[Laser] 21 mile daytime laser contact durin ARRL 10GHz & Up contest

[Kerry Banke]

 Yesterday Lee, KD0IF and I made a mid day laser contact over a distance of 21 miles near San Diego  as part of the ARRL National  10 GHz and Up contest. Last year we did a 7 mile daytime contact but experienced very heavy scintillation which we have found to be typical for warm weather in the San diego area.  This year we added narrow wavelength optical bandpass filters ahead of our optical receivers and are using a fast AGC provided in the Spectrum Lab software.  This was our first two way  daytime communications  tests with the filters. The scintillation on the raw signal appears to be very minimal compared to our contact last year. We don't know if the narrow optical filters have provided this improvement or if we just had unusually  good conditions so we need to do more daylight tests with and without filters for comparison. The filters are at 920 nm with a 30 nm half power bandwidth. When operating at high power with  1W  collimated to  a 4"  dia beam, the laser
 transmitters delivered  signals that  were a stable 50 dB above the noise in a 1 Hz BW at 21 miles.   Communications was done using PSK31 with a center frequency of 755 Hz.  
  Does anyone know if adding the  narrow optical filters should reduce scintillation? Thanks also to Greg, K6QPV for assisting with the contact.
   - Kerry N6IZW -