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A Low-Noise 'Urban' 11 element ultra low-noise (close spaced) LFA Yagi for 144MHz

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.

Revised 30th August 2009 V1.0

If you suffer with noise from living in the city, or want the perfect quite EME single antenna or array,  this is another low-noise example from G0KSC

This LFA has been designed for maximum gain and front to back. The result is an good 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.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 on order to create new models for each (geographic) 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

 

The 11el 144MHz LFA Yagi installed at HA5UK

 

2 x 11el 2m LFAs in between a 6el 6M LFA at KA0KYZ

 

 

The 11el LFA at ZL1LDS. The SWR plots recorded at ZL1LDS is below:

 

Freq Z X SWR
143.6 43 5 - 1.1
143.7 45 6 - 1.1
143.8 46 5 - 1.0
143.9 48 4 - 1.0
144 49 3 - 1.0
144.1 50 3 - 1.0
144.2 51 1 - 1.0
144.3 51 0 - 1.0
144.4 51 0 - 1.0
144.5 50 0 - 1.0
144.6 50 1 - 1.0
144.7 49 1 - 1.0
144.8 49 1 - 1.0
144.9 49 1 - 1.0
145 50 1 - 1.0
145.1 51 1 - 1.0
145.2 52 0 - 1.0
145.3 54 0 - 1.0
145.4 56 0 - 1.0
145.5 58 0 - 1.1
145.6 60 0 - 1.2

 

 

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 11el 144MHz LFA exhibits an nice clean pattern

 

The 11el 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 at 144.100MHz

 

In order to demonstrate pattern stablility within the LFA model, the above is the pattern as generated at 144.300MHz

 

The last example presents the same at 144.600MHz. Not there are still not unwanted forward lobes.

Download the European version of this antenna in EZNEC format HERE

 

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

Performance                                  

Forward Gain:                                   15.14dBi at 144.100MHz                  

Front to Back Ratio:                         30.87dB at 144.100MHz                  

Peak Gain:                                        15.15dBi                                          

Peak F/B:                                        31.64dB                                          

Bandwidth:                                     1MHz below 1.1:1                            

Build Dimensions for European Version

Element     Spacing (m) - Half element Length (m)          Element Notes

Reflector          0              .5075                             8mm Diameter tube or solid rod

DE1               .208           .445                               12mm Tube

DE2               .374           .445                               12mm Tube

D1                 .58            .4795                              8mm Diameter tube or solid rod

D2                1.031          .4635                              8mm Diameter tube or solid rod

D3                1.496          .4555                              8mm Diameter tube or solid rod

D4                2.073          .4505                              8mm Diameter tube or solid rod

D5                2.79             .447                               8mm Diameter tube or solid rod

D6                3.564           .4425                              8mm Diameter tube or solid rod

D7                4.394           .435                                8mm Diameter tube or solid rod

D8                5.265           .4275                              8mm Diameter tube or solid rod

D9                6.084            .425                               8mm Diameter tube or solid rod

 

Notes:

DE1 and DE2 are joined at the ends by either 10mm 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 11el 144MHz LFA Yagi as displayed in EZNEC Pro/4

 

The above plot is the SWR as presented in 4nec2 (with nec4.1 calculation engine installed).

 

Antenna Elevation Plot within EZNEC Pro/4

 

The amazing Azimuth Plot of this fantastic wide-band 11el 144MHz LFA

 

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. Below is the TanT output screen showing that sky temperature is 229.3 Kelvin for this array which is excellent for only 2.90W/L and having such wide bandwidth. 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 (-2.50dB). 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 is better than any other antenna of this boom length (2.90W/L), period.

 

4 x 11 element LFA Yagis configured in a 4 Bay array 3.55 metres Vertically and 3.7 metres horizontally. With more time, even better results can be achieved.

 

Even in the elevation plane massive suppression of unwanted side, rear and upward lobes contribute to the exceptional low temperature of this antenna array.

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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