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WS715446 & WS28162 Low Q Yagis available from Roger Banks GW4WND of the DXShop ideal for UKAC!
WS715446 & WS28162 Low Q Yagis available from Roger Banks GW4WND of the DXShop ideal for UKAC!
PowAbeam Antennas professionally made by Roger Banks GW4WND of the DXShop... built with round booms (2M and up), sealed driven element molding, and unique ParAclips for no compromise in performance!

50 Ohm Advanced OWA (AOWA) style Low Q Yagis for the VHF/UHF bands

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Build date 24-01-2017

Introduction

Although this is my introduction it also concludes six years and more of research culminating in a comprehensive range of 50Ω Low Q Yagis for the VHF/UHF bands! All of the designs detailed here are Advanced OWA (AOWA) style yagis. A simple split dipole ensures ease of construction!

Selection

I have been brutal in selecting the final designs presented here. The criteria for selection is based on average Q-factor <25, and lowest antenna temperature seen in TANT for both G/Ta @ 30° and G/Ta @ 90° elevation.

Research

My research has revealed that yagis designed this way (as in my selection criteria detailed above) are more likely to deliver performance shown in software than any other designs out there!

Design

Designed in K6STI's professional version software my presentation here uses the free, powerful and unique 4nec2 by Arie Voors! Good designs stand up to examination and scrutiny in any software package!

Dimensions

Dimensions and stacking distances can be found in the .nec files which are the latest and most up to date versions. They are the actual design files so accuracy is assured! Optimal stacking depends on yagi aperture and sidelobe content. I have used DL6WU, or 0.95 of, or 0.9 of, dependant on design for best overall results.

A conductive boom shortens the electrical length of an element that is close or passes through it!

ALL DIMENSIONS SHOWN IN MY ANTENNA FILES ARE FREE-SPACE

ELEMENTS NEED TO BE INSULATED FROM AND RAISED SUFFICIENTLY HIGH ABOVE 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. However, on the higher bands (432MHz and up) even well designed high quality element mountings exhibit some boom effect requiring correction!

Don't use plastic end caps on the parasitic elements unless specifically directed to do so, otherwise it can cause problems with the tuning. End caps can be used to deliberately lengthen elements!

Stray Reactance

Keeping individual lead lengths as short as possible when making connections to the driven element is so important on the higher bands (144MHz and up). Stray feedpoint reactance can degrade SWR and increase mismatch loss. It can also account for VNA plot differences when comparing identical antennas, due to slight variance in construction!

Stacking yagis and mutual coupling

When stacking horizontally polarized yagis one above the other then mutual coupling is greatest, this can impact on matching and may require some adjustment. Stacking yagis side by side reduces coupling. All of this will depend on a particular design, some yagis are less affected than others, low Q designs most resilient.

Element diameters

Element diameters are as follows: 6M & 4M Bands, all elements 5/8 Inch (15.8750mm) round OD tube. For the 2M & 70CM Bands the Driven Element is 5/8 Inch (15.8750mm) round OD tube, whilst all parasitic elements are 3/16 Inch (4.7625mm) round OD solid rod. If you are interested in an alternative then my Wave Antennas Projects designs use all 1/2 Inch (12.7mm) round OD elements throughout!

Internet Nonsense

Some commercial websites make highly questionable statements:

1. We do not use "amateur" programs like NEC4, NEC2...!

These are not "amateur" programs...

NEC is the reference-accuracy Numerical Electromagnetics Code (Method of Moments) from the United States Lawrence Livermore National Laboratory.

NEC is a sophisticated and powerful program for electromagnetic-field analysis. It evolved from mainframe computer programs written in the 1970s. Gerald Burke at the Lawrence Livermore National Laboratory has since brought NEC to its present form. NEC-2 is the latest release authorized for unrestricted distribution. Professionals and academics use NEC for a variety of electromagnetics problems, including antenna analysis. They have thoroughly characterized the code and validated it against measurement.

2. Using EZNEC Pro/6 with the NEC4/2 engine means accuracy is as good as it gets and 30 years worth of bugs do not remains as they do in NEC2 based applications...!

There are no bugs in NEC...

NEC-3 is a modified version of NEC-2 designed to include a Sommerfeld model to properly model wires buried in or close to the ground...

NEC-4 is an enhanced version of NEC-3 designed to better model very small antennas, including those on cellular phones and WiFi routers. The most recent release, 4.2 also includes a better version of the Sommerfeld model used in NEC-3 for in- and near-ground wires. Also added current sources instead of just voltage sources as in previous models, and uses a new memory management system allowing arbitrarily large designs. NEC-4 remains proprietary with the Lawrence Livermore National Laboratory including the University of California, and requires a license.

New Website

This new website consumes much less Internet bandwidth and presents only the supporting information...

73

Derek Hilleard G4CQM


Build or Buy?...

My commercial involvement ended in 2013, it was then that I handed over to Richard Mason G6HKS and also Roger Banks GW4WND of the DXShop ownership and production of PowAbeam Antennas. So, please contact Richard for kits & parts and Roger for ready made yagis! Make sure you send them a link of the actual design you are interested in. Please note that Richard's website contains important build information!

Also check out the page of Sven SM7DTT who stocks a comprehensive range of Antenna-Accessories including suitable ferrite and test equipment!

4 x WS718562 Yagis built and operated by Richard Mason G6HKS, makes a super EME array!
4 x WS718562 Yagis built and operated by Richard Mason G6HKS, makes a super EME array!

TOPICS...


VHF/UHF Bands...

6M Band - 50MHz...

Design IDλBoom
(m)
BW
Az°
BW
El°
Gain
(dBi)
F/B
(dB)
DEQ-factor
(Avg)
WS650650.653.956809.5920.7Split Dipole4.3
WS660820.824.9526810.720.9Split Dipole8.8
WS671161.166.9548561225.9Split Dipole15.1
WS681621.629.672404813.224Split Dipole15.3

4M Band - 70MHz...

Design IDλBoom
(m)
BW
Az°
BW
El°
Gain
(dBi)
F/B
(dB)
DEQ-factor
(Avg)
WS450650.652.78456809.620.8Split Dipole4
PA0712H1.235.247445212.221.7Split Dipole10.7
WS481791.797.651404413.519.4Split Dipole4

2M Band - 144MHz...

Design IDλBoom
(m)
BW
Az°
BW
El°
Gain
(dBi)
F/B
(dB)
* Ta (°K)
@ 30° Elev
* G/Ta (dB/°K)
@ 30° Elev
DEQ-factor
(Avg)
WS260750.751.565567210.322.4230.3-7.53Split Dipole21.5
WS271161.162.41748561227.4233.1-5.96Split Dipole17.7
WS281621.623.357404813.126.7232.6-4.95Split Dipole17.4
CQM8C41.683.480445212.826.7229.4-4.98Split Dipole11.3
CQM9C42.134.428404413.728.2230.6-4.11Split Dipole9.4
CQM10C42.364.890404414.125.6223.0-3.84Split Dipole15.3
144NX13S3.857.980323216.027.7218.3-1.57Split Dipole23.9
144NX143.857.980323216.037.5221.7-1.58Split Dipole18.7
XX144.08.3283216.231.4221.4-1.41Split Dipole18.6
WS2154464.469.25283216.528.3223.4-1.27Split Dipole10.2

70CM Band - 432MHz...

Design IDλBoom
(m)
BW
Az°
BW
El°
Gain
(dBi)
F/B
(dB)
* Ta (°K)
@ 30° Elev
* G/Ta (dB/°K)
@ 30° Elev
DEQ-factor
(Avg)
4323WL503.02.092323615.330.236.45.63Split Dipole16.4
WS7154464.463.093282816.728.234.17.33Split Dipole9.2
WS7185625.623.9282817.53230.78.52Split Dipole21.7

 

Note * = 4 x Yagis (f = 144.1MHz or 432.1MHz)


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# Low Q Yagis - G4CQM - 2017!

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