Airspy radios, and runs on Linux.

In the past we've seen several other posts about RTL-SDRs being used to decode VOR signals, but Thierry's implementation appears to be the easiest way to get a bearing straight away. You'll get the most use out of the software if you install it on a portable device like a Raspberry Pi and take it out for a drive as you'll be able to see the VOR angle changing then.

VOR stands for VHF Omnidirectional Range and is a way to help aircraft navigate by using fixed ground based beacons. The beacons are specially designed in such a way that the aircraft can use the beacon to determine a bearing towards the VOR transmitter. VOR beacons are found between 108 MHz and 117.95 MHz, and it's possible to view the raw signal in SDR#.

A DVOR Ground Station at an Airport. Source Wikipedia.
A DVOR Ground Station at an Airport. Source Wikipedia.
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