A Low-Noise 'Urban' 28 element  LFA Yagi for 432MHz

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.

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!

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 28el 70cms LFA installed at W4TMW

Azimuth Pattern

Elevation Pattern

10m Above ground Elevation plot. Note how 'tight' the rear bubble is

SWR Plot

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:                                   20.09dBi at 432.300MHz

Front to Back Ratio:                           38.76dB at 432.300MHz

Peak Gain:                                       20.10dBi

Peak F/B:                                          38.81dB

Bandwidth:                                       432-433MHz below 1.2:1

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                                       .086                                          .147                                                 12.7mm - 1/2inch tube

DE2                                       .158                                          .147                (feedpoint)                 12.7mm - 1/2inch tube

D1                                         .212                                         .159                                                  6.35mm - 1/4 inch rod

D2                                         .352                                         .1525                                                6.35mm - 1/4 inch rod

D3                                         .521                                         .1475                                                6.35mm - 1/4 inch rod

D4                                         .705                                         .1465                                                6.35mm - 1/4 inch rod

D5                                         .920                                         .1445                                                6.35mm - 1/4 inch rod

D6                                         1.180                                       .1425                                                6.35mm - 1/4 inch rod

D7                                         1.467                                       .1405                                                6.35mm - 1/4 inch rod

D8                                         1.770                                       .1385                                                6.35mm - 1/4 inch rod

D9                                         2.079                                       .1375                                                6.35mm - 1/4 inch rod

D10                                       2.396                                       .1365                                                 6.35mm - 1/4 inch rod

D11                                       2.715                                       .1365                                                 6.35mm - 1/4 inch rod

D12                                       3.024                                       .1355                                                 6.35mm - 1/4 inch rod

D13                                       3.355                                       .1355                                                 6.35mm - 1/4 inch rod

D14                                       3.668                                       .1355                                                 6.35mm - 1/4 inch rod

D15                                       3.986                                       .135                                                  6.35mm - 1/4 inch rod

D16                                       4.304                                       .1345                                                6.35mm - 1/4 inch rod

D17                                       4.624                                       .134                                                  6.35mm - 1/4 inch rod

D18                                       4.946                                       .133                                                  6.35mm - 1/4 inch rod

D19                                       5.269                                       .1315                                                6.35mm - 1/4 inch rod

D20                                       5.594                                       .130                                                  6.35mm - 1/4 inch rod

D21                                       5.919                                       .1285                                                6.35mm - 1/4 inch rod

D22                                       6.242                                       .1265                                                6.35mm - 1/4 inch rod

D23                                       6.568                                       .1235                                                6.35mm - 1/4 inch rod

D24                                       6.897                                       .119                                                  6.35mm - 1/4 inch rod

D25                                       7.232                                       .114                                                  6.35mm - 1/4 inch rod

D26                                       7.521                                       .1175                                                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