First tests of the LimeSDR with GQRX

The LimeSDR is a new SDR $299 USD currently seeking crowdfunding over on CrowdSupply. At the time of this post the LimeSDR is currently 60% funded, with 29 days left to go. The LimeSDR is a RX/TX capable device, with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and 61.44 MHz bandwidth. From the price and specs, we consider it to be a potential next generation HackRF type device which will have vastly improved RX performance.

Over on the MyriadRF blog, Alexandru Csete has received a demonstration unit, and has written about his first thoughts on the LimeSDR. Alexandru was able to easily set the device up by using SoapySDR and GQRX on Linux. He first did the “hello world” of SDR and was able to successfully receive broadcast FM signals. Next he tried to receive Amateur Satellite signals and was successful in receiving the FO-29 satellite. Finally he was also successful in receiving NOAA weather satellite images.

From a quick judge of the waterfall images it looks as though the LimeSDR has a very clean spectrum with a low noise floor, which looks good for RX. In future posts Alexandru hopes to test out the transmit capabilties of the LimeSDR, as well as its shortwave RX performance.

LimeSDR receiving the FO-29 satellite on GQRX.
LimeSDR receiving the FO-29 satellite on GQRX.
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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.
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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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