A Low-Noise 'Urban' 21 element Plus2 LFA Yagi for 144MHz Revised 6th December 2009 V1.0 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 sort. The new LFA Plus2 range includes an addtional 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 tepmerature 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 21el Plus2 when built 
4nec2 (with nec4 engine) Elevation plot of the 21el Plus2 LFA Yagi
The 21el 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 HEREPerformance European Version Forward Gain: 18.47dBi at 144.300MHz Front to Back Ratio: 34.48dB at 144.300MHz Peak Gain: 18.47dBi Peak F/B: 40.51dB 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 .520 Above and below loop by 200mm Reflector .455 .518 8mm Diameter tube or solid rod DE1 .592 .441 10mm Tube DE2 .785 .441 10mm Tube D1 0.999 .480 8mm Diameter tube or solid rod D2 1.472 .4665 8mm Diameter tube or solid rod D3 1.909 .450 8mm Diameter tube or solid rod D4 2.405 .4525 8mm Diameter tube or solid rod D5 3.108 .450 8mm Diameter tube or solid rod D6 3.916 .444 8mm Diameter tube or solid rod D7 4.779 .4395 8mm Diameter tube or solid rod D8 5.673 .4355 8mm Diameter tube or solid rod D9 6.577 .4325 8mm Diameter tube or solid rod D10 7.510 .428 8mm Diameter tube or solid rod D11 8.452 .425 8mm Diameter tube or solid rod D12 9.390 .422 8mm Diameter tube or solid rod D13 10.341 .4175 8mm Diameter tube or solid rod D14 11.300 .4125 8mm Diameter tube or solid rod D15 12.276 .4065 8mm Diameter tube or solid rod D16 13.230 .402 8mm Diameter tube or solid rod D17 14.229 .3915 8mm Diameter tube or solid rod D18 15.145 .3865 8mm Diameter tube or solid rod D19 16.062 .4015 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 (7.72W/L) that comes close in Sky Temperature or G/T performance (VE7BQH List) Stacking distances 5.35 High, 5.45 wide Below are the figures from Tant with the stacking set at 5.7m x 5.7m. 
Download both the European EZNEC files HERE As always, any questions please ask! Justin G0KSC
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21el Plus2 144MHz
