23rd October 2023... You've arrived at the new 'Yagi Antenna Design by G4CQM' website. A selection of technical articles and analysis offering guidance and insight to enable you to recognise and build your own 'high performance yagi' design.
Amateur Radio station operators can still enjoy the satisfaction and pleasure derived from antenna home construction but require the necessary information/knowledge to achieve a good outcome. Yagi designs by G4CQM offer an 'easy to build' approach with readily available parts.
Pictured above is the 2M7N50LY yagi design built by Richard G6HKS... In August (2023) Richard (QTH in Milton Keynes) managed a Tropospheric QSO of around 2500Km distant with CT9 (Madeira Island), a new one for him! 2M7N50LY is a well proven low Q long yagi design, but not too long, ideal for limited space locations. During this years Sporadic E's Richard found this antenna to deliver exceptional results. This particular design set amongst other low Q long yagis can be seen here...
Low Q Long Yagis by G4CQM for Terrestrial VHF/UHF DXing
Meanwhile a selection of unique AOWA (Advanced Optimized Wideband Antenna) yagi designs by G4CQM can be seen here...
Antenna Designer UK - 'Specialist Yagi Designs' by G4CQM
73 Derek G4CQM
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... 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...
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. K6STI 88-108 MHz
5. Pat W0OPW Nec2Go Nec2 modeling by equation!
6. Richard Mason G6HKS Yagi Kits & Parts
7. Steve (G0UIH/VK2IAY/3D2FI) q82.uk antenna homebrewers and experimenters website
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