It’s that time of year again! Regular science crew transportation missions to and from Antarctica using US Air Force aircraft. Communications occur via Military Satcom in the Pacific Ocean Region. Below are a few recent satcom intercepts as well as ACARS from AERO-I via Inmarsat. I will post more intercepts to this thread as they occur.
Photo by afrc.af.mil. C-17 offloading in Antarctica.
Currently there are 9 AERO-I 600 Baud GMSK channels on POR. Quite a bit of ACARS and CPDLC traffic along with the usual Call Management signaling units. These signals are huge as you can see from the “tightness” of the phase diagram shown below. The AERO-I decoder shown below is simultaneously decoding all channels using just one SDR. There are also some 1200 Baud AERO-I channels present on POR, something to look at next.
Finally found an Aero H/H+ call that was encrypted. Supported crypto services on Aero are US-STU-III (Secure Telephone Unit), STE (Secure Terminal Equipment), FNBDT (Future Narrow Band Digital Terminal). Not clear which service this actually is but I suspect it’s STE. Nice to see encryption being used appropriately. This particular aircraft is a Gulfstream and is registered to Bank of Utah.
This call was not likely intended to be routed via the AMBE voice path. The AMBE codec bandwidth is not sufficient to run crypto.
Most of the popular Inmarsat activity is associated with ships and planes in AOR-E, AOR-W, POR and IOR. There is an Inmarsat satellite called 4F3 parked at 98W that gives CONUS coverage. This satellite is inclined and so does move up and down a bit. This satellite has quite a bit of BGAN services but there is also low rate paging (standard-D) and well as mini-c (standard-C) for fleet tracking. What is fleet tracking? It gives the ability to a company to track and communicate with all of the vehicles that make up a “fleet”. Two way message is possible as well as “polling” (group or individual). The dispatcher can see truck location and provide driving directions as needed.
Example of truck with fleet management.
98W coverage is on left.
On 98W there are currently two mini-c signals, both designated as “private LES” with LES ids of 252 and 253. The protocol is the same as the usual standard-c for the ocean regions but the NCS and LES stations are combined into one. Making some small changes to an existing decoder it was really quite easy to see what fleet tracking is all about. See screenshot below for one bulletin board packet identifying services.
Bulletin Board output.
See the screenshot below for example decode of both private LES simultaneously.
Example fleet tracking decode.
There are many different kinds of trucks that are tracked, some carry petroleum, some carry UPS, FED-EX and AMAZON loads, others more clandestine loads.
Below is a sample antenna that you may see on the top of some trucks that are under fleet management.
The AOR AR2300 is a PC Controlled All-Mode Communications Receiver that spans 40kHz to 3.15GHz. Since the radio is simply a black box with no front panel one must either use the software that comes with it or roll your own. I chose the latter path and wrote my own.
The AOR AR2300 Receiver.
The radio is used with an SDR and so all demodulation occurs in software, therefore only very basic controls are necessary. One feature is a software link to RF Space SprectraVue so that any frequency changes are automatically tracked. Also, the ability to adjust actual frequency for converters that employ a local oscillator.
Too many signals on different bands and tired of manually changing feed lines? Mini-circuits has a nice line of RF Matrix Switches that are USB controlled. I recently acquired a USB-4SPDR-A18 and have now finally gotten around to mounting and installing the new switch.
The switch is made of 4 independent relays that must be wired for proper group operation. The relays are controlled by a small embedded processor with a USB interface.
USB-4SPDT-A18 configured as SP5T (except for one missing jumper).
Since the relays have SMA connectors it is necessary to jumper to some additional SMA to N Female bulkhead adaptors for proper stress relief and cable management.
5 inputs and 1 output.
Bank od sma to N female bulkheads and grounding block.
The final placement, just before wiring. Note the station ground block, this will connect all receivers to station ground system (located near the coax entry area in another room).
Freshly installed microwave switch along with station grounding block.
Here is screenshot of the software that comes with the switch to control the relays.
The sample software from mini-circuits for relay control.
Luckily Mini-Circuits includes a DLL that can be used to customize your own application, which is exactly what i did.
Another new decoder project is in the works. This is another Multi-Channel decoder for Aero but instead of just ACARS and CPDLC it does AMBE and LPC voice decode. The screenshot below shows call logging status output from the prototype decoder. Like the Aero-P project this decoder uses the same control or NCS channels that carries the ACARS/CPDLC traffic except this application focuses on call “following” and directs up to 8 other decoders for actual voice demodulation. Note the captured call highlighted in yellow below. That is a 519 second AMBE call that was classified as non-safety from the aircraft associated with ICAO address 7CF865, which happens to be an Airbus A-300 registered to the Royal Australian Air Force (RAAF). You can look it up yourself at airframes.org.
Status output from decoders.
The AMBE algorithm for Aero is owned by DVSI and therefore requires licensed HW or SW. I am using licensed HW as shown below. This card was available from DVSI but may no longer be due to the inability for them to acquire all the legacy parts to build the boards! I purchased the board a couple years ago for a Mini-M project.
DVSI AMBE DSP Board.
More updates later as the project continues development.This software is intended for commercial use so please don’t ask if you can download it.
Based on the latest Horizons update by JPL (based on Arecibo observations) I have measured the frequency drift of the spacecraft TX frequency (transponder A RHCP). It appears to be drifting upward at a rate of 3.3 Hz per hour. Not bad for such an old spacecraft. This is unlocked carrier frequency measurement over a 3 hour period.
Updated my Horizons data for ISEE-3 today and found this nice note:
Trajectory updated to JPL solution #32 (s32), based on 42 coarse Arecibo plane-of-sky angular measurements spanning May 22 – Jun 23 …
Upon updating things and re-acquiring the signal we have so far a solid signal tracking with little change to frequency. We will see how it performs in next few hours but previously we would observe a 3 Hz per hour change in the frequency. But of course that can just be the unlocked carrier drifting…