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A Low-Noise 'Urban' 15 element LFA Yagi for 50MHz

Revised 10th September 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, 12, 13 and 14 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 30 metres long, not for every ham in the neighbourhood! However, this antenna does have a massive .3dB advantage over the smaller 14 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 15 element LFA Yagi for 50MHz. How it will look when completed

 

4nec2 (with nec4 engine) Elevation plot of the 15el 50MHz LFA

 

15el 50MHz Azimuth plot from the 4nec2 antenna modelling package

 

SWR as presented in the 4nec2 antenna modelling package using nec4.1 Double Precision calculation engine

 

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:                                   16.68dBi at 50.150MHz                 16.7dBi at 50.150MHz

Front to Back Ratio:                           34.60dB at 50.150MHz               34.48dBi  at 50.150MHz

Peak Gain:                                       16.70dBi                                           16.73dBi

Peak F/B:                                          35.11dB                                           35.00dB

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                                                             1.484                                               3/8 Diameter tube or solid rod

DE1                                       .400                                                         1.232                                               1/2 inch Tube

DE2                                       .965                                                         1.232                                               1/2 inch Tube

D1                                         1.712                                                       1.394                                               3/8 Diameter tube or solid rod

D2                                         3.316                                                       1.363                                               3/8 Diameter tube or solid rod

D3                                         5.239                                                       1.341                                               3/8 Diameter tube or solid rod

D4                                         7.489                                                       1.322                                               3/8 Diameter tube or solid rod

D5                                         9.857                                                       1.305                                               3/8 Diameter tube or solid rod

D6                                         12.339                                                     1.289                                               3/8 Diameter tube or solid rod

D7                                         14.907                                                       1.272                                               3/8 Diameter tube or solid rod

D8                                         17.497                                                     1.257                                               3/8 Diameter tube or solid rod

D9                                         20.105                                                     1.24                                                 3/8 Diameter tube or solid rod

D10                                       22.717                                                     1.213                                               3/8 Diameter tube or solid rod

D11                                       25.396                                                     1.193                                               3/8 Diameter tube or solid rod

D12                                       28.014                                                     1.172                                               3/8 Diameter tube or solid rod

D13                                       30.316                                                     1.161                                               3/8 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

Download both the European and UK/USA EZNEC files HERE

SWR Plot for the UK/USA version of the G0KSC 15el 50MHz LFA Yagi

 

Download both the European and UK/USA EZNEC files HERE

 

Build Dimensions for European Version - mail me if you need 13mm tube driven loop sizing

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           1.483                                               10mm Diameter tube or solid rod

DE1                                       .400                                                      1.229                                                12mm Tube

DE2                                       .965                                                      1.229                                                12mm Tube

D1                                         1.712                                                    1.393                                               10mm Diameter tube or solid rod

D2                                         3.316                                                    1.362                                               10mm Diameter tube or solid rod

D3                                         5.239                                                    1.34                                                 10mm Diameter tube or solid rod

D4                                         7.489                                                    1.321                                               10mm Diameter tube or solid rod

D5                                         9.857                                                    1.304                                               10mm Diameter tube or solid rod

D6                                        12.339                                                   1.288                                               10mm Diameter tube or solid rod

D7                                        14.907                                                   1.271                                               10mm Diameter tube or solid rod

D8                                        17.497                                                   1.256                                               10mm Diameter tube or solid rod

D9                                        20.105                                                   1.239                                               10mm Diameter tube or solid rod

D10                                      22.717                                                   1.212                                               10mm Diameter tube or solid rod

D11                                      25.396                                                   1.192                                               10mm Diameter tube or solid rod

D12                                      28.014                                                   1.171                                               10mm Diameter tube or solid rod

D13                                      30.316                                                   1.160                                               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 UK/USA version of the G0KSC 15el 50MHz LFA Yagi

 

3D plot image of this fantastic 15el 50MHz antenna

 

Download both the European and UK/USA EZNEC files HERE

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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