[Laser] Simple optical beacon experiment ...some questions

[Charles Pooley]

Kerry Banke <kbanke at qualcomm.com> wrote:
   
  ... The beacon is a Luxeon 1W red LED with 15 Degree (30 deg 
total) integrated lens. It is powered by a square wave at about 700 Hz 
and has an identification of N6IZW once each minute. At 8 miles the beacon 
was visible through a 7X20 mm rifle scope mounted on my K3PGP type...
  ---------------------------
   
  1) Are most optical link experiments based on the K3PGP design, which is as I   understand, a low frequency unfiltered detector with discrete transistor?
   
  2)  how about use of an interference filter for the receiver?  ie, if a 650 nm laser is used and a 660 nm filter, tilted to "tune" to 650 (15-20 deg from normal), wouldn't background noise be a lot less?
   
  3)  Instead of baseband, how about a carrier based systyem?  FM front end ic's like NE604 are very sensitive, have an RSSI output and a wide dynamic range.
  Or, alternatively, a PD-toRF converter device to feed a radio receiver?
   
  4) To what extent are APD's used?  
   
  Charles Pooley   KD6HKU