A Low-Noise 'Urban' 8 element LFA Yagi for 50MHz

Revised 24th August 2009 V1.1 

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 built, tested and used at the RSGB Field Day, July 2009. South America being the best result during that contest from this fantastic performer. As with all LFA's I publish now, this is a wide-band, low noise antenna and will not shift dramatically in wet weather or when placed near other antennas.

Download the EZNEC Project files for this antenna HERE

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
• 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
• This is a 50 Ohm Antenna, no matching arrangement is needed. A simple 1:1 or choke balun will be fine. see 'creating a Balun' here
• Please read the 'how to make the LFA Loop' page here

In use at G0KDV for RSGB Field Day. Boom is 1.5 inch box tube and 3/8 inch elements with 1/2 inch main loop.

Performance                                   European Version                             UK/USA Version

Forward Gain:                                   14.07dBi at 50.150MHz                 14.06dBi at 50.150MHz

Front to Back Ratio:                           24.87dB at 50.150MHz                 25.2dBi at 50.150MHz

Peak Gain:                                        14.14dBi                                           14.11dBi

Peak F/B:                                          31.62dB                                           32.26dB

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

Download the EZNEC Project files for this antenna HERE 

Build Dimensions for European Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                  0                                                          1.481                                              10mm Diameter tube or solid rod

DE1                                        .397                                                      1.229                                               13mm Tube

DE2                                        .952                                                      1.229                                               13mm Tube

D1                                         1.81                                                      1.386                                               10mm Diameter tube or solid rod

D2                                         3.525                                                     1.351                                               10mm Diameter tube or solid rod

D3                                         5.572                                                     1.329                                               10mm Diameter tube or solid rod

D4                                         7.873                                                     1.31                                                 10mm Diameter tube or solid rod

D5                                        10.213                                                    1.288                                               10mm Diameter tube or solid rod

D6                                        12.493                                                    1.265                                               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

SWR Plot for the European version of the G0KSC 8el 50MHz LFA Yagi

Build Dimensions for UK/USA Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                0                                                           1.482                                               3/8 inch Diameter tube or solid rod

DE1                                       .397                                                      1.229                                                1/2 inch Tube

DE2                                       .952                                                      1.229                                                1/2 inch Tube

D1                                        1.811                                                     1.387                                               3/8 inch Diameter tube or solid rod

D2                                        3.525                                                     1.352                                               3/8 inch Diameter tube or solid rod

D3                                        5.572                                                     1.33                                                 3/8 inch Diameter tube or solid rod

D4                                        7.873                                                     1.311                                               3/8 inch Diameter tube or solid rod

D5                                       10.213                                                    1.289                                                3/8 inch Diameter tube or solid rod

D6                                       12.493                                                    1.266                                                3/8 inch Diameter tube or solid rod

Download the EZNEC Project files for this antenna HERE

Notes:

DE1 and DE2 are joined at the ends by 3/8 inch 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 8el 50MHz LFA Yagi

Antenna Elevation Plot

European version Azimuth Plot

UK/USA Azimuth Plot

Download the EZNEC Project files for this antenna HERE 

As always, any questions please ask!

Justin G0KSC