G0KSC LFA aerials

[VK4WTN]

I am looking to build a new 6M yagi and come across an aerial designed by G0KSC which is a 5el LFA aerial on a 4.7 meter boom and reportably has a gain of 11dbi. The nearest aerial in gain to it is the new DK7ZB 6el yagi on a 6 meter boom with a gain of 11.65 dbi. It would be interesting to hear from anyone who have built a G0KSC LFA yagi and how does it compare to the more standard yagi designs.

[VK2GOM]

Hi there VK4WTN,

I am currently building a 7ele LFA for 2m which is nearly complete.

I got the green plastic insulators from Justin directly, and I'm building the elements from 10mm tube, and the LFA loop from 12mm tube. I bent up the end pieces using a proper pipe bender, so the loop goes together nicely and is completely adjustable, as per my diagram on Justin's web page of 'How to build the LFA loop'.

I currently need more M6 nuts and bolts to fit the remaining elements on. All being well I can get it in the air at some point this weekend and give it a test for the VHF field day.

My previous antenna was a 9ele Tonna for /P 2m work, so I will have a good idea of how it compares once I get it going.

73 - Rob VK2GOM / G0MOH

[VK4WTN]

TNX for the reply Rob, look forward to hearing how the aerial performs, the driven element design is unique.Just a quich question on the insulators that you bought, I take it they are the green ones in the photos,can you use these on the DE1 element where the coax terminates or did you make it out of perspex?
regards Wayne

[VK3AUU]

I hope your antenna works out for you, but as the man said. "If you want gain, there is no substitue for boom length."

David

[VK2GOM]

Hi Wayne,

Yes, I used the green insulators for everything. Where the feed on DE1 is, I riveted two small pieces of angle aluminium to the side of the boom to 'widen' it a bit, and fitted an insulator each side. The parts of DE1 then come towards the centre of the boom through each insulator, where they can be attached to the coax feed.

If you need a picture, let me know.

73 - Rob VK2GOM / G0MOH

[VK6OX]

Hi Wayne,

Yes, I used the green insulators for everything. Where the feed on DE1 is, I riveted two small pieces of angle aluminium to the side of the boom to 'widen' it a bit, and fitted an insulator each side. The parts of DE1 then come towards the centre of the boom through each insulator, where they can be attached to the coax feed.

If you need a picture, let me know.

73 - Rob VK2GOM / G0MOH

Hi Rob and Wayne,

I also use the "green" insulators (in my case for Justin's 2m 9el OWA) and have purchased them locally. Google "Stauff tube clamps" and you'll find many distributors across VK.

My DE mounting arrangement is the same as yours Rob!

DE mounting arrangement

73

[VK4WTN]

Thanks for the information Andy and Rob I will chase up those insulators and start planing the project.Might have to source a new heavier rotator and go for a 6meter boom.
tnx Wayne

[VK2GOM]

One tip I would give (from experience this afternoon ) is the green plastic is relatively soft. I had managed to short one side of the dipole to the boom, via the M6 bolts that were starting to tear through the plastic.

So, tighten them only so the elements are snug. Beware of the socket cap screw head trying to 'dig in'. I notice on the Stauff website, they do metal locating washers that are designed to be used with these insulators to prevent the screws deforming the plastic, but the prescence of more metal might affect the tuning.

I'll be testing the antenna out tomorrow for the VHF field day.

73 - Rob VK2GOM / G0MOH

[VK6OX]

Hi Rob,

Rather than socket head screws, I opted for Philips head. Thanks for the tip nonetheless, I'll check mine later this evening...

...and GL in the FD!

73

[G0KSC]

Guys,

the metal top plate is steel and very heavy, it adds a great deal to the overal wieght of the antenna. I use serrated washers and only pull down enough that the element does not move and there is no 'twist' action on the boom itself. No need to over engineer, the light wieght has a big benefit of it's own. Do let me know how the antennas perform. Here are some comments form ES2FL who just finished the 8el 2M LFA:

Hi Justin,

No. No more news on your design on my tower. My friend took a couple of pictures of antenna and myself climbing, but I don't have them yet. I will send them to you as soon as I get them.

No news are good news:

SWR is low and wide for a beam (narrower than at ground level, but still less than 1,2:1 from 144 to 147MHz with a little high resonance at around 146). It rains often here and no change from wet to dry in SWR, as expected. We even had freezing temperatures and some snow a couple of weeks ago, but not at the beach were I live. Now temp is high (almost 20ºC), and I guess we will go back to our winter average 10º with lots at rain. We have had high winds yesterday, and antenna is still there (or I think so). Gain is almost equal to my old Tonna 13 elements which was just a little longer than the LFA-8. I have had some weird noises (maybe from some Xmas-tree lights) at certain direction, actually with not one but two max at 15º and 40º, with an S-7 signal that disappeared when turning the beam. Maybe there were two Xmas trees from different neighbours... Who knows... Pattern seems to be OK with just one single max, since I get just one max signal from every station I work.

I have been lazy but I still want to build another pair stacked for vertical polarization, and something similar for UHF. Let's see what brings us new year.

I wish you a very happy and succesful new 2010 year.
Thanks and 73's,
Jose

[VK3OP]

I too will be building Justin's LFA designs, most likely 7 or 8 elements on a 10 to 12 metre boom for 6mx and I am currently looking at the
Plus 2 LFA's for 2mx and eagerly awaiting the 70cm designs. Because of the issues of High UV here in southern VK3 and my location ( top of
a hill and high winds ) I am going to get the element to boom insulators made from Delrin. There is a guy here locally that can manufacture up
most things you require for antennae in either 1 off or quantity and his prices are reasonable.

The direct 50 Ohm connect design for me is a no brainer simple, minimum number of connections (and therefore points of failure). I am even considering
bringng the feedline from the 6mx LFA all the way down past the rotator as my flexible tail, eliminating one connector pair from the feedline path.

To quote Sam Kekovitch "You know it makes sense"

Frank VK3OP

[VK3AUU]

http://www.bigskyspaces.com/w7gj/6mAnte ... VE7BQH.txt
http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm

David
VK3AUU

[VK4QB]

Hi all,
Frank 3OP whats the UV properties of Delrin like ? Its a good plastic re strength tho. What costs ?
73,
Brian 4QB

[G0KSC]

Hi Guys,

Here is a preview of a 70cms LFA

Azimuth



Elevation


I have 18el to 27el completed and will work to around 32elements versions. The above numbers speak for themselves. VE7BQH has also confirmed nothing else comes close. Infact the 70cms LFA G/T and sky temp figures were so much better than everything else, he checed the calculations several times. They were good.

I have a lot of designs to publish on the site so was planing on adding the 70cms stuff in February sometime. However, if you have a need, let me know I can send you the construction info.

Justin G0KSC

[VK3AUU]

The important first side lobe is pretty ordinary, so why is the G/T so good.


David
VK3AUU

[G0KSC]

Side lobes close to the main lobe do not have any impact on G/T at all. IT is the rear 'bubble' which effects the temperature part of the G/T figure. If an antenna has good gain per metre of boom and high supression of the rear bubble, G/T is good.

[VK4WTN]

hi Justin, just wondering if you have any LFA 6 meter designs on boom lenths of 5 to 6 meters.Also can the DE1 connection point be mounted through a PVC box to keep the weather out of the DE1 connection without any ill effects? Regards Wayne.

[G0KSC]

Hi Wayne,

5-6 metres is not a good length for 6M antennas (existing designs from others prove this). You either get poor bandwidth or (if you push the optimiser hard for bandwdith) see greatly reduced gain per metre of boom. This is at least for the LFA design. I have some designs for the unrelase OWL (Optimised Wideband Low impedance) Yagi which fit within this band. However, there is a lot to know about this particular antenna and until the details are released in the next issue of DUBUS magazine, those designs will not become public. There are some ham in the UK and IReland that have some early LFA designs which are 5.X metres long. However, as already mentioned F/B does suffer on a 5el after 4.7M and the swr curve is not so flat.

The feed point can be placed in a box if you wish. For me, I waterproof the connection with silicone. From experiance, The boxes once wet inside, stay that way. People tend not to waterproof the coax when in the box so the first bit of damp comes along and the coax is shot!

J

[VK3OP]

Hello all,

Firstly Brian, delrin is very high strength and with good UV stability, however it is a bit pricey, but in the context of the antennae I am going to build
the benefits out weigh the costs. If you do a search on the net there are some resources which outline Delrin's physical and chemical characteristics, it is also
known under another name which escapes me at present.

Secondly, Thank you justin for the heads up on the 70cm LFA's there is no rush, so I will wait for the published designs. Given that I am planning a complete install
of tower with 6mx, 2mx, 70cm, and 23cm there is a bit of work to do. I am just getting together all the design stuff, so that I can plan feedlines, mounting hardware,
power dividers, preamps etc.

Cheers

Frank VK3OP

[VK4WTN]

Thanks for the info Justin,I think I will stick with your 4.7m design, its a great size in regards to using a smaller rotator and with 11dbi gain gives a performance equal to a lot of larger beams.OK in regards to using a box at the feed point, i'll stick with your idea and seal it with silicon.Thanks again for providing such a great design. Regards Wayne