Modern planes use something called an ADS-B (Automatic Dependent Surveillance-Broadcast) Mode-S transponder, which periodically broadcasts location and altitude information to air traffic controllers. The RTL-SDR can be used to listen to these ADS-B signals, which can then be used to create your very own home aircraft radar system.
When people consider upgrading from the RTL-SDR, there are three mid priced software defined radios that come to most peoples minds: The Airspy, the SDRplay RSP and the HackRF. These three are all in the price range of $150 to $300 USD. In this post we will review the three units and compare them against each other on various tests.
With the right additional hardware, the RTL-SDR software defined radio can be used as a super cheap radio telescope for radio astronomy experiments such as observing the Hydrogen Line and meteor detection.
By using an RTL-SDR dongle together with a low cost noise source it is possible to measure the response of an RF filter. Also, with an additional piece of hardware called a directional coupler the standing wave ratio (SWR) of antennas can also be measured.
The RTL-SDR software defined radio can be told to run in a mode called “direct sampling mode”, which with a small hardware mod allows the dongle to tune to the HF frequencies where ham radio and many other interesting signals are found. This means that no upconverter circuit is required.
Recently Jared Boone, creator of the HackRF portapack posted on his blog about his experience with trying to receive Iridium satellite signals. The HackRF is 8-bit, ~0 – 6 GHz, RX/TX capable SDR, and the Portapack is a kit that allows the HackRF to go portable, by adding an LCD screen, battery pack and control wheel. Iridium is an L-band satellite service that provides products such as satellite phones and pagers. Back in December 2014 we posted how it was found that Iridium pager messages could be decoded.
To receive Iridium Jared used a simple ceramic patch antenna mounted on a piece of cheap copper clad fibreglass. This simple antenna was good enough to receive the Iridium signals with good strength. With this set up Jared was able to easily go outside and receive some packets and record them. He writes his next steps are to try and run the Iridium pager decoder on them and see what packets he captured.
The KiwiSDR is a software defined radio with 30 MHz of bandwidth and a tuning range that covers 0 – 30 MHz (VLF to HF). It is intended to be a low cost web based SDR that can be accessed from all over the world via a browser interface. It is designed as a cape for the BeagleBone Black mini embedded computer, and uses a LTC 14-bit 65 MHz ADC and Xilinx Artix-7 A35 FPGA. It also has an integrated SDR based GPS receiver which is used to automatically compensate for any frequency drift from the main 66.6 MHz oscillator. It runs on the OpenwebRX web based software, which many RTL-SDR users have already been using to stream live radio to the web.
In a previous post we mentioned that the KiwiSDR project had some ethical issues attached to it. The creator of the OpenWebRX software, Andreas, was upset over the fact that the KiwiSDR had forked his open source project and had said that they would not share any profits. However, it appears that KiwiSDR have now struck a deal with Andreas, with both sides being happy, thus resolving any ethical issues.
After a few delays our RTL-SDR blog TCXO/SMA/Metal Case units are back in stock at the Chinese warehouses. The restocking of Amazon USA will follow shortly, and they should be ready for purchase on Amazon by the end of next week. See our store for information on purchasing.
As some readers may know, we’ve been working on finding ways to improve upon and add features to the RTL-SDR’s we sell, whilst trying to maintain the attractive low cost. In previous batches we added upgrades such as a TCXO, bias tee, SMA connector and a shielded metal case with passive cooling. For future modifications we’d like to poll the community on what is most desired.
In the poll below please choose your top 3 desired improvements. If you desire something else please comment on this post. Thanks!
The secret to doing this cheaply is revealed by KD0CQ. He shows that a very cheap $5 Directv SUP-2400upconverter can be converted into a 2.4 GHz downconverter simply by removing some filters. He writes that he hasn’t uploaded the full set of steps to modify the SUP-2400 yet, but he intends to do so in the near future.
There is also a discussion about this mod on Reddit. Several posters have been discussing what applications a cheap downconverter could open up. Some mentioned applications include receiving various satellites in the C/S bands, DECT cordless phones @ 1.9 GHz, SiriusXM satellite radio @ 2.3 GHz, ISM @ 2.4 GHz, RADARs, RC aircraft control/telemetry/video and ham beacons.
In his new video CNLohr demonstrates that AM radio can be broadcast by attaching a short wire antenna to the ESP8266 ethernet output, and then using an RTL-SDR to receive one of its harmonics at 150 MHz. He shows that by varying the size and speed of the packets he can change the received tones, and even create notes to play music. This essentially gives a simple way to ‘hear’ ethernet.
Over on his blog VK4ZXI has been testing the Airspy with the Spectrum Spy software. The Airspy is a $199USD software defined radio that can be considered as a high end upgrade to the RTL-SDR as it has 10 MHz of bandwidth and a 12-bit ADC. The Spectrum Spy software allows the Airspy to be used as wideband spectrum analyzer. In a previous post we reviewed the Spectrum Spy software with the Airspy and found it to have an extremely fast refresh rate. Recent updates since the review have made it even faster.
Back in March we posted about the FlightBox, a portable RTL-SDR ADS-B 1090ES and 978UAT receiver built for use by pilots in small aircraft. 1090ES provides ADS-B which allows a pilot to see on a map where other aircraft are, and 978UAT provides other services such as weather radar. The FlightBox is essentially a Raspberry Pi 2 combined with two RTL-SDR dongles, two antennas, a GPS receiver and is preloaded with the stratux software. The two channel FlightBox receiver currently sells for $250 USD.
The product receives 978UAT and 1090ES ADS-B signals using two RTL-SDR dongles, and then transmits the data via WiFi to an Android or iOS tablet running flight navigation software.
The Kickstarter early backer price is $150 USD for a single channel 978UAT only capable receiver or $200 USD for the dual channel 1090ES and 978UAT receiver. This contrasts with the FlightBox price of $200 and $250 USD for similar products, however the standard backer price for the RF-Connect ADS-B receiver is the same as the FlightBox.
RF-Connect have also uploaded a video showing their ADS-B on Android app in action.
The Massdrop service also allows for the group to vote on the most desired product. Currently the group is voting for several SDR’s including the SDRplay, HackRF, BladeRF, Airspy, USRP, Red Pitaya, Apache Labs and Perseus SDRs. Currently winning the vote at the time of this post going live is the SDRplay, with the HackRF coming in a close second. Once 200 total votes are reached a representative from Massdrop will contact the manufacturer of the most desired SDR and try to work out a deal for the group buy. There are 147 total votes at the moment, so they are almost at the threshold of being able to initiate negotiations.