Category: Applications

Android App Aerial TV Banned from Google Play – Now Available on Amazon

Aerial TV is an Android app that allows you to watch DVB-T TV with an RTL-SDR on a mobile device. We posted about Aerial TV back in April and it was available on the Google Play store back then. Unfortunately Aerial TV has recently been banned from the Google Play store as apparently the app can be used to display copyrighted material from TV. The author writes the following on a Facebook post:

Google Play has suspended Aerial TV due to “[Aerial TV] claims to provide copyrighted contents from TV channels”. According to Google apps that display live TV are of “questionable nature”. I am trying to clarify what they mean. I would like to apologize to all affected users. If you have any concerns, feel free to get in touch with Google directly.

This is quite odd and probably a mistake. But if you are looking for Aerial TV it is now available on the Amazon app store with a current 35% discount. If you bought the app on the Google Play store then to get new updates you will need to uninstall it, contact the developer for a refund, and then purchase it again on the Amazon store. More info about that is available on the Facebook page. Updates about it’s availability will always be provided on the official website at aerialtv.eu.

Using National Weather Service Stations for Forward Scatter Meteor Detection

Over on his blog Dave Venne has been documenting his attempts at using National Weather Service (NWS) broadcasts for forward scatter meteor detection with an RTL-SDR. Forward scatter meteor detection is a passive method for detecting meteors as they enter the atmosphere. When a meteor enters the atmosphere it leaves behind a trail of highly RF reflective ionized air. This ionized air can reflect far away signals from strong transmitters directly into your receiving antenna, thus detecting a meteor.

Typically signals from analog TV and broadcast FM stations are preferred as they are near the optimal frequency for reflection of the ionized trails. However, Dave lives in an area where the broadcast FM spectrum is completely saturated with signals, leaving no empty frequencies to detect meteors. Instead Dave decided to try and use NWS signals at 160 MHz. In the USA there are seven frequencies for NWS and they are physically spaced out so that normally only one transmitter can be heard. Thus tuning to a far away station should produce nothing but static unless a meteor is reflecting its signal. Dave however does note that the 160 MHz frequency is less than optimal for detection and you can expect about 14 dB less reflected signal from meteors.

So far Dave has been able to detect several ‘blips’ with his cross-dipole antenna, RTL-SDR and SDR#. He also uses the Chronolapse freeware software to perform timelapse screenshots of the SDR# waterfall, so that the waterfall can be reviewed later. Unfortunately, most of the blips appear to have been aircraft as they seem to coincide with local air activity, and exhibit a Doppler shift characteristic that is typical of aircraft. He notes that the idea may still work for others who do not live near an airport.

A possible meteor detection in SDR#.
A possible meteor detection in SDR#.
Aircraft detection doppler
Aircraft detection doppler

We note that if you are interested in detecting aircraft via passive forward scatter and their Doppler patterns, then this previous post on just that may interest you.

SDR-Console V3 Latest Update: Signal History & Receiver Panes

SDR-Console is a popular RTL-SDR compatible multi purpose SDR software package which is similar to programs like SDR#, HDSDR and SDRuno. Currently SDR-Console V2 is the stable version and SDR-Console V3 is in a beta state. A few days ago SDR-Console V3 Preview 6 was released. It comes with some very interesting new features including a built in Airspy server, a recording scheduler, a new feature called signal history and a new receivers pane.

Over on his blog Nils Schiffhauer (DK8OK) has been reviewing the new release of SDR-Conosle V3 and writes the following information about some of the new features:

  • “Signal History” takes the signal strength of the given bandwidth each 50 milliseconds, which can be saved in a CSV file. It is also shown in three different speeds on a display.
  • “Receivers’ Pane” shows up to six combos of spectrum/spectrogram of the complete up to 24 parallel demodulators (they additionally can be shown in the Matrix, as in former versions).

“Signal History” offers many applications, to name just three:

  • analyze fading and its structure with an unsurpassed time resolution of 50 ms
  • document fade-in and fade out
  • measure signal-to-noise ratio of signals

In addition Nils has also uploaded a very useful 19 page PDF where he writes step by step instructions and shows numerous examples of the new signal history tool.

DK8OK's SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.
DK8OK’s SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.
DK8OK's screenshot of the signal history toolbox.
DK8OK’s screenshot of the signal history toolbox.

Receiving NOAA 19 HRPT with a HackRF, LNA4All and Cooking Pot Antenna

Over on his YouTube channel Adam 9A4QV has uploaded a video that shows him receiving the NOAA 19 HRPT signal at 1698 MHz with his HackRF, LNA4ALL and the simple circularly polarized cooking pot antenna that we saw in his last videos.

HRPT stands for High Resolution Picture Transmission and is a digital protocol that is used on some satellites to transmit much higher resolution weather images when compared to the APT signal that most people are familiar with receiving. The HRPT signal is available on NOAA19, which also transmits APT. However, unlike APT which is at 137 MHz, HRPT is at 1698 MHz, and is typically a much weaker signal requiring a higher gain motorized tracking antenna.

However in the video Adam shows that a simple cooking pot antenna used indoors is enough to receive the signal (weakly). The signal is probably not strong enough to achieve a decoded image, but perhaps some tweaks might improve the result.

Over on his Reddit thread about the video Adam mentions that a 90cm dish, with a proper feed and two LNA4ALLs should be able to receive the HRPT signal easily. User devnulling also gives some very useful comments on how the software side could be set up if you were able to achieve a high enough SNR.

GNU Radio has HRPT blocks in the main tree (gr-noaa) that work well for decoding and then David Taylor has HRPT reader which will generate an image from the decode GR output. http://www.satsignal.eu/software/hrpt.htm

http://usa-satcom.com has a paid HRPT decoder that runs on windows that has some improvements for lower SNR locking and works very well.

– devnulling

On a previous post we showed @uhf_satcom‘s HRPT results where he used a motorized tracking L-band antenna and HackRF to receive the signal. Some HRPT image examples can be found in that post.

Decoding and Listening to HD Radio (NRSC-5) with an RTL-SDR

HD Radio is a high definition terrestrial digital broadcast signal that is only used in North America. It is easily recognized by the two rectangular blocks on either side of a broadcast FM station signal on a spectrum analyzer/waterfall display. Since HD Radio uses a proprietary protocol, finding a way to decode it has been difficult and so this signal has been inaccessible to SDR users for a long time. Back in February of this year we posted about Phil Burrs attempt, where he was able to create a partial implementation (up to layer 2) of the HD Radio standard, but didn’t get far enough to decode any audio in layer 3.

However, now cyber security researcher ‘Theori’ has created a full RTL-SDR based decoder for the HD Radio protocol. In his post Theori explains that the HD Radio system is split into three layers. Layer 1 finds the signals and does decoding and error correction. Layer 2 is a multiplexing layer, which allows various layer 3 applications to share the bandwidth. Layer 3 is the audio data layer. In his post he explains how these layers work in detail. 

One of the main findings was the discovery of the audio compression codec. Theori found that the codec was essentially HE-AAC with some minor modifications. The modifications were minor enough that he was able to adapt the open source FAAD2 library for HD Radio audio decoding.

Theori’s code is open source and available on GitHub. The code includes the patch to modify FAAD2 for HD Radio and it is automatically applied during the build. A sample file for testing the decoder is also provided and we tested the decoder with the sample and it worked well. The decoding can also be performed in real time and examples of that are also on the git readme.

HD Radio Spectrum
HD Radio Spectrum

Precisely Synchronizing Multiple HackRFs

Recently Marco Bartolucci & José A. del Peral-Rosado wrote in and wanted to let us know about their work in creating multiple precisely synchronized HackRF’s. They plan to use the synchronized HackRFs for solving at a low cost some interesting navigation problems which are described in detail in their academic paper (IEEE link). The abstract of the paper reads:

This paper describes a new method for the synchronisation of multiple low-cost open source software-defined radios (SDR). This solution enables the use of low-cost SDRs in interesting navigation applications, such as hybrid positioning algorithms, interference localisation, and cooperative positioning among others. Time synchronisation is achieved thanks to a time pulse that can be generated either by one of the SDRs or by an external source, such as a GNSS receiver providing 1PPS signal. Experimental results show that the proposed method effectively reduces the synchronisation offset between multiple SDRs, to less than one sampling period.

In simple terms, hybrid positioning is the process of using multiple signals such as WiFi, Bluetooth and cell phone signals etc together to get an accurate position of the receiver. By using several sources localization accuracy can be improved, but to do this each receiver much be precisely synchronized to the same clock source.

The system they created uses a 1PPS GNSS based time source connected to the SYNC_IN inputs on both HackRFs. The synchronization code is run in hardware on the HackRF’s onboard CPLD (complex programmable logic device). Furthermore they also write the following regarding the system and code which has been adopted into the HackRF repository:

A new time synchronization feature has been recently adopted in the HackRF official repository thanks to the collaboration between SPCOMNAV group, Università di Bologna, and the European Space Agency (ESA).

This contribution allows any user to precisely synchronize multiple HackRF devices below 50 ns, by means of a minor hardware modification and the firmware update. 

More information about the driver updates and instructions for use can be found in this Git pull request. The team also write that their work was presented at the NAVITEC 2016 conference.

HackRF Synchronization with a 1PPS GNSS Reference.
HackRF Synchronization with a 1PPS GNSS Reference.

PagerMon: A browser based app for displaying pager messages from multimon-ng

Thank you to Dave for submitting information about his new pager message display software called PagerMon. PagerMon is a web browser based tool for displaying POCSAG pager messages decoded by multimon-ng. It is based around nodejs and uses a sqlite database for storing the messages. Multimon-ng is an RTL-SDR compatible digital mode decoder which can decode multiple protocols including POCSAG pagers.

PagerMon and the features and future features are listed below:

PagerMon is an API driven client/server framework for parsing and displaying pager messages from multimon-ng.

It is built around POCSAG messages, but should easily support other message types as required.

The UI is built around a Node/Express/Angular/Bootstrap stack, while the client scripts are Node scripts that receive piped input.

Features

  • Capcode aliasing with colors and FontAwesome icons
  • API driven extensible architecture
  • Single user, multiple API keys
  • SQLite database backing
  • Configurable via UI
  • Pagination and searching
  • Filtering by capcode or agency
  • Duplicate message filtering
  • Keyword highlighting
  • WebSockets support – messages are delivered to clients in near realtime
  • Pretty HTML5
  • May or may not contain cute puppies

Planned Features

  • Multi-user support
  • Other database support (MongoDB and DynamoDB planned)
  • Horizontal scaling
  • Enhanced message filtering
  • Bootstrap 4 + Angular 2 support
  • Enhanced alias control
  • Graphing
  • Push notifications
  • Non-sucky documentation

The GitHub readme has a getting started section which shows how to set up the server and get it running on your local machine.

PagerMon displaying POCSAG messages
PagerMon displaying POCSAG messages

The Outernet Dreamcatcher: A Linux Based ARM PC with Built in RTL-SDR

Recently Outernet released their new ‘Dreamcatcher’ hardware which is an RTL-SDR + L-band LNA & filter + computing board all on the same PCB. The Dreamcatcher costs $99 USD and can be bought directly from their store. For your $99 you get the Dreamcatcher board, as well as a new ceramic L-band patch antenna which has a built in L-band LNA and filter. The built in LNA is useful as it allows you to use a few meters of extension cable in order to get the patch antenna in a good position outdoors.

At the moment the Dreamcatcher can be run with two different SD card images: the Skylark Outernet software, or Armbian (Linux). The Armbian image is basically just standard Armbian and at the moment does not actually run any Outernet software, and cannot decode their signal – but this is being worked on. Eventually they hope to depreciate the Skylark image and instead use an Outernet receiver app that runs on Armbian.

When running on the standard Armbian image, the Dreamcatcher can be used as a regular RTL-SDR connected to Linux, as there is a bypass port which bypasses the built in L-band LNA and filter. This port is enabled by default, but can be software switched to the L-band port if desired. There is also a 4.8V bias tee on the bypass port that can be turned on in software and used to power external devices via the coax cable. Currently there is no display support on the Dreamcatcher so the unit must be run headless, meaning that you must connect to it via UART or SSH from another PC.

The Outernet Dreamcatcher
The Outernet Dreamcatcher

The Dreamcatcher is advertised with the following specifications:

  • L-band SAW filter (1525 – 1559 MHz)
  • Two-stage L-band LNA with 34dB gain
  • 1 PPM TCXO
  • RF bypass for tuning from 24 – 1600 MHz – use as a regular RTL SDR!
  • Software switchable bias tee
  • 3 USB ports
  • GPIO forest
  • UARTs, I2C, SPI headers (unpopulated) for driving external hardware
  • Two microSD card holders – for boot and storage!
  • 1 GHz CPU
  • 512 MB RAM
  • USB wifi dongle (based on RTL8188CUS chipset) – AP mode capable!
  • Lots of LEDs!
  • Switches!
  • microUSB OTG
  • microUSB power port
  • Audio In/Out
  • Fully mainline (4.10) kernel and Uboot (2017.01) support!

Also as explained on the forums, Dreamcatcher uses an Allwinner A13 SoC, which has inside an ARM Cortex A8 @ 1 GHz CPU. They’ve also added 512MB of RAM. The PCB measures 12 cm x 12 cm.

Currently the Dreamcatcher is being advertised as beta hardware, as they give the following warning:

Although some assistance can be found on our forums, Outernet provides no direct support for this product. If you are not a tinkerer, hobbyist, or hardware hacker, you may be disappointed with your purchase.

The Dreamcatcher also comes with Outernet’s latest L-band patch antenna. The new patch antenna uses a ceramic patch and a 12 cm x 12 cm PCB ground plane. The antenna is ‘active’, as it has a built in L-band LNA and filtering. It is powered by the bias tee on the Dreamcatcher, and can also be powered by the bias tee on our V3 RTL-SDR’s. An active antenna is a good idea as this allows you to place the antenna outdoors (you’d need to waterproof this antenna in a plastic box though), and run a coax cable inside. The LNA should help overcome the coax cable loss which can be quite high at the L-band Outernet frequency of 1.5 GHz.

Outernet has provided us with a sample of this kit, and we plan to release a full review of the unit within the next few weeks.

Outernet active ceramic patch antenna (Front)
Outernet active ceramic patch antenna (Front)
Outernet active ceramic patch antenna (Rear)
Outernet active ceramic patch antenna (Rear)