Category: Satellite

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

Building a simple NOAA APT Antenna out of an Umbrella

In order to optimally receive NOAA weather satellite images a special satellite antenna tuned for 137 MHz should to be built. Generally either a QFH or turnstile antenna is recommended as these receive signals coming from the sky very well. If you are interested in receiving weather satellite images from NOAA satellites with an RTL-SDR dongle then we have a tutorial available here.

While QFH and turnstile antennas are not difficult or expensive to build, they still do require a small amount of electrical and construction skills. Over on YouTube user Wanderlinse shows us a possible alternative NOAA antenna that is simply made out of an old umbrella (the video is narrated in German, but it is easy to understand from the visuals). He uses a short BNC cable with crocodile clips, and connects one clip to the spines of the umbrella, and the other to the central metal shaft. For some reason this seems to create a good antenna that receives NOAA APT signals very well. To prevent wind issues he also cuts out some holes in the umbrella fabric.

Wanderlinse also shows that he can receive other signals with this umbrella antenna too, such as long wave, medium wave, shortwave, aircraft radio and ham radio.

Regenschirm Antenne NOAA APT Umbrella Antenna (quick n dirty)

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.

Listening to an Astronaut Transmitting from the International Space Station

Over on YouTube user surfrockuk shows a fun and educational use of the RTL-SDR. Every now and then astronauts will arrange a ham radio session where they will communicate with a school. An RTL-SDR can be used to listen in on at least the downlink (astronaut talking) portion of these transmissions. 

The following video shows astronaut Tim Peake transmitting from the international space station (ISS) on Feburary 19th 2016. He was speaking to Oasis Academy in the UK. To receive the signal surfrockuk used an RTL-SDR with a QFH antenna. Many people have reported that other simple antennas such as discones, quartwave ground planes and even long wire antennas have been good enough to receive transmissions from the ISS too.

Other transmissions that can be received from the ISS include SSTV, space walk communications, and in the future DATV.

Tim Peake Transmitting from the International Space Station - 19th February 2016

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