Google Translate

Message
  • EU e-Privacy Directive

    This website uses cookies to manage authentication, navigation, and other functions. By using our website, you agree that we can place these types of cookies on your device.

    View e-Privacy Directive Documents

18el 144MHz LN LFA

A Low-Noise 'Urban' 18 element ultra low-noise (close spaced) LFA Yagi for 144MHz

Revised 31th August 2009 V1.0 

Premium commercial versions of this antenna at Innovantennas

 

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, or want the perfect quiet EME single antenna or array,  this is another low-noise example from G0KSC

 

This is an 18 element 144MHz LFA Yagi produced using 3/8 inch elements with a 1/2 inch loop section.  There is also a European version using 10mm and 12mm tube. Other sizes available upon request.

 

This LFA has been designed for maximum suppresion of side, rear and elevation lobes. The result is an ultra clean antenna which will be a stunning performer for 144MHz. The antenna is super wide-band too with an SWR of less than 1.1:1 over more than 1MHz. Uncharacteristically of a Yagi, the LFA maintains F/B over this wide bandwidth and more importantly maintains its pattern too, some example pattern plots are given below for 144.100MHz, 144.300MHz and 144.600MHz. One of the reasons for pattern stablility and bandwidth is the close spacing of the elements on this range of LFAs.

This antenna is particularly good for EME purposes due to the class leading low noise (Sky Temperature) and G/T figures mentioned above. See the bottom of this page for more information.This low-noise property also means less man made noise will be picked up by the antenna too.

I have started to model individual antennas on individual diameter elements in order to achieve the best all round results. Using the same element spacing and changing element diameter has not shown consistant results and therefore, I will spend more time in order to create new models for each (geographic) regions tubing requirements. 

PLEASE NOTE:

  • This antenna WILL NOT show the true SWR in any antenna modelling package unless you are using one which uses the latest NEC4.1 calculation engine. Do not confuse nec versions with EZNEC versions. Unless you have EZNEC pro/4 you are using nec2 NOT nec4
  • 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

 

 

A 17el LFA of EA3AXV who modified the loop size in order to use 8mm rod all the way through the antenna

 

 

Quim made an excellent job of the feed point

 

Did you really expect the SWR to look any different to this?

 

 

A 17el LFA installed at 9A9SF

'Hi Justin !

Yes ...
I put up the antenna and it  works very good
I make the LFA from one piece of 6mm
swr is 1:1.1  
antenna is 25m high


I DON'T MOVE ANY ELEMENT ...ALL DIMENSIONS AND DISTANCE ARE EXACTLY  HOW YOU CALCULATE   !'

9A9SF

 

Performance                                    UK/USA Version  -  18 element LFA Yagi                     

Forward Gain:                                   17.81dBi at 144.300MHz                  

Front to Back Ratio:                         31.75dB at 144.300MHz                                                      

 

Bandwidth:                                       Better than 1MHz below 1.1:1 

Sky Temperature:                           213.1Kelvin

G/T:                                                   -5.48dB

Stacking Information:

Vertical Stacking:                             4.95m

Horizontal Stacking:                        5.20m

4 x antenna Sky temp:                    210.1K

4 x antenna G/T:                              +0.60dB

4 x antenna Gain:                            23.82dBi

 

Build Dimensions for UK/US Version

Element                             Spacing in metres Half element Length in metres     Element Notes

Reflector                                0                         .510            3/8 inch Diameter tube or solid rod

DE1                                       .174                    .436            1/2 Tube (feedpoint)

DE2                                       .338                    .436            1/2 Tube

D1                                         .589                    .475            3/8 inch  Diameter tube or solid rod

D2                                        1.005                   .447            3/8 inch Diameter tube or solid rod

D3                                        1.357                   .453            3/8 inch Diameter tube or solid rod

D4                                        1.988                   .4505          3/8 inch Diameter tube or solid rod

D5                                        2.768                    .4435          3/8 inch Diameter tube or solid rod

D6                                        3.614                     .438           3/8 inch Diameter tube or solid rod

D7                                        4.489                     .4335         3/8 inch Diameter tube or solid rod

D8                                        5.385                      .430          3/8 inch Diameter tube or solid rod

D9                                        6.294                      .427          3/8 inch Diameter tube or solid rod

D10                                      7.221                       .4235       3/8 inch Diameter tube or solid rod

D11                                      8.147                       .419        3/8 inch Diameter tube or solid rod

D12                                      9.089                       .415        3/8 inch Diameter tube or solid rod

D13                                     10.025                      .406         3/8 inch Diameter tube or solid rod

D14                                     10.984                      .399         3/8 inch Diameter tube or solid rod

D15                                      11.994                     .392         3/8 inch Diameter tube or solid rod

D16                                      12.734                    .4035        3/8 inch Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 3/8 tube bent to 'trombone' inside the 1/2 inch tube. Adjust for best SWR.

Feed point is the centre of DE1

Please read the 'how to make the LFA Loop' page here

 

Build Dimensions for European Version

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                         .5095          10mm Diameter tube or solid rod

DE1                                       .174                     .444           12mm Tube (feedpoint)

DE2                                       .338                     .444           12mm Tube

D1                                         .589                     .475          10mm  Diameter tube or solid rod

D2                                        1.005                    .4465        10mm Diameter tube or solid rod

D3                                        1.357                    .4525        10mm Diameter tube or solid rod

D4                                        1.988                    .450          10mm Diameter tube or solid rod

D5                                        2.768                     .443         10mm Diameter tube or solid rod

D6                                        3.614                     .4375       10mm Diameter tube or solid rod

D7                                        4.489                      .433        10mm Diameter tube or solid rod

D8                                        5.385                      .4295      10mm Diameter tube or solid rod

D9                                        6.294                      .4265      10mm Diameter tube or solid rod

D10                                      7.221                      .423        10mm Diameter tube or solid rod

D11                                      8.147                      .4185      10mm Diameter tube or solid rod

D12                                      9.089                      .4145       10mm Diameter tube or solid rod

D13                                     10.025                     .4055       10mm Diameter tube or solid rod

D14                                     10.984                     .3985       10mm Diameter tube or solid rod

D15                                      11.994                    .3915        10mm Diameter tube or solid rod

D16                                      12.734                    .403         10mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 8mm tube bent to 'trombone' inside the 12mm tube. You can use 10mm tube also, Adjust loop for best SWR.

Feed point is the centre of DE1

 

 

 

The Azimuth Plot

 

 

The Elevation Plot

 

 

The Elevation Plot 12m above ground

 

 

The Stunning SWR of this fantastic Antenna!

 

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

Google Translate