A Low-Noise 'Urban' 18 element  LFA Yagi for 432MHz

 Revised 30th January 2010 V1.1

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. 

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.

How the 18el 70cms LFA will look.

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 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

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 here

As always, any questions please ask!

Justin G0KSC