I suggest that you do two things:
1. Read the extensive discussion of terrain interaction in general and
HFTA in particular in the ARRL Antenna Book.
2. Generate some sample terrain plots see for yourself the impact of a
small peak in the foreground of a large peak and vice versa. The
terrain files are a very simple text format of paired numbers, with
distance in the first column and height in the second column. You can
edit any existing file with Notepad to create a different terrain profile.
By the way, the wave that is altered by the low foreground peak does not
have to be aligned with the wave passing over the taller distant peak in
order to combine with it. If that were true, waves reflected off the
ground in front of your antenna wouldn't ever combine with waves beaming
directly outward toward the horizon. Think about it.
On 4/25/2010 8:04 AM, Gary Schafer wrote:
> If you think about your example of the two ground peaks at different
> heights, what would the shadow of the larger one have to do with direction?
> If the receive path has the small peak in the shadow of the larger peak so
> that it isn't seen by the incoming signal then the small peak will not be
> seen by the outgoing signal either.
> Yes it could be in the path of the outgoing signal for a particular angle
> but not for the same angle that clears the larger peak.
> Outside of some amount of refraction over the peaks, a low angle outgoing
> signal is not going to bounce off the smaller peak and combine with the
> energy in a slightly higher angle wave that clears the higher peak. Any
> signal that bounces off the lower peak is going to keep going up at the
> reflection angle and right thru the higher angle energy wave that is
> clearing the higher peak. The reflected wave from the low peak is not going
> to bend and combine with the higher angle wave as it intercepts it.
> If I understand what you are getting at in your non-reciprocal path
> Gary K4FMX
TowerTalk mailing list