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A Low-Noise 'Urban' 7 element LFA Yagi for 144MHz

Revised 26th 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 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
  • Please read the 'how to make the LFA Loop' page here

Download the EZNEC files for this antenna HERE

 

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:

'In my qrz pic , I have pops yu7ef  7 element for 2m and 12 element for 70cm above your duel band yagi which work
fine compared to the tonna I had up, but as I live in a mid terrace block, I was suffering from very high noise levels which
was masking the weak signals, Now the Lfa has basically cured that problem unless I am aiming at the house
concerned, it is like I have a DSP antenna!!!
GB3VHF IS now a clean signal ...that's why I'm now a fan of them.  It Is a pity I cant put mono band lfa's up for 6 and 4m,
It is a case of only one or the other because of the westerly winds that funnel down the estuary and the railway line that
puts limitations of my mast....'

 


VK2GOM using his 7el 144MHz LFA on Field Day 2010

 

The VK2GOM 7el ready for action!

 

Rob made an excellent job of his antenna and used G0KSC commercial clamps

 

Choke balun arrangement beneath the boom

 

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

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

Download the EZNEC files for this antenna HERE

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

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

Download the EZNEC files for this antenna HERE

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

Download the EZNEC files for this antenna HERE

 

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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