W3A Europe Transponder A12 in Northern Kenya

Looking at the Broadsat coverage map:

At Turkana you are close to or just beyond the beam edge contour line, shown as 40 dBW downlink EIRP power.
Given that the EIRP power in the beam centre region is around 51 dBW, you are going to need a dish size 12.5 times the area or 3.5 times the diameter compared with that used in central Europe.

Note that there is uncertainly as to the accuracy of the map in the edge region.  Also that slight movement of the satellite will cause large changes in level at your location.

It is possible that a 2m dish might just work, with little or no rain margin.  Since there is a risk it will not work, I wonder if you could you borrow a dish to test ?.  

Best regards, Eric.

You are at the southern edge of the Europe/North Africa  beam and the signals will be very weak and that is why you need a large dish.  You will be looking at Vertical name polarisation and there is no other high power traffic that I can see in the transponder plan for your location.

There is no risk of overloading the LNB and no need to worry about needing a special low gain LNB.

However, if you were to operate Horizontal polarisation, then you will see some high power carriers (45 dBW transponder power) in the main Africa beam. Carriers on those transponders are operating to 1.2m VSAT dishes throughout west, central, east and south Africa (e.g. Bentley Walker HX service).  Using a 3.7m dish on that polarisation would give you some very strong signals - but I doubt the total even then would be sufficient to overload a standard LNB.

With a 3.7m dish, two things will be critical:
Surface profile:  It is really important to have the assembly done delicately.  It is quite difficult with such larger dishes.
Feed horn: The feed horn must match the F/D ratio of the dish.  

Invacom do suitable LNBs.

Consult Broadsat regarding type of receiver and software required. I presume you are intending to use a terrestrial phone line modem or similar for the return link to the internet.

Best regards, Eric.