[TowerTalk] Takeoff Angles and Non-Reciprocal Propagation

[Jim Lux]

I too have access to such things. Rather than do a complex sculpted terrain model,one might want just use a simple geometric shape (like a quarter round).

If you do it at somethiing like 2.4 GHz, then it could more easily duplicate a ham's setup (like a 3el yagi). The model will be bigger  (40 m:0.12m is about 300:1... A 1000 ft ridge is 3 ft high)
Jim Lux

-----Original Message-----
From: "David Gilbert" <xdavid at cis-broadband.com>
To: richard at karlquist.com; "TowerTalk" <towertalk at contesting.com>; "Bob Houf at Comcast" <k7zb at comcast.net>; jimlux at earthlink.net
Sent: 11/4/07 09:14 AM
Subject: Re: [TowerTalk] Takeoff Angles and Non-Reciprocal Propagation


Rick Karlquist wrote:
> "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.

Jim Lux Wrote:

"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"

******

Bob, K7ZB (a very good friend of mine not on the TowerTalk reflector) wrote:

"My approach is a bit different than yours, though, Dave.  Rather than 
using an actual ham transmission from DX, I was thinking of doing an 
experiment in a controlled environment - an RF anechoic chamber and at a 
very high frequency so that the terrain modeling could be measured and 
the results applied at HF.

I have several of these rooms scattered around the world - I wonder how 
much effort would be required to come up with a believable answer?

Bob, K7ZB"

*********************************************************


Bob is an engineering director for a large global appliance company, so 
when he says he has several anechoic chambers scattered around the world 
he isn't exaggerating.  It might therefore actually be possible to work 
up an experiment such as suggested by Rick, Jim, and Bob that could test 
the theory.  My first thought would be to sculpt a terrain with paper 
mache' or something like that, then paint it with conductive paint.  I 
just bought some cold galvanized spray paint claimed to be 97% zinc when 
dry.  We could maybe even spray on a thin top coat of some other 
material to simulate a lossy dielectric if anyone thought that was a 
requirement.

Keep in mind that Bob hasn't committed to any of this ... he just 
offered some thoughts and a possible means of exploring them.  I'll chat 
with him some more to see if we can actually do something.  If we can 
get something going I'll try to set up some means off the reflector 
(Google Docs or whatever) to share ideas on how to do it properly.

73,
Dave   AB7E