Category: Digital Signals

Trunking with the Latest DSD+ 1.08t Fast Lane Version

DSD+ stands for Digital Speech Decoder Plus and is a software program that can allow you to decode digital voice signals such as P25 and MotoTRBO/DMR. DSD+ is under continual development, and in their last public update they began offering early access to the latest DSD+ features in development through their fast lane subscription. The fast lane subscription costs $10 USD for one year and $25 for unlimited early access. Information about joining the fast lane service can be found in the readme file of the latest DSD+ 1.074 public release.

Over on YouTube user John Miller has been testing the latest early access version DSD+ 1.08t. This new version adds trunking support which allows you to follow conversations. Previously other software like Unitrunker was required to follow the trunking signal. On YouTube John has uploaded a video first showing trunking in action, and a second video showing how to set up DSD+ 1.08t for trunking.

DSDplus 1.08t trunking

DSDplus Trunking Setup 1.08t

Monitoring FBI Surveillance Aircraft with ADS-B and an RTL-SDR

After reading an article by the Washington Post about FBI surveillance aircraft spotted in the air after the West Balimore riots, John Wiseman decided to look for more information about these aircraft. Fortunately, John had on his hands a database of about 2 months of ADS-B data that was collected by his continuously running RTL-SDR + BeagleBone Black ADS-B decoder set up.

From reports on the internet John found out that FBI aircraft squawked with 4414 or 4415 codes, and used call signs like JENNA or JENA. With this information John decided to take a look through his ADS-B logs to see if if he could find anything similar. Out of 15,000 aircraft he had tracked, he found 9 aircraft in his logs that matched the criteria, and saw that they did exhibit suspicious behaviour such as circling over LA for hours at a time. Then by looking up their FAA records of the tail numbers of the suspicious aircraft, he was able to discover that these aircraft where licensed to companies with names like NG Research, OBR Leasing, Aerographics Inc. and PXW Services which are suspected Department of Justice front companies. John also writes:

If you Google the tail numbers of aircraft registered to those companies, you start to find forum and mailing list posts (often at sites that tilt toward paranoid/conspiracy/right wing, but not always) with people discussing these specific tail numbers and linking them to the FBI. Some of the supposed evidence includes details of radio communications that people have heard, e.g. talking about “being on station” or using callsigns that start with JENNA, JENA or ROSS, which are supposedly used by the FBI. Other posts claim that DOJ/FBI surveillance aircraft often squawk 4414 or 4415 on their transponders.

An article from the startribune talks about the surveillance planes and says:

The planes use “persistent wide-area surveillance” to photograph large areas for hours at a time, Stanley said. The captured images allow authorities to go back in time, if necessary, to trace pedestrians and vehicles who come to their attention.

Other devices known as “dirtboxes,” “Stingrays” or “IMSI catchers” can capture cellphone data. Stanley said it’s still unclear what technologies have been used in the surveillance flights.

 

Possible FBI Surviellance Aircraft Path from flightradar24.com
Possible FBI Surviellance Aircraft Path from flightradar24.com

How coax cable loss affects ADS-B reception

Over on YouTube user Adam Alicajic has uploaded a video showing how coax cable loss affects the frame rate when receiving ADS-B. To do this test Adam uses a precision attenuator in between his ADS-B antenna and RTL-SDR dongle to simulate attenuation from coax cable loss. His results show that for every 1 dB of attenuation the frame rate drops by about 10%.

Coax cable loss for common type of cable can be estimated with calculators available at http://www.net-comber.com/cable-loss.html and http://www.arrg.us/pages/Loss-Calc.htm. RG-6 cable has a low loss at 1090 MHz of about 0.23 – 0.32 dB per meter, whereas RG58 has a loss of about 0.5 – 0.6 dB per meter and RG174 (stock antenna cable on most RTL-SDR units) has a greater loss of about 1.2 dB per meter.

Coax length loss contribution to the bad ADS-B reception

New EAS SAME Weather Alert Decoder

Over on Reddit and GitHub user cuppa-joe has released a Python based EAS SAME Alert message decoder called dsame which is compatible with the RTL-SDR. EAS is an acronym for Emergency Alert System and is a system that is most commonly used to alert the public to local weather emergencies such as tornadoes, flash floods and severe thunderstorms.

Local EAS weather alerts are encoded with the SAME (Specific Area Message Encoding) protocol. They are transmitted on the local weather radio frequency in the USA and Canada and some weather radio’s are capable of decoding the EAS SAME data. Cuppa-joe’s dsame EAS decoder outputs full EAS weather messages such as:

The National Weather Service in Pleasant Hill, Missouri has issued a Required Weekly Test valid until 12:30 PM for the following counties in Kansas: Leavenworth, Wyandotte, Johnson, Miami, and for the following counties in Missouri: Clay, Platte, Jackson, Cass. (KEAX/NWS)

To use the software you will still need to use a EAS demodulator such as multimon-ng which is available for Windows and Linux, and you will also need Python 2.7+ installed.

An example EAS SAME alert can be heard in the player below:

Receiving SSTV from FleetSatcom Pirates

Radio pirates often make use of the Fleetsatcom satellites to send and receive slow scan television (SSTV) pictures over a wide distance. Fleetsatcom is a satellite communications system used by the US Navy for radio communications. Since these satellites are simply radio repeaters with no authentication mechanisms, pirates soon discovered that they could take over the satellites for their own use.

Over on YouTube user LEGION ELMELENAS has uploaded a video showing his reception of some pirates transmitting a SSTV image at a Fleetsatcom frequency of 252 MHz. To receive the image he used a home made turnstile antenna, an RTL-SDR dongle, SDR# and the RX-SSTV decoder. The image appears to be a photo of a pirates son.

We previously posted more information about Fleetsatcom SSTV pirates in this post.

SSTV from Satcom satellites. RTL-SDR SDRSharp FLTSATCOM pirates

New Version of Digital Speech Decoder DSD+ 1.071 Released

The latest version of Digital Speech Decoder+ (DSD+) has just been released, bringing it up to version 1.071. There appears to be no changelog, so we are unsure as to what is new, but one obvious change is that they now include a new program called FMP which is a simple NFM demodulator, similar to rtl_fm, although it does have a GUI with point and click tuning. FMP can be used as a replacement for SDR# or similar software, and is especially useful to use on low end devices such as netbooks.

An active discussion on the latest release of this software can be found in this thread on the RadioReference.com forums.

The FMP NFM demodulator tuned to a MotoTRBO signal.
The FMP NFM demodulator tuned to a MotoTRBO signal.

DSD+ is a Windows program which can be used to decode and listen to digital voice protocols such as D-STAR, NXDN4800, NXDN9600, DMR/MotoTRBO, P25 Phase 1, X2-TDMA and ProVoice with an RTL-SDR or other radio. On some DMR systems you may also be able to use the included LRRP software, which allows you to view the GPS locations of broadcasting radios. The last major release was version 1.05.

DSD+ GUI
DSD+ GUI

The DSD+ team are now also offering a “fast lane” early access program, which for a small donation will allow you to have early access to new and upcoming DSD+ features. They aim to release a new update to donators every 7 to 30 days, while stable public releases will continue to be released every 4 to 6 months. The donation costs $10 for one year of early access, and $25 for lifetime updates. Some features they are currently working on include:

  • Better tablet support
  • IDAS/NEXEDGE/Cap+/Con+/TIII trunk voice following
  • Per-call audio recordings
  • Other needed DSD+ upgrades
  • FMP upgrades
    • Squelch
    • Drift tracking
    • Selectable sampling rates
    • Adjustable windows sizes
    • TCP client/server mode (eliminates VAC / VB-C)
    • Multiple VFOs
    • Airspy support

Reverse Engineering a Radio Weather Station with an RTL-SDR

On his blog Josef Gajdysek has posted about his experience with using an RTL-SDR to reverse engineer the radio protocol used by his home weather station. Josef’s weather station is an ISM band device and transmits at 433 MHz. First he opened up GQRX and tuned to his weather station’s transmit frequency of 433.6 MHz and recorded some audio in AM mode. Josef initially assumed that the device would use on-off-keying (OOK) to encode the data. However, when he opened the sound file in Audacity and looked at it’s waveform he found that the weather station instead used Differential Pulse Position Modulation. In this modulation scheme the distance between pulses determines whether or not the binary bit is high or low.

Differential Pulse Position Modulation in Audacity
Differential Pulse Position Modulation in Audacity

To decode this Josef then wrote a python script to measure the distance between pulses and thus convert the pulses into a binary string. Then by decoding and analyzing the captured packets he was able to isolate the checksum, temperature, channel, and status flags. Knowing all this information finally allowed him to create a real time decoder that uses rtl_fm. The python script can be downloaded from his post.

The weather station transmitter.
The weather station transmitter.

AISRec for Android: New AIS Decoder

Back in December last year we posted about Jane feverlay’s work on his software called AISRec, which was a Windows AIS decoder for the RTL-SDR that he had developed.

AIS is an acronym for Automatic Identification System and is a system used by ships to broadcast position and vessel information. By monitoring AIS transmissions with the RTL-SDR we can build a boat radar system. We have a tutorial on this here.

Now from YouTube it looks as though Jane has developed a new Android version of AISRec which he describes as a high performance dual-channel AIS receiver for use with a single RTL-SDR dongle. The features of AISRec include:

1. Functions include AIS and GPS NMEA I/O, from/to USB devices and serial ports (special android devices with serial ports).
2. It supports TCP server and UDP forwarding jointly or independently for AIS and GPS.
3. It supports steaming in WIFI in AP or station modes and Ethernet.
4. It supports auto run on boot for especially rooted devices.

He also writes that AISRec also has companion implementations for Windows desktop and metro, Linux on Raspberry Pi 2 and the Radxa pro.

Unfortunately, at the moment there does not seem to be a link available to download the software and the video may only be a preview. The video does link to his Taobao shop at http://shop114459024.taobao.com/ (in Chinese use Google Translate), which is where he might release the software when it is ready.