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.

YouTube video showing Meteor-M2 being decoded in real time

Yesterday we posted about a tutorial showing how to decode Meteor-M2 LRPT weather satellite images in real time with a new QPSK decoder plugin for SDR# and a modified version of Lrptdecoder. 

Over on YouTube user max30max31 (a.k.a IZ5RZR) has uploaded a video showing some of the steps in the tutorial as well as the real time result of decoding of the weather satellite image.

RTL-SDR Tutorial: Decoding Meteor-M2 Weather Satellite Images in Real-Time with an RTL-SDR

Back in September last year we posted a tutorial written by RTL-SDR.com reader Happysat which showed how to receive and decode high resolution Meteor-M2 LRPT satellite images. The tutorial required several offline manual processing steps to be performed and therefore could not decode the image in real time.

Now Vasili, a SDR# plugins programmer, and Oleg who is the coder of Lrptdecoder have combined ideas to create a new QPSK demodulator plugin for SDR# that allows the real time reception and decoding of Meteor-M2 LRPT images (in Russian use Google translate). The demodulator also offers the advantage of faster and longer signal locking, and also works much better with weak signals compared to the old method. 

At the same time Vasili has also released another plugin called DDE Tracker which allows a satellite tracking program such as Orbitron to interface with and control SDR#. The plugin can be downloaded on the same page as the QPSK plugin. This is similar to the already existing DDE plugins, but now also comes with a scheduler which allows users to automatically schedule recordings of Meteor-M2 and NOAA satellite passings.

Tutorial

To help users get set up with this new method, Happysat has again come forth with another tutorial which can be downloaded here (.pdf) (.docx) (.txt w/ images in .rar). At first glance the tutorial may seem more complicated than the old method, but in the end it is a much faster and more efficient way at decoding LRPT images. The basic steps involve setting up Orbitron and the DDE plugin to automatically track the Meteor-M2 LRPT satellite and signal, and then setting up the QPSK plugin and the new version of Lrptdecoder to talk to one another in real time via a local TCP connection.

Real time decoding of Meteor-M2 with two new SDR# Plugins.
Real time decoding of Meteor-M2 with two new SDR# Plugins.
QPSK Decoder SDR# Plugin
QPSK Demodulator SDR# Plugin
DDE Orbitron Interface SDR# Plugin.
DDE Orbitron Interface SDR# Plugin.

AMIGOS

One more Meteor-M2 related thing to look forward to in the future is the AMIGOS project which stands for Amateur Meteor Images Global Observation System. This will be a system where users around the world can contribute LRPT images through the internet to create a worldwide LRPT receiver. Oleg of LrptDecoder writes:

There is an idea to merge LRPT receive amateur radio stations in a network through the Internet and create a super LRPT receiver.
I see the benefit of professionals from the control center in the operational monitoring of the condition of the equipment MSU-MR, and for fans of the fullest reception of images from Meteor-M.

All is in testing phase and need some setup for the servers,  data is beeing shared thru a VPN connection to a central server which will have a continous flow of images from all over the world.
Users can join and share in realtime the data more info on:
http://meteor.robonuka.ru/for-experts/amigos/

What is Meteor-M2?

If you don’t understand what all this is about: The Meteor-M N2 is a polar orbiting Russian weather satellite that was launched on July 8, 2014. Its main missions are weather forecasting, climate change monitoring, sea water monitoring/forecasting and space weather analysis/prediction.

The satellite is currently active with a Low Resolution Picture Transmission (LRPT) signal which broadcasts live weather satellite images, similar to the APT images produced by the NOAA satellites. LRPT images are however much better as they are transmitted as a digital signal with an image resolution 12 times greater than the aging analog NOAA APT signals. Some example Meteor weather images can be found on this page and the satellite can be tracked in Orbitron or online.

A software defined radio such as the low cost RTL-SDR, or the higher end Airspy and Funcube dongles can be used to receive these signals.

An Example LRPT Image Received with an RTL-SDR from the Meteor-2 M2.
An Example LRPT Image Received with an RTL-SDR from the Meteor-2 M2.

Updates

The DDE plugin can also be used for tracking NOAA satellites. Some people have been having trouble with set up. Happysat writes a solution:

Download TLE from: http://www.celestrak.com/NORAD/elements/noaa.txt. Make sure the names are the same in DDE Sat Tracking Client schedule. https://dl.dropboxusercontent.com/u/124465398/NOAA_Setup.jpg. Same one as i post in the howto – https://dl.dropboxusercontent.com/u/124465398/DDESchedule.rar

Listening to a Radio Amateur Stratosphere Balloon with an RTL-SDR

Over on YouTube user kpappa has uploaded a video showing his reception of the J43VHF radio amateur stratosphere balloon with an RTL-SDR dongle and discone antenna. On the 10th of May radio amateurs in Greece launched a high altitude balloon. The balloon carried a transceiver payload which allowed amateurs to talk to each other via the balloon at a frequency of 144.200 MHz. The video shows good reception of the balloon and also shows it’s tracking via APRS.fi.

More information about the balloon can be found at https://j43vhf.wordpress.com/ and http://hellashab.blogspot.gr/.

The high altitude balloon's radio payload recovered after landing.
The high altitude balloon’s radio payload recovered after landing.

Adding a Low Pass Filter to an External Local Oscillator Source for the RTL-SDR

At the end of last month we posted about Milan’s work on using an Si535A voltage controlled oscillator with breakout board as a stable replacement for the default RTL-SDR’s low quality 28.8 MHz local oscillator.

Now in order to reduce the number of spurious signals produced at multiples of 28.8 MHz by the external local oscillator, Milan has added a simple low pass filter to the oscillator output. He used a 3-pole Butterworth filter with a 30 MHz cut off point. This filter acts to the convert the Si535A’s square wave output into a sine wave, which should help reduce the number of spurious signals produced.

Square wave before filtering.
Square wave before filtering.
Closer to a sine wave after filtering.
Closer to a sine wave after filtering.

Milan tested his filtering by creating a wideband comparison sweep with rtl_power. With the low pass oscillator inserted, the spurious signals were clearly reduced a significant amount. Then by reducing the drive level from 8mA to 2mA, the spurious signals were reduced even more. By using a filter with more poles it’s possible that the spurious signals could be reduced even further.

Spurious signals with no low pass filter added.
Spurious signals with no low pass filter added.
Spurious signals are reduced after adding the low pass filter.
Spurious signals are reduced after adding the low pass filter.

RTL-SDR vs. Airspy on ADS-B Reception

With the recent release of ADSBSpy, an ADS-B decoder for the Airspy software defined radio, many people have been wondering how much better the Airspy is compared to the low cost RTL-SDR dongle at ADS-B reception. Over on his blog, Anthony Stirk has performed a test comparing an E4000 RTL-SDR with the Airspy.

In his test Anthony uses an A3 ADS-B antenna from Jetvision.de, and a HABAMP which is an LNA plus 1090 MHZ SAW filter. To create a fair test he used an antenna splitter and measured the reception of both dongles at the same time. He ran one instance of ADSB# for the E4000 RTL-SDR, and one instance of ADSBSpy for the Airspy over 24 hours and recorded the results.

Airspy vs E4000 RTL-SDR
Airspy vs E4000 RTL-SDR

The results showed that the Airspy had approximately 50 km more range compared to the E4000 in some areas. More interestingly the stats showed that the Airspy received approximately 7 million more ADS-B messages compared to the RTL-SDR.

While there is no doubt the Airspy will perform better, one thing to note about this test is that it used an E4000 RTL-SDR which is widely considered to have inferior performance at the 1090 MHz ADS-B frequency when compared to the R820T/2 dongles.

Airspy vs. E4000 RTL-SDR
Airspy vs. E4000 RTL-SDR

An interesting RTL-SDR direct sampling modification

Over on the Reddit RTL-SDR discussion board user pksato has posted an image of his direct sampling modified RTL-SDR dongle. His mod includes a simple common base amplifier with 9dB gain, an impedance transformer with calculated output impedance of 50 Ohms and a 5V power filter.

The direct sampling mod allows you to modify your RTL-SDR to receive HF frequencies, without the need for an upconverter. It requires a hardware mod that can be as simple as soldering a wire to one of the RTL2832U pins, but for improved results you will need filters, impedance transformers and amplifiers. There is more information about direct sampling here.

More information and images about pskato’s mod can be found on the Reddit thread.

We also note that amateur radio hobbyist KN0CK (aka Marty Wittrock) sells direct sampling modified dongles that are modified in a similar way to pskato’s mod (circuit placed on top of the RTL-SDR PCB). His products can be found at http://www.kn0ck.com/HF_SDR/.

Direct Sampling Modified RTL-SDR.
Direct Sampling Modified RTL-SDR.
Direct sampling mod with amplifier circuit schematic by pskato.
Direct sampling mod with amplifier circuit schematic by pskato.

Tutorial on Combining and Rebroadcasting ADS-B Feeds with ModeSMixer2

Last week we posted about how the author of the SonicGoose.com blog had written a tutorial on the use of ModeSDeco2 for decoding ADS-B with an RTL-SDR. Now the same author has continued his tutorial by writing how to use the ModeSMixer2 software to combine multiple ADS-B datastreams into a single stream. This is useful for example if you have several RTL-SDR’s at different locations receiving ADS-B data. ModeSMixer2 can also combine data even if you are using different ADS-B decoding software such as dump1090, RTL1090 or ADSB#.

The author’s tutorial goes over setting up ModeSDeco2 to broadcast data over the network, setting up ModeSMixer2 to receive data, and also setting up the basestation.sqb file to add airline logos and silhouettes to the web based GUI of ModeSMixer2.

Screenshot of the ModeSMixer2 web based GUI.
Screenshot of the ModeSMixer2 web based GUI.