[hornychz]

As said before, your work in this matter is greatly appreciated, so, please continue...
If possible, try to do your tests with the UV sensor connected to the TX unit, creating test conditions as close as possible to real use conditions.

Hi again,

Maybe, now it's the formula OK (finally). Now I'm not doing any tests, I'm only calculating like our WeatherDuino TX and RX Thank you for your help again, Werk_AG. I think, our formula has to be:
 

IndiceUV = ((((ADC1 * 1100.0 / 1024.0 ) / Transmission - 135 ) * 10.9 ) / 1023.0) ;

Here is a proof:
 

The spreadsheet with calculating is in attachement. Value "Transmission" is for example 0.9 for transmission 90%, 0.8 for 80%, etc. This value has to be experimentally detected, as we discussed it above.