A Low-Noise 'Urban' 7 element 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.

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

This one is really nice and compact, has good bandwdith (1MHz 1.1:1) and yet has maintained an excellent pattern at the same time. Stacked in 4, you would not be unhappy with this very low-noise LFA for EME working. This antenna will be particularly good for EME purposes due to it's very low noise (Sky Temperature) and excellent 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. Do not confuse your version of EZNEC with nec version. 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

The 7el 144MHz LFA installed at K3UAZ completed with G0KSC Antenna Balun above the boom

The 7el 2m LFA by MW0CXH - Below is the SC6-4-8D Dualband G0KSC (4m/6m) Yagi

Peter comments:

Note: performance figures centred on 144.100MHz the centre EME frequency

Performance European Version                             UK/USA Version

Forward Gain:                                 12.83dBi at 144.100MHz                 12.81dBi at 144.100MHz

Front to Back Ratio:                        21.21dB at 144.100MHz                 21.33dBi at 144.100MHz

Peak Gain:                                        12.88dBi                                           12.87dBi

Peak F/B:                                           23.46dB                                           23.67dB

Bandwidth:                                       1MHz below 1.1:1                       1MHZ below 1.1:1

Build Dimensions for European Version - If you need 12mm Loop sizing mail me

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           .52                                               10mm Diameter tube or solid rod

DE1                                       .088                                                      .435                                              13mm Tube

DE2                                       .261                                                      .435                                              13mm Tube

D1                                         .399                                                      .476                                              10mm Diameter tube or solid rod

D2                                         .809                                                      .461                                              10mm Diameter tube or solid rod

D3                                        1.471                                                     .449                                              10mm Diameter tube or solid rod

D4                                        2.2                                                         .438                                              10mm Diameter tube or solid rod

D5                                        2.894                                                     .434                                              10mm 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

SWR Plot for the European version of the G0KSC 7el 144MHz LFA Yagi

Build Dimensions for UK/USA Version

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                            .52                                               3/8 Inch Diameter tube or solid rod

DE1                                       .088                                                      .434                                              1/2 inch Tube

DE2                                       .261                                                      .434                                              1/2 inch Tube

D1                                         .401                                                      .475                                              3/8 inch Diameter tube or solid rod

D2                                         .809                                                      .461                                              3/8 inch Diameter tube or solid rod

D3                                        1.471                                                     .449                                              3/8 inch Diameter tube or solid rod

D4                                        2.2                                                         .438                                              3/8 inch Diameter tube or solid rod

D5                                        2.894                                                     .434                                              3/8 inch Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by either 3/8inch tube. Feed point is the centre of DE1

SWR Plot for the European version of the G0KSC 7el 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 237.3 Kelvin. There is no other array this short on the VE7BQH list. However, the sky temperature is lower on this array than many of the longer arrays listed (VE7BQH G/T list, Google search).

There are no antennas as short as this on the VE7BQH G/T list. However, this array still outperforms longer arrays in all respects

4 x 7 element LFA Yagis configured in a 4 Bay array  and showing current distribution. 2.25 metres Vertically and 2.975 metres horizontally. Optimum spacing still to be defined

As always, any questions please ask!

Justin G0KSC

UPDATED 8/09/09

Note: In the table below data for 4 antennas configured in a 4 bay array are given. The important areas are G/T and Bandwidth measured between 144 and 145MHz, Ta (Sky Temperature) and G/T. The Lower the Ta figure the the lower noise the antenna will receive and hence, it will receive wanted signals better. The G/T figure is a combination of the antennas gain and noise figure resulting in a score presenting the antennas ability to receive wanted signals.

Generally, G/T and Temperature improve with boom length. Note most G0KSC antennas out perform anything of the same or smaller boom length. In some cases, other designs need to be much longer or very narrow band (Check SWR at G/T Bandwdith) before they get close to the LFAs.