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A Low-Noise 'Urban' 20 element Plus2 LFA Yagi for 144MHz

Revised 6th December 2009 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 commercial gain exists, express permission of G0KSC must be sought.

The new LFA Plus2 range includes an additional 2 reflectors which are used in order to maintain pattern stability throughout the 1MHz coverage (144-145MHz).

This is the ultimate in 2m VHF performance today, the new LFA Plus2 is the one to beat showing flat SWR, pattern stability throughout and better sky temperature and G/T figures than any other Yagi of the same boom length (VE7BQH list).

Currently these antennas are available in METRIC SIZES ONLY. Imperial will be launched at a later date.

As with ALL LFAs this antenna requires no matching, it has a 50 Ohm input impedance. PLEASE do not alter dimensions, unless your software package uses NEC4 calculation engine, you will not see SWR correctly.

 

Download both the European and UK/USA EZNEC files HERE

The look fo the 20el Plus2 when built

 

4nec2 (with nec4 engine) Elevation plot of the 20el Plus2 LFA Yagi

 

The 20el Plus2 Azimuth plot from the 4nec2 antenna modelling package

 

SWR as presented in the 4nec2 antenna modelling package using nec4.1 Double Precision calculation engine

 

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 EZNEC with the NEC engine. 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
  • 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

Download both the European EZNEC files HERE

Performance European Version

Forward Gain:                                   18.35dBi at 144.300MHz

Front to Back Ratio:                           28.79dB at 144.300MHz

Peak Gain:                                       18.37dBi

Peak F/B:                                          39.56dB

Bandwidth:                                       144-145MHz below 1.1:1

 

Build Dimensions for European Version - mail me if you need 13mm tube driven loop sizing

Element                             Spacing in metres Half element Length in metres            Element Notes

Plus2 Rear Reflectors                0                                                           .519                                                Above and below loop by 200mm

Reflector                                .350                                                       .5145                                              8mm Diameter tube or solid rod

DE1                                       .494                                                      .448                                                 10mm Tube

DE2                                       .659                                                      .448                                                 10mm Tube

D1                                         0.881                                                    .479                                                8mm Diameter tube or solid rod

D2                                         1.384                                                    .464                                                8mm Diameter tube or solid rod

D3                                         1.821                                                    .4485                                               8mm Diameter tube or solid rod

D4                                         2.296                                                    .4525                                               8mm Diameter tube or solid rod

D5                                         3.004                                                    .449                                                8mm Diameter tube or solid rod

D6                                         3.818                                                    .444                                                8mm Diameter tube or solid rod

D7                                         4.686                                                    .4395                                              8mm Diameter tube or solid rod

D8                                         5.580                                                    .4355                                              8mm Diameter tube or solid rod

D9                                         6.488                                                    .4325                                              8mm Diameter tube or solid rod

D10                                       7.416                                                    .4285                                              8mm Diameter tube or solid rod

D11                                       8.352                                                    .427                                                8mm Diameter tube or solid rod

D12                                       9.275                                                    .423                                                8mm Diameter tube or solid rod

D13                                       10.357                                                  .4195                                              8mm Diameter tube or solid rod

D14                                       11.225                                                  .4155                                              8mm Diameter tube or solid rod

D15                                       12.145                                                  .406                                                8mm Diameter tube or solid rod

D16                                       13.073                                                  .402                                                8mm Diameter tube or solid rod

D17                                       14.085                                                  .395                                                8mm Diameter tube or solid rod

D18                                       14.955                                                  .411                                               8mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by 8mm tube

Feed point is the centre of DE2

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

There is simply no other antenna of a similar size (7.19W/L) that comes close in Sky Temperature or G/T performance (VE7BQH List)

 

Download both the European EZNEC files HERE

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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