Archive of low Q VHF/UHF yagi designs
by Derek Hilleard G4CQM (2017)

A superior range of AOWA yagi designs by Derek Hilleard G4CQM (2017)

SCQM70UC 70 element 1296MHz compact AOWA built by John Lemay G4ZTR

Introduction

27th August 2026... Welcome to the 'Archive of low Q VHF/UHF yagi designs by Derek Hilleard G4CQM (2017)', a website dedicated to home construction and my AOWA yagi designs.

I've made this URL the new permanent home for my Advanced OWA designs and to share them with fellow Radio Amateurs interested in building their own high performance yagi antennas. These are aimed at the VHF and UHF bands up to and including 1296MHz.

Simplicity of construction along with 'Direct Feed' is the main theme in all my designs!

73

Derek Hilleard G4CQM

NEC and calibration

Some ill-informed individuals think NEC-2 is an amateurish program or full of bugs, they are wrong!

All CQM designs are calibrated to NEC, the reference-accuracy Numerical Electromagnetics Code from the Lawrence Livermore National Laboratory. Professionals and academics use NEC for solving a variety of electromagnetics problems, including antenna analysis. They have thoroughly characterized the code and most importantly validated it against actual measurement.

There are no bugs with the NEC-2 release authorized for unrestricted distribution. Just certain limitations that need to be managed/avoided when designing yagi antennas, particularly so on the VHF/UHF bands, they are mainly...

1. Wires that are spaced too close to one another.

2. Junctions, the point at which the size of one wire transitions to that of a different size.

3. Fat wires set amongst thin wires.

4. Bent elements.

Avoid these limitations and good accuracy is assured!

NEC divides each element into segments for analysis, results converge to accurate values as you increase the number of segments. However, at higher frequencies avoid the situation where segments are shorter than the wire diameter.

Modeling yagis at VHF/UHF

Modeling yagis at VHF/UHF... Creating a computer model of a yagi design at HF frequencies poses less of a problem because the impact of boom, stray capacitance/inductance and dielectric effects are on a much smaller in scale than on the higher bands.

As an example at 30MHz a 50mm diameter boom when compared to the wavelength of 10M is insignificant in size! Conversely at 144MHz a 25mm diameter boom is now large enough when compared to the 2M wavelength to have a noticeable effect on overall tuning.

Mitigation for the boom can include adopting the 'DL6WU mounting directive', this requires that each element is raised more than the boom radius (r) above boom.

Capacitance and inductance at VHF/UHF particularly when connecting to the 'Driven Element' will require connections to be kept as short and small as is possible. Practices adopted for the HF bands must not be used!

To be continued...

Please carefully read the following notes... If you haven't built your own yagi before, construction guidance offered here will hopefully stop you making mistakes that will prevent your build from working as it should! These designs won't require any adjustment!

• Boom size
  
  High Band featured designs require 3/4 Inch (19.05mm) square section aluminium, and use heavy wall gauge for strength. However, some form of overhead or underside bracing is required for the very longest booms. Meanwhile Low Band designs will require a larger boom size of 1 Inch (25.4mm) square or above.

• Element size
  
  High Band parasitic elements require 3/16 Inch (4.7625mm) diameter solid rod whilst the DE 5/8 Inch (15.875mm) is tube. However, those Low Band designs listed will use different size tubing for the elements. It is very important therefore to double check the .nec files to ascertain the correct build dimensions.

• Measuring
  
  Lay out boom, mark position of reflector element, measure all other element positions from this point.
  
  Aim for the nearest mm!

• Tolerances
  
  Measure and cut the parasitic elements to the nearest mm. However, it is better to cut them 1mm too short than 1mm too long. Reason: Yagis have a frequency response similar to a Low Pass Filter so it is very important to keep the cut off frequency out of and above the desired pass band.

• Element Mounting
  
  ALL DIMENSIONS ARE FREE-SPACE
  
  ELEMENTS NEED TO BE INSULATED FROM AND RAISED SUFFICIENTLY HIGH ABOVE THE BOOM TO AVOID BOOM CORRECTION AS PER DL6WU MOUNTING DIRECTIVE! I.E. RAISED MORE THAN THE BOOM RADIUS (r) ABOVE THE BOOM...
  
  No boom correction is required if you follow this advice!

• Boom Correction
  
  Specialist element mounting clips designed by G4CQM available from G6HKS Yagi Kits & Parts don't require correction!

• End Caps
  
  Avoid using plastic, vinyl, or rubber end caps on any of the elements (reflector, driven and directors), these will affect tuning and make wet weather performance worse! Seal the DE with flush mounting end plugs.

• Driven Element
  
  The DE length is end to end which must include the centre gap of 15mm!
  
  Example 2M7N50LY - From the YO7 elements table the driven element total length is 481.5mm x 2 = 963mm. To achieve this in practice deduct the center gap dimension of 15mm from the total, and cut a length of tube to 948mm. Finally, cut this into two pieces, each will then be 474mm in length!

• Boom length
  
  Allow an additional +30mm at either end of the boom to maintain tuning across its entire length, and also give a professional look...
  Example: 2M7N50LY Reflector to D5 spacing is 3478mm + 30mm + 30mm = 3538mm BOOM LENGTH!

• VSWR
  
  It is unlikely that reflected power will be exactly 1:1 in the operational bandwidth, a small amount of reflected power is normal due to software limitations and construction tolerances... Don't tune with your test equipment, use as a guide/reference only!

• WARNINGS
  
  DOUBLE CHECK YOUR MEASUREMENTS BEFORE YOU CUT & DRILL!
  
  DON'T ALTER THE DESIGN IN ANY WAY I.E. NUMBER OF ELEMENTS, LENGTHS, DIAMETERS OR POSITIONS. IF BUILT CORRECTLY THESE DESIGNS WON'T REQUIRE ANY ADJUSTMENT...
  
  Finally... When stacking beam antennas using a power splitter to feed them, all of the dipoles need to have the same polarity, identify the live side with red tape!

Useful External Links

1. Arie Voors powerful and truly excellent 4nec2 free NEC based antenna modeler and optimizer

2. BADLAND BRACKETS, HIGH FREQUENCY & VHF ANTENNA ACCESSORIES

3. Contest and DX Library by KA9FOX Software for Contesters and DXers

4. Jan Alvestad Solar Terrestrial Activity Report

5. K6STI 88-108 MHz

6. M0MAT RF Devices - Loads - Couplers - Splitters - Connectors - Cable assemblies

7. Pat W0OPW Nec2Go Nec2 modeling by equation!

8. Richard Mason G6HKS (Yagi Kits & Parts)

9. Steve (G0UIH/VK2IAY/3D2FI) q82.uk antenna homebrewers and experimenters website

Terms and conditions

• These yagi antenna designs aren't for commercial use of any kind without prior consent!

• Private experimenters are free to use these designs for their own personal enlightenment. However, no guarantee or warranty is offered or implied.

• THIS WEBSITE DOESN'T USE COOKIES, EXTERNAL LINKS MIGHT!