"MRW" wrote in message
ups.com...
In my physics book, it mentions constructive and destructive wave
interference especially in reference to the the one-slit diffraction
experiment. From reading about radiowave propagation, they also
mention diffraction effects on radiowaves.

To me, it sounds like with constructive interference, the wave's
amplitude will have the chance of increasing more than what the source
actually outputted. But I wonder if this is helpful in terms of radio
communication.

the amplitude can be more in one direction than another, but the total power
can not exceed the transmitter output of course. for each constructive
interference peak there must be an area of destructive interference to make
up for it.


In reference to a single frequency transmitted, when I think about
constructive interference and radiowave propagation, I keep picturing
a delayed signal transmitted at time_0 and another signal transmitted
at time_1 later with the same phase arriving at the receiver at the
same time.

In terms of AM, I would think this would be problematic.

yep, that is what ghosts on tv signals are... if the delay is long with
respect to the modulating signal you can get effects like that. the most
common desirable uses are in antennas where there is a phase delay about
equal to the spacing of the elements of the antenna which lets you create a
stronger signal in one direction, and of course a weaker one in other
directions, allowing you to put more of the transmitter power in the
direction you want it to go. because the delays are small there is not the
problem with ghosts.



Any comments? Really, what I'm trying to understand here is: if
constructive interference does any good in radiowave propagation. I
was thinking that with an increase in amplitude the signal would be
able to travel a little further, but the signal received may not be
accurate in terms of the information it is conveying.

yes, constructive interference is what antenna design is all about...
destructive interference has its part also to help reject interference from
undesired sources as well.