A Low-Noise 'Urban' 17 element ultra low-noise (close spaced) LFA Yagi for 144MHz
Note: I have a 6mm element version of this antenna now available. Email for details
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, or want the perfect quite EME single antenna or array, this is another low-noise example from G0KSC
This LFA has been designed for maximum suppresion of side, rear and elevation lobes. The result is an ultra clean antenna which will be a stunning performer for 144MHz. The antenna is super wide-band too with an SWR of less than 1.1:1 over more than 1MHz. Uncharacteristically of a Yagi, the LFA maintains F/B over this wide bandwidth and more importantly maintains its pattern too, some example pattern plots are given below for 144.100MHz, 144.300MHz and 144.600MHz. One of the reasons for pattern stablility and bandwidth is the close spacing of the elements on the EU range of LFAs.
This antenna is particularly good for EME purposes due to the class leading low noise (Sky Temperature) and G/T figures mentioned above. See the bottom of this page for more information.This low-noise property also means less man made noise will be picked up by the antenna too.
I have started to model individual antennas on individual diameter elements in order to achieve the best all round results. Using the same element spacing and changing element diameter has not shown consistant results and therefore, I will spend more time on order to create new models for each (geographic) regions tubing requirements. UK and USA versions will follow shortly.
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 nec versions with EZNEC versions. Unless you have EZNEC pro/4 you are using nec2 NOT nec4
- 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
The 17el LFA of EA3AXV who modified the loop size in order to use 8mm rod all the way through the antenna
Quim made an excellent job of the feed point
Did you really expect the SWR to look any different to this?
The 17el LFA installed at 9A9SF
'Hi Justin !
Yes ...
I put up the antenna and it works very good
I make the LFA from one piece of 6mm
swr is 1:1.1
antenna is 25m high
I DON'T MOVE ANY ELEMENT ...ALL DIMENSIONS AND DISTANCE ARE EXACTLY HOW YOU CALCULATE !'
9A9SF
IV3MUR built this 'Rope Ladder' version of the 17el LFA for EME
Noise floor results of the IV3MUR 17el LFA version - Moon reflections recorded on marker
In order to show how clean the pattern is on this antenna, I have presented below first a 3D side shot of the antenna pattern followed by the Elevation plot then the Azimuth plot from 4NEC2 modelling program. These plots show much more clearly then EZNEC.
The 17el 144MHz LFA exhibits an incredible super-clean pattern
The 17el Elevation plot presented in the 4nec2 antenna modelling package. As with all LFA's plenty of rearward suppression without loss of forward gain.
The all important 'Super Clean' Azimuth pattern as presented within 4nec2 at 144.100MHz
In order to demonstrate pattern stablility within the LFA model, the above is the pattern as generated at 144.300MHz
The last example presents the same at 144.600MHz. Not there are still not unwanted forward lobes.
Note: Performance figures given at 144.100MHz, the EME centre frequency
Performance European Version UK/USA Version
Forward Gain: 17.28dBi at 144.100MHz -
Front to Back Ratio: 33.71dB at 144.100MHz -
Peak Gain: 17.30dBi -
Peak F/B: 36.80dB -
Bandwidth: 1MHz below 1.1:1 -
Build Dimensions for European Version
Element Spacing in metres Half element Length in metres Element Notes
Reflector 0 .508 8mm Diameter tube or solid rod
DE1 .244 .445 10mm Tube
DE2 .410 .445 10mm Tube
D1 .608 .481 8mm Diameter tube or solid rod
D2 1.07 .468 8mm Diameter tube or solid rod
D3 1.546 .4595 8mm Diameter tube or solid rod
D4 2.12 .453 8mm Diameter tube or solid rod
D5 2.807 .45 8mm Diameter tube or solid rod
D6 3.571 .445 8mm Diameter tube or solid rod
D7 4.41 .4395 8mm Diameter tube or solid rod
D8 5.288 .434 8mm Diameter tube or solid rod
D9 6.185 .4295 8mm Diameter tube or solid rod
D10 7.121 .424 8mm Diameter tube or solid rod
D11 8.049 .4175 8mm Diameter tube or solid rod
D12 9.018 .408 8mm Diameter tube or solid rod
D13 9.952 .4055 8mm Diameter tube or solid rod
D14 10.924 .4015 8mm Diameter tube or solid rod
D15 11.724 .405 8mm Diameter tube or solid rod
Notes:
DE1 and DE2 are joined at the ends by either 8mm tube
Feed point is the centre of DE2
SWR Plot for the European version of the G0KSC 17el 144MHz LFA Yagi as displayed in EZNEC Pro/4
The above plot is the SWR as presented in 4nec2 (with nec4.1 claculation engine installed).
Antenna Elevation Plot within EZNEC Pro/4
The amazing Azimuth Plot of this fantastic wide-band 17el 144MHz LFA
EME Notes
This antenna makes an excellent EME antenna When used with 2 or 4 stack versions, performance becomes second to none at this boom length. Below is the TanT output screen showing that sky temperature is 208.4 Kelvin for this array which is excellent for only 5.64W/L. Not only this, G/T which is the figure of merit used to determine an antennas ability to receive signals is better than any other antenna of this length (+0.05dB). As with all 2M LFA's listed on this site, there is no other antenna listed on the VE7BQH G/T table that has the same length (or shorter) Boom with the same or better G/T figure.
G/T and Sky Temperature are better than any other antenna of this boom length (5.64W/L), period.
4 x 17 element LFA Yagis configured in a 4 Bay array 4.5 metres Vertically and 4.75 metres horizontally. With more time, even better results can be achieved.
The incredible Azimuth pattern of the 4 x 17 LFA EU array. Find another array that looks this good.
Even in the elevation plane massive suppression of unwanted side, rear and upward lobes contribute to the exceptional low temperature of this antenna array.
As always, any questions please ask!
Justin G0KSC
