A Low-Noise 'Urban' 21 element Plus2 LFA Yagi for 144MHz
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.
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
- 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
- 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
Performance 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
DE1 and DE2 are joined at the ends by 8mm tube
Feed point is the centre of DE2
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.
As always, any questions please ask!