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Low-Noise LFA Yagi for 70MHz

A 9 element LFA Yagi for 70MHz with a 10.42mtr boom

Revised 7th September 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 designed in order to minimise the upward and downward lobes typically seen the the EL plane on Yagi antennas. By doing this, a drastic reduction in pick up of unwanted noise in City locations is the result. The double bonus is the likelihood of reducing transmitted interference too. If you suffer with very bad noise on 70MHz and have room for an antenna of this size, Email me for details of the very high suppression version.

This antenna can be built with Metric or Imperial sized tubing:

 

The 9el 70MHz LFA at G8APB

 

'Justin,
 
This mornings 4m contest was the first time I had a real chance to try out the newly built 9 ele LFA, that you designed for me.  I have now mounted it on a trailer mounted 60' versatower, as it was too much for the 12m Clarke mast, and I had it up for todays contest.
 
Great to have a fantastic antenna for this band, even using just 35 watts out every one I could hear came back to me with good signal strengths.  First time I have worked Cornwall on 4m, and logged 4 GMs from my eirey on the Pennines at IO83wd.
 
I connected my Mini VNA to check the system this morning and even without GB3BUX being on the VNA trace was showing recieved signals at -30dB, the VSWR at 10m height is <1.05:1 across 70 to 70.5 MHz.  It was so easy to make given your instructions that all my older antennas will be gradually replaced this next summer (when it gets here, right after the contest this morning a thunder storm rolled in right overhead for 3 hours, fortunately without damage to aerial farm or rigs), the only problem is that I need to monopolise the farms yard during final construction ( as long as the horses don't get hurt... XYL stipulation)
 
Now that it is getting warmer outside to work on antennas I have plans for  two off 6m 7 eles the same length as the 4m 9 ele.
 
73 de Chris G8APB'

(awaiting Photo)




The 9el 4m LFA installed at ZS6NK

 

'Hi Justin, ZS6WAB ( 2 x 10 YU7EF yagis, IC756+ ME TX-verter + QRO amp) made the first TEP QSO on 4m SSB with SV2DCD. FWIW I worked sv2dcd on CW on 4m with my barefoot FT847 and 9 Ele LFA. SV2DCD was running FT847 and 7 ele DK7 yagi. CU at the BBQ if all goes as planned.'


73 de Paul
ZS6NK KG46rc

 

 


The 9el 70MHz LFA installed at CT1HZE

 

 

The 9el 4m LFA installed at EI9E/P Contest Station

 

 

Performance

Peak Gain: 14.6dBi @ 70.180MHz

Peak F/B: 45.01dB @ 70.140MHz

SWR: Below 1.1.1 from 69.9MHz to 70.600MHz

Construction

Download the EZNEC files for this antenna HERE

For full details of how to make the LFA, read here: http://www.g0ksc.co.uk/making-the-lfa-loop.html

Antenna Dimensions for UK/USA sized tubing

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.056                                           3/8 inch or 10mm tube or rod

DE1                      .321                          .882                                            1/2 inch or 12mm tube

DE2                      .714                          .882                                            1/2 inch or 12mm  tube

D1                       1.246                          .993                                            3/8 inch or 10mm tube or rod

D2                       2.395                         .964                                            3/8 inch or 10mm tube or rod

D3                       3.816                         .948                                             3/8 inch or 10mm tube or rod

D4                       5.41                           .935                                             3/8 inch or 10mm  tube or rod

D5                       7.089                         .921                                              3/8 inch or 10mm tube or rod

D6                       8.862                         .903                                              3/8 inch or 10mm tube or rod

D7                       10.421                       .898                                              3/8 inch or 10mm tube or rod

The ends of DE1 and DE2 are connected together with 3/8 inch or 10mm tube or rod. the Feed point is the centre of DE1.

 

NOTE: SWR will not read as per the graph below if you use a package with mininec or nec2. DO NOT Get your version of EZNEC confused with nec versions. Unless you have EZNEC Pro/4 you do not havew nec4. The swr graph is correct and confirmed within nec4 and through building this antenna.

 

Pattern is identical when using metric or imperial tubing. This is the Elevation Plot

 

Azimuth Plot of this super antenna

 

SWR as presented in 4nec2 Antenna Modelling package (nec4.1 double precision engine installed)

 

 

SWR Plot when European/metric tubing (12mm/10mm) is used - Altering the loop size will better this

SWR Plot when Imperial (1/2 inch, 3/8 inch) tubing is used

Download the EZNEC files for this antenna HERE

 

Any questions, please ask!

 

Justin G0KSC

 
 
 
 

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