[Laser] Re: Troposcatter and Information Theory-2

[Andrew T. Flowers, K0SM]

Tim Toast wrote:

>  And i also
>think sine waves will be the way to go - having less
>wasted power and less potential for interference. 
>
The power of the fundamental frequency in the audio spectrum will be 
identical in both the sine and the square wave, provided they have the 
same P-P amplitude.  If you take a square wave and filter out all 
harmonics except the fundamental, you will have a sine wave of the same 
peak amplitude.  I happen to like 50% duty cycle square waves because 
they require minumum parts and don't require linearity.  I designed my 
coding scheme in such a way that the harmonics don't interfere with the 
detection algorithm.   Of course, if you already have a nice linear 
system, go for it!  Nobody has come back to me and said "The frequency 
is in use, old man"...at least not yet!

As a side note, PSK could be generated by throwing an inverter in and 
out of line with a clock pulse to create the 180-degree phase 
inversions.  Talk about EASY!  It would be interesting to see what kind 
of longterm phase stability there is on troposcatter paths.  I imagine 
it's pretty good, since lidars  and cloud radars work on this priciple.

Andy K0SM/2