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 Modern computer optimised AOWA (Advanced OWA) yagi designs have no need for outdated/primitive matching systems such as hairpins (shunt matching) and the like!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.
All G4CQM's Antennas (Homebrew Yagi Projects) designs benefit from a carefully balanced lobe distribution regime in both E & H planes in order to deliver a quiet antenna system!
Unfortunately man-made noise in urban/residential environments may not be emanating from one direction alone, but all around instead, and most likely in differing magnitudes on different beam headings!
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 observed!
Do you really understand the significance of Lionels new interactive VE7BQH Antenna Tables which now incorporates both rural and residential local noise temperatures, simulating local environments? This is truly a game changer, revealing those yagi antenna designs that really are low noise. You will soon learn that there is much more required in the design process than just enhancing F/B (Front to Back) or F/R (Front to Rear) power ratio in order to achieve the lowest temperature yagi. Instead, looking at overall sidelobe content, in particular the forward lobes, has a major impact on delivering a quiet EME antenna system for the higher bands (144MHz and upward)!
|TANT Vs AGTC - Residential Comparison|
|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.
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!...
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 - 30
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 yagis exhibit 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!...
|DL6WU 10 element yagi - Average Q-factor = 20.32 (144-146MHz)|
|WA10XX 10 element yagi - Average Q-factor = 12.94 (144-146MHz)|
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.