A Low-Noise 'Urban' 18 element LFA Yagi for 432MHz
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.
Firstly, do not be put off by the close frontal side lobes on these 70cms Yagis. Those who follow my work within DUBUS magazine know I have proven forward side lobes have little effect on G/T figures as long as they are kept close to the main lobe, it is the size of the rear 'bubble' and F/R ratio that makes the most impact. By allowing these side lobes and amount of 'controlled' space in the forward direction, I have been able to suppress the rear lobes to produce antennas with never-seen-before G/T and Sky temperature figures!
Mini G/T Table with data of non G0KSC antennas from VE7BQH
G G+4 L T G/T
G0KSC18 17.94 24.01 2.0 20.6 10.88
DK7ZB 18 17.5 23.39 4.7 29.4 8.70
YU7EF19B 18.29 24.15 6.1 26.7 9.89
YU7EF19B 18.29 24.15 6.1 26.7 9.89
YU7EF 21 18.67 24.51 7.5 27.0 10.21
YU7EF 24B 19.19 25.0 7.5 26.7 10.74
Currently these antennas are available in IMPERIAL SIZES ONLY. Mail me if you need anything different.
As with ALL LFAs this antenna requires no matching device, 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 18el 70cms LFA at WB9WOZ
Azimuth Pattern
Elevation Pattern
Elevation plot 10M up. Note the tight rear 'bubble' and 1 degree take off.
SWR
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
- 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 UK/USA Version
Forward Gain: 17.94dBi at 432.300MHz
Front to Back Ratio: 36.71dB at 432.300MHz
Peak Gain: 17.94dBi
Peak F/B: 36.42dB
Bandwidth: 432-433MHz below 1.12:1
Build Dimensions for UK/USA Version -
Element Spacing in metres Half element Length in metres Element Notes
Reflector 0 .1.675 6.35mm - 1/4 inch rod
DE1 .085 .149 12.7mm - 1/2inch tube
DE2 .147 .149 12.7mm - 1/2inch tube (feedpoint)
D1 .213 .1575 6.35mm - 1/4 inch rod
D2 .367 .151 6.35mm - 1/4 inch rod
D3 .523 .1465 6.35mm - 1/4 inch rod
D4 .697 .145 6.35mm - 1/4 inch rod
D5 .928 .144 6.35mm - 1/4 inch rod
D6 1.196 .142 6.35mm - 1/4 inch rod
D7 1.485 .140 6.35mm - 1/4 inch rod
D8 1.785 .139 6.35mm - 1/4 inch rod
D9 2.091 .138 6.35mm - 1/4 inch rod
D10 2.398 .138 6.35mm - 1/4 inch rod
D11 2.704 .1365 6.35mm - 1/4 inch rod
D12 3.014 .135 6.35mm - 1/4 inch rod
D13 3.324 .1335 6.35mm - 1/4 inch rod
D14 3.643 .131 6.35mm - 1/4 inch rod
D15 3.963 .125 6.35mm - 1/4 inch rod
D16 4.246 .1295 6.35mm - 1/4 inch rod
Notes:
DE1 and DE2 are joined at the ends by 9.525mm - 3/8inch tube
Feed point is the centre of DE2
Please read the 'how to make the LFA Loop' page
As always, any questions please ask!
Justin G0KSC