Getting close to releasing XHRPT decoder. Upgraded to now decode MetOp-A/B, FengYun-3A/B/C in addition to the previously supported NOAA-18/19/15 and Meteor-MN2. Here is a short video of a typical pass of MetOp-B AHRPT. The video has been speed up, so the entire pass is just 26 seconds.
NOAA’s GOES-13 (East), GOES-15 (West) and now GOES-16 produce some amazing images. Both GOES-13 and GOES-15 broadcast weather images to users with suitable ground stations using a protocol called LRIT (Low Rate Information Transmission). GOES-16, a more advanced satellite does the same but uses a protocol called HRIT (High Rate Information Transmission). The parameters of each satellite are shown below.
In general, the LRIT and HRIT signals are not strong. There is not much room for a non-optimal setup. You need a good low noise figure LNA, a filter if you have nearby interference, high quality coax and a suitable antenna. Antennas can be a 1m or larger dish, a grid-style antenna or even a Yagi with suitable gain. The polarization from the satellites are Linear, so if you decide to use a circular feed just be aware that you will loose 3dB of the signal.
The latest version of the decoder software is shown below. It’s made up of two GUI panels. One for controlling demodulation and the other for controlling ingesting and image generation.
Currently, there is support for the AirSpy, AirSpy Mini and SDRplay RSP2. The supported sample rates are 2.5 MSPS and 3 MSPS. IQ data flows from a dedicated streamer application over UDP to the demodulator.
AirSpy Streamer GUI Interface
If you have the proper equipment, are able to receive a high quality signal from any of the GOES satellite, and are interested in this software then please contact me for a demo package. The streamers, actual GUI application, including the ingestor and supporting libraries are free, however the core DSP is not and must be licensed. The cost is $100 USD for this license.
The HackRF one PCB is manufactured with an option for a shield. This shield is available from NooElec. It’s a simple and quick addition, just some easy soldering. The hardest part is just removing the HackRF one from it’s plastic case.
Below you can see the shield framing installed.
Shield frame installed.
Now with the lid installed and the job is complete.
Shield frame and lid installed.
Next up is adding a small (20mm x 20mm x 6mm) aluminum heatsink to the ARM processor. The ARM processor runs pretty hot on the HackRF and this heatsink will reduce the operating temperature, extending the life of the part. The heatsinks can be found for around $0.50 each on amazon. The most important item is the Arctic Alumina thermal *adhesive*, this ensures the heatsink makes good thermal contact and remains attached under high temperatures. The thermal adhesive can also be found in amazon for $7.99.
HackRF prep for heat sink.
Below you can see my improvised method of ensuring good contact during the curing phase.
Weighting the adhesive.
After about 1 hour the “delicate” process is now complete.
My new AirSpy SDR arrived last week. The goal this weekend was to make a small application to stream the IQ over Ethernet and then test it with one of the Inmarsat decoders that I have previously developed.
The API is very similar to the HackRF One and so it did not take long to get the streaming to work. The AirSpy currently supports either 10MSPS or 2.5MSPS. I choose to work with 2.5MSPS as I will need to decimate it even at that rate.
Here is the small application that runs on the host machine where the AirSpy is plugged into USB.
AirSpy Streamer Application.
This application will take the IQ samples at 2.5MSPS and then decimate by 8 to give 312.5KSPS. This is then sent over Ethernet using UDP. The decoder can then be located anywhere on the network, including the host machine (loopback). Below is the received L-Band spectrum after decimation as received by the decoder.
IQ Stream from AirSpy.
Here is the main decoder log window showing various events along with notification of any messages written to disk.
Decoder status console.
Below are the two decoder windows showing real time status.
Real time decoder status.
And finally the overall SDR/Message status and statistics.
SDR and message statistics.
The AirSpy is performing very well and decoder has been running 2 channels for 24 hours now without any frame loss or disruptions. Excellent performance. I will be placing an order for another one this week for another project I have in mind.
In an serious effort to reduce patch panel management, another Mini-Circuits USB 4SPDT-A18 RF Switch has been added. Now, along with the original RF Switch, selections can be made from up to 10 different RF sources, including various dishes, yagis, omnis, etc. Custom software is used to control the relays and tie them into the AR2300 control software.
Blue Force Tracking is a GPS-enabled system that give US Military the location of “friendly” military forces. You can read more about it on Wikipedia.
Inmarsat is one of the commercial satellite providers that has a contract with the the US Military to provide coverage in certain areas. Below is a public domain image showing US Navy soldier preparing his Blue Force Tracker before departing.
Use of BFT by US Navy.
Maps like the one below of Baghdad International Airport is an example of how troops show up overlaid on a map.
US Army Image of BFT at Baghdad International Airport.
Below are two channels of the Blue Force Tracking waveform as discovered on one of the Inmarsat satellites. Rest assured this waveform is completely secure and highly encrypted.
Inmarsat L-Band signals from both CONUS and POR need to be routed to various receivers and SDRs, this distribution system is a pretty simple solution (as shown below).
Inmarsat Antenna Distribution.
It’s based on taking an L-Band signals from a dish, where pre-amplification at the feed is already done and then feeding it to another L-Band amplifier, followed by a band-pass filter (since the previous amplifier is rather wide) and then finally to an L-Band splitter. Various receivers and SDRs are then connected to the output of the splitters. The amplifiers, band-pass filters and splitters are all from mini-circuits. Another view is shown below.
Inmarsat Antenna Distribution.
The two L-Band amplifiers require 12V for proper operation. Control of the supply voltage is feed through a “web relay” for remote control. The web control relay is a compant called KMtronic – thet are available on Ebay. Below is a closeup of the web relay.
Web Control Relay.
There is some built in web server application that you can access from ant browser as shown below.
Web browser interface.
While it’s convenient to have access via a web browser I prefer to use a standalone application, so that will be my next project, stay tuned.