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A short 5 element LFA Yagi for 50MHz with a 4.7mtr boom

Revised 22nd January 2010 V1.5

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.

There are 2 versions of this antenna below. One using 1/2 inch and 3/8 inch (12mm and 10mm) tube, the other 16mm 5/8 inch tube.

If you suffer with noise from living in the city, this is another low-noise antenna from G0KSC


This antenna has been designed in order to minimise the upward and downward lobes typically seen the the EL plane on Yagi antennas. By doing this, a drastic reduction in pick up of unwanted noise in City locations is the result. The double bonus is the likelihood  of reducing transmitted interference too. However, this version is not a model with optimum suppression which would see a reduction in forward gain of 1dB. If you suffer with very bad noise on 50MHz and have room for an antenna of this size, Email me for details of the very high suppression version.

This antenna can be built with Metric or Imperial sized tubing:


The 5el 4.7 mtr LFA on test at G0KSC




Martello Tower Group have the 5 element 4.7mtr 50MHz LFA and a 9el 4.5mtr 144MHz LFA



13mm 10mm and  1/2 inch 3/8inch element version

Performance

Gain: 10.93dBi @ 50.150MHz

F/B: 20.6dB @ 50.150MHz

Peak Gain: 11dBi

Peak F/B: 21.4dB

SWR: Below 1.1.1 from 50MHz to 50.500MHz

Construction

Download the EZNEC files HERE

For full details of how to make the LFA, read here: http://www.g0ksc.co.uk/making-the-lfa-loop.html

Antenna Dimensions

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.488                                             10mm or 3/8 inch

DE1                      .290                          1.247                                             13mm or 1/2 inch

DE2                      .821                          1.247                                             13mm or 1/2 inch

D1                       1.477                         1.392                                             10mm or 3/8 inch

D2                       2.919                         1.3485                                           10mm or 3/8 inch

D3                       4.728                         1.293                                            10mm or 3/8  inch

 

The ends of DE1 and DE2 are connected together with 10mm or 3/8 inch tube. the Feed point is the centre of DE1.





16mm/ 5/8inch element version

Performance

Gain: 11dBi @ 50.150MHz

F/B: 22.37dB @ 50.150MHz

Peak Gain: 11.1dBi

Peak F/B: 25dB

SWR: Below 1.1.1 from 50MHz to 50.500MHz

Construction

Download the EZNEC files HERE

For full details of how to make the LFA, read here: http://www.g0ksc.co.uk/making-the-lfa-loop.html

Antenna Dimensions

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.483                                             16mm or 5/8 inch

DE1                      .287                          1.258                                             16mm or 5/8 inch

DE2                      .828                          1.258                                             16mm or 5/8 inch

D1                       1.375                         1.384                                             16mm or 5/8 inch

D2                       3.027                         1.325                                             16mm or 5/8 inch

D3                       4.728                         1.3                                                 16mm or 5/8 inch

 

The ends of DE1 and DE2 are connected together with 13mm or 1/2 inch tube. the Feed point is the centre of DE1.

NOTE: SWR will not read as per the graph below if you use a package with mininec or nec2 the swr graph is correct and confirmed within nec4 and through building this antenna.

 

 

 

 

Any questions, please ask!

 

Justin G0KSC

 
 
 
 

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