Well, why not wade into this interesting topic? Would have sooner, but spent
most of the weekend working the SS CW contest with W8RJL's group under the
K4IX call.
Had a clean sweep and had a blast!
Let me put my 2 cents in by proposing a simple thought experiment.
At the local transmitting antenna, a radio wave is emitted which spreads out.
Were the transmitting antenna an isotropic radiator in free space, the wave
front would remain spherical in shape as it spreads. In our case, the wave
still spreads out, not exactly spherical, but nonetheless it has a curved
wave front, who's radius of curvature generally decreases as it moves away
from the antenna. This wavefront can reflect and diffract from the surrounding
physical environment, setting up a pattern of waves with destructive and
constructive "interference", depending on the wave phases from the reflections
and diffractions. These interference patterns are ingeniously employed by
hams with yagi's to modify the radiated power pattern to their advantage,
proving gain in the direction of interest along with other advantages.
Now, consider a far away transmitter, sending a similar frequency signal to
our local antenna. In this case, as the radio waves approach our local
antenna, the wave front radius of curvature is VERY much less than the radius
of curvature that our local antenna emitted towards the local diffracting
objects. Because of this, the times of arrival of the wavefront to those
diffracting objects will be different, and the resultant wave phasings will be
different.
As we all know, if the phasing of the wave fronts arriving at the antenna are
different, the constructive and destructive wave interference patterns must
also be different. Therefore, I have a problem believing that "reciprocity"
can exist in a diffracting environment when the geometries are not symmetrical.
I'm sure this will further fan the discussion rather than resolve it, as
these issues are seldom settled in this kind of communications environment;
perhaps reciprocity doesn't exist on Internet reflectors either! But remember:
Just some food for thought, and have fun with it!
Respectfully submitted,
CW, AI4MI
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|