Low Power RTL-SDR ‘Stratux’ Dongles Now Available in our Store

Over on our store we now have a limited amount of “Low Power V2” RTL-SDR dongles available for sale for $16.95 USD incl. free international shipping. These are dongles that were produced for the Stratux project which aims to provide a very low cost ADS-B and UAT receiver for small airplane pilots. These Stratux kits typically consist of a Raspberry Pi, two nano RTL-SDR dongles, a GPS dongle and a Android or iOS tablet. The two RTL-SDR dongles receive both 1090 MHz ADS-B and 978 MHz UAT which are decoded on the Raspberry Pi. The Raspberry Pi then sends the decoded aircraft position and weather data to the tablet via WiFi which is running commercial navigation software.

A full Stratix setup including, Raspberry Pi, two RTL-SDR nano dongles, GPS module, fan, and 1090 + 978 MHz antennas.
A full Stratux setup including: Raspberry Pi, two RTL-SDR nano dongles, GPS module, fan, and 1090 + 978 MHz antennas.

One issue that Stratux users continually run into, is that the Raspberry Pi is sometimes unable to power two or more RTL-SDR dongles. When running a Pi with two RTL-SDR dongles, a GPS dongle, and cooling fan the total power draw is above 1A which can cause power supply problems and glitching. By using a low power RTL-SDR these problems can be avoided by keeping the total current draw under 1A.

The Low Power V2 Stratux RTL-SDR’s draw about 160-170 mA, whereas standard dongles draw about 260 mA, so that’s a saving of almost 100 mA. On battery power this current saving can mean a few hours more of operation. The Low Power RTL-SDR dongle achieves its lower current consumption by using a switch mode power supply instead of a linear regulator which is commonly used on most other RTL-SDR dongles. The trade off is that switch mode supplies are inherently RF noisy, so increased noise can be seen on the spectrum. Despite the increased noise, most applications like ADS-B are not significantly degraded. We have seen switch mode supplies used on some other RTL2832U dongles sold in the HDTV market as well. For example all the R828D based DVB-T2 dongles that we have seen use switch mode supplies as well, and also draw about 170 mA.

We think that these low power RTL-SDRs could be useful in other non-stratux related applications too. For example, they could be used on mobile Android devices. One of the key problems with Android usage is that RTL-SDR dongles tend to drain the battery quickly. They could also be used on solar and battery powered installations to help achieve longer run times. Or like with Stratux they could be used on a Raspberry Pi running other applications, to ensure that multiple dongles can be attached.

Currently we are selling these dongles for $16.95 USD with free international shipping included. Note that these dongles do not come with an enclosure (just a bare PCB), and they do not have a TCXO. Below is more information about these dongles.

Click here to visit our store

The Stratux Low Power V2 Dongle.
The Stratux Low Power V2 Dongle

Back in November 2016 we posted a review on the Low Power V1 dongles. Since then Chris (the man behind producing these dongles) has brought out the Low Power V2 models which improves upon V1 significantly. By switching to a 4-layer PCB the dongle is now much quieter in terms of RF noise produced from the switch mode power supply, and it also now runs significantly cooler. The dongle also now uses even less power and is more sensitive compared with V1.

Over on his Reddit post Chris compared his Low Power V2 dongle against the Low Power V1, a generic nano dongle and a NESDR Nano 2. In terms of noise plots, the generic nano dongle was the quietest, with the low power V2 dongle coming in second. Interestingly the NESDR Nano 2 was almost as noisy as the low power V1 dongle. The improvements on the low power V2 dongle make it usable on VHF now.

Noise Floor Comparisons between four Nano styled dongles.
Noise Floor Comparisons between four Nano styled dongles. NESDR Nano 2 (Blue), Generic Nano (Orange), Low Power V1 (Gray), Low Power V2 (Yellow).

In terms of heat produced and power used, the NESDR Nano 2 is the hottest and most power hungry, followed by the Generic Nano, the Low Power V1 and then the Low Power V2. For comparison the NESDR Nano 2 draws 1.362W of power, the generic nano 1.318W, the Low Power V1 1.003W, and the new Low Power V2 draws only 0.933W.

Thermal Camera Photos of  four Nano Dongles.
Thermal Camera Photos of four Nano Dongles.

Chris summarizes his results as follows:

  1. The NESDR Nano 2 loses in pretty much every aspect except for noise floor on VHF frequencies compared against the Low Power v1.
  2. You can see the effects of heat on the R820T2 above 1.4 GHz.
  3. The “Generic Nano” was always a great performer in terms of sensitivity.
  4. For ~0.8W (in a dual-band build) less power, the cost is 0.41 dB @ 1090 MHz and 0.64 dB @ 978 MHz (compared to the Generic Nano).

The Low Power V2 dongles appear to be a good improvement over the V1 models. They are useful for applications that need low power draw, for example powering multiple dongles on a Raspberry Pi and for use on battery and solar power. The trade off for low power consumption is increased RF noise, but with the Low Power V2 dongles the noise is not significant and interestingly even outperforms the NESDR Nano 2.

Using the SDRplay with a W4OP Loop

Over on YouTube user SignalSearch has uploaded a video showing and explaining the use of a W4OP magnetic loop antenna on a SDRplay SDR. On the video he explains what the W4OP loop is, and demonstrates it’s operation in SDR-Console with his SDRplay. The video description reads:

Experiment: Hookup the SDRPlay RSP 1 (SDR receiver) to the W4OP (Small Transmitting Loop). I’ve always wanted to try hooking up a loop to my SDRPlay. Though different from an active receive loop (one that has a Low Noise Amplifier), this loop can be used for transmitting @ QRP levels – but works great for shortwave listening too! For more info. please visit my website @ www.k5acl.net!


LimeNET SDR Based Wireless Networks Crowdfunding Campaign

Following the success of the LimeSDR, the Lime team have started work on their next SDR project called ‘LimeNET’ which will eventually be released for crowdfunding on CrowdSupply. To be notified when the campaign is released you can sign up here.

The LimeNET SDR is essentially a high-end computer combined together with a LimeSDR board, and all placed in a small box. The goal is to create self contained base stations for cellular and IoT applications. LimeNET devices come in two flavors, the LimeNET Mini and the standard LimeNET.

LimeNET Mini

A software defined radio (SDR) small cell network in a box for mobile and IoT applications, based on an Intel i7 processor and the open source LimeSDR board. This combination makes it an ideal implementation for high data rate communication applications such as to 2-5G radio access to IoT nodes and much more.

  • Processor: Intel Core i7-7500U CPU 2-core 2.7/3.5 GHz
  • Memory: 32 GB DDR4 2133 MHz
  • Storage: 512 GB SSD
  • Connectivity: 1 x USB 3.1 type C, 1 x USB 3.1, 2x USB 3.0, 1 x Gigabit Ethernet
  • Radio: LimeSDR USB Type-A


A software defined radio (SDR) high capacity network in a box for mobile and IoT applications, based on an Intel i7 processor and the open source LimeSDR PCIe card. It covers the same applications as the mini version for wide area networks.

  • Processor: Intel Core i7-6950X CPU 10-core 2011-3 140 W 3.0 GHz 25 MB Cache
  • Memory: 64 GB DDR4 2133 MHz
  • Storage: 1 TB SSD
  • Connectivity: 2 x USB 3.1, 4 x USB 3.0, 1 x Gigabit Ethernet
  • Radio: LimeSDR PCIe
The LimeNET Mini.
The LimeNET Mini.

The LimeNET press release reads:

Confronted with flat revenues, spiralling infrastructure costs and massively escalating data demands, the telco industry is facing a crisis point. It needs exponentially more cost-effective solutions, as well as new revenue streams, and needs to find them quickly. Operators face a simple choice; either revise their business models, or lose market share to new incumbents.

Lime Micro and Canonical are looking to turn the mobile telephony business model on its head. Telco hardware is expensive, slow to develop, and has proven a ‘break’ to innovation in the industry. By ‘open sourcing’ Lime Microsystems’ 5G and IoT capable SDR base station design, Lime and Canonical are looking to effectively ‘commoditise’ network hardware and shift the value centre towards software.

LimeSDR-based base stations can not only run cellular standards from 2G or 5G, as well as IoT protocols like LoRa, Sigfox, NB-IoT, LTE-M, Weightless and others but any type of wireless protocol. Open source base stations allow R&D departments to try out new ideas around industrial IoT, content broadcasting and many more. Commoditised base stations allow any enterprise to run their own base station and get spectrum from their operators as a service. Base stations can have new form factors as well, like being embedded into vending machines or attached to drones.

“It’s clear that existing telco business models are quickly running out of steam,” commented Maarten Ectors, VP IoT, Next-Gen Networks & Edge Cloud, Canonical, “and that operators need to find new revenue streams. Together with Lime Microsystems, we’re looking to initiate a ‘herding’ behaviour that will usher in the age of the largely software-enabled telco network. Through its open sourced SDR design Lime will encourage a wide range of manufacturers to produce more cost-effective base stations. And, following enormous interest in our first crowdfunding initiative, we already have the critical mass of developers required to deliver the significant software innovation the industry requires.”

“This kind of model is, without a doubt, where the industry needs to go,” commented Ebrahim Bushehri, CEO, Lime Microsystems. “There are several reasons why Canonical’s heavy commitment in this project over the past couple of years has been so important. For one, Canonical shares our vision of an entirely software-enabled future for telco and IoT networks. Secondly, Canonical’s efficient, hyper-secure IoT OS Ubuntu Core is the perfect platform to enable this vision. Thirdly, this collaboration has helped us to gather the critical mass of developers required to kick-start the programme.”

Over 3,600 developers are currently involved in efforts to create apps, called Snaps, for LimeSDR, with several free and paid-for apps having already appeared on the open community LimeSDR App Store, as well as Lime’s invite-only app store, LimeNET.


Aerial TV: Android RTL-SDR DVB-T Decoder Officially Released

Last month we posted about Aerial TV, a new Android based DVB-T decoder that works with RTL-SDR dongles. Back then the app was still in beta testing and had a few operational bugs. Now the Aerial TV app has been officially released.

The app is based on the new Android DVB-T driver for RTL2832U devices which is written by Martin Marinov who is also the programmer of Aerial TV. The DVB-T driver is open source, and currently supports RTL2832U devices with the R820T, E4000, R828D, FC0012 and FC0013 tuner chips. Of note is that the R828D also has DVB-T2 support.

Aerial TV is free to download and test, but requires a $7.99 licence to use for more than 30 minutes. To use it you will need an OTG (On-the-go) cable adapter and an RTL-SDR dongle with antenna.

Just watch TV – no data plan or wifi connection required. Aerial TV works by picking up digital TV channels off the air with a regular TV antenna.

You will need a low cost USB TV tuner. You can grab one online for less than €10. Make sure to get an RTL2832 tuner. When it arrives, just connect the provided antenna and start watching. You may need a USB OTG cable to plug the tuner in your Android device. USB OTG cables are inexpensive and easy to find.

Note that your Android device must support USB OTG. If unsure, do a quick search online or consult your Android device manual. Also check that there is DVB-T/DVB-T2 service in your local area by doing a quick search online. Signal needs to be strong enough for Aerial TV to pick it up. For best results use an outdoor aerial.

You get free unlimited access to radio forever. You also get to watch all TV channels and experience all features of Aerial TV during the trial period for free. After the trial period ends you can make a one-off purchase and watch as much TV as you want. Remember: you can keep listening to radio even if the trial has ended!

Q: How do I find a supported dongle?
A: All major RTL2832 (rtl-sdr) dongles are supported. These dongles can be easily purchased online. Just type in “RTL2832” or “RTL2832U” in the search box of your favourite online store.

Q: What tuner do I need to watch DVB-T2?
A: If your country has DVB-T2 broadcasts (such as Freeview HD in UK) you will need a DVB-T2 compatible receiver dongle such as R828D in order to watch DVB-T2 with Aerial TV.

Aerial TV Screenshot
Aerial TV Screenshot

Setting up a FLARM Receiver with an RTL-SDR and Orange Pi Zero: Tracking Gliders and Helicopters

Most people already know about ADS-B aircraft tracking, but few know about FLARM (FLight AlaRM). FLARM is a low cost and low power consumption ADS-B alternative which is often used by small aircraft such as gliders and helicopters for collision avoidance. It is used all over the world, and is especially popular in Europe, however it is almost non-existent within the USA.

Back in 2014 we posted about FLARM reception with the RTL-SDR, and also about the Open Glider Network (OGN). The OGN is an online FLARM aggregator that is similar to sites like flightaware.com and flightradar24.com which aggregate ADS-B data.

More recently, Łukasz C. Jokiel has posted a tutorial on his blog that clearly shows how to set up an RTL-SDR and Raspberry Pi Zero based FLARM receiver for feeding the Open Glider Network

Łukasz’s tutorial uses an Orange Pi Zero which is a very cheap (~$7 USD) Raspberry Pi embedded computing device. He also uses an RTL-SDR dongle and an antenna tuned to the FLARM frequency of 868 MHz. The tutorial goes over the Linux commands for installing the decoder, calibrating the RTL-SDR and setting up the Open Glider Network feeder.

Remember that FLARM is typically 10-100 times weaker than ADS-B so a good tuned antenna is required, and the OGN recommend building (pdf) a collinear coax antenna tuned to 868 MHz.

A Commercial FLARM receiver.
A Commercial FLARM sender/receiver.

Explaining the Dallas Siren Hack

If you’ve been paying attention to the news then you might have heard of the recent Dallas tornado siren hack. Earlier in the month a hacker took control of 156 tornado warning sirens placed all around the city of Dallas, Texas in the United States. The sirens are activated via an RF control signal, and the hacker transmitted the control signal, causing all the sirens to activate causing a city wide false alarm. The attack could have been performed with a transmit capable software defined radio like the HackRF, or any other transmit capable radio such as a handheld radio.

Bastille is a wireless security firm which specializes in RF, SDR and IoT. Over on their blog, employee Balint Seeber has uploaded a video and blog post that discusses some possibilities on how the hacker may have activated the sirens.

In the blog post and video first Balint discusses the difference between a single frequency network, and a repeated network. In a single frequency network, one powerful transmitter up on a hill would be used to activate all the sirens, whereas with a repeater network several dispersed transmitters might be used to repeat the signal over a wide area.

He then discusses the difference between an analog and digital command transmission system. In an analog command transmission a simple series of tones might be used to activate the sirens. In this case the hacker could simply listen for the tones when the siren is activated during the monthly test, and save them away for a future replay attack. In a digital system instead of tones an encrypted packet of data could be used instead. Depending on how the encryption is implemented this could prevent a replay attack.

SpyServer 2.0 Released: More Efficient Streaming for Airspy and RTL-SDR

Back in March the team behind the Airspy SDR and SDRSharp software released the SpyServer, a piece of software that allows you to stream radio data from a remote Airspy receiver over a network. Then later in April they added full support for the RTL-SDR dongle as well.

This Easter the Airspy team have released SpyServer 2.0, which improves the streaming efficiency significantly (changelog). Now the full 8 MHz bandwidth of the Airspy should be easily streamable over an internet connection. With SpyServer 1.0 it was difficult to make use of the full bandwidth of the Airspy because the network data usage was very high, since it was streaming the full raw IQ data for the sampling rate/bandwidth selected. In SpyServer 2.0 the server does not stream the full raw data, and instead only streams the wideband FFT data (for displaying the waterfall and FFT graph), and the raw data from the currently selected IF bandwidth. Of course the full IQ data can still be streamed if desired by selecting the ‘Use full IQ’ checkbox.

This new efficiency means that WFM uses only about 1.3 MB/s, and narrow band modes like NFM/AM/SSB only use about 120 kB/s of network data which is easily achievable over a local network and internet. This data usage is almost independent of the sampling rate/bandwidth selected so you can stream the full 8 MHz offered by the Airspy without trouble. Normally streaming the full raw data for 8 MHz would use about 40 MB/s, which is difficult to achieve over a local network, and impossible over the internet.

We tested the new SpyServer over our local network and were able to stream the full 8 MHz of the Airspy with no problems. With the RTL-SDR we were also able to stream 2.4 MHz without issue. WFM and NFM modes worked clearly and no skips or significant lag was noticed over a local WiFi N connection. Hopefully in the future SpyServer will be developed further to enable compressed audio streaming as well for even lower network data usage.

SpyServer WFM Reception. About 1.3 MB/s network usage.
SpyServer WFM Reception. About 1.3 MB/s network usage.
SpyServer NFM Reception. About 120 kB/s network usage.
SpyServer NFM Reception. About 120 kB/s network usage.

Some Operational Notes:

  • To run SpyServer on Windows simply double click on spyserver.exe. On Linux extract “spyserver_linux_x86” and the config file, and then run “sudo chmod +x spyserver_linux_x86”. Then run it with “./spyserver_linux_x86”.
  • Connect to it on the remote PC in SDR# using the servers IP address which can be found by typing “ipconfig /all” in Windows command prompt, or “ifconfig” on Linux.
  • To select between using the Airspy and RTL-SDR for the SpyServer you will need to edit the spyserver.config file with a text editor and edit the “device_type” string.
  • SpyServer runs on Windows/Linux as well as small embedded computers such as Raspberry Pi’s and Odroids. Download the Raspberry Pi and Odroid servers separately from SDR# at http://airspy.com/download.
  • SpyServer is NOT compatible with software that expects an rtl_tcp server such as SDRTouch.

We have also seen Lucas Teske of the OpenSatellite project use the SpyServer for streaming a GOES16 downlink over a network connection with an Odroid C2. He writes that soon the OpenSatellite project software will directly support SpyServer.

Comparing Two LNA’s for HRIT/LRIT (GOES) Reception

Over on his blog Lucas Teske has been comparing the LNA4ALL and an SPF5189 LNA from eBay on HRIT/LRIT reception from GOES satellites. SPF5189 LNA’s can be found on eBay for less than $8 USD, with free shipping from China, whereas the LNA4ALL costs 27 Euros shipped from Croatia. GOES is a geosynchronous orbit weather satellite which requires a satellite dish or other high gain antenna to receive. It downlinks at about 1.7 GHz, which means that a high quality LNA with low noise figure and good PCB design is needed for reception.

In his post Lucas mentions how he saw a review on eBay stating that the SPF5189 did not work at L-band. However, he found that odd as all of his SPF5189 LNA’s seemed to work just fine with L-band reception. So he did a benchmark comparing the SPF5189 to the PSA5043+ based LNA4ALL which is known to work well on L-band.

From his comparisons he found that the SPF5189 does indeed work well on L-band, and is comparable to the LNA4ALL. He concludes that the reviewer must have received a bad unit, or didn’t know what he was doing.

Lucas also makes an important note regarding the PCB design of these LNA’s. Even though the SPF5189 and PSA5043 chips have similar specs, with LNA’s the design of the PCB is crucial, as a poor design can significantly degrade performance. With the LNA4ALL you can be sure that the design is good, although the SPF5189 LNA’s currently on eBay look to be designed okay as well. Though with some eBay sellers there is no guarantee that you will receive a good board. We note that we have seen some really poor designs for PSA5043 LNA’s out there as well.

The eBay SPF5189 LNA vs the LNA4ALL from 9A4QV
The eBay SPF5189 LNA vs the LNA4ALL from 9A4QV