A Low-Noise 'Urban' 9 element LFA Yagi for 144MHz

Revised 25th 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 sort. 

If you suffer with noise from living in the city, this is another low-noise antenna from G0KSC

This antenna has been built, tested and used at the RSGB Field Day (2 X Stack) , July 2009. South Portugal being the best result during that contest from thisi fantastic performer. As with all LFA's I publish now, this is a wide-band, low noise antenna and will not shift dramatically in wet weather or when placed near other antennas.

This antenna is particularly good for EME purposes due to it's class leading low noise (Sky Temperature) and G/T figures. See the bottom of this page for more information.

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
• 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

RSGB Field Dat 2009. G0KDV using 2 x 9el LFA Yagis

G8FJGs 9el 144MHz LFA installed to work EME

Performance                               European Version                             UK/USA Version

Forward Gain:                                   14.15dBi at 144.300MHz                 14.13dBi at 144.300MHz

Front to Back Ratio:                           24.41dB at 144.300MHz                 24.86dBi at 144.300MHz

Peak Gain:                                        14.2dBi                                           14.18dBi

Peak F/B:                                          26.32dB                                          26.99dB

Bandwidth:                                       1.4MHz below 1.1:1                       1.6MHZ below 1.1:1

Build Dimensions for European Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                0                                                           .515                                               5mm Diameter tube or solid rod

DE1                                       .138                                                      .435                                               13mm Tube

DE2                                       .306                                                      .435                                               13mm Tube

D1                                         .532                                                      .473                                               5mm Diameter tube or solid rod

D2                                         .806                                                      .462                                               5mm Diameter tube or solid rod

D3                                        1.34                                                       .463                                               5mm Diameter tube or solid rod

D4                                        2.052                                                     .4565                                             5mm Diameter tube or solid rod

D5                                        2.837                                                     .45                                                 5mm Diameter tube or solid rod

D6                                        3.659                                                     .44                                                 5mm Diameter tube or solid rod

D7                                        4.447                                                     .435                                               5mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 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 9el 144MHz LFA Yagi

Build Dimensions for UK/USA Version

Element                             Spacing in metres                                Half element Length in metres            Element Notes

Reflector                                0                                                           .515                                               3/16 inch Diameter tube or solid rod

DE1                                       .138                                                      .435                                               1/2 inch Tube

DE2                                       .306                                                      .435                                               1/2 inch Tube

D1                                         .533                                                      .4735                                             3/16 inch Diameter tube or solid rod

D2                                         .808                                                      .462                                               3/16 inch Diameter tube or solid rod

D3                                        1.34                                                       .463                                               3/16 inch Diameter tube or solid rod

D4                                        2.052                                                     .4565                                             3/16 inch Diameter tube or solid rod

D5                                        2.837                                                     .45                                                 3/16 inch Diameter tube or solid rod

D6                                        3.659                                                     .44                                                 3/16 inch Diameter tube or solid rod

D7                                        4.447                                                     .435                                               3/16 inch Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 3/8 tube

Feed point is the centre of DE1

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

SWR Plot for the UK/USA version of the G0KSC 9el 144MHz LFA Yagi

Antenna Elevation Plot

European version Azimuth Plot

UK/USA Azimuth Plot

EME Notes

This antenna makes an excellent EME antenna when configured in a 4 bay stack. Below is the TanT output screen showing that sky temperature is 236.2 Kelvin for this array which is lower than any other array of this boom length (VE7BQH G/T list, Google search). Not only this, G/T which is the figure of merit used to determine an antennas ability to receive signals is also better than any other antenna of this length (-3.72dB).

G/T and Sky Temperature are better than any other antenna of this boom length, period.

4 x 9 element LFA Yagis configured in a 4 Bay array 3 metres Vertically and 3.1 metres horizontally

As always, any questions please ask!

Justin G0KSC