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A Low-Noise 'Urban' 15 element ultra low-noise (close spaced) LFA Yagi for 144MHz

Revised 29th August 2009 V1.1

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 quite EME array,  this is another low-noise antenna from G0KSC

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 the EU 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.

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 on order to create new models for each regions tubing requirements. UK and USA versions will follow shortly.

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 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

Download the European version of this antenna in EZNEC format HERE

 

2 x 15el LFA at ON6ZG - Take a look at the analyser plot below:

 

 

 

A 15 Element 144MHz LFA at HB9BLF

In order to show how clean the pattern is on this antenna, I have presented below first a 3D side shot of the antenna pattern followed by the Elevation plot then the Azimuth plot from 4NEC2 modelling program. These plots show much more clearly then EZNEC.

 

The 15el 144MHz LFA exhibits an incredible super-clean pattern

 

The 15el Elevation plot presented in the 4nec2 antenna modelling package. As with all LFA's plenty of rearward suppression without loss of forward gain.

 

The all important 'Super Clean' Azimuth pattern as presented within 4nec2

Download the European version of this antenna in EZNEC format HERE

 

Note: Performance figures given at 144.100MHz, the EME centre frequency

Performance European Version                             UK/USA Version

Forward Gain:                                   16.73dBi at 144.100MHz                   -

Front to Back Ratio:                         29.86dB at 144.100MHz                   -

Peak Gain:                                        16.73dBi                                           -

Peak F/B:                                        30.5dB                                            -

Bandwidth:                                     1.2MHz below 1.1:1                         -

Build Dimensions for European Version

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           .509                                               8mm Diameter tube or solid rod

DE1                                       .242                                                      .448                                                10mm Tube

DE2                                       .408                                                      .448                                                10mm Tube

D1                                         .596                                                      .4805                                               8mm Diameter tube or solid rod

D2                                        1.07                                                      .4665                                                8mm Diameter tube or solid rod

D3                                        1.549                                                     .4595                                               8mm Diameter tube or solid rod

D4                                        2.127                                                     .4535                                               8mm Diameter tube or solid rod

D5                                        2.821                                                     .45                                                  8mm Diameter tube or solid rod

D6                                        3.581                                                     .4445                                              8mm Diameter tube or solid rod

D7                                        4.428                                                     .4385                                              8mm Diameter tube or solid rod

D8                                        5.31                                                      .434                                                8mm Diameter tube or solid rod

D9                                        6.197                                                     .4295                                              8mm Diameter tube or solid rod

D10                                      7.134                                                     .4215                                              8mm Diameter tube or solid rod

D11                                      8.025                                                     .415                                                 8mm Diameter tube or solid rod

D12                                      8.993                                                     .4085                                              8mm Diameter tube or solid rod

D13                                      9.855                                                     .406                                               8mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 8mm tube

Feed point is the centre of DE2

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

Download the European version of this antenna in EZNEC format HERE

 

SWR Plot for the European version of the G0KSC 15el 144MHz LFA Yagi as displayed in EZNEC Pro/4

 

The above plot is the SWR as presented in 4nec2 (with nec4.1 claculation engine installed). It looks better within this one.

 

Antenna Elevation Plot within EZNEC Pro/4

 

The amazing Azimuth Plot of this fantastic wide-band 15el 144MHz LFA Yagi at 144.1MHz

 

In order to demonstrate pattern stability through a wide portion of the band, above is the AZ plot at 144.300MHz

 

Again at 144.600MHz the single main lobe has remained and only the rearward lobes change shape but at the same time, retain F/B and F/R

 

 

EME Notes

This antenna makes an excellent EME antenna When used with 2 or 4 stack versions, performance becomes second to none at this boom length (4.74W/L). Below is the TanT output screen showing that sky temperature is 214.9 Kelvin for this array which is excellent. Not only this, G/T which is the figure of merit used to determine an antennas ability to receive signals is better than any other antenna of this length (-0.58dB). As with all 2M LFA's listed on this site, there is no other antenna listed on the VE7BQH G/T table that has the same length (or shorter) Boom with the same or better G/T figure.

 

G/T and Sky Temperature are better than any other antenna of this boom length (4.74W/L), period.

 

4 x 15 element LFA Yagis configured in a 4 Bay array 4.45 metres Vertically and 4.6 metres horizontally. With more time, even better results can be achieved.

Download the European version of this antenna in EZNEC format HERE

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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