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7el 9.8mtr Boom LFA

A High-Gain 7 element Low Noise LFA Yagi with a 9.8 metre Boom for 50MHz

Revised  April 2010 V1.2

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.

NOTE: There are many versions of this antenna below in different element diameters, view the whole page

This antenna has been improved for summer 2010 with a little more gain and a much cleaner pattern.

 

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

This antenna has been designed with performance in mind and provides optimum performance for the 9.8mtr boom. However, this is a difficult length to reduce fully the elevation plane lobes (which is one reason I have introduced the LFA2 at this length) and therefore, I have ensured these lobes are 'pushed forward' in order to minimise impact. Good bandwidth and excellent performance characteristics mean this one will surely be a winner!

Metric and imperial tube size versions below.

 

4 x 7el 9.8m long 50MHz LFA Yagis at G8BCG

 

7el 50MHz LFA at N6JV

 

The 7el 9.8m long 50MHz LFA Yagi at G8APB

 

Only W7GJ was heard off of the moon until the LFA was installed at PA0O. Now things are very different!

 

 

The 7el 9.8m long 50MHz LFA at AB5EB

 

 

The 9.8m long 7el 50MHz LFA at OE4VIE. Jo worked many new stations as soon as the antenna was installed.

 

 

The 9.8m 7el 6m LFA at UX0UN above a 15m Yagi

 

 

2 x 7el 9.8m LFAs at G0VHF/P - Built by G0KSC. Note the wind loading on the top antenna! Best DX 8526kms

 

The 2 x 9.8m 7els at G0VHF/P before raising. The Sea take-off can be seen behind

 

SWR plot of the the 9.8m LFA from 49.850MHz to 50.550MHz

 

 

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

 

 

How this antenna looks when built

 

 

Performance                                      European Version                             UK/USA Version

Forward Gain:                                   13.20dBi at 50.150MHz                 13.18dBi at 50.150MHz

Front to Back Ratio:                           24.21dB at 50.150MHz                  24.68dBi at 50.150MHz

Peak Gain:                                       13.21dBi                                           13.21dBi

Peak F/B:                                          29.78dB                                           30.66dB

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

Stacking:                                            Ideal Spacing: 7m - 5m minimum 

Stacking gain improvement:          2.9dB at 7m

Stacking: distances are not critical. 7m gives the best pattern against gain figure.   

 

Build Dimensions for UK/USA Version

                                       Element          Spacing in metres Half element            Element Notes

Reflector                                 0              1.4805                                             3/8 inch Diameter tube or solid rod

DE1                                       .378          1.227           Feed Point                      1/2 inch Diameter Tube

DE2                                       .944          1.227                                                1/2 inch Diameter Tube

D1                                         1.756        1.3875                                              3/8 inch Diameter tube or solid rod

D2                                         3.392        1.3515                                              3/8 inch Diameter tube or solid rod

D3                                         5.417        1.3255                                              3/8 inch Diameter tube or solid rod

D4                                         7.641        1.3005                                              3/8 inch Diameter tube or solid rod

D5                                         9.817        1.2655                                              3/8 inch Diameter tube or solid rod

 

Notes:

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

 

SWR for this excellent antenna

 

 

Build Dimensions for European Version 10mm/12mm elements

                                         Element   Spacing in metres Half element Length          Element Notes

Reflector                                 0            1.4805                                             10mm Diameter tube or solid rod

DE1                                       .378        1.225             Feed Point                   12mm Tube

DE2                                       .944        1.225                                               12mm Tube

D1                                         1.756      1.3875                                             10mm Diameter tube or solid rod

D2                                         3.392      1.3515                                             10mm Diameter tube or solid rod

D3                                         5.417      1.3255                                             10mm Diameter tube or solid rod

D4                                         7.641      1.3005                                             10mm Diameter tube or solid rod

D5                                         9.817      1.2655                                             10mm Diameter tube or solid rod

 

Notes:

DE1 and DE2 are joined at the ends by either 10mm tube

 

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

 

Performance UK/USA Version

Forward Gain:                    13.27dBi at 50.150MHz

Front to Back Ratio:            25.64dBi at 50.150MHz

Peak Gain:                         13.33dBi

Peak F/B:                         25.87dB

Bandwidth:                          500KHZ below 1.1:1

Stacking: Ideal Spacing: 7m - 5m minimum

Stacking gain improvement:          2.9dB at 7m

Stacking: distances are not critical. 7m gives the best pattern against gain figure.

 

 

Build Dimensions for UK/USA Version

                                       Element     Spacing in metres Half element Length            Element Notes

Reflector                                 0              1.4795                                             1/2 inch Diameter tube or solid rod

DE1                                       .369          1.228           Feed Point                      1/2 inch Diameter Tube

DE2                                       .938          1.228                                                1/2 inch Diameter Tube

D1                                         1.746        1.388                                                1/2 inch Diameter tube or solid rod

D2                                         3.452        1.338                                                1/2 inch Diameter tube or solid rod

D3                                         5.495        1.3185                                              1/2 inch Diameter tube or solid rod

D4                                         7.698        1.294                                                1/2 inch Diameter tube or solid rod

D5                                         9.825        1.2635                                              1/2 inch Diameter tube or solid rod

 

 

Performance European Version all 12mm elements

Forward Gain:                                   13.25dBi at 50.150MHz               

Front to Back Ratio:                           25.45dB at 50.150MHz                

Peak Gain:                                       13.31dBi                                        

Peak F/B:                                          25.78dB                                         

Bandwidth:                                       500KHz below 1.1:1

Stacking: Ideal Spacing: 7m - 5m minimum

Stacking gain improvement:          2.9dB at 7m

Stacking: distances are not critical. 7m gives the best pattern against gain figure.

 

 

Build Dimensions for European Version 12mm elements

                                       Element        Spacing in metres Half element Length         Element Notes

Reflector                                 0                 1.480                                              12mm Diameter tube or solid rod

DE1                                       .369             1.226             Feed Point                   12mm Tube

DE2                                       .936             1.226                                               12mm Tube

D1                                         1.744           1.3805                                             12mm Diameter tube or solid rod

D2                                         3.422           1.3425                                             12mm Diameter tube or solid rod

D3                                         5.461           1.320                                              12mm Diameter tube or solid rod

D4                                         7.666           1.2945                                             12mm Diameter tube or solid rod

D5                                         9.830           1.2645                                             12mm Diameter tube or solid rod

 

Notes:

DE1 and DE2 are joined at the ends by either 10mm tube

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

 

Elevation plot for this antenna

 


Azimuth Plot

 

 

As always, any questions please ask and PLEASE send photos of your finished projects.

Regards

Justin G0KSC

 
 
 
 

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