Practical_Antenna_Handbook_0071639586

78 p a r t I I : F u n d a m e n t a l s
in the business but also near-total access to as much of the raw data as we wish, should
we choose to make our own predictions.
Appendix B includes an extensive list of Internet sites pertaining to HF propagation.
Propagation Software
A number of popular software packages for the PC and Mac have tackled ionospheric
signal propagation from different directions. Although not as central to the topic of this
book as the antenna modeling software described in Chap. 25, a few words are in order
about some of them.
W6ELProp is freeware that can be found on the Internet. It is no longer maintained
by its author, but it remains an easy-to-use Windows application with a user interface
that is reminiscent of its DOS predecessor. W6ELProp focuses on conventional F-layer
propagation; as such, it does not incorporate some of the “lesser” modes that may enhance
signals, such as skew paths. It uses approximations that occasionally limit its
accuracy, but it is a wonderful program for quickly getting the feel of propagation between
any two points on the globe. In addition to the software itself, a number of other
personal sites have published their own unofficial how-to guides for this chestnut.
HamCap is freeware offered by Alex Shovkoplyas, VE3NEA. It relies on a separate
propagation prediction program called VOACAP, which must be downloaded and installed
before HamCap can be used. VOACAP was originally developed by NTIA/ITS
for the Voice of America.
VE3NEA also offers IonoProbe, which monitors and displays a number of valuable
space weather parameters on a near-real-time basis.
Other software to check out on the Internet includes CAPMan (and its successor,
WinCAP), DXProp, and HF-Prop. For VHF/UHF applications, look into Radio Mobile
Deluxe, Ground Wave Prediction System, and RFProp.
Terrain Analysis
With few exceptions, antenna modeling packages for PCs or Macs assume a perfectly
flat ground extending infinitely far in all directions from a point directly beneath the
antenna in question. But few radio sites can lay claim to such a terrain, and the question
naturally arises: What is the effect of the terrain on signals?
HFTA (High Frequency Terrain Assessment) is a program designed by R. Dean
Straw, N6BV, to answer just that question. The user must supply details of his or her
location to the software because some propagation statistics (arrival angles, for instance)
vary with the user’s region of the globe. The program can also download detailed
public data files describing terrain contours in the immediate vicinity of the user.
Alternatively, the user may be able to manually create a customized profile for his/her
site by reading the necessary information off topographic maps of the area and manually
entering it into the program. Once it has been provided with all the necessary data,
HFTA assesses the terrain that may stand between the user’s antenna site and a clear
shot at the ionosphere at a variety of takeoff and arrival angles, examining both reflection
and diffraction modes of propagation.
In operation, HFTA creates a profile for a single compass direction. If profiles for
multiple headings are required, separate passes through the process must be completed.
Typically, radio amateurs who wish to locate their antennas so as to maximize