I'm intending to have a go at building this antenna. The only problem I have
is that I cannot find a supplier of aluminium tubing that stocks single
lengths long enough for a 8.3 metre boom. I therefore need to join two
lengths of 25 x 25mm square tube together. Any one recommend a suitable
method of doing this please ?. I'd rather avoid welding as I would have to
buy the kit to do it.

Regards

Steve

Steve,

25 mm is rather skinny to go 8.3 meters with. However, the following should
work. I assume the tubing is available in 3 meter lengths. 10 foot lengths
would be even better.

Get four 3 meter pieces, and cut one down to 2.3 meters. Now bolt and center
this 2.3 meter piece to the side of one 3 meter pieces. The 2.3 meter piece
will be the top of your antenna, the 3 meter piece the bottom. Now bolt the
remaining 3 meter pieces to the bottom piece, and you should have an 8.3
meter boom. Whatever you do, do not use brass or copper hardware. You might
want add a strap to the top side where each of the 3 meter pieces butts up
to the 2.3 meter piece.

Tam/WB2TT

"Steve" wrote in message
...
I'm intending to have a go at building this antenna. The only problem I
have
is that I cannot find a supplier of aluminium tubing that stocks single
lengths long enough for a 8.3 metre boom. I therefore need to join two
lengths of 25 x 25mm square tube together. Any one recommend a suitable
method of doing this please ?. I'd rather avoid welding as I would have to
buy the kit to do it.

Regards

Steve

"Tarmo Tammaru" wrote in message
...
Steve,

25 mm is rather skinny to go 8.3 meters with. However, the following
should
work. I assume the tubing is available in 3 meter lengths. 10 foot lengths
would be even better.

Get four 3 meter pieces, and cut one down to 2.3 meters. Now bolt and
center
this 2.3 meter piece to the side of one 3 meter pieces. The 2.3 meter
piece
will be the top of your antenna, the 3 meter piece the bottom. Now bolt
the
remaining 3 meter pieces to the bottom piece, and you should have an 8.3
meter boom. Whatever you do, do not use brass or copper hardware. You
might
want add a strap to the top side where each of the 3 meter pieces butts up
to the 2.3 meter piece.

Tam/WB2TT

Thanks Tam,

the tubing comes in 5m lengths - so I could cut one down to 3.3m and place
it end-to-end with the remaining 5m tube. Then use the 1.7m offcut bolted to
the underside of the 5m and 3.3m tubes. I could go to 30mm tube if needed.
All I need now is the plans for the antenna but I should have those soon. I
have some 25mm wide earthing strap I could use between the sections.

Steve
G1FQD

Steve wrote:
All I need now is the plans for the antenna but I should have those
soon.

In about as long as it takes to go to the 'VHF/UHF Long Yagi Workshop'
on the site below. Some other questions will be answered there too.

Certainly a shorter sub-boom centred on the balance point is one good
way to go. Another is to use quarter-inch larger square tube for the
middle section, with the inch-square boom running right through, and
hard aluminium shims driven into the end. Don't forget to use a larger
boom correction for that centre section.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Steve,

Here is something else you might want to do. I did this to a KLM50-7 which
has a boom a bit less than 7 meters long. Took 2 pieces of 3/8 inch Al
tubing, about 5 feet long, and flattened both ends in a vise, then bent at
45 degrees. Drilled holes in the flattened portion, and bolted one end of
each to the boom, the other end to the mast through one hole, and a long
bolt, about 3 mm. Makes the boom absolutely stable in a wind.

Tam/WB2TT

"Tarmo Tammaru" wrote in message
...
Steve,

Here is something else you might want to do. I did this to a KLM50-7 which
has a boom a bit less than 7 meters long. Took 2 pieces of 3/8 inch Al
tubing, about 5 feet long, and flattened both ends in a vise, then bent at
45 degrees. Drilled holes in the flattened portion, and bolted one end of
each to the boom, the other end to the mast through one hole, and a long
bolt, about 3 mm. Makes the boom absolutely stable in a wind.

Tam/WB2TT

That's worth serious consideration as I live in a windy location. I was
thinking about using support wires clamped to the mast 2 feet above the boom
but I'll re-think it now.

Steve

"Ian White, G3SEK" wrote in message
...
Steve wrote:
All I need now is the plans for the antenna but I should have those
soon.

In about as long as it takes to go to the 'VHF/UHF Long Yagi Workshop'
on the site below. Some other questions will be answered there too.

Been there, done that. Couldn't find the measurements for the 4 wavelength
version. I have them now though from SV5BYRs site

Certainly a shorter sub-boom centred on the balance point is one good
way to go. Another is to use quarter-inch larger square tube for the
middle section, with the inch-square boom running right through, and
hard aluminium shims driven into the end. Don't forget to use a larger
boom correction for that centre section.

thanks for the advice.
It is much appreciated.
The only question I have now is probably a daft one but here goes....... the
plans for this antenna specify that the reflector should be at position 0 on
the boom and D13 should be at 8300mm relative to the position of the
reflector.. Where would one drill the hole for the reflector ? i.e how far
in from the end of the tube, and how far past the hole for the last director
would the boom actually end ?


--
http://www.ifwtech.co.uk/g3sek

Steve wrote:
The only question I have now is probably a daft one but here
goes....... the plans for this antenna specify that the reflector
should be at position 0 on the boom and D13 should be at 8300mm
relative to the position of the reflector.. Where would one drill the
hole for the reflector ? i.e how far in from the end of the tube, and
how far past the hole for the last director would the boom actually end ?

If the hole is far enough from the end that it doesn't weaken the
element mounting mechanically, that also seems to be OK as regards the
electrical effect of the metal boom.

It's nice to use plastic end caps (most yagi manufacturers will sell you
a few) so the practical distance for the holes is just far enough so
that the end cap will push in without fouling anything inside.

Or make it about pi/2 times the width of your thumb, and then trim the
end cap until it fits... no worries.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

It's nice to use plastic end caps (most yagi manufacturers will sell you
a few) so the practical distance for the holes is just far enough so
that the end cap will push in without fouling anything inside.

Or make it about pi/2 times the width of your thumb, and then trim the
end cap until it fits... no worries.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Lovely. Thanks Ian.

Steve

"Steve" wrote in message
.. .
The only question I have now is probably a daft one but here goes.......
the
plans for this antenna specify that the reflector should be at position 0
on
the boom and D13 should be at 8300mm relative to the position of the
reflector.. Where would one drill the hole for the reflector ? i.e how far
in from the end of the tube, and how far past the hole for the last
director
would the boom actually end ?

There is a mechanical engineering standard on that. The issue came up re the
A310 design after the NY crash where the tail tore off . I believe the
standard is 2 hole diameters. I looked at my VHF beams, and they are about
25mm.

Tam/WB2TT