Yagi Calculator by John Drew, VK5DJ
to develop DL6WU style yagis for VHF/UHF

Yagi Calculator is a Windows program (also runs well on Linux - Ubuntu 8.10 under Wine) to produce dimensions for a DL6WU style long Yagi antenna. Long yagis are commonly used from the 144MHz amateur band to the 2.4GHz band. The DL6WU yagi is highly regarded as being easy to build with repeatable results, broad bandwidth and a useful pattern.

The program on this site was developed in the early 90s as a DOS program. Time moved on and so did operating systems, so the 2003 version was an opportunity to convert to a Windows environment and update the information and modify some of the algorithms. The latest version is 2.6.4 (14 January 2010) with an added dimension for the folded dipole construction. Recent versions added allowance for square or round booms, round, square, flat elements and some impedance calculations. I have also added an "Insert To" distance being the distance from the tip of an element to the edge of the boom to help in construction. There have been minor fixes to improve reliability in different machines and better program flow. No changes were made to the essential algorithms apart from the additions needed to cater for alternate boom and element material shapes and the provision of "through the boom" folded dipole calculation. If you run Vista I recommend you run it as Administrator.


Example printout of a 2M design

Features of the free but copyrighted program include: calculation of the element length and element spacings of a yagi for a particular frequency, different size materials for boom and elements are catered for as are different methods of mounting, dimensions of baluns are calculated, there is provision for entering the dimensions of an existing DL6WU antenna for optimisation through an external program or to gather information on its gain, beamwidth etc. A handy SWR calculator and feedline loss calculator are included as part of the package. Stacking information is also provided as are estimates of gain. A helpfile is included that covers many aspects of yagi design as well as helping with the operation of the program.

Download and view the Windows Help files for Yagi Calculator

Download Yagi Calculator including the Help File
Click link to download. This setup file is approximately 700K, run it to install Yagi Calculator (Version 2.6.4)
Note: On 14 January 2010 I uploaded V2.6.4 with added dimension for folded dipole. Version 2.6.3 provided an improved impedance calculation, while 2.6.2 fixed a printout error when using insulated elements - the wrong boom diameter was being printed. Version 2.6.1 in January corrected an error in the coax.dta file that caused YC to ignore the 1296MHZ data on the SWR form. Also took opportunity in January 09 to tidy up the printout screen to make spacings less confusing.


I strongly recommend that you first uninstall any previous version via the Yagi Calculator start menu short cut and also ensure there is no old copy of YAGISETUP.exe in your internet cache. If your download has proceeded well it should install 2.6.4 not an earlier version.


My satellite system used Yagi Calculator for design on 435.5MHz and 145.5MHz
(strictly speaking the 2M beam is too short to be a DL6WU but it works fine, both beams have very good SWR)

Amateur and commercial manufacturers have made use of the Yagi Calculator to create effective yagi antennas. The examples below are of yagis built using the program and constructed by a non technical person to solve a communication problem in a commercial environment. I have shown this as an example of the non critical nature of the antenna.

A DL6WU design yagi solves a comms problem

A home built 860MHz yagi is used by a local water conservation authority to provide data communications via a mobile phone network. The commercially provided antenna wasn't good enough for reliable communication.

Telemetry from sensors gauge water depth and salinity. Each day the site is accessed by mobile phone (CDMA network) to determine the results from the previous 24 hours. Conventional omni directional antennas were not reliable as the sites are all low lying, often surrounded by scrub and usually many kilometres from a mobile phone cell. The yagis were built from a design by Yagi Calculator.

The yagis were built on a fibreglass rod boom normally sold for use with electric fences. A 3 metre rod costs about $8. The elements are 3mm brazing rod. push fit in 3mm holes. The driven element is a single dipole, split into a channel cut in the fibre glass, fed with 50 ohm foam coax with a quarter wave sleeve balun. The element and balun assembly are fixed using an epoxy product called "Knead it". The pictured yagi was built by a person with no previous experience following conversations with nearby radio amateurs.


View of site

The yagi is shown at the top of a 5 metre pole aimed at the nearest CDMA phone site 30km away.

The photo at right gives a good idea of the problem in gaining good signals at the low lying and wooded site.


A successful yagi built using a fibreglass boom and 'knead it'. I've suggested the builder uses silicone to seal the material as it looks porous.

Steve's (VA3FM/VE3SFV) photo of his insulated construction method

Steve VA3FM has made a superb job of an "insulated through metal boom" design. Check out his website for good definition photos of construction details. When using Yagi Calculator choose insulated construction through metal boom for reflector and directors and fully insulated for the folded dipole.


The pushnuts used by Steve to fasten the elements
He bought his from http://www.pinrestore.com/Hardware.html


Steve's 2m yagi in the air (middle yagi)

VK5DK's 1250MHz 26 element DL6WU Yagi for ATV

The following readings were obtained using an Icom IC910H radio fitted with the 23cm module & readings were taken using a Bird 43 Through Line power meter at the bottom of 13 metres of FSJ4-50E

FREQUENCY
FORWARD PWR REFLECTED POWER SWR bottom of coax Estimated SWR at antenna
1296MHz 9 watts 0.1 watt 1:1.24 1:1.4
1290MHz 8 watts 0.1 watt 1:1.25 1:1.4
1285MHz 10 watts 0.1 watt 1:1.22 1:1.4
1280MHz 8.5 watts 0.1 watt 1:1.24 1:1.4
1275MHz 9 watts 0.2 watt 1:1.35 1:1.5
1270MHz 10 watts 0.1 watt 1:1.2 1:1.4
1265MHz 10 watts . 0.15 watt 1:1.28 1:1.5
1260MHz 10 watts 0.1 watt 1:1.22 1:1.4

It can be seen that the antenna is quite flat across a fair frequency range and the low loss coax should still deliver about 6-7 watts to the antenna.

Observations: The boom seems to be a bit on the large size and may be outside the equations used to calculate the boom effect on element length (I haven't checked the measurements), additionally the presence of the fat heliax may also be influencing things but the bottom line is that the yagi works very well in practice.

Acknowledgements

Yagi Calculator is a program to assist with the design of long yagi antennas. It uses the broad principles developed by DL6WU and printed originally in the German Radio Magazine VHF Communications (March 1982). The article was titled Extremely Long Yagi Antennas.


The work of David VK3AUU (AR Feb 1988) in developing some equations to fit DL6WU's graphs was very valuable. The reflector calculations are based on a Basic program written by KY4Z and W6NBI and with suggestions by DL6WU. The ARRL Antenna Handbook provided information, as did various sources on the Internet. K5OE's site at http://members.aol.com/K5OE is a particularly useful one.

The author acknowledges the 1998 ARRL Handbook for information on coaxial cable impedance, dielectric and velocity factor.
Yagi builders are reminded that DL6WU designs are primarily for long yagis. A boom length of 2 wavelengths (or 10 elements) would be a minimum sized antenna. On the other hand, yagis with as few as 8 elements have used the design and worked very well.

I wish to acknowledge Kevin Schmidt W9CF (http://fermi.la.asu.edu/w9cf/) for the correction factor for square section rod of 1.18 * cross section of round tube and also for the formula to find the equivalent round cross section for both square and flat element materials (Version 2.5.0)

dself = w[0.5 + 0.9t/w - 0.22(t/w)2] where w is width of material and t is thickness.

The formula source for the impedance calculations is from "Round and Square Section Parallel Transmission Lines Theory, Practice and Applications" by Roger Harrison and Andy Sayers VK2AES, GippsTech Conference 2009, Churchhill, Victoria, Australia.

Square section: Zo=0.45 + 344[s/(s+d)] - 345[s/(s+D)]^2 + 411[s/(s+D)]^3 where s is face-to-face spacing, D=width of square-section line.

Circular section line: Zo=972(s/d) - 481(s/D)^2 + 86(s/D)^3-547 where s is centre-to-centre spacing, D=diameter of circular-section line.

Links

Some valuable comments on scaling and boom diameters from W4RNL

Considerations on the effects of boom diameter by Lief Asbrink, SM5BSZ

Construction of a DL6WU yagi using a folded dipole by Jim W6PQL

Experiments on an antenna range by Jim W6PQL

Insulated from boom construction by Steve VA3FM

Various antenna applets and particularly the correction factor for square section versus round rods by Kevin Schmidt.

Some antenna range results by the US National Bureau of Standards

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Last updated: 19 July 2009