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

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.

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

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

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

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

A 11 element LFA Yagi for 70MHz with a 13.74mtr boom

Note: If you do not see this antenna in an element diameter you would like, mail me!

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. 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:

Installed at PA2M

On the way up - the 11el 4m LFA at G0VHF

As always the 11el LFA has an impressive 'constant impedance' and super flat SWR

Ready for action - the 11el ready to go!

The 11el 4m LFAs at G0VHF/P

Performance

15.44dBi @ 70.200MHz

F/B 29.76dB @ 70.200MHz

SWR: Below 1.1.1 from 70MHz to 70.700MHz

Construction

Antenna Dimensions for UK/USA sized tubing

                         Spacing - Half Element Size  in Metres - Element Diameter

Reflector                0             1.0555                                  3/8 inch or 10mm tube or rod

DE1                      .292         .882  (.881 with 12mm tube)      1/2 inch or 12mm tube

DE2                      .688         .882  (.881 with 12mm tube)      1/2 inch or 12mm  tube

D1                       1.214        .9925                                     3/8 inch or 10mm tube or rod

D2                       2.321        .964                                       3/8 inch or 10mm tube or rod

D3                       3.728        .947                                       3/8 inch or 10mm tube or rod

D4                       5.334        .933                                       3/8 inch or 10mm  tube or rod

D5                       7.006        .921                                       3/8 inch or 10mm tube or rod

D6                       8.749        .9065                                     3/8 inch or 10mm tube or rod

D7                       10.516      .895                                       3/8 inch or 10mm tube or rod

D8                       12.365      .8845                                     3/8 inch or 10mm tube or rod

D9                       13.739       .888                                      3/8 inch or 10mm tube or rod

The ends of DE1 and DE2 are connected together with 3/8 inch or 10mm tube or rod. 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.

DE1 and DE2 will have to be cut shorter than the above measurements in order to allow for the radius on the loop ends. Always adjust loop for best SWR.

Feedpoint gap 6-10mm this gap is not critical.

Please send photos of this antenna if you build it.

Azimuth Plot of this super antenna

The much improved elevation plot

Elevation plot at 18m up

The SWR curve is virtually the same with both metric and imperial sized tubing

Any questions, please ask!