A Low-Noise 'Urban' 12 element LFA Yagi for 50MHz

Revised 24th 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. 

I am not sure too many of these will be built due to size but I guess I maybe surprised. This is truley an excellent performer. If you build one let me know.

Like the 9, 10 and 11 element version before it, this antenna has been designed with light-weight in mind and optimum performance through single piece elements. It has all the common attributes of an LFA Yagi, Flat SWR,Excellent Gain, fantastic Front to Back ratio and suppressed unwanted lobes.

A True DX'ers antenna and at over 22 metres long, not for every ham in the neighbourhood! However, this antenna does have a massive .3dB advantage over the smaller 11 element version and at these levels of gain, that can make quite a difference.

Both European and UK/USA versions are available. Build and construction details are below and EZNEC files are available for download on the download page.

Download both the European and UK/USA EZNEC files HERE

The 12 element LFA Yagi for 50MHz. How it will look when completed 

Elevation plot as presented in 4nec2 

Supper clean Azimuth Plot shown by 4nec2

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                                   European Version                             UK/USA Version

Forward Gain:                                   15.83dBi at 50.150MHz                 15.82dBi at 50.150MHz

Front to Back Ratio:                           27.22dB at 50.150MHz                  27.72dBi at 50.150MHz

Peak Gain:                                        15.84dBi                                           15.83dBi

Peak F/B:                                          32.43dB                                           32.72dB

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

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                                                             1.479                                               10mm Diameter tube or solid rod

DE1                                       .409                                                         1.231                                               13mm Tube

DE2                                       .972                                                         1.231                                               13mm Tube

D1                                         1.734                                                       1.392                                               10mm Diameter tube or solid rod

D2                                         3.359                                                       1.358                                               10mm Diameter tube or solid rod

D3                                         5.29                                                         1.338                                               10mm Diameter tube or solid rod

D4                                         7.63                                                         1.316                                               10mm Diameter tube or solid rod

D5                                         9.938                                                       1.303                                               10mm Diameter tube or solid rod

D6                                         12.422                                                     1.287                                               10mm Diameter tube or solid rod

D7                                         15.028                                                     1.264                                               10mm Diameter tube or solid rod

D8                                         17.494                                                     1.249                                               10mm Diameter tube or solid rod

D9                                         20.135                                                     1.213                                               10mm Diameter tube or solid rod

D10                                       22.481                                                     1.205                                               10mm Diameter tube or solid rod

Notes:

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

Feed point is the centre of DE1

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

 Download both the European and UK/USA EZNEC files HERE

SWR Plot for the European version of the G0KSC 12el 50MHz LFA Yagi

Download both the European and UK/USA EZNEC files HERE

Build Dimensions for UK/USA Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                0                                                           1.486                                               3/8 inch Diameter tube or solid rod

DE1                                       .409                                                      1.23                                                1/2 inch Tube

DE2                                       .972                                                      1.23                                                1/2 inch Tube

D1                                         1.734                                                    1.387                                               3/8 inch Diameter tube or solid rod

D2                                         3.359                                                    1.357                                               3/8 inch Diameter tube or solid rod

D3                                         5.29                                                      1.335                                               3/8 inch Diameter tube or solid rod

D4                                         7.63                                                      1.314                                               3/8 inch Diameter tube or solid rod

D5                                        9.938                                                     1.3                                                   3/8 inch Diameter tube or solid rod

D6                                        12.422                                                   1.286                                               3/8 inch Diameter tube or solid rod

D7                                        15.028                                                   1.275                                               3/8 inch Diameter tube or solid rod

D8                                        17.494                                                   1.254                                               3/8 inch Diameter tube or solid rod

D9                                        20.135                                                   1.239                                               3/8 inch Diameter tube or solid rod

D10                                      22.481                                                   1.206                                               3/8 inch Diameter tube of solid rod

Notes:

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

Feed point is the centre of DE1

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

SWR Plot for the UK/USA version of the G0KSC 12el 50MHz LFA Yagi

Antenna Elevation Plot

European version Azimuth Plot

UK/USA Elevation Plot

As always, any questions please ask!

Justin G0KSC