A High-Gain 7 element Low Noise LFA Yagi with a 9.7 metre Boom for 50MHz

Revised 23rd August 2009 V1.0 

 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.

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 9.7mtr 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!

Please read the 'how to make the LFA Loop' page here

Download the EZNEC design files for European and UK/USA versions HERE

How this antenna looks when built

Performance                                   European Version                             UK/USA Version

Forward Gain:                                   13.17dBi at 50.150MHz                 13.16dBi at 50.150MHz

Front to Back Ratio:                           27.21dB at 50.150MHz                  26.98dBi at 50.150MHz

Peak Gain:                                        13.24dBi                                           13.21dBi

Peak F/B:                                          32.73dB                                           31.96dB

Bandwidth:                                       500KHz below 1.1:1                       500KHZ below 1.1:1

Build Dimensions for UK/USA Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                 0                                                             1.485                                               3/8 inch Diameter tube or solid rod

DE1                                       .35                                                           1.232                                               1/2 inch Diameter Tube

DE2                                       .916                                                         1.232                                               1/2 inch Diameter Tube

D1                                         1.687                                                       1.387                                               3/8 inch Diameter tube or solid rod

D2                                         3.375                                                       1.346                                               3/8 inch Diameter tube or solid rod

D3                                         5.416                                                       1.329                                               3/8 inch Diameter tube or solid rod

D4                                         7.597                                                       1.305                                               3/8 inch Diameter tube or solid rod

D5                                         9.714                                                       1.26                                                 3/8 inch Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by 3/8 inch tube

Download the EZNEC design files for European and UK/USA versions HERE

SWR plot for the UK/USA sized material version

Build Dimensions for European Version - If you need 12mm Loop sizing mail me

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                 0                                                             1.482                                               10mm Diameter tube or solid rod

DE1                                       .35                                                           1.228                                               13mm Tube

DE2                                       .916                                                         1.228                                               13mm Tube

D1                                         1.681                                                       1.386                                               10mm Diameter tube or solid rod

D2                                         3.375                                                       1.355                                               10mm Diameter tube or solid rod

D3                                         5.416                                                       1.331                                               10mm Diameter tube or solid rod

D4                                         7.597                                                       1.313                                               10mm Diameter tube or solid rod

D5                                         9.714                                                       1.297                                               10mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 10mm tube

Download the EZNEC design files for European and UK/USA versions HERE

Please read the 'how to make the LFA Loop' page here

SWR plot for the European sized material option

Elevation plot for this antenna. Being 9.7mtrs long it is a little too long for 7 elements and hence, the upwards lobes are starting to appear. I have done my best to push them as far forward as possible. However, I may develop a slightly shorter version in order to return to a nice clean pattern. This one however, is still much better than the elevation plots you would see of most dipole fed Yagis of this size.

Performance plot the the UK/USA version

Performance for the European version

As always, any questions please ask and PLEASE send photos of your finished projects.

Regards

Justin G0KSC