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A Low-Noise 'Urban' 4 element LFA Yagi for 144-145.5MHz

Revised February 2010 V1.0

Premium commercial versions of this antenna at Innovantennas

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 one is really nice and compact, has good bandwdith (over 1MHz 1.1:1) and yet has maintained an excellent pattern at the same time with more than 10dBi.

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. Do not confuse your version of EZNEC with nec version. EZNEC uses nec2 by default.
  • 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 ant element lengths as close as you possibly can to the measurements below to ensure good, solid performance
  • Please read the 'how to make the LFA Loop' page here

2 x 9 element versions of this antenna at the RSGB VHF Field day 2009

 

Note: performance figures centred on 144.300MHz the centre SSB frequency

Performance

Forward Gain:                   10.06dBi at 144.300MHz

Front to Back Ratio:          20.06dBi at 144.300MHz

Bandwidth:                                  1MHZ below 1.1:1

Please read the 'how to make the LFA Loop' page here

 

Azimuth Plot of this wideband 4el 144MHz LFA

 

 

Elevation Plot

 

 

SWR Plot from 144MHz to 145MHz

 

Antenna Layout

 

Build Dimensions for UK/USA/European version Version

 

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           .5155 3/8 Inch -  .5145 10mm  Tube

DE1                                       .136                                                     .426 Either  1/2 inch or 12mm Tube same size for both

DE2                                       .324                                                      .426 Either   1/2 inch or 12mm Tube same size for both

D1                                         .657                                                      .4625 3/8 inch - .4615 10mm  Tube

D2                                        1.224                                                     .4365 3/8 inch - .4355 10mm  Tube

 

Notes:

DE1 and DE2 are joined at the ends by either 10mm or 3/8inch tube. Feed point is the centre of DE1

Please read the 'how to make the LFA Loop' page here

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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