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

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:

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

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.

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

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