G4CQM's Antennas - Homebrew Yagi Projects...


WA718562WA6XXWA10XX
WA45065WA9UX0WA65065

Self build OWA yagi designs taken to the next level!

Special thanks to builders/testers Richard G4WFR, Jerry G4JQN, and Don G0RQL.


Updated 28-03-2020...

A comprehensive range of low noise low Q designs for the VHF/UHF Amateur Radio bands. Very easy to build requiring 1 Inch square booms (restricted to 5M maximum length) and 1/2 Inch round elements...

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 Modern computer optimised AOWA (Advanced OWA) yagi designs have no need for outdated/primitive matching systems such as hairpins (shunt matching) and the like.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.

73

Derek Hilleard G4CQM


Following an investigation - Don't use end caps...

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 CAPSEND PLUG ALLOWED!
DON'T USE END CAPSEND 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!

Wet Weather & Q-factor (140-150MHz) study, continued reading is here...


Calculators by G4CQM

 

Wavelength (λ)

 

A useful calculator to enable accurate cutting of coaxial cable stubs, in-line sections and more...

Vf, Ka etc   
f (MHz)   1 λ =  mm λ/2 =  mm λ/4 =  mm

 

VSWR

 

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!

 

Consider that a VSWR of 1.5:1 equates to a Return Loss of 13.98dB OR a Mismatch Loss of only 0.177dB

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.


Low Noise...

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 TANT4 x WA26075 in AGTC
4 x WA26075 in TANT4 x WA26075 in AGTC

 


Low Q...

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)
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-factorLikely outcome...

< 10

Maximum stability

10 - 20

Very good to reasonable stability

20 - 40

Can become unstable in certain conditions

> 40

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!

The DL6WU 10 ele yagi exhibits an ideal average Q-factor plot (shallow gradient). Meanwhile WA10XX as an example offers an even lower Q, keep this in mind when choosing your next design...

Wet Weather & Q-factor (140-150MHz) study, continued reading is here...

 

DL6WU 10 ele Q-factor

DL6WU 10 element yagi

DL6WU 10 element yagi - Average Q-factor = 20.32 (144-146MHz)
DL6WU 10 element yagi
RX

 

| DL6WU10.nec | DL6WU10GNU.gnumeric |

 

WA10XX 10 ele Q-factor

WA10XX 10 element yagi

WA10XX 10 element yagi - Average Q-factor = 12.94 (144-146MHz)
WA10XX 10 element yagi
RX

 

| WA10XX.nec | WA10XXGNU.gnumeric |

 

G0KSC 8 ele OWL GT Q-factor

G0KSC 8 ele OWL GT

8OWLGT 8 element yagi - Average Q-factor = 57 (144-146MHz)
8OWLGT 8 element yagi
RX

 

| 8OWLGT.ANT | 8OWLGTGNU.gnumeric |


YO7 Pro and AO Professional running in DOSBox on Windows 8.1 Professional OS

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...

 

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.


NEC Amateur or Professional program?

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.


G4CQM's Antennas...

  • THESE YAGI ANTENNA DESIGNS ARE NOT 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.
  • MY WEBSITE DOES NOT USE COOKIES, EXTERNAL LINKS MIGHT!
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