Category: RTL-SDR

Receiving the Recently Launched BY70-1 Satellite

BY70-1 is a Chinese amateur Cubesat satellite which was recently launched on December 29, 2016. It is expected to stay in orbit for only 1 – 2 months due to a partial failure with the satellite releasing into an incorrect orbit. The purpose of the satellite is for education in schools and for amateur radio use. The receivable signals include an FM repeater and BPSK telemetry beacon both of which can be received at 436.2 MHz. The telemetry beacon is interesting because it also transmits images from an on board visible light camera. These signals can easily be received with an RTL-SDR or other SDR with an appropriate antenna.

Over on his blog Daneil Estevez has been posting about decoding these telemetry images. He’s been using telemetry data collected by other listeners, and the gr-satellites GNU Radio decoder which is capable of decoding the telemetry beacons on many amateur radio satellites. So far the decoded images haven’t been great, they’re just mostly black with nothing really discernible. Hopefully future decodes will show better images.

If you want to track the satellite and attempt a decode, the Satellite AR Android app has the satellite in its database.

Not many people seem to have gotten telemetry decodes or images yet, but below we show an image decoded by  on Twitter.

BY70-1 Image Decoded by @bg2bhc
BY70-1 Image Decoded by @bg2bhc

Building a Wideband Vivaldi Antenna for SDR Use

Vivaldi’s are linearly polarized broadband antennas that have a directional radiation pattern at higher frequencies. The high end SDR manufacturer RF Space produces their own Vivaldi antennas made from PCB boards which they sell online. The larger the antenna, the lower its receiving frequency, and ones that go down to about 200 MHz are almost the size of a full adult person. But all sizes receive up to 6 GHz maximum. Typically smaller versions of Vivald antennas have been used in the past for L-Band satellite reception.

Over on his blog KD0CQ noted that he always had trouble trying to purchase a Vivaldi from RF Space because they were too popular and always out of stock. So he decided to try and build his own out of PCB boards. On this page he’s collected a bunch of Vivaldi cutout or transfer images. On his second page he shows a Vivaldi antenna that he built out of PCB material, just by using scissors and semi-rigid coax. With the Vivaldi placed outdoors he’s been able to successfully receive and decode L-Band AERO on his Airspy Mini even without an LNA. 

KD0CQ writes that he’ll update his blog soon with more results.

Simple Vivaldi antenna by KD0CQ cut out of PCB board.
Simple Vivaldi antenna by KD0CQ cut out of PCB board.

A Guide to Using RPiTX and an RTL-SDR to Reverse Engineer and Control ASK/OOK Devices

Erhard E. has been experimenting with capturing, analyzing, reverse engineering and then transmitting new ASK/OOK signals with his RTL-SDR and Raspberry Pi running RPiTX. Erhard has written a very informative guide/tutorial (pdf) that explains how he did it for wireless doorbell and for remote control toy cars. RPiTX is software for the Raspberry Pi which allows it to transmit almost any signal via modulation of a GPIO pin. RPiTX related posts have been featured on this blog several times in the past.

First Erhard records a copy of the doorbell signal using his RTL-SDR and then views the waveform in Audacity. He then writes that you’ll need to find the waveform characteristics either manually using Audacity, or by using the rtl_433 decoder. In the tutorial he uses rtl_433 which automatically gives his the pulse width, gap width and pulse period.

Next in order to actually generate the signal using RPiTX he uses the waveform characteristics that he found out and manually creates a .ft hex file that describes the signal to be generated. Then using using the rpitx command, the .ft file can be transmitted.

Later in the tutorial he also shows how he performed the same reverse engineering process with a cheap RC car toy (forward/reverse commands only), which uses OOK encoding on the wireless controller.

The tutorial can be downloaded in PDF form here.

Showing the Pulse Width, Gap Width and Symbol Period of a signal in Audacity.
Showing the Pulse Width, Gap Width and Symbol Period of a signal in Audacity.

Simulating GPS with LimeSDR and Receiving it with an RTL-SDR

In previous posts we showed how Phillip Hahn had been trying to use his RTL-SDR as a GPS receiver on a high powered rocket in order to overcome the COCOM limits which prevent commercial GPS devices from operating when moving faster than 1,900 kmph/1,200 mph and/or higher than 18,000 m/59,000 ft.

In order to test future flights with the RTL-SDR GPS receiver, Phillip has been simulating GPS rocket trajectory signals and using his LimeSDR. The RTL-SDR then receives the simulated GPS signals which are then fed into SoftGNSS for decoding. The simulation simulates the Japanese SS-520-4 rocket which is a 32′ long, 2′ diameter small high powered rocket capable of putting loads like cubesats into orbit affordably. Using the simulated data Phillip is able to calculate the trajectory and see all the motor burns in the velocity profile.

While Phillip intends to use the RTL-SDR on a similar rocket in the future, he notes that the simulation does not take into account problems such as thermal noise, or RF interference, rocket jerk, satellite occlusion and vibration problems.

LimeSDR Simulated GPS Rocket Trajectory Received with RTL-SDR.
LimeSDR Simulated GPS Rocket Trajectory Received with RTL-SDR.

Radio For Everyone new Posts: RTL-SDR Accessories, 5 Easy Mods, FAQ, Legal/Moral Issues and Portable SDR

Akos from the radioforeveryone.com blog (previously sdrformariners/rtlsdrforeveryone) has recently added several new posts. The first new post is a beginners guide to RTL-SDR accessories. In this post he shows and links to his reviews of various RTL-SDR accessory products such as upconverters, baluns, filters, preamps and adapters.

In the second post he shows a guide to 5 easy mods that can be performed on RTL-SDR dongles which will improve their performance. The mods include using a ground plane, using a wire antenna, extending the coax, removing the IR and LED diodes, and putting the dongle into a metal tin.

In the third post he discusses portable software defined radio and shows exactly what products and software you need to set up a an Android or Raspberry Pi based mobile SDR station.

In the remaining new posts Akos has created an RTL-SDR FAQ and a guide to understanding the legal and moral issues of SDR. Finally the last new post we saw is where Akos tests a cooled RTL-SDR V3 vs a stock V3. His results appear to show that the cooled dongle achieves slightly more (avg. 3.73%) position reports.

Akos' guide to RTL-SDR Accessories.
Akos’ guide to RTL-SDR Accessories.

Decapping the R820T and RTL2832U Chips

Over on YouTube the electronupdate channel has posted a video showing the decapping of the R820T and RTL2832U chips. Decapping is the process of removing the plastic packaging on integrated circuit chips, thus exposing the internal circuits printed on the silicon die for viewing. In the video he shows microscope images of each of the decapped chips and explains a bit about what each part of the chip does.

Over on his blog he’s also posted the full decapped images of the R820T and RTL2832U for viewing.

The decapped R820T tuner die.
The decapped R820T tuner die.
SOFTWARE DEFINED RADIO TEARDOWN: R820/RTL2832U DECAP

3D Printing an RTL-SDR Cooler Block

Over on the 3D printing sharing site Thingiverse, user “Way” has uploaded a 3D printer design for an RTL-SDR cooler block. The block works by allowing a PC cooling fan to blow air efficiently over the dongle body, removing any heat generated.

Cooling a dongle helps to avoid the L-Band problem, which is when R820T/2 units get hot and stop working about ~1.3-1.5 GHz. Generally passive cooling is enough (like with the thermal pad and metal cases used on our V3 dongles), but further cooling can apparently help increase sensitivity slightly although we are unsure if there is any statistically significant difference.

“Way” has made two designs, one to fit a 40 x 40 mm fan, and another to fit a 50 x 50 mm fan. The fan simply screws to the top of the block, and the dongle is placed at the bottom. Air is ducted over the dongle body and escapes out the back.

RTL-SDR 3D Printed Cooler
RTL-SDR 3D Printed Cooler

30% Off Outernet L-Band RTL-SDR DIY Kits – $70 for RTL-SDR, LNA, Antenna, CHIP and Battery

Outernet is an L-band satellite service that aims to be a “library in the sky”. They are constantly transmitting data such as up to date news, weather updates, Wikipedia pages, books, ISS APRS repeats and much more. Their DIY receiver kit consists of a lithium battery pack, L-band patch satellite antenna, LNA with built in filter, C.H.I.P mini Linux computer and an RTL-SDR E4000 or V3.

The DIY kit is normally priced at $99 USD, but right now they are running a 30% off Christmas promotion, bringing the price down to $69.30 USD. If you don’t need the battery pack, the sale price is then only $55.30 USD. This seems like a very good deal as normally just the patch antenna and Outernet LNA would be almost $50 USD in total.

To get the discount you must purchase directly from their store and use the coupon 30OFF. The promotion ends 31 December 2016 at 11:59 PM CST so get in quick.

The Outernet items you get for $70 USD.
The Outernet items you get for $70 USD.