G0KSC - Simple to build, High Performance Yagi and Quad Antennas - Home of the LFA Yagi

144MHz LFA Yagis

Low Noise LFA Yagis designed by G0KSC free to build for personal use.

70cms LFA Yagis

Twin-Boom G0KSC Quads

G0KSC Twin-Boom Quads

G0KSC Custom Dish feeds - Above installation @ HB9Q

Custom low-noise dish feeds

G0KSC Custom Dish Feeds

Above installation @ HB9Q

Read Time: 12 - 24 minutes

Premium commercial versions of this antenna at Innovantennas

A Low-Noise 'Urban' 30 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 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!

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 30el 70cms LFA Yagi at EA4LU maximum SWR is 1.08:1

The 30el 70cms LFA at W4TMW

Tom had this report on his new antenna:

'Just a short note to let you know of my success with my new 70cm 28el LFA. I originally got on 70cm to join the long running 70cm Wednesday night net originating from Charlotte, North Carolina about 250km north of me. Last night was the second time I was ready to check into the net. The first time was not too successful since the band was very poor and the net coordinator was not able to be QRO.

However, last night was a different story. I was able to work about 5 or 6 stations, mostly in the Charlotte area and a few stations south of me in Georgia. Also was just barely able to work (cw) one station in Florida, about455km from my station. He was running a single 25 ele antenna at 12M and 50W, with mast mtd preamp. I am only running 25W, no preamp and flex coax to 1/2" hardline down the tower and into the shack. And one last note, the members of the net said conditions were "flat" last night. I don't have enough experience on 70cm to know 'poor' from 'average' condx.

Considering I have a TS811A which is a 20 year old rig, I'd attribute all my success last night to Justin's antenna design. But help will be on the way as I add a mast mounted preamp and 350W amp later this year.

The fun continues !!'

Tom

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: 20.45dBi at 432.300MHz

Front to Back Ratio: 44.32dB at 432.300MHz

Peak Gain: 20.49dBi

Peak F/B: 44.46dB

Bandwidth: 432-433MHz below 1.1:1

Build Dimensions for UK/USA Version -

Element Spacing in metres Half element Length in metres Element Notes

Reflector 0 .1.67 6.35mm - 1/4 inch rod

DE1 .086 .148 12.7mm - 1/2inch tube

DE2 .158 .148 (feedpoint) 12.7mm - 1/2inch tube

D1 .215 .158 6.35mm - 1/4 inch rod

D2 .359 .152 6.35mm - 1/4 inch rod

D3 .519 .147 6.35mm - 1/4 inch rod

D4 .698 .146 6.35mm - 1/4 inch rod

D5 .918 .1445 6.35mm - 1/4 inch rod

D6 1.183 .1425 6.35mm - 1/4 inch rod

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

D8 1.768 .1385 6.35mm - 1/4 inch rod

D9 2.077 .137 6.35mm - 1/4 inch rod

D10 2.395 .136 6.35mm - 1/4 inch rod

D11 2.715 .1355 6.35mm - 1/4 inch rod

D12 3.031 .135 6.35mm - 1/4 inch rod

D13 3.356 .135 6.35mm - 1/4 inch rod

D14 3.670 .135 6.35mm - 1/4 inch rod

D15 3.988 .1345 6.35mm - 1/4 inch rod

D16 4.307 .134 6.35mm - 1/4 inch rod

D17 4.625 .1335 6.35mm - 1/4 inch rod

D18 4.946 .1325 6.35mm - 1/4 inch rod

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

D20 5.593 .130 6.35mm - 1/4 inch rod

D21 5.919 .128 6.35mm - 1/4 inch rod

D22 6.244 .126 6.35mm - 1/4 inch rod

D23 6.569 .123 6.35mm - 1/4 inch rod

D24 6.900 .119 6.35mm - 1/4 inch rod

D25 7.234 .1135 6.35mm - 1/4 inch rod

D26 7.572 .1125 6.35mm - 1/4 inch rod

D27 7.910 .1105 6.35mm - 1/4 inch rod

D28 8.189 .1165 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

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