LFA antennas

[G8JVM]

Hi All
sitting outside on this nice sunny day is all the aluminium to build a 6 ele LFA for 4 mtrs.
Justin has reduced /streamlined his web site, and some of the useful info has gone.

The LFA loop he gives the length of each element , but he doesn't give the overall length of the loop either end to end or center of the boom to the out of the loop.
I've got thick wall 12mm & 9 mm for the loop , its close to an interference fit, so going to be a pig to adjust.

Any hint appreciated

[G4RUL]

In Justin's design the length of the driven element is the distance from the centre of the boom to the outer edge of the loop. Depending on the radius of the smaller loop inserts it should only require very minor adjustment to get that perfect match. A brake pipe bending tool is useful to get consistent results, although I found that some of the aluminium I had, needed to be annealed to prevent cracking. Heat it in a flame - smear some soap on it first and when the soap goes black it's cooked. I bent it hot then quenched in cold water. If you are using rod rather than tube for the end loops you may have no choice but to do it hot.

I used some aluminium stock that was left over from another project and the loops didn't fit into the tube so I had to use a 10mm drill to open it up a little - with a steady hand and cooling oil it worked ok - if you need to do this clamp the tube very firmly and don't be tempted to try a sliding fit until it has cooled - I had a fantastic shrink fit that wouldn't move on the first trial.

A friend has built LFAs for a 2m EME set up and I have made one for 70 cm, both versions were built following the method above and were OK with no adjustment.

Like you I have the aluminium for a 70 MHz beam and will be building it soon. I recently built a 50 MHz OWA following G0KSC dimensions and it worked well, his software does seem to give well matched aerials.

AL

[G8JVM]

Thanks for the info

Its built and up on the tower, just one big problem, it doesn't like other antennas around it.
on the ground with the tower tilted over the VSWR is 1.2:1, and resonant around 70.2 MHz.
But as soon as it get any height the vswr goes up to 1.7:1 and the resonance drops to 69 MHz.

There's a piccy of my antenna farm on qrz.com

I did have a modified 5 ele 6mtr Tonna and that sorta worked. All the other antennas are Vargarda, OZ5HF,
and they are not fussed by metal near them, they just match well.

I think the problem is Justin's design is very touchy with anything near it.
He recommend at least half the boom length separation.
And there is no room to do it.
I could go for a dual band antenna , but the gain is always much lower on 4. I want that the other way around..

Can anyone recommend a good antenna design that works well in proximity to other antennas ????

Now I got a bird perch up there , 4 is guaranteed to open.
TIA
Richard

[G8JVM]

I'll
update this a bit more
By placing the 70 MHz 6ele LFA at the bottom of the stub mast, 3mtrs, I have managed to get the VSWR down to 1.2:1 in the shack.
But this meant putting the 5ele 50 MHz Vargada 1.5 mtrs above it and I've noticed that the performance of the
2x 9 ele Vargada on 144 MHz has deteriorated.
The beacons I can hear are not much stronger than the 5 els cut down 6mtrs Tonna, it could be conditions,
but I was hoping for noticeable difference on the upgrade. That I've not seen.
The weight distribution of the whole array has changed which will give problems in the winter, when ever it ends.

I'll leave it up for the summer, but I'll take it down afterwards and use the metal work to make a dual band YU7EF.
Which will put the weight distribution better for the winter gales.
LFAs may be good antennas when used on a lightly loaded stub mast , but with something like mine
with antennas for 6,4,2,70cm,23 cms, 13 & 6cms. I personally would not recommend one.
There is a picture of my earlier array on qrz.com, not a lot of space left on it