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9el 15.0mtr Boom LFA

A Low-Noise 'Urban' 9 element LFA Yagi for 50MHz

Revised 27th 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.

 

If you suffer with noise from living in the city or just don't want to hear stations behind or to the side of you try this, another low-noise antenna from G0KSC

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 15 metres long, not for every ham in the neighbourhood!

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.

 

An InnovAntennas supplied 9el 50MHz LFA at EA7KW

 

The first in a stack of 3 x 9el 50MHz LFA Yagis at W3LPL

 

The 9el LFA at WA4NJP

 

The 9el 50MHz LFA (1/2 inch elements) at MI0AYR

 

 

Download both the European and UK/USA EZNEC files HERE

 

The 9 element LFA Yagi for 50MHz how it will look when completed

 

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
  • 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:                                   14.51dBi at 50.150MHz                 14.5dBi at 50.150MHz

Front to Back Ratio:                           32.52dB at 50.150MHz                 32.53dBi at 50.150MHz

Peak Gain:                                        14.56dBi                                           14.54dBi

Peak F/B:                                          34.59dB                                          34.86dB

Bandwidth:                                       600KHz below 1.1:1                       600KHZ 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                                                              1.48                                              10mm Diameter tube or solid rod

DE1                                       .405                                                         1.225                                              13mm Tube

DE2                                       .967                                                         1.225                                              13mm Tube

D1                                         1.808                                                       1.387                                               10mm Diameter tube or solid rod

D2                                         3.469                                                       1.352                                               10mm Diameter tube or solid rod

D3                                         5.499                                                       1.327                                               10mm Diameter tube or solid rod

D4                                         7.801                                                       1.306                                               10mm Diameter tube or solid rod

D5                                         10.238                                                     1.283                                                10mm Diameter tube or solid rod

D6                                         12.771                                                     1.249                                                10mm Diameter tube or solid rod

D7                                         15.016                                                     1.247                                                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 9el 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                                                           1.481                                               3/8 inch Diameter tube or solid rod

DE1                                       .405                                                      1.225                                               1/2 inch Tube

DE2                                       .967                                                      1.225                                               1/2 inch Tube

D1                                         1.809                                                    1.388                                               3/8 inch Diameter tube or solid rod

D2                                         3.469                                                    1.353                                               3/8 inch Diameter tube or solid rod

D3                                         5.499                                                    1.328                                               3/8 inch Diameter tube or solid rod

D4                                         7.801                                                    1.307                                               3/8 inch Diameter tube or solid rod

D5                                        10.238                                                   1.284                                               3/8 inch Diameter tube or solid rod

D6                                        12.771                                                   1.25                                                 3/8 inch Diameter tube or solid rod

D7                                        15.016                                                   1.248                                               3/8 inch Diameter tube or solid rod

Notes:

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

Feed point is the centre of DE1

 

Build Dimensions for UK/USA Version with all 1/2 inch elements

Performance 

Forward Gain:                                   14.63dBi at 50.150MHz                

Front to Back Ratio:                           38.38dB at 50.150MHz             

Peak Gain:                                         14.65dBi                                        

Peak F/B:                                            38.92dB                                      

Bandwidth:                                         500KHz below 1.1:1                    

 

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           1.477                                               1/2 inch Diameter tube or solid rod

DE1                                       .406                                                      1.226                                               1/2 inch Tube

DE2                                       .970                                                      1.226                                               1/2 inch Tube

D1                                         1.801                                                    1.381                                               1/2 inch Diameter tube or solid rod

D2                                         3.476                                                    1.3435                                             1/2 inch Diameter tube or solid rod

D3                                         5.537                                                    1.319                                               1/2 inch Diameter tube or solid rod

D4                                         7.826                                                    1.300                                               1/2 inch Diameter tube or solid rod

D5                                        10.230                                                   1.280                                               1/2 inch Diameter tube or solid rod

D6                                        12.743                                                   1.248                                               1/2 inch Diameter tube or solid rod

D7                                        15.018                                                   1.2465                                             1/2 inch Diameter tube or solid rod

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 9el 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

 
 
 
 

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