[TowerTalk] Takeoff Angles and Non-Reciprocal Propagation

[Jim Lux]

Rick Karlquist wrote:
> David Gilbert wrote:
> 
>> I've read the pdf file written by N6BV that accompanies HFTA several
> 
>> "It is fascinating to reflect on the thought that received signals
>> coming down from the ionosphere to the receiver are having encounters
>> with the terrain, but from the opposite direction.  It is not
>> surprising, given these kinds of interactions, that transmitting and
>> receiving might not be totally reciprocal."
>>
>> It occurs to me that there might be a way to see if this actually
>> happens.  A station in the U.S. could pair up with a station in Europe
> 
> We need to distinguish between reciprocity of diffraction vs
> reciprocity of ionospheric processes.  A much easier way to
> demonstrate the reciprocity of diffraction would be to connect
> microwave horn antennas to a network analyzer and measure S12
> and S21 in real time.  You could insert whatever objects you
> wanted between the horns in an effort to cause a difference between
> S12 and S21.
> 


One might want to do this in an anechoic chamber (or, at least, on a 
open field test site sort of place), just to reduce the confusion from 
multipath effects.

   What would folks want to see as far as "terrain simulation" for such 
a demonstration. And, how closely do we need to match the dielectric 
properties of the earth?  HFTA uses horizontal pol only, so for almost 
all angles, you get pretty close to perfect reflection, so aluminum foil 
covered "ridges" made of cardboard would be what I'd be thinking of.

If you work at, say, 30 GHz, the wavelength is 1 cm.  Comparing to, say, 
40m, that's a factor of 1:4000, so a 5000 ft high mountain ridge would 
be a model 1 foot high, which is reasonable.


Jim, W6RMK