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

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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

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Leif SM5BSZ’s Testing of the SDRplay

Over on YouTube Leif (SM5BSZ) has uploaded two videos showing some of his tests with the SDRplay. Leif is fairly well known within the SDR community for writing the program Linrad and for doing various tests on different SDR’s on YouTube and his website.

In his first video he first shows that the SDRplay has some susceptibility to USB noise and FM broadcast coming in through the USB cable which can cause some problems. He first shows that a quick fix is to simply coil up the USB cable to create a choke, and that a better fix is to wrap the SDRplay in aluminum foil. Later in the video he also tests dynamic range and reciprocal mixing.

In his second video he shows how he modifies his SDRplay unit to be properly shielded to avoid the USB and broadcast FM interference.


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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

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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#.
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Receiving Inmarsat L-Band AERO with a DVB-T Antenna, Amplifier and Airspy Mini

To show that a specialized antenna is not required to receive L-band Inmarsat AERO satellite signals, YouTube user SkyWatcher has uploaded a video showing how he was able to receive these signals with a cheap DVB-T antenna. SkyWatcher writes:

I’ve recently upgraded from my RTL-SDR sticks (E4000, R820T2) to an Airspy Mini.

I did some testing during the last week and found it very interesting that I was able to receive Inmarsat L-Band signals indoors, with just a DVB-T antenna and amplifier behind the window, no downconverter, no special antenna, no super low-noise amplifier. The window is facing south, with a few degrees to the east and the satellite I’ve received was Inmarsat 15.43W. So, angle antenna to satellite should be estimated 20 degrees.

I’ve used a 18dB DVB-T/Satellite-TV inline amplifier as a ‘LNA’ (noise < 5dB) and a VHF/UHF DVB-T antenna which seems to be a stacked dipole, and therefore should be quite wideband and should make a reasonable general purpose antenna. Anyway, I did not expect it to work on 1.5GHZ at all. Also, I want to mention that the inline amplifier is rated 5 to 18V, but it works just fine with the 4.5V from the Airspy Mini.

It seems that with 10dB S/N, Aero reception is possible and with about 12dB S/N, it is getting reliable.

In general, I am very satisfied with the upgrade to the Airspy Mini. It has a much lower noisfloor and a much cleaner spectrum, compared to my old RTL SDRs. Also, I am very happy with the CPU-usage which is only about 12% on my i5-3210M when using 2.4MHz bandwith, and 18-20% with a bandwith of 4.8MHz.

Together with the ability to use SpectrumSpy and the very useful decimation-feature, the Airspy Mini is the best option to upgrade from a RTL-SDR for me at the moment. Anyway, of course this is just my very personal opinion… 😉

AERO is essentially the satellite based version of ACARS, and the L-band signals contains short ground to air messages with things like weather reports and flight plans intended to be transmitted to aircraft. To decode it with an SDR, the JAERO software can be used.

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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
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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

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