Category: Digital Signals

New DSD Block Available for GNU Radio

The popular digital speech decoder (DSD) software has now been wrapped into a GNU Radio Companion block. Previously, DSD required use of virtual audio cables to get decoding to work with GNU Radio, but now the signal audio can be passed directly into this block.

Luke Berndt from the HackRF-dev forums has posted his work to make the functionality of DSD available to GNU Radio users in the form of a GRC block. “I have been playing around a bit and found an easy way to receive and playback digital LMR. More and more of the radio systems are going from narrow band FM to Digital. This makes it tough to listen to them on GQRX. DSD is a great program which can decoded the audio you get when you tune in a system in GQRX, but you either have to run it on another machine with a audio cable in between or figure out how to do a virtual audio cable on your machine.

Luckily, someone wrapped the DSD libraries so they can be accessed as GRC blocks. I have put together a GRC file and a Python program that make it a little easier to use the block.

If you have a chance, give them a try and let me know if they work. There is a good chance I have messed up the values in the filters or else where, but I have gotten clean audio out of it.”

Download the files from GitHub.

DSD is a Linux and Windows software program capable of decoding popular digital speech codecs such as APCO P25 and MOTOTRBO/DMR.

Via DangerousPrototypes

Rain Scatter 10 GHz Reception with the RTL-SDR

YouTube user feri67000 who last month showed us that the RTL-SDR can receive 10 GHz signals with a cheap avenger LNB PLL now shows an interesting experiment where he uses a technique known as rain scatter to receive a 10 GHz beacon with his satellite dish pointed in the opposite direction of the beacon transmitter.

Usually communications at 10 GHz are line of sight only, but by using the rain scatter technique, the 10 GHz signal can be bounced off a precipitation cloud and received with line of sight to the cloud, rather than the transmitter.

rain scatter 10ghz LX1DB beacon

Setting up an APRS iGate with the RTL-SDR

Over on Pawel Janowski’s blog (SQ7MRU) a writeup on how to set up an APRS iGate receiver with an RTL-SDR and cubieboard mini computer has been posted. The article has been written in Polish, but can be translated using Google Translate.

APRS stands for Automatic Packet Reporting System and is usually used by Amateur radio operators to broadcast the current GPS coordinates of something such as a transmitter site/car/boat or high altitude amateur balloon. These APRS packets are received by an iGate and then put onto the internet. Check out aprs.fi for an example.

To create an APRS iGate, Pawel runs a RTL-SDR compatible python program called pymultimonaprs which is used to receive and broadcast the APRS data on to the internet.

aprs_fi_rtlsdr

HackRF Receiving HRPT Weather Satellite Images

On Twitter user @uhf_satcom has been using a HackRF software defined radio together with GNU Radio, a tracking L-Band antenna and this HRPT decoding software to receive and decode HRPT weather satellite images. He used GNU Radio to output to a .RAW16 file, which the HRPT decoding software was then able to use to produce an image.

 

 

HRPT is a picture transmission protocol which stands for High Resolution Picture Transmission. There are multiple satellites which broadcast weather images in this format including the NOAA, GOES, Metop-A and Feng Yun satellites. These satellites transmit HRPT at about 1.7 GHz.

@uhf_satcom also tried to receive these images with the RTL-SDR, but was unsuccessful. But you can still receive the lower resolution APT weather satellite images using the RTL-SDR.

Below are some examples of the images he was able to receive.

hrpt_hackrf1_thumb hrptdata_noaa19a_thumb

Update: This is an image of the L-band antenna he used.

Tracking of Low Earth Orbit Satellites with the RTL-SDR

Over on travisgoodspeed.blogspot.com, Travis shows us an interesting project where he set up a satellite dish that automatically tracks and receives moving satellites, such as those in low earth orbit. Travis uses an old satellite dish salvaged from a maritime vessel as the receiving dish, a RTL-SDR for receiving the signal, and a BeagleBone for motor control and running rtl_tcp. The dish motors use satellite positional data from celestrak.com to automatically track a desired currently visible moving satellite.

tracking_satellite

GR-Air-Modes GNU Radio ADS-B Decoder for the RTL-SDR Updated

Reddit user bistromat has recently updated the GNU Radio based Mode S ADS-B decoder gr-air-modes. He has added Google maps view, a legend and zoom support to the azimuth map view, and has restructured the underlying code. The new gr-air-modes requires the latest GNU Radio 3.7 version.

Check out the original post here (with cute puppy included), and clone the latest version via github from the following link.

https://github.com/bistromath/gr-air-modes

gr-air-modes google maps screenshot

 

Decoding RDS in GNU Radio with the RTL-SDR

DangerousPrototypes.com have brought to attention a GNU Radio RDS decoding project from the website at Anotherurl. Check out the original post here. Anotherurl uses a GNU Radio Companion flowgraph and a .NET program to decode FM RDS messages. RDS is an acronym for Radio Data System, which is used in FM radio transmissions to embed information such as radio station and programme/song information. Some conventional FM radios display this information on an LCD screen. The popular SDRSharp SDR receiver also has RDS decoding built into it’s FM receiver already, but a GNU Radio implementation is very useful for learning how RDS works.

GNU Radio RDS Decoder

via dangerousprototypes.com

Combining Multiple RTL-SDRs for Improved ADS-B Reception

Over on Gough’s Tech Zone blog, Lui has posted a writeup about his experiences with combining multiple remote RTL-SDR ADS-B receivers to privately obtain ADS-B aircraft data from multiple antenna’s at multiple locations. His setup is shown in a diagram below. He has one remote antenna connected to a Raspberry Pi, one to a remote PC and one to his main PC.

Combining Multiple ADSB Receivers

In order to do this he used the Linux based dump1090 ADSB-B decoder and hub software on his main PC. Lui was even able to compile and run the ADS-B hub portion of dump1090 on his Windows PC using Cygwin, but was unable to get the decoder part to work. It doesn’t matter though because the dump1090 hub can receive data from any ADSB decoder, such as ADSB#. His results look very promising as can be seen by the timelapse of plane traces in the image below.

nearairport

Lui also has some other interesting ADS-B + RTL-SDR posts that you should check out where he tests ADS-B reception with a Mini R820T dongle.