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A Low-Noise 'Urban' 7 element LFA2 Yagi for 50MHz

Revised 22nd August 2009 V1.2

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.

 

If you suffer with noise from living in the city, this is another low-noise antenna from G0KSC

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

This is the first airing of the LFA2 design. 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.

Note too the exceptional F/B ratio which is in excess of 43dB at 50.150MHz. Yes, this antenna will take a little longer to make but boy, it is worth it!

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.

 

7el LFA2 x 4 at K2LZQ


 

The Bent Reflector can clearly be seen on 9Y4VU's version of the 7el LFA2

 

A 7element tapered LFA in use at CT1HZE

 

Performance European Version                             UK/USA Version

Forward Gain:                                   12.81dBi at 50.150MHz                 12.81dBi at 50.150MHz

Front to Back Ratio:                          41.42dB at 50.150MHz                 43.33dBi at 50.150MHz

Peak Gain:                                        12.83dBi                                           12.82dBi

Peak F/B:                                       42.12dB                                          44.56dB

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 7el 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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