General information on the ITS HF Propagation Analysis PackageVOACAP Quick Guide: Home
[This document is part of the help files integrated into the ITS HFBC software package.]
The development of this set of HF propagation analysis programs was made possible by funding from the Voice of America (VOA), the U.S. Army, and the U.S. Air Force. Anyone interested in continued development is encouraged to do so at any level of funding. Further enhancements can only be achieved by continued funding.
The models available here come from a variety of sources.
VOACAP - was developed by VOA beginning with the 1983 version of IONCAP. VOA then funded the Naval Research Laboratory (NRL) to make specific changes to the IONCAP methodology, and renamed it to VOACAP so as to avoid confusion. That version of VOACAP was completed in April 1993 and distributed to participants at IES 93 (Ionospheric Effects Symposium May 1993) in Alexandria, Virginia. Simultaneous to funding NRL to enhance the model, VOA also funded NTIA/ITS to enhance the user interface. Beginning in early 1992, ITS began developing the HF Antenna program with a software package purchased from BottleWorks called SoftCode. It allowed easy development of input screens and data validation. Once the HFANT program demonstrated the feasibility of a full screen input approach, work began on the input processor for VOACAP for VOA so that it would work on PCs and laptops. Frequency coordinators desired to use laptops to do calculations at coordination meetings with other countries.
REC533 - For VOA to keep in line with the international community, REC533 (CCIR Recommendation 533) was also included as one of the propagation models to be made available. REC533 is the ITU "blessed" HF propagation model used by most European countries. It is also the model that would be used by the ITU for any HF planning software that might be developed, and therefore, VOA is concerned about how their circuits perform with the ITU propagation model.
ICEPAC - At around the same time, ITS completed work on enhancements to IONCAP and renamed the model ICEPAC to indicate the inclusion of the ICED (Ionospheric Conductivity and Electron Density) profile model which included a better representation of the auroral trough. This now replaces IONCAP as the HF propagation prediction model that NTIA/ITS will distribute and support. In 1995, it was decided to convert the GUI interface from the DOS text screen to a fully Windows application. This was accomplished through the use of the Salford FTN77 compiler with ClearWin+. A side effect of this Fortran compiler is that the propagation module calculates about 60% faster than the DOS version. The Windows inplementation has been available since February 1996.
In the past, these models generally consisted of one program and a few ionospheric coefficient data files, and could easily be supplied on one computer diskette. This Windows implementation includes 10 programs and about 400+ data files (antennas, coefficients, cities, fonts, help, news, world boundaries, user saved). In compressed form, the delivered software can reside on 5 1.4Mbyte diskettes. It can also be accessed via ANONYMOUS FTP through internet. Source code for most of the programs cannot be distributed because it was developed with proprietary software and distribution is prohibited by the purchase agreement. Since REC533 is the international HF propagation prediction program, its source code is available. Source code for the VOACAP propagation model can only be obtained from VOA. ICEPAC source is not available for distribution. Changes in the ICEPAC methodology can be performed on a contract basis. It is hoped that this will cause enhancements to ICEPAC to be made available to everyone, and when the ICEPAC model is discussed, everyone will have access to the same version. In the past, once source for IONCAP was released, in short order, there were countless versions all with the name IONCAP but all producing different answers.
All three propagation models may be used to perform HF predictions in the Point-to-Point mode. Point-to-Point implies from a transmitter to a single receiver for a variety of hours (24), frequencies (11), and month/SunSpot pair combinations (10). These results may appear in either the classical printer output, or contours of any output parameter may be plotted on a Hour by Frequency graph.
All three propagation models may be used to perform HF predictions in the Area Coverage mode. Area Coverage implies from a transmitter to a grid of receivers for a single hour, frequency, and month/SunSpot pair. These results appear as contours of any output parameter plotted on a map background that may include world political boundaries, city locations, and CIRAF zones. Maps can be produced in black/white or color. By generating area coverage maps and using the COMBINE feature, complicated planning analysis can be performed.
A Point-to-Point Signal-to-Interference capability has been added to ICEPAC and VOACAP. This allows the user to determine the effect of unwanted signal interference on a wanted transmission at a singal receive location. To observe the S/I effect over an area, use the S/I operation in the COMBINE feature of the Area Coverage models.
It is hoped that these propagation models will be available from NTIA/ITS. By maintaining the source code in one location, everyone can have access to the current state-of-the-art propagation models. The models can be made accessible via ANONYMOUS FTP on one of NTIA/ITS's computers. Whenever enhancements or corrections are made, anyone with internet access can immediately obtain the latest version. This cannot however be done without continued funding. It is hoped that by charging a small consulting fee, the availability of these models can be maintained.