A 14 element LFA Yagi for 70MHz with a 19.306mtr boom
Revised July 2010 V1.2
Premium commercial versions of this antenna at Innovantennas
Note: If you do not see this antenna in an element diameter you would like, mail me!
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:
2 x 7el 4m LFAs at G0VHF/P
16.53dBi @ 70.200MHz
F/B 30.98dB @ 70.200MHz
SWR: Below 1.1.1 from 70MHz to 70.600MHz
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 1.0555 3/8 inch or 10mm tube or rod
DE1 .296 .881 (.880 with 12mm tube) 1/2 inch or 12mm tube
DE2 .692 .881 (.880 with 12mm tube) 1/2 inch or 12mm tube
D1 1.245 .9915 3/8 inch or 10mm tube or rod
D2 2.352 .966 3/8 inch or 10mm tube or rod
D3 3.728 .9495 3/8 inch or 10mm tube or rod
D4 5.323 .9345 3/8 inch or 10mm tube or rod
D5 7.007 .9225 3/8 inch or 10mm tube or rod
D6 8.765 .910 3/8 inch or 10mm tube or rod
D7 10.529 .8975 3/8 inch or 10mm tube or rod
D8 12.368 .885 3/8 inch or 10mm tube or rod
D9 14.210 .878 3/8 inch or 10mm tube or rod
D10 16.059 .8735 3/8 inch or 10mm tube or rod
D11 17.911 .871 3/8 inch or 10mm tube or rod
D12 19.306 .886 3/8 inch or 10mm tube ot 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.
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.
DE1 and DE2 will have to be cut shorter than the above measurements in order to allow for the radius on the loop ends. Always adjust loop for best SWR.
Feedpoint gap 6-10mm this gap is not critical.
Please send photos of this antenna if you build it.
Azimuth Plot of this super antenna
The much improved elevation plot
Elevation plot at 20m up
The SWR curve is virtually the same with both metric and imperial sized tubing
Dave, G1OGY operating at G0VHFD had this to say ' The antenna was very sharp, it had a 30 degree beamwidth and if you went out side of this, there was nothing there !! This made it ideal beign able to block out some very strong signals coming in from behind the beam.. ' .
Any questions, please ask!