Attaching Coax to Aluminum Rods?

[KA1OWC]

Hello: I am just starting into antenna building and have a question...Using aluminum rods, how do I connect wires (coax) to to them...I understand that you cannot solder to aluminum...Advice appreciated!


Steve KA1OWC

[K7SGJ]

Best thing I can suggest is to use closed ring crimp connectors on the inner and outer conductors of the coax, and then use the appropriate size screws (bolts) and nuts to attach them to the aluminum. Depending on what material the crimps are made of, you may experience some electrolysis or galvanic action, best minimized by using a paste that is made to go on all the connection points. It is readily available on the web or in many hardware stores. Next time you are in a place that sells TV antennas, or a ham store, look at how they are done. Most use rivets, which is also doable, but for the DIYer, I think screws will provide a better long term connection.

But then, I could be full of shit, too.

[NQ6U]

La Rata is not full of shit (for once), that is the best way. Another method I've used is stainless steel worm drive hose clamps. Just stick the conductor under the clamp and tighten it down.

https://static.grainger.com/rp/s/is/image/Grainger/2UTD8_AS02?$smthumb$If you can find them in the correct size, you can also use these things. Put a ring terminal on the conductors, then attach that to the screw (stainless steel is best) that tightens the clamp.

The advantage to the last two methods is that they allow for feed point adjustment when it's needed.

[KG4CGC]

Tin your copper leads with solder first. I would get an SO-239 connector and mount it in a weather proof box and connect your leads to the antenna from that. If the individual leads are longer than 1 inch then insulate each one and slide ferrite beads over them. Hell, I'd do the same even if the were an inch.

[N8YX]

All good suggestions.

As Eddie stated: Make sure to coat your element rods with NoAlox or similar paste where the clamps will attach (if you use them).

[HUGH]

There is alumium solder and aluminium flux. I've used the solder, it works but doesn't flow well so I force it into shape using "wiped" joints just as you'd use in plumbing to join copper and lead pipes.

As for the flux, which claims to solder any metal to aluminium, well I don't think it works reliably well.

With Al tube, if you can plug the ends with solid aluminium rod and tap a thread right through for a long screw, I think it gives you a good contact area out of the weather, leaving less sealing required

Looking at the reactivity table for metals (goes M A Z I T L as in magnesium, aluminium, zinc, iron, tin, lead) it is much of a guide to the screw material? One thing though, stainless steel has a poor conductivity.

[WZ7U]

One thing though, stainless steel has a poor conductivity.

Now that I wasn't aware of.

[KG4CGC]

The stainless steel conductivity issue confuses me. Is there more information on this.

[HUGH]

The stainless steel conductivity issue confuses me. Is there more information on this.

Obviously there are at least 2 common grades of stainless steel and I haven't checked precisely what the difference is but when I worked at a motor drive manufacturer, we carried out some tests using stainless steel screws for the terminals both inside and out (user terminals) of DC drives.
The screws became very hot at full current (the 200A region) compared to the normal plated mild steel and, as the inner ones carried the coils which were the current measurement transformers, the coils were sacrificed to the great smoke god.

Consider the domestic utensils made from stainless steel which includes pans, mugs, kettles and so on. Our saucepans are copper based otherwise they would take an age to heat up. Drinking mugs and kettles don't become as hot on the outside as those made from, say, aluminium.

One of our local radio club members uses stainless steel electric fence wire for an antenna and the total resistance is measured in tens of ohms. Another, experimenting at LF and VLF, reports that, with about 3kW RF out, the stainless steel screws connecting various bits together were literally a dull red heat, damaging some of the other bits of hardware. I suggested using smaller screws with a copper sleeve.

This seems a comprehensive guide:

http://eddy-current.com/conductivity-of-metals-sorted-by-resistivity/

[KG4CGC]

Thank you. This is good information.

[WZ7U]

Interesting. Thank you!

[K7SGJ]

Who Gnu thanks Hugh

DooDah DooDah

[KG4CGC]

Who Gnu thanks Hugh

DooDah DooDah

Hugh knew. Now what? See that? Chicken butt.

[K7SGJ]

Hugh knew. Now what? See that? Chicken butt.

Well, there is that , too.

[WZ7U]

Buy a truck. Run amok. Get it stuck. What the fuck?

[K7SGJ]

As we said in the Army transportation unit I was in, "you call, we haul, that's all; if you can't truck it, fuck it

[WZ7U]

Nice!

Wait a minute! They had trucks in the Spanish/American war? WTF?

[KG4CGC]

Mastodon trailers pulled by woolly mammoths.

[K7SGJ]

I've got your woolly mammoth, right here....................

[WØTKX]

Steel fence wire works OK for a Beverage antenna due to it's internal resistance?

Never mid. Fake News. :lol:

[KG4CGC]

I've got your woolly mammoth, right here....................

Speak to the Hircus Circus Ringmaster. He will see to your woolly needs.

[KG4CGC]

Steel fence wire works OK for a Beverage antenna due to it's internal resistance?

Never mid. Fake News. :lol:

Not midding. Welp. I'm getting a mid to sling some wire in the air.

[WZ7U]

Speak to the Hircus Circus Ringmaster. He will see to your woolly needs.

Step right up....

[hamguy]

I know I'm a little late to the dance, but one more thing to consider.
If you are just running coax up to the antenna elements and using good crimp-on lugs with good hardware and a good conductive grease you've done almost everything.
Now, don't forget to tin the shield where you twisted it to go into the crimp lug. Tin it after you've crimped it, and allow the tinning to go under the coax insulation just a tad. Goes for the center conductor as well if it is stranded wire. This fills the braid/strands and prevents water from wicking up the twisted shield/center conductor leads and into the coax. Water will ruin coax. Then seal the coax with a good quality UV resistant exterior caulk/sealant making sure all entry paths into the coax are blocked and sealed well back over the coax insulation.
When using solder out of doors, use a good quality silver solder. Standard tin/lead solder seems to deteriorate in the weather.

[HUGH]

16125

As an indicator about the idea of using aluminium solder, the lower antenna in the photo, a 2m Hentenna with reflector, is made by soldering bits together. It was impossible to bend two rectangles in one piece so they're in 2 parts and the cross members are soldered in seperately by drilling holes in two larger tubes and sliding these over the main assembly. Likewise joints are reinforced with a larger tube soldered over.

If you ever had to solder copper pipes into lead pipes, unlikely though, it might be familiar but it's not advisable to heat to much because the solder will never run and the tubes will probably melt (I've done it). There should be just enough heat to force the solder in a sort of pasty form into the joints with a cotton, linen or leather rag and carefully wipe it round to look neat.

The 70cm antenna above is copper so no notes needed for that apart from the fact that the horizontal sections are fibreglass rod wrapped with copper tape to save weight.

[K4PIH]

I've found that with aluminum antenna elements (tubing), not to plug them on the ends. Water will seep in and when it freezes it'll break. In areas where it doesn't freeze the trapped moisture will cause corrosion. Best to leave the ends open so they can drain.