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8el 12.5mtr Boom LFA

A Low-Noise 'Urban' 8 element LFA Yagi for 50MHz

Revised 24th 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, this is another low-noise antenna from G0KSC

This antenna has been built, tested and used at the RSGB Field Day, July 2009. South America being the best result during that contest from this 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.

Download the EZNEC Project files for this antenna HERE

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 millimeters' 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
  • This is a 50 Ohm Antenna, no matching arrangement is needed. A simple 1:1 or choke balun will be fine. see 'creating a Balun' here
  • Please read the 'how to make the LFA Loop' page here

The 8el LFA At XE2K

'Justin
Here just  a sample
 
more photos monday after the test, this is in a hurry  ONE man 95% of the time installation  (me)
 
the 8 ele ROCKS at 100ft'

 

The 8el LFA installed at VK7AB

 

 

The 8el 6m LFA at N6SS at 105' up

 

The final photo is of the antenna at 70' on the way up to 105'.  Band condx have been poor so no chance to run
checks with distant stations.  But tests with a beacon 190 miles away show a small gain for the LFA vs. an M2
6M7, 7el on 27' boom, both ants at 70'.  Direct wave tests with a station 60 miles distance showed an 8dB
gain for the LFA altho that is too good to be true.  I should have more data E season 2011.

At the shack end of a ~200' feedline the SWR is near 1:1 from 50.001 to 50.500.

Thanks for a great easy to duplicate design and tnx for taking the time to modify your 8el on 12.5m boom to my
12m boom.

73 & hope to C U on 6'

Press N6SS

 

In use at G0KDV for RSGB Field Day. Boom is 1.5 inch box tube and 3/8 inch elements with 1/2 inch main loop.

 

The 8el 50MHz LFA at GW3YDX

The analyser of GW3YDX. I do not think anything more needs to be said

 

The 8el 6m LFA At G8BCG

 

SWR for the LFA has become legendary. Maximum radiated power!

 

The G8BCG RF Choke installed at the feedpoint

 

Performance European Version                             UK/USA Version

Forward Gain:                                   14.07dBi at 50.150MHz                 14.06dBi at 50.150MHz

Front to Back Ratio:                        24.87dB at 50.150MHz                 25.2dBi at 50.150MHz

Peak Gain:                                        14.14dBi                                           14.11dBi

Peak F/B:                                       31.62dB                                           32.26dB

Bandwidth:                                     500KHz below 1.1:1                       500KHZ below 1.1:1

Download the EZNEC Project files for this antenna HERE

 

Build Dimensions for European Version

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                  0                                                          1.481                                              10mm Diameter tube or solid rod

DE1                                        .397                                                      1.229                                               13mm Tube

DE2                                        .952                                                      1.229                                               13mm Tube

D1                                         1.81                                                      1.386                                               10mm Diameter tube or solid rod

D2                                         3.525                                                     1.351                                               10mm Diameter tube or solid rod

D3                                         5.572                                                     1.329                                               10mm Diameter tube or solid rod

D4                                         7.873                                                     1.31                                                 10mm Diameter tube or solid rod

D5                                        10.213                                                    1.288                                               10mm Diameter tube or solid rod

D6                                        12.493                                                    1.265                                               10mm Diameter tube or solid rod

Notes:

DE1 and DE2 are joined at the ends by 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 8el 50MHz LFA Yagi

 

Build Dimensions for UK/USA Version

Element                             Spacing in metres Half element Length in metres            Element Notes

Reflector                                0                                                           1.482                                               3/8 inch Diameter tube or solid rod

DE1                                       .397                                                      1.229                                                1/2 inch Tube

DE2                                       .952                                                      1.229                                                1/2 inch Tube

D1                                        1.811                                                     1.387                                               3/8 inch Diameter tube or solid rod

D2                                        3.525                                                     1.352                                               3/8 inch Diameter tube or solid rod

D3                                        5.572                                                     1.33                                                 3/8 inch Diameter tube or solid rod

D4                                        7.873                                                     1.311                                               3/8 inch Diameter tube or solid rod

D5                                       10.213                                                    1.289                                                3/8 inch Diameter tube or solid rod

D6                                       12.493                                                    1.266                                                3/8 inch Diameter tube or solid rod

Download the EZNEC Project files for this antenna HERE

 

Notes:

DE1 and DE2 are joined at the ends by 3/8 inch 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 8el 50MHz LFA Yagi

 

Antenna Elevation Plot

 

European version Azimuth Plot

 

UK/USA Azimuth Plot

Download the EZNEC Project files for this antenna HERE

As always, any questions please ask!

 

Justin G0KSC

 
 
 
 

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