It would be nice to have the schematics available so that, for example, the SAW filter can be removed/bypassed, which unnecessarily tie the boards to Inmarsat.
Other projects I would love to see:
Software GPS receiver for accurate lab time source - 10 or 50 MHz.
I am a sailor. I am interested in Decoding Inmarsat STD-C EGC Messages.
There is java software (http://www.tekmanoid.com/egc.shtml) for it.
I haven’t this software yet. It is send on e-mail request.
It could be used on D.C. or Raspberry Pi, I think.
Regards,
Fredrikson
I had this running a few weeks ago and it works reasonably well. Turning it into a GPS-disciplined clock could be interesting but I’m not sure where to start. Would you replace the rtlsdr’s xtal with a 28.8MHz OCXO and control the oven until the signal frequencies look right? Then you’d have the task of deriving a stable lab clock out of that weird frequency, and frankly that seems like more trouble than it’s worth. (Or get a 10MHz OCXO and synthesize the 28.8 from it? But still, awkward every which way.)
Inmarsat traffic looks a lot more interesting, and it’s in-band for the existing L-band antenna and LNA equipment, so I’m completely on-board with this plan. (It would’ve been neat for skylark to decode that and include it in the regular interface, but I suspect there wasn’t enough CPU to do both at once.)
What other stuff is out there on L-band? I feel like the moving-pictures-talking-heads people have really good lists of free-to-air channels and programming, but we data nerds haven’t assembled a good listing of free-to-air data services.
I had this running a few weeks ago and it works reasonably well. Turning it into a GPS-disciplined clock could be interesting but I’m not sure where to start. Would you replace the rtlsdr’s xtal with a 28.8MHz OCXO and control the oven until the signal frequencies look right? Then you’d have the task of deriving a stable lab clock out of that weird frequency, and frankly that seems like more trouble than it’s worth. (Or get a 10MHz OCXO and synthesize the 28.8 from it? But still, awkward every which way.)
Inmarsat traffic looks a lot more interesting, and it’s in-band for the existing L-band antenna and LNA equipment, so I’m completely on-board with this plan. (It would’ve been neat for skylark to decode that and include it in the regular interface, but I suspect there wasn’t enough CPU to do both at once.)
What other stuff is out there on L-band? I feel like the moving-pictures-talking-heads people have really good lists of free-to-air channels and programming, but we data nerds haven’t assembled a good listing of free-to-air data services.
I’ve not done this before, but I can offer some ideas as to how to attack the problem: One way to start such a project is to do a survey of what’s already been done. Here are some links:
GPS Frequency Reference - This homebrewed 10MHz frequency reference is locked by the GPS satellite system and achieves an estimated accuracy of 10,000,000.000 +/- 0.002Hz in normal operation.
The L-Band antenna is relatively broad. But, the SDRx and the DreamCatcher 2.03 are nice boards that have a nice LNA and SAW filter on them, with nice gain in a band of 1525 - 1559 MHz, with a center frequency of 1542 MHz. This is known as the MSS or the SATCOM band. This band is used in the Aviation Service, and the Mobile Satellite Service (MSS). This band is allocated for both Federal and Non-Federal use. There’s a lot of very interesting stuff out on that 34 MHz-wide part of the L-Band. There’s also much more out there than just the Inmarsat 4-F3 satellite. I think the first thing to do is a survey of the sky … let’s see what interesting signals we can hear.
The primary Federal use of the band 1535-1559 MHz is for earth stations in the space-to-Earth
direction in conjunction with commercial mobile-satellite service (MSS) systems. The band
1525-1559 MHz is paired with the band 1626.5-1660.5 MHz which is used for Earth-to-space
communications. The commercial satellite service providers include the London-based
INMARSAT and the U.S.-based LightSquared. The Coast Guard and the Federal Aviation
Administration (FAA) operate mobile earth terminals in the band in support of maritime and
aeronautical emergency communications, respectively, via the INMARSAT commercial
satellites. In addition to emergency communications, the Federal agencies operate mobile earth
terminals, including aeronautical, land, and maritime, using commercial satellite systems.
The Department of Commerce National Oceanic and Atmospheric Administration (NOAA)
operates the Local User Terminal (LUT) ground stations in the 1544-1545 MHz portion of the
band. The LUT ground stations receive information from polar orbiting and geostationary
satellites that carry the Search and Rescue Satellite-Aided Tracking (SARSAT) payloads
providing distress alert and locations information from Emergency Position-Indicating Radio
Beacon (EPIRB) and Emergency Locator Transmitter (ELT) to public safety rescue authorities
for maritime, aviation, and land users in distress.
As of 2016, Ligado Networks seeks FCC permission for terrestrial deployment of its mid-band spectrum in the 1500 MHz to 1700 MHz range.[8][10] The company plans to make its spectrum available to industry and government to serve emerging Internet of Things and 5G technologies.
Inmarsat plc (LSE: ISAT) is a British satellite telecommunications company, offering global mobile services. It provides telephone and data services to users worldwide, via portable or mobile terminals which communicate with ground stations through twelve geostationary telecommunications satellites. Inmarsat’s network provides communications services to a range of governments, aid agencies, media outlets and businesses with a need to communicate in remote regions or where there is no reliable terrestrial network.
I have been looking for the silver bullet in Linux distributions that support software defined radios natively.
Pentoo – A hacker’s Linux. It came to a grinding halt in 2015 Kali Linux – Another hacker’s linux used by security professionals Skywave Linux – Skywave Linux is an operating system using bleeding-edge technology to robustly access broadcast, utility, military, and amateur radio signals from almost anywhere in the world, including countries with restrictive internet environments.
I’m going to download and try Skywave. I’m interested in using it to hear what’s on the 1525-1559 MHz band. Maybe decoding some of these signals … who knows.
When your goal is just to get a very stable frequency for some random purpose like locking a synthesized hamradio transceiver or SHF transverter to it, and it is not to be used for time reference, this is a nice GPSDO:
It is the size of a (largish) matchbox and comes with a small magnetic antenna. Connect it to a computer using USB, set the frequency using the included program (400Hz … 810 MHz!) and then just power it from USB (no computer required, just the 5V). It has an LED that indicates lock. It has a modern GPS chip and is very sensitive (certainly when compared to our old and rusty professional GPSDOs from Datum etc).
Of course this is not a re-purposing of existing equipment and has little to do with tinkering, but it works very well.
@pe1chl Rob, thanks. This is a good GPSDO reference.
A software GPS receiver using SDRx or DC2.03 is actually not taking advantage of the SAW filter / LNA combination because the GPS signals is out of the receive passband of the filter.
Update on Skywave Linux I’m quite happy with it a couple of hours after installing it. It’s based on Unbuntu and runs Mate for the desktop. It’s loaded full of Ham radio and especially SDR applications. The installed version fo GQRX works very well with the SDRx board.
