VK Logger Ham Radio Forum Archive

Hi all,
Has anyone built a 6m yagi using flat strip for the folded dipole?
If so, what thickness/width did you use?

Cheers
Nev

Hi Nev,

This site has a calculator for flat/round etc driven elements.

I've used it with no issues ..

http://www.vk5dj.com/yagi.html

Cheers,

Lloyd

If you use some insulated spacers periodically along the folded dipole so as to tie the top and bottom sections together it will strengthen the structure and you will get away with a thinner strip (ie: trying to simulate an "I" beam). A round tube would be a better way to go, but even then spacers can be used to advantage. I have done this using extended ex CH2 TV antenna dipoles using the insulated that came with the TV antenna.

I suspect that the size of the flat strip is likely to be too big to be practical on 6M. Different situation though on 2M and above.

Lloyd
That is the prog I have been playing with.
I should have given a bit more info in my query. I am interested in how saggy that form of dipole can be.
Igor
I have thought about using spacers to make it more rigid but wonder how much that would detune it, given the dimensions are calculated for free air conditions.
I would like to hear from anyone who has gone down this path.
I don't know whether I could bend tubing successfully around a 50 or even 60+ mm semicircle; flat strip would be a lot easier.

Cheers
Nev

Nev, when I made my 6m loop fed yagi I needed to be able to form the bends accurately so I bought a tube bender kit.
It has all the bits required to bend 8,10,12,14,16 mm tube. I cannot find one the same on ebay but a single size one looks like this
http://www.ebay.com.au/itm/10mm-Tube-Be ... Swl8NVeTOu

You could just buy the size you need for your tube.
My 10mm and 12 mm benders will bend a 180 deg bend with 50mm inside diameter.
the 14mm and 16mm benders will bend a 180 deg bend with 75mm inside diameter.

Hope that helps

VK3LU wrote:... I don't know whether I could bend tubing successfully around a 50 or even 60+ mm semicircle

Try a 'tube bender' search at places like eBay (or TradeMe in ZL).
I got one as below for a few dollars and used it for folded dipoles and LFA loop corners.
73,

Refrigeration part suppliers have them,but could be more costly.

73 Ross

Hi Mike,
I was trying to be a miserly old sod and avoid buying a bender for 2 bends.
A plumber lives next door and a refrig man lives just up the road so I should have access to something.
I'll have a look at the local hardware too.
BTW, I am legal again since Xmas eve

Nev

Or If you are down this way anytime you can borrow mine. I bought it thinking I would use it from time to time and so far I have used it to make the 6m beam and 1 other job in 7 years.

One el cheapo way is to fill the bit you want to bend with sand and bend round a bottle or round wood

I made this simple cheap bending jig from parts in the back yard shed. You need to find the correct pulley size to ensure correct spacing. I practiced on several off cuts and you must allow for the 'spring" effect.

More details from this website : http://www.ifwtech.co.uk/g3sek/diy-yagi/dipoles.htm

73

Nev

A cheaper option may be to buy a bending spring pumbers use to bend 1/2" copper pipe. You can get them from the local "Big" hardward shop. It may not suit if you are looking for a tight bend.

Nev

These are the TV antenna bits I mentioned earlier that can be obtained for the right price during a council pickup. Extend the folded dipole using aluminium from the antenna and use the original spacers used on the antenna.

6M antenna made from TV antenna parts as installed at portable location at Bremer Bay. Antenna uses the original center insulator for the folded dipole as this was still in one piece when the TV antenna was picked up.

Fixed bearing at this stage but hope be able to have a second antenna (also from TV antenna parts) that can be rotated but this may take a while to arrange.
All I need is to be at Bremer Bay when the 6M band is open!!!

Thanks all for your suggestions but the question remains; has anyone used flat strip on 6m folded dipoles?

Edit: I could build the folded dipole as Igor has. Lay it flat which would put the strip on edge and be much stronger.


Cheers
Nev

I have a 1m piece of 19mm x 6mm strip or bar, excellent, but HEAVY, HEAVY.
19mm x 3mm would be too bendy in lengths of 1.5m (6m 1/4 wave).
The 20 x 10 angle 1.5mm thick for floor tile edging was very tempting for 6m use.
Fly screen edging, a flat box section, is also tempting.

If you have the 6mm, well OK, it will definitely work, note though it's weight
will need heavier boom and mountings.

10 or 12 mm tube is much more suitable in this mild Sydney weather.

Our needs for a 6m beam are for only a 1/2 MHz range, 50 - 50.5 MHz.
Then, a 5/8 vertical for FM.
Standard calls, requirement for 52MHz is a bit of a problem,

Main thing, get an antenna out there. 6m is fun.

I would suggest that rather than flat strip you consider a section of angle or U-channel. The angle or channel webs could be removed for a short length around the bends, or alternatively just notched depending on how pretty you what the bends to look.
You could make the angle section by folding a thin strip. The bent angle will give much greater strength and rigidity than a flat strip.

Regards
David ZL4DK

From the structural perspective, a tube will provide strength from bending in all directions for the minimum amount/weight of material. All other shapes will require more material/weight, especially a flat strip as the shape offers poor resistance to bending in the direction of the flat side (and in the other due to the element warping). It all comes down to basic engineering structure principles.

I my view flat elements for antennas are not viable from the structural point of view other than for UHF antennas (and to a lesser extent the higher VHF frequencies).

Of course you already have plenty of flat material available to use and size and weight/size of the strucure is not an issue then the situation changes - but structurally it will finish up being a less elegant solution than a tube one.