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 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
- 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
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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8el 12.5mtr Boom LFA
