VOACAP Type-13 Files for Amateur Band Antennas

L. B. Cebik, W4RNL

Amateur interest in the use of propagation software is growing, especially as VOACAP becomes more readily available. The best way to obtain the most accurate propagation forecasts and analyses for a given amateur installation is to use within VOACAP an antenna that closely resembles the actual station antenna at each frequency of operation. The resemblance need not be physical, but needs only to have a radiation pattern that closely fits the performance of the station antenna.

VOACAP has a provision for using a special file type, type-13, which is a file of the radiation pattern in all azimuth direction and for all elevation angles in 1-degree increments. Each antenna at each frequency of operation requires an ASCII file about 260 KB long to include all elements of the pattern in the proper format. The file uses the compass rose (clockwise) convention and counts elevation from the horizon. In addition, each antenna must be over ground, and for many types of antennas, performance may vary with the ground quality. All antennas that can be rotated and are directional are oriented to place the main lobe due North (0 degrees azimuth). Use VOACAP controls to re-aim the antenna at a desired target communications region. Fixed antennas present different challenges for the user, and individual description sheets that accompany each collection will make suggestions on how to best use the files.

Amateurs versed in the use of NEC or MININEC can create custom models of their actual antennas. Since NEC and MININEC generally use phi and theta conventions to produce the radiation pattern report, radiation-pattern data conversion is tedious at best. The latest version of EZNEC at its Plus and Pro levels can produce the desired type-13 files by use of the 3-dimension plot option.

Amateurs who are not familiar with antenna modeling may not have access to radiation patterns of typical amateur station antennas. Therefore, I have begun a process of producing type-13 files of monoband antennas to cover most of the HF amateur bands. The files come in collections as the download list below indicates. Each file is zipped and contains a considerable number of files internally. Each collection contains models of the same antenna for each band. Where relevant--for horizontal rotatable antennas especially--there are variations of files at each frequency for different heights above ground. For vertical antennas, especially those using a ground or near ground mounting, there are variations for ground qualities known as very good, average, and very poor. Where relevant, there are also variations for different sizes of radial fields, namely, 4, 16, and 64 buried radials.

Each file collection contains a 1-page document describing the specific file-name coding used for that group. VOACAP restricts type-13 files to 8 characters, requiring a careful coding to provide key file data. Since all antennas are monoband antennas, the group document also specifies any key features. For example, the collections for Yagis include the free-space gain (dBi) and boom length (wavelengths) of the model to allow the user to select an antenna whose performance most closely matches the station antenna, even if the station antenna is a multi-band array. A number of directional antenna types can be omitted for similar reasons. For example, those who use quagis, log-periodic dipole arrays, and similar antennas may select the Yagi or the quad pattern shape and gain that most closely match the performance of the actual station antenna.

The collection does not attempt to model commercially built (or even home built) multi-band antennas. With the facilities available to most antenna makers, developing type-13 files for each antenna in their line at each operating frequency should be standard practice and would allow the maker to classify the file as authorized. Until makers take this step, most amateurs will have to estimate the performance of their antennas and select from the collections (as they slowly emerge) the model that is closest in performance and other variables to the station antenna.

Despite the relative ease of constructing an individual type-13 file using the latest modeling software, the development of generally usable collections of files is a long-term task. For example, each zipped Yagi file contains 28 separate type-13 files for 80 through 10 meters. Zipped file collections include from 15 to 45 individual type-13 files. The basic collection is now as complete as I can effectively make it. Since each zipped file is itself very large, I recommend that you only download those files that are potentially useful to your station.

The following list is what is presently available for download. For sample azimuth patterns, see the link at the bottom of this page.

Horizontal Rotatable Arrays

All rotatable arrays in the following list have separate versions for each HF band from 80 through 10 meters so that the free-space E-plane (azimuth) pattern and performance level are the same within a collection to very small limits of variation. Each antenna has a type-13 file for each band at a specific height above average ground. (Horizontal antennas are generally less sensitive to ground quality variations than ground-mounted vertical antennas.) The heights for the upper HF region (20 through 10 meters) are 35', 55', 75', and 95', corresponding generally to typical amateur tower heights. For the lower HF bands from 80 through 30 meters, different files exist for heights of 75' and 100'. Selecting a file for use within VOACAP is a matter of determining the installation height and the performance level that most closely matches an available file. Some multi-band Yagi and quad designs might require selections from different collections on different amateur bands. The goal is to match performance levels and height, not to match the exact number of elements and boom length.

All horizontal rotatable arrays use elements oriented east-to-west so that the file main lobe points toward 0 degrees azimuth. Use VOACAP controls to change the direction of the main lobe. One might change the orientation of the main lobe of a truly rotatable array to different sections of the world. If the directional array in use is fixed, then a single orientation setting is required to reflect the actual orientation of the array.

1. Monoband Yagi Antennas: The Yagi collection consists of versions using 2 through 8 elements, with a long-boom and a short-boom version of the 3-element Yagi.

2-element driver-reflector Yagis (6.2 dBi free-space gain)

3-element short-boom Yagis (7.1 dBi free-space gain)

3-element long-boom Yagis (8.2 dBi free-space gain)

4-element Yagis (8.8 dBi free-space gain)

5-element Yagis (10.1 dBi free-space gain)

6-element Yagis (11.5 dBi free-space gain)

7-element Yagis (12.4 dBi free-space gain)

8-element Yagis (13.3 dBi free-space gain)

2. Monoband Quad Beams: The quad collection consists of versions using 2 through 6 elements, with a wider-band and a higher-gain version of the 3-element quad. (Heights refer to the hub or center points of the square quad elements.)

2-element quads (7.0 dBi free-space gain)

3-element wider-band quads (8.6 dBi free-space gain)

3-element higher-gain quads (9.2 dBi free-space gain)

4-element quads (10.4 dBi free-space gain)

5-element quads (11.1 dBi free-space gain)

6-element quads (11.7 dBi free-space gain)

3. Other Rotatable Horizontal Arrays

2-element Moxon rectangles (6.0 dBi free-space gain)

2-element phased array (or 2-element driver-director Yagi) (6.7 dBi free-space gain)

2-element bi-directional W8JK flat-top with 1 wavelength elements and 1/2 wavelength spacing

2-element bi-directional W8JK flat-top with 1 wavelength elements and 1/4 wavelength spacing

Collinear, 2 wavelengths with phasing sections

Bi-Square with 1/2 wavelength legs

Fixed Horizontal Multi-Band Wire Antennas

Many amateur stations employ fixed wire antennas, such as a center-fed doublet or a large horizontal loop, for all HF amateur bands. The following lists of available type-13 file collections provide samples of popular configurations, but by no means all configurations. All linear wire antennas are oriented east-to-west so that one of the two main lobes on the lowest band will project due north (0 degrees azimuth). The user must within VOACAP re-orient the antenna to reflect the actual station installation. Horizontal loops come in too many variations to sample adequately. The small collection provided here are square loops with the feedpoint located at the center of the south side. Using these files requires reorientation so that the file feedpoint is on the opposite side of the loop from the aiming direction. End-fed wires have their feedpoint on the west end (270 degrees) of the array. Using the end-fed files requires careful re-orientation within VOACAP to ensure both wire alignment and feedpoint position relative to the actual installation.

All fixed wire antennas and arrays are evaluated at heights of 35', 55', 75', and 95' on all bands within the normal coverage range of the antenna. For example, the 135' doublet has files for 80 through 10 meters, but the 44' doublet has files only from 40 through 10 meters. There are no sample free-space azimuth-equivalent patterns for this group of antennas, since the patterns will change with each band change. All models underlying the type-13 files use AWG #12 wire. The type-13 files show only the performance and patterns data; they do not include limitations and possible losses relative to various methods of feeding them. Note that the file-name coding system for these antennas differs from the one used for rotatable horizontal beams. See the individual information sheets that accompany each collection for details.

1. Linear Center-Fed Doublets: The doublet collection contains center-fed doublets with lengths from 270' (lowest band = 160 meters) down to 44' (lowest band = 40 meters).

270' doublet for 160-10 meters

135' doublet for 80-10 meters

102' doublet for 80-10 meters

88' doublet for 80-10 meters

67' doublet for 40-10 meters

44' doublet for 40-10 meters

2. End-Fed Linear Wire Antennas: The end-fed collections include unterminated wires that are 270' and 135' long. (Note: above the band on which an end-fed unterminated wire is 1/2 wavelength long, its pattern will differ from patterns for a center-fed wire of the same physical length.)

270' doublet for 160-10 meters

135' doublet for 80-10 meters

3. 30-Degree Inverted Vs: The inverted-V collection consists of center-fed wires that slope 30 degrees from the horizontal on each side of the center point. The heights listed in the files represent the feedpoint heights. Due to the 30° angle of the wires, some versions are not available at the lowest heights.

270' inverted-V

135' inverted-V

102' inverted-V

67' inverted-V

4. Horizontal Square Mid-Side-Fed Loops: Horizontal loops range from a circumference of 288' (about 1 wavelength at 80 meters) to 1152' (about 2 wavelengths at 160 meters). (Note: due to variations in the feedpoint locations and the shapes of actual installations, the samples are less certain guides to actual lobe formation and strength.)

1152' circumference for 160-10m

576' circumference for 160-10m

288' circumference for 80-10m

5. Terminated Folded Dipoles: Each antenna is terminated with a 900-Ohm resistance at the point opposite the center feedpoint.

165' terminated folded dipole for 160-10 meter

90' terminated folded dipole for 80-10 meters

6. Multi-Band Wire Arrays: Bi-directional wire arrays for either 20-10 meters or 40-20 meters

W8JK with 88' elements spaced 44' apart (40-20 meters)

W8JK with 44' elements spaced 22' apart (20-10 meters)

Lazy-H with 88' elements spaced 44' apart (40-20 meters)

Lazy-H with 44' elements spaced 22' apart (20-10 meters)

Vertically Polarized Antennas: General Note

The collections of type-13 files for vertically polarized HF antennas have several distinctive features relative to the collections of files for horizontally polarized HF antennas. 1. They are generally used on the lower amateur bands from 160 through 30 meters. With some exceptions, file collections will be restricted to these bands. 2. Vertically polarized antennas are more sensitive in performance to differences in the ground quality beneath the antenna. Therefore, models will use samples over three different soil qualities: very good (0.0303 S/m, 20), average (0.005 S/m, 13), and very poor (0.001 S/m, 5). Over the bands covered, performance differentials due to ground quality tend to be larger at lower frequencies. Other differences may be specific to the type of antenna in question. Although amateur antennas employ a wide variety of materials, all files rest on the use of AWG #12 copper wire.

Basic Vertical Monopoles and Dipoles

Basic vertical antennas include ground-mounted vertical monopoles with buried radials, elevated vertical monopoles with attached radials, vertical dipoles, and multi-band vertical doublets. The ground-mounted vertical monopoles include 1/4 wavelength and 1/2 wavelength versions using models with buried radials in field sizes of 4, 16, and 64 total radials. The other antennas in this group do not use buried radials. All antennas in the group use AWG #12 copper wire as conductors. Unless otherwise indicated, patterns are available for 160-30 meters. Patterns are available for very good, average, and very poor ground.

Ground-mounted 1/4-wl monopoles

Ground-mounted 1/2-wl monopoles

Elevated monopoles with 4 attached radials at 20' (80-10 meters)

Vertical dipoles with 0.05-wl base heights (160-10 meters)

Multi-band vertical doublet, center-fed, 44', 5' above ground (30-10 meters)

Self-Contained Vertically Polarized Phased Arrays (SCVs)

SCVs are 2- or 3-element vertical broadside arrays with in-phase feeding of each vertical using a single feedpoint. They do not require ground radial systems. Feedpoint placement determines the polarization of these antennas. All arrays align a main lobe (or the main lobe) due North (0° azimuth). Reorient patterns within VOACAP to coincide with the actual installation. Patterns are available for very good, average, and very poor ground.


Bobtail curtains

Equilateral delta loops

Right-angle delta loops

Side-fed rectangular loops

5-element Bruce array

Phased Vertical-Element Arrays

The collection of representative basic phased arrays contains both monopole and dipole versions of many types. Because of the complexity of the arrays and because any array in the collection will only approximate an actual installation, the monopole models in NEC-4 employ a MININEC ground, which is roughly equivalent to a radial field of between 32 and 64 elements. All dipole arrays set the base of the dipole at 0.05 wavelength above a high-accuracy ground system with no radial system. The collection includes monopole and dipole versions of triangular arrays that use a fed driver vertical element and two parasitic reflector elements. All arrays are situated so that a main lobe (or the main lobe) points due North (0 degrees azimuth). Hence, broadside arrays have elements on an East-West line, while in-line phased arrays have elements on a North-South line. The 4-square array forms a diamond with the elements at 0, 90, 180, and 270 degrees. In all cases, reorient the patterns within VOACAP to coincide with the actual installation. Patterns are available for very good, average, and very poor ground.

2 In-Phase Monopoles, Broadside Pattern

3 In-Phase Monopoles, Broadside Pattern

2 Phased In-Line Monopoles

2 In-Phase Dipoles, Broadside Pattern

3 In-Phase Dipoles, Broadside Pattern

2 Phased In-Line Dipoles

Triangle of 3 Monopoles with 2 Parasitic Reflectors

Triangle of 3 Dipoles with 2 Parasitic Reflectors

4-Square Array

The total collection has many omissions relative to antennas and systems used by radio amateurs. Some omissions, such as the inverted-L, have too many variations for any one version to capture its specific behavior. Other omissions, such as stacks of Yagi antennas, are too variable from one installation to another for inclusion. However, despite the present size of the type-13 file collections (61 zipped files, with over 1500 individual type-13 files), future additions are always possible.

When selecting a type-13 file, remember that the pattern shape, the forward gain, and the elevation angle are more important factors to consider than the name applied to the array. The goal is to match the type-13 file to your best estimate of the performance of your own array or antenna. The sample patterns in the linked gallery of model plots can go a long way in assisting in the selection. If a closer approximation is required by a specific application, then you should consider modeling your actual antenna or array.

One way to simplify the file structure within your version of VOACAP is to download only the collection (or collections) that have the most promise of closely matching your station antenna (or antennas). Unzip the files into a separate hard-drive directory. Then copy only the relevant files to your directory within the VOACAP program. You may rename the files within the 8-character limit, retaining the extension. As well, you may open the files within Notepad or Wordpad and revise the top line description to suit your needs. However, do not disturb the format of the remaining lines of the file.

These notes are no substitute for mastering your particular VOACAP software. Moreover, the collections are made available without charge and without warranty. Use of the files is the sole responsibility of the user.

Book Radio Wave Propagation Volume 4 (VOCAP Explained) - ON5AU.

Updated 08-4-2007. © L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.

Sample Azimuth Patterns

Return to Index