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5el 3.38mtr Boom LFA

A short 5 element LFA Yagi for 70MHz with a 3.38mtr boom - 5LFA4KST

Revised 25th 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, 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 70MHz 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:

Download both the European and UK/USA EZNEC files HERE
 

ON4KST built this antenna and saw no reflected power through the whole 4M band

 

The 5el 70MHz LFA at G8DTF

 

The same antenna this time built by John, G4ZTR

 

The above analyser plot is from John's finished antenna. 1.05:1 at 70.292MHz with a flat curve for the rest of the band

 

 

The 5el 4m LFA at ZS2EZ

 

 

Installed at ZS2GK

 

 

Installed at ZS2EK

 

 

 

 

Performance

Peak Gain: 11.01dBi @ 70.150MHz

Peak F/B: 21.45dB @ 70.150MHz

SWR: Below 1.1.1 from 70MHz to 70.500MHz

Construction

 

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

Antenna Dimensions 12mm element version below:

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.0565                                           12mm

DE1                      .205                          .898                                                12mm

DE2                      .592                          .898                                                12mm

D1                        .983                          .9865                                              12mm

D2                       2.164                         .9445                                              12mm

D3                       3.38                          .9265                                               12mm

 

The ends of DE1 and DE2 are connected together with 10mm (if 13mm elements are used) or 3/8 inch tube (if 1/2 inch elements are used). The feed point is the centre of DE1.

 

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

Antenna Dimensions 12.7mm/13mm elements

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.056                                            13mm or 1/2 inch

DE1                      .205                          .901                                              13mm or 1/2 inch

DE2                      .592                          .901                                              13mm or 1/2 inch

D1                        .983                          .986                                              13mm or 1/2 inch

D2                       2.164                         .944                                              13mm or 1/2 inch

D3                       3.38                          .926                                               13mm or 1/2 inch

 

The ends of DE1 and DE2 are connected together with 3/8 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. DO NOT Get your version of EZNEC confused with nec versions. Unless you have EZNEC Pro/4 you do not havew nec4. The swr graph is correct and confirmed within nec4 and through building this antenna.

 

Pattern is identical when using metric or imperial tubing. This is the Elevation Plot

 

Azimuth plot, the usual plot diagram we see with antenna data

 

 

SWR Plot when European/metric tubing (13mm/10mm) is used

SWR Plot when Imperial (1/2 inch, 3/8 inch) tubing is used

Any questions, please ask!

 

Justin G0KSC

 
 
 
 

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