Category: RTL-SDR

Decoding the NOAA Weather Satellite Telemetry Beacons

It is well known that the NOAA satellites broadcast weather satellite images which can be received and displayed with an RTL-SDR and computer. What is less known is that there is a telemetry beacon that is also transmitted by the same satellites. The telemetry not only contains data such as the current spacecraft time, day and ID, but also contains scientific data from on board instruments such as:

  • The HIRS/3 and HIRS/4 instruments which is a high resolution infrared sounder which can be used to create a low resolution multi-spectral scan of the earth. (more info)
  • The Space Environment Monitor (SEM-2) which has a Medium Energy Proton and Electron Detector (MEPED), and a Total Energy Detector (TED). This experiment is used to measure the effect of the sun on satellite communications. (more info)
  • The experimental DCS/2 transmitter which retransmits signals from 401.65 MHz sea buoys, arctic fox collars, sea ice monitors, weather balloons and more. (more info pdf)
  • The ARGOS Advanced Data Collection System (ADCS) which amongst other uses is used in research for tracking animal GPS collars around the world.

On GitHub user nebarnix has been working on a standalone C based decoder for these NOAA satellite telemetry beacons. So far from her wiki log, it appears that she has been able to get HIRS decoding and producing an image, receive and graph SEM-2 data, and decode the locations of some fixed DCS transmitters.

A HIRS multispectrum scan of the earth from the NOAA-18 satellite telemetry beacon.
A HIRS multispectrum scan of the earth from the NOAA-18 satellite telemetry beacon.

Building a very low cost satellite tracker for your RTL-SDR

A satellite tracker is a motorized unit that points a directional antenna towards passing satellites. Most satellites are not in a fixed orbit, and will fly over your head a few times a day and will be receivable for a few minutes, and a directional antenna is usually recommended since the signals can be weak. The goal of the SatNOGS project is to set up various volunteer satellite tracker stations around the world, and network the received data on the internet, so that satellite data is always being received and shared.

Over on his blog, Paul has written up a tutorial showing how he’s managed to make a super cheap satellite tracker for his RTL-SDR using some pan/tilt servos, a Yagi antenna made from measuring tape, and and Arduino running the SatNOGS tracking software. When he tested the tracker he was able to receive NOAA 18 and some of the XW-2 satellites.

Although the tracker works, he admits that there are some problems and that it is probably not as good as the SatNOGS recommended build, which is a more permanent solution. But the SatNOGS build requires access to a 3D printer and higher quality components, so Paul’s solution is a much cheaper solution to implement at least for experimentation.

The low cost satellite tracker built by Paul.
The low cost satellite tracker built by Paul.

Satellite Tracker NOAA 18 40x

Demonstrating the IF Processor and Notch Filter Plugin in SDR#

Over on YouTube user  FMDX HUN (Luc1f3rk0) has uploaded a video showing how useful the SDR# IF Processor and Notch Filter Plugin can be when attempting to DX FM broadcast stations. He shows that it can be used to listen to stations that are almost overlapping by cutting out the unwanted signal.

The plugin itself can be downloaded from http://rtl-sdr.ru/page/para-novyh-plaginov.

SDRSharp+IF Processor & Tracking Notch Filter Plugin demostration

QSpectrumAnalyzer Updated to Version 1.4.0

QSpectrumAnalyzer is a Linux based opensource GUI front end for rtl_power or rtl_power_fftw and can be used with an RTL-SDR to scan for signal activity on wide swaths of the frequency spectrum. Recently QSpectrumAnalyzer was updated to version 1.4.0 and the new updates add the following features:

  • Max peak hold
  • Min peak hold
  • Averaging
  • Spectrum Persistence (RTSA fosphor-like effect)
  • Smoothing

Previously we posted about QSpectrumAnalyzers ability to use rtl_power_fftw, which is a much faster version of rtl_power. The new features help make the spectrum view clearer especially when using rtl_power_fftw at a very short interval.

qspectrumanalyzer_screenshot qspectrumanalyzer_screenshot2

Building a Tuning Knob for SDR#

If you love using SDR’s on the PC but miss the old feeling of tuning the frequency with a knob then 19max63 has a solution for you. On his blog he’s posted about how he built his own tuning knob by using a USB mouse PCB circuit and replacing the mouse wheel with a rotary encoder with no detents. Detents are the little clicks or steps that you can feel in some knobs, but for accurate frequency tuning you don’t want those.

His post shows the exact parts he bought (knob, mouse, buttons), the mods he made to the knob and mouse PCB, and how he put it all together. He writes that parts can all be found cheaply on eBay or Aliexpress and the total cost to produce a single knob was only about $4 (though he had to buy some parts in lots of 5 to 10).

The finished tuning kob for RTL-SDR and SDR#.
The finished tuning kob for RTL-SDR and SDR#.

Using Aisdecoder to decode both AIS channels simultaneously

Recently SV3EXP wrote in to let us know that he has been documenting his experiences with trying to get aisdecoder to decode both AIS channels simultaneously. AIS stands for Automatic Identification System, and is a system used to track the locations of marine vessels. With an RTL-SDR or other SDR radio, and appropriate decoder software you can plot ship positions on a map. As the AIS system uses two separate channels for redundancy, you can get a faster and more reliable update rate if you monitor and decode both channels.

On his blog SV3EXP shows how he uses Linux and the "demod" and "csdr" tools to demodulate multiple channels at the same time from IQ data generated by rtl_fm. The demodulated data is then fed to the aisdecoder software for decoding, and then fed to aisdispatcher for feeding the AISHub.net AIS data aggregation website.

Of course the easier solution to decode both AIS channels at once is to use decoding software that already supports this, such as AISdeco2 or AISrec which can be downloaded at http://xdeco.org, and https://sites.google.com/site/feverlaysoft respectively. But regardless SV3EXP's method does show an interesting way to demodulate multiple streams using only command line tools.

SV3EXP also wanted to point out that he is selling a bias tee powered PSA4-5043+ based LNA on eBay which is compatible with the bias tee on our RTL-SDR Blog SDR units.

AISHub Coverage Areas
AISHub Coverage Areas

P25 Decoding: OP25 + RTL-SDR vs a Uniden BCD996T

APCO P25 is a digital voice signal and is commonly used like public safety departments such as police and fire. With an RTL-SDR and the open source Linux based OP25 decoder these signals can be decoded, assuming they are unencrypted. Software like DSD+ can also be used, but OP25 can supposedly decode more systems. Before the RTL-SDR, hardware scanners like the $~360 USD Uniden BCD996T digital scanner radio were typically used. 

Over on YouTube user Rob Fissel has uploaded a video showing a comparison between an RTL-SDR using the OP25 decoder and a Uniden BCD996T. Both radios are used to decode a weak P25 Phase 1 LSM signal. He uses a Scantenna antenna with an antenna splitter to run both radios at the same time. His results show that even though the constellation is poor, OP25 does a good job at decoding the signal and producing voice, whereas the BCD996T doesn’t even manage to hear the control channel.

OP25 VS BCD996T - Weak Signal P25

RTLSDR4Everyone Review: SDRplay RSP vs RTL-SDR

Akos of the rtlsdr4everyone blog has recently written up a comparison of the RTL-SDR and SDRplay. The SDRplay is a $149 USD software defined radio with a 100 kHz to 2 GHz frequency range, a 12-bit ADC, and up to 8 MHz of bandwidth. It now competes heavily with the $99 Airspy Mini which is a similarly specced SDR.

Akos compares the two units and comes to the conclusion that the RTL-SDR is still the best choice for beginners, but that the SDRplay is definitely a good choice if you have good antennas in place and if the receiver is the major bottleneck in your setup.

In his review he goes over several points covering the costs involved, aesthetics, customer support, PC hardware requirements, setup, operation and finally reviews the performance of the SDRplay. His results show that the SDRplay generally receives much better than the RTL-SDR, but has some problems with broadcast FM imaging.

Also check out our own previous review which compared the SDRplay, Airspy and HackRF here.

Akos' test shows that the RSP has some problems with FM broadcast imaging.
Akos’ test shows that the RSP has very good reception, but has some big problems with strong signal imaging.