About this site

This site aims to provide radio amateurs with easy-to-use tools to help them design simple, light but effective wire antennas which are especially suitable for portable use while participating in any of these (and other) amateur radio outdoor award schemes:

Currently, the site offers tools to help the user design these different types of antenna:

Extras

About the designers

Each of the designers listed here share a common structure and form, while presenting combinations of controls specific to the type of antenna covered.

In each case, the user is presented with a group of controls in the upper left portion of the page: these controls enable the user to completely specify the characteristics of the antenna, namely frequency, wire lengths, angles, length units, and so on.

Example designer layout

In the upper right portion of the page is a graphics area where the modelled antenna is presented in a 3D context. The graphic can be zoomed, panned and rotated. Antenna feed-points are shown as colored markers; the user may also choose to toggle the appearance of a semi-transparent plane at the height (1.85 meters) of an average person, in order to gain some perspective on how large the antenna would be when erected.

In the lower half of each of the designers, a group of controls enable the calculation of an antenna's performance, and the presentation of charts and diagrams showing the performance in various ways, in any combination of the following:

Example antenna performance controls section

Calculation of an antenna's performance is achieved using a version of the NEC2 (Numerical Electromagnetics Code v.2) code. Results of the calculations, and the resulting charts and diagrams, have been compared with those presented by programs such as EZNec and 4nec2, for similar antennas, and have been found to be closely comparable. Notwithstanding that, we make NO claims as to the accuracy of such information or results; the graphics and data presented in this site are provided "as-is" for the general interest and edification of the user. Refer to the Disclaimer below for more information.

 

Linked dipole designer

The linked dipole antenna designer page enables the user to very quickly design a multi-band linked dipole antenna for portable use in the field, or on a mountain top.

This type of antenna is constructed with one or more sections in series, each for a particular amateur radio band, and which are capable of being linked, or unlinked, as required, to make the antenna resonant on whichever band the radio operator wishes to use. Linking or unlinking sections has, however, the downside of having to lower the antenna to physically reach the very highest links.

4-band linked dipole antenna example

Linked dipole antennas are especially easy to erect, requiring just one support in the center - this could be a pole or a cord suspended from a tree - amd have the added benefit of giving good results even when erected in thick forest, since the antenna radiates horizontally polarized, while the trees present little obstacle since they are not only physically, but also electrically vertical. So the trees have little influence on the radiated signals - good for heavily-forested SOTA summits.

 

OCFD antenna designer

The OCFD antenna designer page enables the user to quickly design a multi-band OCFD (off-center-fed dipole) antenna for portable use in the field, or on a mountain top. OCFD antennas consist basically of two wires, together comprising one half-wavelength in length, and fed in a similar manner to a center-fed dipole, but fed off-center at a point usually about 1/3 in length from the end; the designer, however, allows the feed-point position to be configured for optimal performance for those bands of interest to the operator.

40-meter OCFD antenna example

The OCFD antenna is often stated to present an impedance of around 200 ohms to 250 ohms at the feed-point, and is often fed through an unun, usually 4:1, to match a 50-ohm system. A current choke is often also needed to suppress common-mode currents on the feed-line. However, the actual impedance values of a particular OCFD antenna configuration will most often be quite different, and will vary with:

Actual values for the impedance at the antenna base frequency can vary between 73 ohms to several hundred ohms, depending on the configuration (refer to the 4th column in the table below).

One big advantage of the OCFD antenna, as compared to a center-fed dipole, is that it can exhibit low VSWR minima on two, three or four higher bands above the principal band for which it has been designed: for example, with a judicious choice of feed-point position, a 40-meter OCFD can resonate also on the 20-meter, 15-meter and 10-meter bands, with the 6-meter band being an added possibility.

The performance of an OCFD antenna is very sensitive to the choice of feed-point position, as the table below demonstrates. This table lists VSWR values at the stated frequencies across several bands for a 40-meter OCFD, principal frequency 7.1 MHz, erected as a flat-top at 10 meters above average ground. VSWR values for the stated frequencies in each band are displayed as a function of the percentage split between the two separate sections of the antenna, here listed as "Left" and "Right":

Split Ratio,
R/L
Estimated
impedance,
ohms
Band Bands*
Left
%
Right
%
40m
(7.1 MHz)
30m
(10.1 MHz)
20m
(14.2 MHz)
17m
(18.1 MHz)
15m
(21.2 MHz)
12m
(24.9 MHz)
10m
(28.5 MHz)
* where VSWR is <= 3.5,  with alternatives where it's possible to tune out up to 10:1 VSWR

The animation below uses the same antenna configurations as the table, and demonstrates graphically how sensitive an OCFD antenna is to the relative ratios of the two sections, left and right:

From these data, it can be seen that the most often-used 1/3 to 2/3 (or 33% / 67%) ratio section lengths used for a 40-meter OCFD antenna will result in the antenna being resonant on three amateur bands, 40m, 20m and 10m, but NOT on 15m. In order to get a 40-meter OCFD antenna to be resonant also on the 15m band, a different lengths ratio between the antenna sections must be used.

One of the best ratios to be used, as both the graphic and the table show, is close to a 18% / 82% ratio which gives good VSWR minima on all four bands 40m, 20m, 15m and 10m. This is also borne out by the comments made in Part 4 of this document on OCFD antennas:
   https://rsars.files.wordpress.com/2013/01/study-of-the-ocf-dipole-antenna-g8ode-iss-1-31.pdf
where the author suggests a 1/6 to 5/6 (or 16.67% / 83.33%) ratio would be the best choice to bring the antenna to resonate on four HF bands 40m, 20m, 15m and 10m, and incidentally also on the 6-meter band.

Changing the angles (within reasonable limits) of the two arms of an OCFD antenna has a much less profound effect on VSWR and bands coverage than the choice of feed-point position. Angling one or both arms downward, however, has the effect of lowering the antenna impedance somewhat.

The OCFD antenna can be a very useful and time-saving field antenna in the field - simply change TRX band to one of the antenna's resonant bands, and start transmitting.

 

EFHW antenna designer

The EFHW antenna designer page enables the user to quickly design a multi-band EFHW (end-fed half-wave) antenna for portable use in the field, or on a mountain top. EFHW antennas consist basically of one single wire, a half-wavelength in length, which can be configured in several ways:

40-meter EFHW antenna example, configured as a sloping inverted-L

Being end-fed, the EFHW is voltage-fed and presents a high impedance (around 2500 ohms to 3500 ohms) at the feed-point, and hence needs an unun, typically 49:1, to match a 50-ohm system.

One big advantage of the EFHW antenna is that it can exhibit low VSWR minima on several bands above the principal band for which it has been designed: for example, a 40-meter EFHW can resonate also on the 20-meter, 15-meter and 10-meter bands, with 6-meters being thrown in for good measure. This can readily be seen in the diagram below:

40-meter EFHW antenna: VSWR curve over several bands, including impedance curves

Careful optimization of the EFHW antenna characteristics is needed to ensure good performance in the field. Ground conductivity plays a part, as well as choice of principal frequency, configuration, and inductive/capacitive loading of the antenna. If done right the EFHW antenna can be a very useful and time-saving field antenna - simply change TRX band to one of the antenna's resonant bands, and start transmitting.

 

Delta loop antenna designer

The delta loop designer page enables the user to quickly design a single-band vertically-polarized delta loop antenna for portable use in the field, or on a mountain top. It needs just one support, a pole or cord suspended from a tree.

This type of antenna is constructed as a closed triangular loop, with the apex at the top, and is designed for one particular amateur radio band. It is fed on one of the sides, close to a lower corner: the coax center conductor is connected at a point 1/4 wavelength down from the apex, and the coax shield is connected to the short part of the same side: in this way it propagates predominantly vertically-polarized waves.

20-meter delta loop antenna example

The delta-loop antenna generally features a low vertical take-off angle, even though such antennas are erected with their lower side only a couple of meters above the ground. The low take-off angle makes this kind of antenna a worthwhile prospect for DX-ing, especially while operating portable. If erected on a summit where the ground drops away appreciably from the summit, the take-off angle will be even lower; placing the delta-loop antenna higher up on its' center support will also lower the take-off angle.

Another feature of the delta-loop azimuthal propagation is the very deep low at high elevation angles (see the diagram below), meaning much less power is dissipated at high angles. This means, however, that this antenna is not a good choice for NVIS communications.

Delta loop antenna designer - interactive propagation pattern display

The delta-loop antenna is also fairly broadband on its' designated band - the 2.0:1 VSWR range on the 20-meter band for example, at ~350kHz wide, covers the entire band.

Two slight disadvantages can be encountered when erecting the delta-loop antenna:

In addition, one should note that the center of the antenna horizontal side (its' foot) is a voltage high-point, which is why the antenna should be erected high enough (2 meters minimum) that a casual passer-by cannot easily come into contact with that side.

 

Half-square antenna designer

The half-square antenna designer page enables the user to quickly design a half-square antenna for portable use in the field, or on a mountain top. This type of antenna needs two supports: a combination of pole(s) and/or cord(s) suspended from a tree. Half-square antennas can be configured in one of two ways:

40-meter half-square antenna example, configured as a multi-band EFHW
Half-square antenna configured as a full-wave single-bander

When configured as a full-wave single-bander, the impedance at the upper corner feed-point is approximately 50 ohms, and hence does not necessarily need an unun at the feed-point, although a 1:1 unun is often used. It's important to run the coax feed-line at 90° to the antenna for a couple of meters in order to minimize common-mode currents on the coax sheath.

This configuration results in a fairly low angle (~ 20° to 25°) elevation propagation pattern, with good broadside lobes, deep (typically better than 12dB) rejection in the plane of the antenna, and a deep (~15dB) minimum at high elevation angles. This makes this configuration a good choice for single-band DX work.

Half-square antenna configured as an EFHW half-wave multi-bander

When configured as a half-wave multi-bander, the impedance at the end of the wire is around 2500 ohms to 3500 ohms, and hence an unun, typically 49:1, is needed at the feed-point. In addition, the antenna will also most often need a short (~1/8 wavelength) counterpoise.

Like other EFHW antennas, this configuration can exhibit low VSWR minima on several bands above the principal band for which it has been designed: for example, a 40-meter half-square configured in this way can resonate also on the 20-meter, 15-meter and 10-meter bands, with 6-meters being thrown in for good measure.

 

Moxon antenna designer

The Moxon antenna designer page enables the user to quickly design a Moxon 2-element beam antenna for portable use in the field, or on a mountain top. This type of antenna needs a single support only.

First designed in the early 1950's, and later further developed by L.B.Cebik in the 1980's, the Moxon antenna has become a firm favourite for those interested in building a lightweight beam antenna for home or portable use.

10-meter Moxon antenna example

Since the Moxon is a beam antenna consisting of a driver element and a single parasitic reflector element, both folded toward each other, it makes for a usefully compact array. It can be made of wire supported by spreaders, or from lightweight tube which is mostly self-supporting. In both cases, however, a single support only is needed, which is very handy when erecting the antenna for portable operations.

The Moxon offers a broad forward lobe giving modest directivity of about 2dB, with a deep null toward the back end, giving a high front-to-back ratio: gains of up to 9.7dBi are possible.

10-meter Moxon antenna at 8 meters above average ground: propagation patterns
 

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Acknowledgments

The software used in this site to generate antenna propagation plots data, and also the plots themselves, is open source and freely available for non-commercial use:

We are grateful for the opportunity to use all of these resources, and acknowledge our debt of gratitude to their respective developers.

Please note:  due to the reliance on sizeable graphics and groups of controls in this site, it is not suited to display on small screens. We apologize for any inconvenience this may cause.

 

Disclaimer

All information on this web site is provided "as is", for general information purposes only, to the amateur radio community and those with an interest in radio technical matters.

The operator of this web site makes no representations or warranties of any kind, express or implied, about the content, completeness, accuracy, reliability, legality, suitability or availability, with respect to the website or the information, products, services, or related graphics contained on the website, for any purpose. Any reliance you place on such information is therefore strictly at your own risk.