Tagged: satellite

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.

Using an RTL-SDR on a high powered rocket to capture GPS data

Over on the SDRGPS blog Philip Hahn and fellow aerospace engineer Paul Breed have been working together to try and use an RTL-SDR to help get accurate GPS data for tracking small high powered rockets. They write that their end goal is to be able to “track high power rockets in high acceleration / speed / altitude environments”.

In their latest attempt they launched a rocket with an RTL-SDR on board with it capturing GPS data to be later processed with GNSS-SDR. The goal was to get a GPS fix throughout the flight. Unfortunately they found that a good fix was only obtained while the rocket was on the ground, and not much data was obtained while it was in the air. They write that they suspect that the fault lies in the vibration in the rocket which can affect the frequency stability of the crystal oscillator, or in the GPS satellite tracking loop algorithm.

They still hope to be able to get some usable information from the flight by trying other algorithms on the data, but they are also seeking advice from anyone who might know how to help them, so please contact them if you know anything that may help.

If you are interested in this, then see our previous post about how Philip showed us how to use an RTL-SDR to receive and plot GPS data.

RTL-SDR + GPS antenna plus an Intel NUC computing platform.
RTL-SDR in aluminum case + GPS antenna + an Intel compute stick and IMU.
The rocket carrying the RTL-SDR.
The rocket carrying the RTL-SDR.

Meteor M-N2 now active again

According to various reports the Russian Meteor M-N2 satellite appears to be active again once more. The Meteor M N-2 is a polar orbiting Russian weather satellite that was launched in July 2014. It transmits with the LRPT protocol which allows us to receive weather satellite images with an RTL-SDR that are of a much higher resolution than the NOAA APT satellites. 

Unfortunately late last year Meteor M N-2 had some problems and LRPT transmissions were turned off for the time being. During this downtime the Russian space agency switched the LRPT transmitter on the older Meteor M N-1 satellite back on, even though the satellite was tumbling in orbit. Currently people are not reporting any signal from Meteor M N-1, so this may have been turned off, perhaps temporarily.

Now however, it seems that Meteor M N-2 has been switched back on again and various people have already successfully received its signal. If you want to receive these Meteor M N-2 weather images with an RTL-SDR dongle or other SDR then you can view the tutorial written by Happysat here.

Another Sample LRPT Image
A Sample LRPT Image from Meteor M N-2

Finding GPS Signals from within the Noise Floor with an RTL-SDR

If you were to try to simply spot a GPS signal at 1.575 GHz in the spectrum on a waterfall in a program like SDR# you would probably fail to see anything. This is because GPS signals are very weak, and operate below the thermal noise floor. Only through clever processing algorithms can the actual signal be recovered.

Previously GPS and SDR enthusiast “e.p.” showed us on his blog how to use an RTL-SDR and the GNSS-SDRLIB and RTKLIB software to receive GPS and get a position lock.

Now more recently e.p. has uploaded a post that explains a bit about how GPS signals are actually detected from below the noise floor. In his post he uses GPS data collected by his RTL-SDR dongle, and a fairly simple GNU Radio program consisting of a Fast AutoCorrelation Sink block.

With real data passed through the fast autocorrelation block he is able to observe GPS signal peaks that occur every millisecond. E.p. explains the reason for this:

Why every millisecond? The coarse/acquisition code for GPS (C/A) has a period of 1023 chips which are transmitted at a rate of 1.023 MBit/s. This results in period of 1 millisecond. BAM!

In a later post e.p. has also uploaded some sample GPS data collected with his RTL-SDR so anyone can play around with GPS decoding.

Autocorrelation of a GPS signal resulting in peaks every millisecond.
Autocorrelation of a GPS signal resulting in peaks every millisecond.

YouTube video showing Inmarsat C-Band AERO Reception

Last week we posted how programmer Jonti had successfully implemented a C-Band AERO decoder into his JAERO software. C-band AERO signals are the earth downlink portion of AERO. Planes transmit data upwards towards the satellites and then the Inmarsat C-band transmitter re-transmits the information back to a basestation on earth. This is different to the L-band AERO signals which are signals transmitted from the satellites to the aircraft. C-band signals are interesting because they contain plane position info, and so can be used to track aircraft much like what is done with ADS-B reception, but over a much larger area. However, C-Band signals are much more difficult to receive as they are at 3.616 GHz and require a 1.8m or larger satellite dish.

Over on YouTube user AceBlaggard has uploaded a video showing an example of C-Band signals being received with an Airspy SDR and being decoded with the new version of JAERO. About the hardware used AceBlaggard writes:

Hardware is a 1.8M PF dish and Titanium Satellite C1 PLL LNB feeding a Prof-Tuner 7301 sat card which loops out to an Airspy SDR.

Inmarsat C Band aero feed.

Comparing LHCP and RHCP Reception of a Thuraya Satellite with an RTL-SDR and MIX4ALL

Over on YouTube Adam Alicajic 9A4QV (creator of the popular LNA4ALL) has uploaded a video showing a comparison of reception of Thuraya satellites with a LHCP (left hand circular polarization) and RHCP (right hand circular polarization) patch antennas. To receive Thuraya satellites, a LHCP antenna should be used, and Adam’s results show that using an antenna with the wrong polarization (RHCP) produces a signal that is as theoretically expected almost 20dB lower. Shortly after initially posting this Adam wrote in to comment on the following:

Thuraya LHCP original patch antenna have 2 patches stacked inside the panel antenna and the hand made RHCP patch antenna is made only of 1 patch. Theoretically, this should give the 3dB more gain for the Thuraya antenna.

The difference in the received signal due to polarization should be (theoretically) 20dB, thats RHCP vs. LHCP and I experience some 18dB of difference which is good result. Why not 20dB? First of all it is impossible to get 3dB more gain stacking the antennas, this is just the theory, more likely 2db in the practice.

To receive the signals Adam uses the patch antennas, which are connected to the MIX4ALL (a downconverter that he is currently developing), which is then connected to a RTL-SDR dongle.

In the first video Adam shows the difference the wrong polarization makes, and in the second he shows some information about the Thuraya LCHP antenna he uses.

Receiving Thuraya sat - LHCP and RHCP comparison using MIX4ALL

Thuraya antenna L-band + GSM

Building a Wideband Helix Antenna for L/S/C Bands

Over on YouTube user Adam Alicajic (creator of the popular LNA4ALL low noise amplifier) has uploaded a video showing the performance of a home made wideband helix antenna that he has created for receiving signals such as ones from L-Band Inmarsat satellites. See our tutorial for more information on receiving Inmarsat signals.

Adams helix antenna is built out of an old used can and is based on a 1.1 turn design. In the first of three videos he shows that the SWR of the antenna is all well below 2.0 from 1.5 GHz to 3 GHz. In the second video Adam shows the performance of the helix antenna on actual L-band signals being received with an RTL-SDR dongle. In the final video Adam compares the helix again a patch antenna and finds that the two receive with very similar performance.

Wideband L/S/C band helix antenna Part.1

Wideband L/S/C band helix antenna Part.2

Wideband L/S/C band helix antenna Part.3

Meteor M-N1 Still Working, Meteor M-N2 Still Down

The Meteor M N-2 is a polar orbiting Russian weather satellite that was launched in July 2014. It transmits with the LRPT protocol which allows us to receive weather satellite images that are of a much higher resolution than the NOAA APT satellites. For a while since the launch RTL-SDR users had a good time receiving beautiful images from Meteor M-N2, but unfortunately since late last year the N2 LRPT transmitter has been turned off, due to technical problems with the IR sensors as cited by Russian meteorologists.

Fortunately for Meteor N2 enthusiasts the old Meteor M N1 satellite which was thought to be dead sprung back into life around November 2015. Recently Matthew A., a reader of our blog wrote in to let us know that while N2 is still not transmitting, N1 is still transmitting, albeit with somewhat distorted images. Matthew also mentions this link: http://homepage.ntlworld.com/phqfh1/status.htm, which contains up to date info on the status of all weather satellites. He also writes: 

  • While transmissions are readily detectable and decodable at night, it seems that M N-1’s infrared sensors are not functioning. Yielding only black, with the typical noise bars of Red, Green, or Blue
  • As has been previously mentioned, Meteor MN-1’s stabilization system has obviously failed, and the horizon is clearly visible. Perhaps not of scientific value, but certainly beautiful. 

We also note that there are several comments over on the Meteor-M N2 news and support website regarding receiving images from N1 and N2. It seems that sometimes N1 also has some problems with transmission, but they are usually quickly fixed.

Meteor M-N1 Image Received by Matthew
Meteor M-N1 Image Received by Matthew