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11el 19.8mtr Boom LFA

A Low-Noise 'Urban' 11 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.

 

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 and the 10 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 almost 20 metres long, not for every ham in the neighbourhood! However, this antenna does have a massive .5dB advantage over the smaller 10 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.

 

The 11 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 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:          15.59dBi at 50.150MHz                 15.57dBi at 50.150MHz

Front to Back Ratio:  25.11dB at 50.150MHz                  25.3dBi at 50.150MHz

Peak Gain:              15.61dBi                                           15.6dBi

Peak F/B:               37.73dB                                           38.86dB

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 (m) -  Half element Length (m) -  Element Notes

Reflector          0                1.482                                10mm Diameter tube or solid rod

DE1               .351             1.228                                13mm Tube

DE2               .913             1.228                                13mm Tube

D1                1.74              1.386                               10mm Diameter tube or solid rod

D2                3.373            1.355                               10mm Diameter tube or solid rod

D3                5.352            1.331                               10mm Diameter tube or solid rod

D4                7.732            1.313                               10mm Diameter tube or solid rod

D5              10.128            1.297                               10mm Diameter tube or solid rod

D6              12.538            1.281                               10mm Diameter tube or solid rod

D7              15.005            1.256                               10mm Diameter tube or solid rod

D8              17.554            1.246                               10mm Diameter tube or solid rod

D9              19.82              1.238                               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 11el 50MHz LFA Yagi

 

Download both the European and UK/USA EZNEC files HERE

 

Build Dimensions for UK/USA Version

Element - Spacing (m) - Half element Length (m) -  Element Notes

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

DE1              .351           1.23                               1/2 inch Tube

DE2              .913           1.23                               1/2 inch Tube

D1              1.736           1.387                              3/8 inch Diameter tube or solid rod

D2              3.373           1.357                              3/8 inch Diameter tube or solid rod

D3              5.352           1.335                              3/8 inch Diameter tube or solid rod

D4              7.632           1.314                              3/8 inch Diameter tube or solid rod

D5            10.128           1.3                                  3/8 inch Diameter tube or solid rod

D6            12.538           1.286                              3/8 inch Diameter tube or solid rod

D7            15.005           1.275                              3/8 inch Diameter tube or solid rod

D8            17.554           1.254                             3/8 inch Diameter tube or solid rod

D9            19.82             1.239                             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

SWR Plot for the UK/USA version of the G0KSC 11el 50MHz LFA Yagi

 

Antenna Elevation Plot

 

European version Azimuth Plot

 

UK/USA Elevation Plot

 

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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