A High-Gain 7 element Low Noise LFA Yagi with a 9.8 metre Boom for 50MHz
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.
NOTE: There are many versions of this antenna below in different element diameters, view the whole page
This antenna has been improved for summer 2010 with a little more gain and a much cleaner pattern.
If you suffer with noise from living in the city, this is another low-noise antenna from G0KSC.
This antenna has been designed with performance in mind and provides optimum performance for the 9.8mtr boom. However, this is a difficult length to reduce fully the elevation plane lobes (which is one reason I have introduced the LFA2 at this length) and therefore, I have ensured these lobes are 'pushed forward' in order to minimise impact. Good bandwidth and excellent performance characteristics mean this one will surely be a winner!
Metric and imperial tube size versions below.
4 x 7el 9.8m long 50MHz LFA Yagis at G8BCG
7el 50MHz LFA at N6JV
The 7el 9.8m long 50MHz LFA Yagi at G8APB
Only W7GJ was heard off of the moon until the LFA was installed at PA0O. Now things are very different!
The 7el 9.8m long 50MHz LFA at AB5EB
The 9.8m long 7el 50MHz LFA at OE4VIE. Jo worked many new stations as soon as the antenna was installed.
The 9.8m 7el 6m LFA at UX0UN above a 15m Yagi
2 x 7el 9.8m LFAs at G0VHF/P - Built by G0KSC. Note the wind loading on the top antenna! Best DX 8526kms
The 2 x 9.8m 7els at G0VHF/P before raising. The Sea take-off can be seen behind
SWR plot of the the 9.8m LFA from 49.850MHz to 50.550MHz
How this antenna looks when built
Performance European Version UK/USA Version
Forward Gain: 13.20dBi at 50.150MHz 13.18dBi at 50.150MHz
Front to Back Ratio: 24.21dB at 50.150MHz 24.68dBi at 50.150MHz
Peak Gain: 13.21dBi 13.21dBi
Peak F/B: 29.78dB 30.66dB
Bandwidth: 500KHz below 1.1:1 500KHZ below 1.1:1
Stacking: Ideal Spacing: 7m - 5m minimum
Stacking gain improvement: 2.9dB at 7m
Stacking: distances are not critical. 7m gives the best pattern against gain figure.
Build Dimensions for UK/USA Version
Element Spacing in metres Half element Element Notes
Reflector 0 1.4805 3/8 inch Diameter tube or solid rod
DE1 .378 1.227 Feed Point 1/2 inch Diameter Tube
DE2 .944 1.227 1/2 inch Diameter Tube
D1 1.756 1.3875 3/8 inch Diameter tube or solid rod
D2 3.392 1.3515 3/8 inch Diameter tube or solid rod
D3 5.417 1.3255 3/8 inch Diameter tube or solid rod
D4 7.641 1.3005 3/8 inch Diameter tube or solid rod
D5 9.817 1.2655 3/8 inch Diameter tube or solid rod
Notes:
DE1 and DE2 are joined at the ends by 3/8 inch tube
SWR for this excellent antenna
Build Dimensions for European Version 10mm/12mm elements
Element Spacing in metres Half element Length Element Notes
Reflector 0 1.4805 10mm Diameter tube or solid rod
DE1 .378 1.225 Feed Point 12mm Tube
DE2 .944 1.225 12mm Tube
D1 1.756 1.3875 10mm Diameter tube or solid rod
D2 3.392 1.3515 10mm Diameter tube or solid rod
D3 5.417 1.3255 10mm Diameter tube or solid rod
D4 7.641 1.3005 10mm Diameter tube or solid rod
D5 9.817 1.2655 10mm Diameter tube or solid rod
Notes:
DE1 and DE2 are joined at the ends by either 10mm tube
Performance UK/USA Version
Forward Gain: 13.27dBi at 50.150MHz
Front to Back Ratio: 25.64dBi at 50.150MHz
Peak Gain: 13.33dBi
Peak F/B: 25.87dB
Bandwidth: 500KHZ below 1.1:1
Stacking: Ideal Spacing: 7m - 5m minimum
Stacking gain improvement: 2.9dB at 7m
Stacking: distances are not critical. 7m gives the best pattern against gain figure.
Build Dimensions for UK/USA Version
Element Spacing in metres Half element Length Element Notes
Reflector 0 1.4795 1/2 inch Diameter tube or solid rod
DE1 .369 1.228 Feed Point 1/2 inch Diameter Tube
DE2 .938 1.228 1/2 inch Diameter Tube
D1 1.746 1.388 1/2 inch Diameter tube or solid rod
D2 3.452 1.338 1/2 inch Diameter tube or solid rod
D3 5.495 1.3185 1/2 inch Diameter tube or solid rod
D4 7.698 1.294 1/2 inch Diameter tube or solid rod
D5 9.825 1.2635 1/2 inch Diameter tube or solid rod
Performance European Version all 12mm elements
Forward Gain: 13.25dBi at 50.150MHz
Front to Back Ratio: 25.45dB at 50.150MHz
Peak Gain: 13.31dBi
Peak F/B: 25.78dB
Bandwidth: 500KHz below 1.1:1
Stacking: Ideal Spacing: 7m - 5m minimum
Stacking gain improvement: 2.9dB at 7m
Stacking: distances are not critical. 7m gives the best pattern against gain figure.
Build Dimensions for European Version 12mm elements
Element Spacing in metres Half element Length Element Notes
Reflector 0 1.480 12mm Diameter tube or solid rod
DE1 .369 1.226 Feed Point 12mm Tube
DE2 .936 1.226 12mm Tube
D1 1.744 1.3805 12mm Diameter tube or solid rod
D2 3.422 1.3425 12mm Diameter tube or solid rod
D3 5.461 1.320 12mm Diameter tube or solid rod
D4 7.666 1.2945 12mm Diameter tube or solid rod
D5 9.830 1.2645 12mm Diameter tube or solid rod
Notes:
DE1 and DE2 are joined at the ends by either 10mm tube
Elevation plot for this antenna
Azimuth Plot
As always, any questions please ask and PLEASE send photos of your finished projects.
Regards
Justin G0KSC
