ACARS 1.0 Decoder.rar
Apolinario Mukherjee
Everyday multiple NOAA weather satellites pass above you. Each NOAA weather satellite broadcasts an Automatic Picture Transmission (APT) signal, which contains a live weather image of your area. The rtl-sdr dongle combined with a good antenna, SDRSharp and a decoding program can be used to download and display these live images several times a day.
This tutorial will show you how to set up a NOAA weather satellite receiving station, which will allow you to gather several live weather satellite images each day. Most parts of this tutorial are also applicable to other software radios, such as the funcube dongle and HackRF, but the rtl-sdr is the cheapest option. Hardware radio scanners can also work, provided the radio has a large IF bandwidth (30 KHz +) and a discriminator tap.
We will assume you have the rtl-sdr dongle set up and working already. If you have not bought a dongle yet, see the Buy rtl-sdr page for information, and the check out the Quickstart Guide for an easy setup routine with SDRSharp. You will also need to have an audio piping method installed and set up. Audio piping will allow the audio from SDRSharp to be passed to a decoding program. You can use either windows stereo mix, VB-cable (free) or virtual audio cable (paid with trial version).
The sampling rate of your audio piping method should be set to at least 48000 samples/sec. To set this in Windows, right click your device in the Windows sound recording tab, go to properties and under the advanced tab, set the sample rate to 48000 Hz. Do the same to the same device under the Playback tab as well.
The NOAA APT weather satellites broadcast their signal at about 137 MHz, and their signals are also right hand circularly polarized (RHCP), which means you will need a right hand circularly polarized antenna to properly receive the signals. This is because as the satellites broadcast their signal, they also rotate, rotating the signal polarization. Three options for easy homemade circularly polarized antennas are presented below.
A Quadrifilar Helix (QFH) is a circularly polarized antenna that can be constructed out of PVC pipe and coax cable. Most people report that the QFH antenna has slightly superior reception compared to the turnstile.
A tutorial on building a QFH out of coax cable and PVC pipe can be found here. Another home brew QFH antenna constructed out of copper wire is here. Also, a good calculator for determining QFH antenna dimensions for 137 MHz can be found here.
WXtoImg is a free weather satellite decoding program, which can decode the APT signal, and also tell you the times and frequencies of the satellites passing overhead. There is also a paid version of WXtoImg which can unlock more features, however it is not required for use with rtl-sdr. To use WXtoImg and SDRSharp together follow the instructions below.
WXtoImg should now be decoding and showing the weather satellite image as it is received. You may need to periodically adjust the frequency to center the signal as the Doppler effect will cause it to move. But, with the rtl-sdr adjusting for the Doppler shift is not critical as the filter bandwidth can be simply set larger than 34 KHz (try 36 -40 KHz) so that it is large enough to receive the entire signal even as it as it shifts.
It is not entirely necessary for these NOAA satellites, but if you want the Doppler effect to be automatically adjusted for in SDRSharp, you can use free a program called Orbitron, which with the aid of a plugin, will interface with SDRSharp.
The EAS is a national public warning system that requires broadcasters, cable television systems, wireless cable systems, satellite digital audio radio service (SDARS) providers, and direct broadcast satellite (DBS) providers to provide the communications capability to the President to address the American public during a national emergency. The system also may be used by state and local authorities to deliver important emergency information, such as AMBER alerts and weather information targeted to specific areas.
Reddit user rtlsdr_is_fun is working on software to automatically detect an EAS broadcast from a NOAA Weather Radio stream using an rtl-sdr (or any SDR, or even an internet stream) and then immediately play it and record it. This will allow the EAS alert to be heard up to 2 minutes faster than email/sms alerts, without the need to constantly listen to the NOAA WX Radio.
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.
The first post discusses antennas that are useful for NOAA satellite reception, and shows how to build a homemade turnstile and QFH antenna. His second post shows a beginners guide to the software that can be used to decode the APT signal in order to obtain a live weather satellite image.
There are now dozens of software defined radio packages that support the ultra cheap RTL-SDR. On this page we will attempt to list, categorize and provide a brief overview of each software program. We categorize the programs into general purpose software, single purpose software, research software and software compatible with audio piping.
SDR# is a simple to use program that also has some advanced features. It has a useful modular plugin type architecture, and many plugins have already been developed by third party developers. The basic SDR# download without any third party plugins includes a standard FFT display and waterfall, a frequency manager, recording plugin and a digital noise reduction plugin. SDR# also decodes RDS signals from broadcast FM.
HDSDR is based on the old WinRAD SDR program. HDSDR supports the RTL-SDR through use of an ExtIO.dll module. To install HDSDR, download the program from the link on the main HDSDR page, then to use the RTL-SDR you will need to download the ExtIO_RTL2832.dll file an place it into the HDSDR folder. When opening HDSDR, select the newly copied ExtIO_RTL2832.dll. The other dlls that come with HDSDR will not work with the RTL-SDR, even though they have RTL-SDR in their filename. The official installation instructions can be found here.
SDR-RADIO.COM V2 is a popular SDR program with many advanced features. As such is it a fair amount more difficult to learn and use compared to SDR# and HDSDR. Be sure you install version 2 and not V1.5 as only V2 has RTL-SDR support.
Once sdr-radio is installed, to get it working with the RTL-SDR you will need to compile or download three .dll files (SDRSourceRTL2832U.dll, rtlsdr.dll and libusb-1.0.dll) and place them into the sdr-radio folder. To compile your own dlls see the instructions here, otherwise download the dlls directly from the bottom of this link. If the dlls were placed in the correct folder you will be able to add your RTL-SDR as a receiver by clicking on the +Definitions button, and then finding and adding the RTL SDR (USB) option under the search drop down menu.
Like HDSDR, not only does sdr-radio have a RF FFT signal and waterfall display, but also an optional audio spectrum FFT and waterfall display. Built in are also several DSP features like a noise blanker, noise reduction filter, notch filter and squelch options. The EMNS noise reduction filter is particularly good at automatically cleaning up and clarifying voice signals.
To add to the feature list, sdr-radio also has built in PSK, RTTY and RDS decoders, and also comes with a satellite tracker. Furthermore, sdr-radio has an excellent remote server which will allow you to easily set up and connect to a remote RTL-SDR server over a network or the internet. Finally, sdr-radio is capable of listening to up to 6 signals in the same chunk of visible spectrum at a time.
Linrad is a free advanced SDR program with a steeper learning curve compared to most other SDR programs. Many users prefer to use Linrad as it can be set up to have a very high amount of information density on the screen and it also has an advantage with receiving signals with the E4000 tuner as it can be made it run in a special linearity mode which significantly improves the dynamic range.
To install Linrad on Windows first download and run the setup-dll installer, and then download and extract the actual Linrad program. You will need to go through a text based set up at the very beginning.
GQRX is a free simple to use SDR receiver which runs on Linux and Mac systems. It is similar to SDR# in terms of features and simplicity of use. GQRX comes with a standard FFT spectrum and waterfall display and a number of common filter settings.
Studio1 is a non-free commercial SDR receiver with advanced DSP capabilities, and is claimed to have the lowest CPU usage of any general purpose SDR software. Studio1 supports the RTL-SDR through use of an ExtIO.dll module.
ShinySDR is an SDR application built in GNU Radio with a web based interface. It is currently in a usable state, but is still undergoing major development. Since ShinySDR is controlled via a web interface it can easily be controlled over a network or the internet. It also has a plugin type development feature which allows demodulators to be easily written and integrated.
The current main technical advantage to ShinySDR is that it has a persistent waterfall, meaning that the waterfall can be moved, zoomed and re-tuned without loss of any history like in other SDR software.
WebRadio is a Linux based application that is attempting to build an open source system for the RTL-SDR and other software defined radios similar to the closed source WebSDR . The WebSDR system allows for multiple public users to connect to a radio over the internet and tune to various frequencies. WebRadio is currently functional but still under development.
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