LowCostLongRange

Low cost 1.4km IR link
Use a low cost TSOP1838 InfraRedLeds from the the linux http://www.lirc.org design for the receiving Rx side. Use a Jewelers Loupes 13cm lens for Rx and Tx as per FreeSpaceOptics to extend the lirc.org design to 1.4km. For Tx use the HPWT-BD00 Lumiled as per RonjaChips(http://bit.ly/2hKngp), TransImpedenceAmp(http://bit.ly/10Mi8h) and http://luxeonstar.blogspot.com. For closer 100m distances use smaller plastic magnification lenses as per Kemo Kit nr.b213 #24-194(http://www.kemo-electronic.com/).

This allows an extremely low cost, slow bitrate(115Kbit) long distance links for use on farms for example to switch valves and pumps, eliminating the need for expensive RadioModems.

Slow bit rate video transmission
In most instance it is not needed to obtain full motion video at 115Kbit with SerialCameras(http://tinyurl.com/5bj5t5). A snapshot every 5sec or a snapshot only on motion detection will do. If the TSOP1838 can do 115Kbit then full motion real-time video can be transmitted over such a FSO link. The SerialCameras modules have inbuilt motion detection functionality. Combine these serial cameras with the low cost IR link and populate all over a large premise for surveillance purposes. The SerialCameras are CMOS based and 0.01Lux sensitive. Only CCD at present allows for 0.003lux. Note that there is no such thing as 0lux or 0.00000000....00lux, the CCTV sites claiming 0lux with InfraRedLeds on are lying.

Combine RF radio with FSO
Populate a large area with FSO links. Surround each FSO tower will low power consuming RadioModems to send out a signal on a PIR or IR beam trigger, indicating an intrusion.

IRDA specification
The IrDa protocol has to deal with LED flashover due to the very tight spacing between two adjacent leds used for Rx and Tx in a small embedded device. Flashover is solved by separating the the Tx and Rx parts with a pipe container.