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Satellite Ground Station

Page history last edited by David-Taylor 1 year, 5 months ago Saved with comment


INMARSAT Project overview


(Overview image being updated following INMARSAT satellite changes)




Starting on a shoestring!


For a taster of what can be achieved at minimum cost, please take a look at John Locker's guide to "Inmarsat L-band on a shoestring".  It's a PDF file.


Articles and notes by Chris van Lint


Here is a link to an article written by Chris van Lint which you will find very helpful.  It's in PDF format.

Chris has also written a note about adding a TCXO to the LNB to improve the temperature stability.

Receiving and decoding multiple C-band Inmarsat transmissions - anther first-class Chris van Lint article.


Chris writes about dish pointing:


  You are probably aware that a 1.8m dish is required to have enough gain to get reliable decodes, but it also has a comparatively narrow beam-width.  This makes dish positioning in terms of Azimuth and Elevation rather critical.  Inmarsat 4F3 varies in latitude between 3.0° N to 3.0° S - i.e. a aggregate variation of 6.0° .  Similarly  Inmarsat 3F5 also varies to roughly the same extent.  There is a time period of between 4-5 hours when the satellite approaches the 0.0°  latitude point, that there is very little variation in elevation.  There is not a lot of variation in longitude.  Although Plane Plotter will track these satellites in real time you might consider when initially aligning your dish, to use David Taylor's WXtrack program, which allows you to enter the time manually.  By doing this, you can determine during which time period there is a minimum of lateral movement in the satellite position, minimizing one of the variables influencing correct dish alignment.


This is preliminary information


From John Locker


It now looks like you need a 1.2 m satellite dish which can point at the Inmarsats [one of the birds is very close to the Astra [Sky] group]. However, Emmanuel in France has been getting excellent results from a small 90cm dish.  So if you have a Sky dish, then the direction of Inmarsat 25 east is just to the right of where your Sky dish points when you stand behind that dish and look up into the sky.

That dish will need a C band LNB [that's the little box thing on the end of the arm] which costs around £25 , plus a scalar mount...so in total about £40.

A bit of DIY (do it yourself) to fix the LNB on the dish and then a dongle, old sat receiver with loop through, and some software: SDR#  and JAERO 


DJT: Alternatively, any satellite receiver, with a 2-way splitter, power in just one leg.  Connect the power-pass leg to the satellite receiver, and the other to your dongle etc.

If you are a radio amateur you may well have a high quality wideband scanner, which is sitting there out of use.  Well, that might be sensitive enough to use for reception rather than the dongle.

The frequencies are around 1520 to 1540 MHz depending on which bird you tune to,

So basically the C band 1.2 m dish - possibly less as Emmanuel is using a 90 cm dish - and once you have that , the rest is easy :O).


Satellite stations are needed in Australia and the USA, plus backup stations across Europe.  It doesn't matter how many users look at the same satellite as this will provide redundancy.  Each satellite downlinks just one or two T channels and at any one time up to 50 aircraft can be logged into each channel




I'll put odd notes here until the page is made a more coherent whole.  Starting to look more like an FAQ!


What frequencies are used?


Andy Jermaks notes:

The C band downlinks are actually at around 3620 MHz and the LNB is down-coverting them to around 1535 MHz so enabling the RTL dongle to receive them.  The satellites are circularly polarized.  I can only receive 3F-2 at 15 West which seems to be RHCP (well, it works best for me) but I can't comment on the others.


Anywhere between 1520mhz and 1540 MHz upper sideband (USB).  It seems to vary satellite to satellite.  For example Inmarsat 15 west transmits the T channels between 1535 and 1536 MHz


Why is a satellite receiver necessary if using a loop back into a RTL-SDR?

You need to power the LNB, and a satellite receiver (with loop through) may be the easiest way, but you can use a power inserter instead.


What LNB do I need?


You need an LNBF (Low-Noise Block + Feedhorn) and a conical scalar kit if you are using a 90 cm dish (ex. satellite TV).



LNB e.g. https://www.amazon.co.uk/gp/product/B00HVM6LFS/


Conical scalar kit e.g https://www.amazon.co.uk/gp/product/B00HVMKXCA/


These items may also be found elsewhere e.g. eBay.



Inmarsat C-band setup diagram



At what geostationary positions are the Inmarsat satellites?


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