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A Low-Noise 'Urban' 8 element Dual Reflector LFA2 Yagi for 50MHz

The LFA design has a patent pending and all G0KSC designs are copyright. Any ham can build for their own use or those of a friend. Where profit or commerical gain exists, express permission of G0KSC must be sought.

Revised 20th August 2009 V1.0

So, is this an 8 element antenna or a7 element antenna with 2 reflectors? I prefer the later as this sits on a typical 7 element boom. However, I will leave what you call it, up to you..


This antenna is for experianced builders only and therefore, no build information is detailed below. However, EZNEC files are available for download on the download page of this site: Download page


The difference between the LFA ad the LFA2 is within the parasitic elements. The Reflector and in some cases the First Director are bent towards the feeding loop. This helps increase pattern cleanliness and provide a super-flat SWR curve along with a worthwhile increase in Front to Back ratio.

Another first for me and the LFA is tapered elements. Some Hams wanted tapered designs due to difficulties in getting longer sizes of tubing delivered although I much prefer single peice elements.

This antenna has been designed with pattern cleanliness, bandwdith, SWR and Front to Back in mind. Anyone with Yagi Optimizer and 5 spare minutes can produce an antenna with a similar boom length to this one with similar gain. However, the art is being able to maintain gain while increasing F/B, Bandwidth, reducing SWR to an absolute minimum and reducing unwanted lobes which cause interference and receive unwanted noise.

One of the reasons for the dual reflectors on this one is to reduce Elevation lobes which is difficult to do with an antenna of this boom length/number of elements.

I have 2 versions of this antenna, one with metric and the other with imperial sized elements.

European metric and UK/USA imperial design files upon the download page.

PLEASE NOTE:

  • This antenna WILL NOT show the true SWR in any antenna modelling package unless you are using one which uses the latest NEC4 calculation engine. This is especially the case when bent elements are used. Do not adjust anything, this antenna will be just fine when built!
  • There are two sets of measurements listed below. One uses imperial sizes, the other uses metirc sizes. Ensure you use the correct one for the material you have
  • 'within one or two millimetres' Will not do! take the time to ensure you get the spacing and element lengths as close as you possibly can to the measurements below to ensure good, solid performance
  • This is a 50 Ohm Antenna, no matching arrangement is needed. A simple 1:1 or choke balun will be fine. see 'creating a Balun' here
  • Please read the 'how to make the LFA Loop' page here
  • Please do not alter segmentation or try to 'tune' the antenna unless you have nec4 or better. SWR will not read true within anything else
  • Note the First Director bends in opporsite directions for the European and UK/USA versions. This is correct.

 

Performance European Version                             UK/USA Version

Forward Gain:                                   13.01dBi at 50.150MHz                 13.02dBi at 50.150MHz

Front to Back Ratio:                          28.88dB at 50.150MHz                 29.15dBi at 50.150MHz

Peak Gain:                                        13.12dBi                                           13.06dBi

Peak F/B:                                       29.84dB                                           29.86dB

Bandwidth:                                       600KHz below 1.1:1                       600KHZ below 1.1:1

 

Download the EZNEC antenna files HERE

 

SWR Plot for the European version of the G0KSC 8el 50MHz LFA2 Yagi

 

SWR Plot for the UK/USA version of the G0KSC 8el 50MHz LFA Yagi

 

Antenna Elevation Plot

 

European version Azimuth Plot

 

UK/USA Azimuth Plot

 

A close up of the Reflector, Driven Loop and First Director showing the bends after the taper point

As always, any questions please ask!

 

Justin G0KSC

Download the EZNEC antenna files HERE

 
 
 
 

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