Sunday, May 27, 2012

28MHz 4el LFA Yagi

A 4 element LFA Yagi for 28MHz with a 5mtr boom - 4LFA10NXD

Revised September 2010 v1.0
Premium commercial versions of this antenna at Innovantennas


This is a high-gain, wideband LFA (Loop Fed Array) Yagi which covers 28 - 28.5MHz with an SWR of less than1.2:1. It has options with both UK/USA and European sized tube and has a 2 section taper. It was designed for VK4NXD and now available for all to use.
This Antenna has been modelled using NEC4 and confirmed by FEKO. This is thousands of dollars of the very latest antenna design software available and the results are highly accurate. When loading into your software, you will see similar SWR but not the same. Please do not alter the model, build to these dimensions for the best results.
Contact me if you are unsure what correction (if any) you require for the element holders/stand-offs you will use or any other questions you may have.

Also read 'An Intro to LFA Yagis' and 'Making the LFA Loop' and 'Creating a Balun'

The 4LFA10NXD at VK4NXD - G0KSC 'Antenna Balun' installed on top of the boom

'Attached are photos of the 10m LFA Yagi.
I completed the yagi today and installed it on the tower. I will let you know how it proforms as the propagation improves in VK. The antenna's SWR plot is as you sent. Thank you very much for all your help and time. I found this antenna easy to make as I have the tooling and with all the information on your web site it was hard to go wrong. I have only made one at this stage but I will set up a stack within the next few weeks.

Thanks again
Dave VK4NXD'

Antenna Layout and Construction:

9.21dBi @ 28.250MHz
22.35dB @ 28.250MHz
SWR: Below 1.2.1 from 28MHz to 28.500MHz

Construction details:

Refer to the above drawing.

Antenna Dimensions for UK/USA and European sized tubing
Taper: Inner Section, 3/4 inch or 20mm Tube (total length 3.2m, 1.6m either side of the boom). Outer section 5/8 inch or 16mm tube. Lengths of end sections as per the schedule below:

                            Spacing                  End Section Length (All below sizes in Metres)
Reflector                0                              1.130
DE1                         .359                        0.640 - FEEDPOINT
DE2                       1.372                        0.640
D1                         2.398                         0.876
D2                         5.020                         0.694
Adjust loop width for best SWR upon completion. Fit antenna with a 1:1 balun

Stacking distance: 5m -  10m - 6.5m recommended
Gain at 6.5m:                          11.85dBi
F/B at 6.5m:                             22.48dB

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