A Low-Noise 'Urban' 12 element Plus2 LFA Yagi for 144MHz
Revised 23rd December 2009 V1.0
Premium commercial versions of this antenna at Innovantennas
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 commercial gain exists, express permission of G0KSC must be sought.
The new LFA Plus2 range includes an additional 2 reflectors which are used in order to maintain pattern stability throughout the 1MHz coverage (144-145MHz).
This is the ultimate in 2m VHF performance today, the new LFA Plus2 is the one to beat showing flat SWR, pattern stability throughout and better sky temperature and G/T figures than any other Yagi of the same boom length (VE7BQH list).Currently these antennas are available in METRIC SIZES ONLY. Imperial will be launched at a later date.
As with ALL LFAs this antenna requires no matching, it has a 50 Ohm input impedance.
The 12el Plus2 144MHz LFA installed at ON6NL
ON5GS who built the Plus2 for ON6NL stands proudly by his work.
'Hello Justin!
Thanks! It was a great QSO with UA3PTW (Via EME). His best signal was -21db and I got -29db.
The antenna used was a 12 el. G0KSC +2LFA made by Dirk, ON5GS.
Find attached some pictures we made during the antenna party last week Nov. 11
when Dirk, ON5GS and Leo, ON6LEO helped me to put the antenna in the mast.
You see Dirk on the picture, proud on his great job done. Next to the +2LFA on the
ground you see my 25 year old DL6WU who did a fine job until his last day.
The guy in the mast wearing a red jacket is Anton, ON6NL.
The first tests with the new antenna were very positive. We heard several 4 yagi stations from the
moon! The SWR is incredible! 1:1.0 from 144.000 to 144.750 and 1:1.1 for the rest of the band.
We checked it with 2 analysers!
| QRG | R | Xj |
| 144000 | 55 | 0 |
| 144250 | 56 | 0 |
| 144500 | 58 | 0 |
| 144750 | 55 | 3 |
| 145000 | 51 | 7 |
| 145250 | 51 | 6 |
| 145500 | 54 | 0 |
| 145750 | 55 | 6 |
| 146000 | 50 | 7 |
Today I worked in MS SV2JL, who copied me through a local thunderstorm, and
YU1IO. After that I copied some nice signals from the moon and worked UA3PTW.
Rig here is a IC756Pro2+transverter+PA giving 130W into 40m Ecoflex cable and a masthead
SSB preamp. And now a 12el +2LFA on an 18 meter mast in total at 50 meter asl.
I think Dirk will be satisfied with the results and finish his 4 stack of this antenna.
Thanks for donating the design to the ham community! It is really appreciated.
If I can you help with more info or higher definition photos, let me know.
73, Anton, ON6NL'
4nec2 (with nec4 engine) Elevation plot of the 12el Plus2 LFA Yagi
The 12el Plus2 Azimuth plot from the 4nec2 antenna modelling package
SWR as presented in the 4nec2 antenna modelling package using nec4.1 Double Precision calculation engine
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 DO NOT confuse EZNEC with the NEC engine. EZNEC uses nec2 by default
- 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
- Please read the 'how to make the LFA Loop' page here
- Please do not alter segmentation or try to 'tune' the antenna unless you have nec4 or better. SWR will not read true within anything else
Performance European Version
Forward Gain: 15.72dBi at 144.300MHz
Front to Back Ratio: 33.78dB at 144.300MHz
Peak Gain: 15.73dBi
Peak F/B: 38.44dB
Bandwidth: 144-145MHz below 1.1:1
Build Dimensions for European Version - mail me if you need 12 or 13mm tube driven loop sizing
Element Spacing (m) - Half element Length (m) - Element Notes
Plus2 Rear Reflectors 0 .508 above and below loop by 225mm 8mm tube
Reflector .207 .514 8mm Diameter tube or solid rod
DE1 .369 .442 10mm Tube
DE2 .534 .442 10mm Tube
D1 .765 .4795 8mm Diameter tube or solid rod
D2 1.237 .4635 8mm Diameter tube or solid rod
D3 1.668 .4515 8mm Diameter tube or solid rod
D4 2.177 .451 8mm Diameter tube or solid rod
D5 2.874 .4475 8mm Diameter tube or solid rod
D6 3.685 .4415 8mm Diameter tube or solid rod
D7 4.554 .4345 8mm Diameter tube or solid rod
D8 5.435 .428 8mm Diameter tube or solid rod
D9 6.359 .418 8mm Diameter tube or solid rod
D10 7.135 .4295 8mm Diameter tube or solid rod
Notes:
DE1 and DE2 are joined at the ends by 8mm tube
Feed point is the centre of DE2
Please read the 'how to make the LFA Loop' page here
Stack and bay at 3.75 Vertically and 3.95 metres Horizontally for the best G/T figure for this boom length, period.
As always, any questions please ask!
Justin G0KSC
