A Low-Noise 'Urban' 13 element LFA Yagi for 50MHz

Revised 25th 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 sought.

I am not sure too many of these will be built due to size but I guess I maybe surprised. This is the ultimate single Yagi for 50MHz. If you build one, I must come and work the DX with it!

Like the 9, 10, 11 and 12 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 25 metres long, not for every ham in the neighbourhood! However, this antenna does have a massive .3dB advantage over the smaller 12 element version and at these levels of gain, that can make quite a difference.In addition, I have supressed further the lobes around the centre of the antenna in order to improve receive performance even more.

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

4nec2 (with nec4 engine) Elevation plot of the 13el 50MHz LFA

13el 50MHz Azimuth plot from the 4nec2 antenna modelling package

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

Download both the European and UK/USA EZNEC files HERE

Performance European Version                             UK/USA Version

Forward Gain:                                   16.15dBi at 50.150MHz                 16.14dBi at 50.150MHz

Front to Back Ratio:                           29.34dB at 50.150MHz                  29.1dBi  at 50.150MHz

Peak Gain:                                       16.18dBi                                           16.16dBi

Peak F/B:                                          37.25dB                                           36.96dB

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                                                             1.484                                               10mm Diameter tube or solid rod

DE1                                       .371                                                         1.232                                               13mm Tube

DE2                                       .936                                                         1.232                                               13mm Tube

D1                                         1.681                                                       1.392                                               10mm Diameter tube or solid rod

D2                                         3.279                                                       1.361                                               10mm Diameter tube or solid rod

D3                                         5.214                                                       1.338                                               10mm Diameter tube or solid rod

D4                                         7.477                                                       1.318                                               10mm Diameter tube or solid rod

D5                                         9.871                                                       1.301                                               10mm Diameter tube or solid rod

D6                                         12.351                                                     1.285                                               10mm Diameter tube or solid rod

D7                                         14.937                                                     1.265                                               10mm Diameter tube or solid rod

D8                                         17.51                                                       1.252                                               10mm Diameter tube or solid rod

D9                                         20.176                                                     1.229                                               10mm Diameter tube or solid rod

D10                                       22.695                                                     1.205                                               10mm Diameter tube or solid rod

D11                                       25.178                                                     1.19                                                 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 13el 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                                                           1.485                                               3/8 inch Diameter tube or solid rod

DE1                                       .371                                                      1.233                                                1/2 inch Tube

DE2                                       .936                                                      1.233                                                1/2 inch Tube

D1                                         1.681                                                    1.393                                               3/8 inch Diameter tube or solid rod

D2                                         3.272                                                    1.362                                               3/8 inch Diameter tube or solid rod

D3                                         5.214                                                    1.339                                               3/8 inch Diameter tube or solid rod

D4                                         7.477                                                    1.319                                               3/8 inch Diameter tube or solid rod

D5                                        9.871                                                     1.302                                               3/8 inch Diameter tube or solid rod

D6                                        12.351                                                   1.286                                               3/8 inch Diameter tube or solid rod

D7                                        14.937                                                   1.266                                               3/8 inch Diameter tube or solid rod

D8                                        17.51                                                    1.253                                               3/8 inch Diameter tube or solid rod

D9                                        20.176                                                   1.23                                                3/8 inch Diameter tube or solid rod

D10                                      22.695                                                   1.206                                               3/8 inch Diameter tube or solid rod

D11                                      25.178                                                   1.191                                               3/8 inch Diameter tube or 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 13el 50MHz LFA Yagi

Antenna Elevation Plot

European version Azimuth Plot

UK/USA Elevation Plot

Download both the European and UK/USA EZNEC files HERE

As always, any questions please ask!

Justin G0KSC