G4CQM's Antennas (Homebrew Yagi Projects) represent a quantum leap in Derek's development of the AOWA (Advanced OWA) style yagi beam using a simple Split Dipole as the Driven Element, see Dipoles Explored to expose the myths! There are no bent elements or different diameters to contend with so construction could not be more straightforward... A clear advantage is to deliver 50Ω Direct Feed with maximum efficiency. Modern computer optimised AOWA (Advanced OWA) yagi designs have no need for outdated/primitive matching systems such as hairpins (shunt matching) and the like.
AOWA (Advanced OWA) yagis situated in a noisy urban/residential environment outperform LFA's and designs with bent elements in most cases, much lower temperature and better G/Ta. Each design has a relatively shallow Q-factor gradient like that of a highly stable DL6WU long yagi! Meanwhile radiation efficiency >98% in all featured designs ensures best overall performance.
A forensic analysis presentation using Arie Voors free and powerful 4nec2 (NEC based antenna modeler and optimizer) along with detailed build instructions will guide the homebrew Ham Radio constructor toward a successful outcome.
Derek Hilleard G4CQM
Don't use end caps on any of the elements (driven and parasitics), these will affect tuning, making wet weather performance worse! End caps become capacity hats whilst element ends are a voltage anti-node, the worst possible place to attach/place anything!
|DON'T USE END CAPS||END PLUG ALLOWED!|
Conversely it is possible to seal the ends of the elements by using a plastic end plug as seen above, provided that they are completely flush with the element end and don't cover any of the radiating surface area!
A useful calculator to enable accurate cutting of coaxial cable stubs, in-line sections and more...
Regard VSWR readings as a guide only particularly when trying to establish just how good your antenna is. Completely flat VSWR when measured at the station patch panel could for example indicate that the system may have hidden losses, be warned!
Enter any one of the first three parameters below, then click SUBMIT to calculate % Reflected and Mismatch loss;
Please note that these VSWR calculators are intended for use in the context of VHF/UHF yagi antennas connected with 50-Ohms coaxial feeder cable.
Some authors quote Return Loss as a negative number, and this convention is still widely found in professional radio communication and telecommunications literature. However, caution is required when discussing increasing or decreasing Return Loss as these terms strictly have the opposite meaning when Return Loss is defined as a negative quantity.
Unfortunately man-made noise in residential or city environments may not be emanating from one direction alone, but all around instead, and most likely in differing magnitudes on different beam headings? Even those who live in a rural location can suffer at times from problems with overhead power lines, especially during damp and wet weather.
Despite all of this a 'Low Noise' yagi design can help in copying weaker signals by reducing the overall noise pickup. If attention is paid by the designer to delivering a cleaner pattern in both planes (E & H) then noticeable and real improvements will be achieved!
AOWA yagi designs by G4CQM benefit from being low temperature (Ta is the total temperature of the antenna or array in Kelvin) with good G/Ta...
For EME DXers the VE7BQH's Antenna Tables are published by Lionel Edwards VE7BQH and widely circulated for more than the past two decades in a Microsoft Excel spreadsheet format (.xls file). The idea was to promote G/T (strictly G/Ta) as a definitive reference of the overall merit of a yagi antenna, the more positive figure the better a yagi design would be regarded!
TANT (a DOS program) by Sinisa YT1NT/VE3EA was used in the tables exclusively for several years, until quite recently that is. However, in the latest presentations AGTC_lite (runs directly in Windows) by F5FOD/DG7YBN has also been brought into use.
|TANT Vs AGTC - Residential Comparison - Note difference around 30° elevation, which one is right?|
|4 x WA26075 in TANT||4 x WA26075 in AGTC|
Yagis exhibit a frequency response similar to that of a Low Pass Filter (LPF), it is most important to ensure that the cut-off frequency is well above the desired upper bandwidth limit!
Q-factor can have a major impact on stability in bad weather and proximity to other structures. It's not just about available VSWR bandwidth. The lower 'Q' designs offer greater stability, and should be considered as the first choice in locations suffering extreme climatic conditions, perhaps even above other desirables?
Don't confuse true resonance with matching, the point of lowest Q and minimun VSWR are not always on the same frequency! A good match on a spot frequency can be achieved no matter where Q is, but the available (useable) VSWR bandwidth around that spot frequency reduces as average Q-factor rises.
|High Q design Vs Low Q design - Note SWR (140-150MHz)|
|NEXTGEN 8 ele (2009)||WA8C9 8 ele (2019)|
Genuine low Q yagi designs are more likely to deliver performance shown in software models because they are less sensitive to their surroundings.
You cannot assume a yagi to be low Q just because the VSWR bandwidth looks good, this would be a mistake! An example of this fact as seen below is the G0KSC 8 ele OWL GT, at 145MHz the VSWR looks very good? However, Q-factor rises rapidly soon after giving an average (144-146MHz) of just over 57.
Average Q-factor (144 - 146MHz) in the real world: Guide based on field trials (during my six year research project) and recent analysis (updated 2019)...
|Avg Q-factor||Likely outcome...|
10 - 20
Very good to reasonable stability
20 - 40
Can become unstable in certain conditions
Prone to instability
The simple rule, the lower the 'Q' the better is stability. Yagi designs sporting an exponential curve (very steep average Q-factor plot) are not ideal. This dramatically raises the average 'Q' and warns that the cut-off frequency is too close or may already be in band? Dielectric loading effects caused by wet weather will drag the cut-off frequency even further LF and give rise to instability!
|DL6WU 10 element yagi - Average Q-factor = 20.32 (144-146MHz)|
|WA10XX 10 element yagi - Average Q-factor = 12.94 (144-146MHz)|
|8OWLGT 8 element yagi - Average Q-factor = 57 (144-146MHz)|
Wave Antennas (G4CQM's Homebrew Yagi Projects) are very special yagi designs for the Amateur Radio VHF/UHF bands created by Antenna Designer Derek Hilleard G4CQM, and were first conceived in K6STI's YO7 Pro and AO Professional version software.
The Numerical Electromagnetics Code (NEC) was developed (January 1981) at the Lawrence Livermore National Laboratory in California (USA), sponsors included the Naval Ocean Systems Centre and Air Force Weapons Laboratory. It was clearly intended in the first instance for professional use by those sponsor government organisations and was not developed as an amateur program!
The current version of NEC/MOM is due to extensive work carried out by Messrs G.J. Burke and A.J. Poggio.
NEC-2 is user-oriented, the computer code intended for analysis of the electromagnetic response of antennas and metal structures. There are several versions of NEC, NEC-2 was released to the public and is now available on most computing platforms. NEC-2 has been used by several software developers in their antenna software as a reference and method of providing calibration.