Construction tips for Alford slot

[VK3VB]

Interested in anyone's first hand experience on building Alford slot for 1.2

[VK7JG]

Yes please .
I would like to build one for the VK7RAE Beacon.
Any help appreciated .

73
Joe
VK7JG

[VK4TI]

Interested in anyone's first hand experience on building Alford slot for 1.2

You need a very good machinist , and the understanding of how to stack them , I have run them on 2.4 , see Vhttp://www.qsl.net/kd2bd/superturnstile.html
Eventually we found a broadloop was useable "see http://jpier.org/PIER/pier128/25.12042405.pdf" and finally settled on a stacked array of folded dipoles , very conventional but for the cost of a cheap tube bender of ebay worked very well offering high reliability ( very strong)and excellent radiation angles , all offer something so without being confusing which suites your mechanical skills ?
Barry

[VK3XL]

well I have made one, but have not tested it yet. I am fortunate to have a small milling machine (attached to my lathe) so I didnt find it a difficult task to make the slot. I may get a chance to put a feedline on it over easter and if so I will let you know how it goes

[VK3ZAZ]

Interested in anyone's first hand experience on building Alford slot for 1.2

No but have first hand on TV Band 111 UHF arrays made from 6 inch pipe (brass) with windows cut symmetrically along outer and big inner to match impedance and a tuning stub at the end.

Can look up design but it is standard scalar construction used on many tv sites on UHF bands
All just hardware nothing critical

[VK3WRE]

I have built 3 and all have worked ok but I have trouble getting a return loss better than 15db. The slot needs to be the same width all the way along and
it is difficult to do as the 32mm tube I used tends to spring appart when the slot is cut.
I have had to put 2 small tabs at the feed point to form a very low value cap to assist with tuning.
Its also critical to have the feed line from the balun run down the back of the inside of the tube, if not the return loss will drop off.

Ralph VK3WRE

[VK3VB]

Thanks for the feedback to date. Was looking at this for the vk3rlp beacons. I should be able to get machining done if necessary.

[VK3BJM]

G'day Phil.

I've only tried making one on 1296, and I suffered the same problem Ralph describes. I used a miniature cut-off wheel on a Dremel, and getting the slot cut accurately wasn't too hard. But the springiness of the copper tube is an issue.

And reading Ralph's posting made me think about why this is so. It's because the copper tube is hard-drawn. Therefore, perhaps the cure for this is to anneal the copper tube first; maybe that would remove the springiness? I.E., heat the copper up with a blow torch until it gets to a cherry red colour, then let it cool slowly.

Good luck with it!

73,
Barry
VK3BJM

[VK3VB]

Would there be a better metal then copper? I think the answer is "no", but....

[VK3XL]

copper is the material of choice and Barry is right anneal the copper first, cool slowly or quench in water makes no difference to the hardness of the copper after heating to a nice red. Quenching in water will leave the copper cleaner than letting it air cool. I have a mill so I used an appropriate sized slot drill to cut the slot in mine, but as said before mine is untested.

[VK5ZD]

Would there be a better metal then copper? I think the answer is "no", but....

Yes; silver
A tad on the expensive side, however