Although I have both YT and TA, most of my terrain analysis experience is
while using K6STI's TA. However, I believe that both of these programs take
the same basic approach.
1) The free space antenna pattern is used. In other words, no ground
effects are included in the antenna pattern used by the terrain analysis
program.
2) The antenna(s) are treated as point sources.
3) Mutual inductances/capacitances between stacked antennas are NOT taken
into account. Since two stacked antennas are treated as two point sources,
the terrain analysis program uses the same individual free space patterns
produced by the point sources, regardless of spacing of the antennas.
4) Ray tracing and diffraction analysis are used to calculate the final
combined pattern of the stacked antennas. This calculation takes into
account the relative phase differences of the two point sources (stacked
antennas) "seen" by a point on the terrain. TA includes the ability to
toggle the phasing of the two stacked antennas (bip/bop).
5) The ray tracing and diffraction analysis is constrained to two dimensions.
Obviously, this calculational approach results in somewhat less than a
"real world" result. However, these programs are useful because they
provide us with a much better appreciation of antenna patterns over real
terrain than the "flat earth" assumption of all antenna modeling programs.
The ideal antenna modeling program would include both the NEC/MININEC
analysis of antenna elements and 3D reflection/diffraction analysis for
underlying terrain. Unfortunately, to my knowledge, this doesn't exist and
would probably be very slow running if it did.
73 de Bruce, WA7BNM (bhorn@hornucopia.com)
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|