> ... I need to be able to measure signal magnitude to let me know if
> I am close or far from the TX.

That should probably read "... I intend to measure signal magnitude in 
the hope that it will let me know if  I am close or far from the TX.".

Then either :-) or :-( depending on how Murphy is feeling in your 
application.
In the absence of 'confounding' inputs light level is proportional to 
the inverse square of distance - no problem. In the real world you are 
liable to have 'quite some fun' picking out the signal of interest. 
I'd be extremely interested in how you intend to do this and in what 
sort of result you achieve. It *sounds* simple enough :-). Short range 
range detection by simple techniques is an often sought after 
objective and I don't recall seeing one that successfully used optical 
signal amplitude - which is not to say that it's not achievable. Are 
you able to tell us more about the application?


            Russell


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