How to connect antenna base to powder-coated steel?

Gents,

Ran into a wee snag during a design. The metal enclosure is plain steel that is powder-coated. The guys at the metal shop said that they cannot provide a nice connection surface for a bulkhead connector like this:

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I was hoping they could provide a masked nickel-plated area but ... nope. They can only provide a threaded stud like those safety ground ones. Not so cool at several GHz. Ok, we could make a wide shunt strip for that but that's yet another custom BOM item. Corrosion is also a major concern here since this gets deployed in coastal regions. So straight bolting onto bare steel is out.

Anyone know of a clever way to handle this? If someone knows of a cheaper bulkhead SMA feedthrough connector that would also be nice. Four bucks is a bit steep.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg
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Joerg,

Is it possible to use a threaded tube to, later, mount a weather tight box that contains or mounts the RF connector? The feed line can run through the tube.

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Reply to
Jon

Maybe you need to try other powder coating operations. I use one here on Washington St., in Phoenix. They can mask anything I want. I would think you could do it two step.... powder coat with mask, then plate the masked area. Ask around.

Or nickel plate first, then mask that and powder coat. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

You have to do it the second way, to provide a way to clip the return. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

It's not such a good idea to use Ni plated connectors at microwave frequencies due to intermod. Ni is a magnetic metal and can provide the non-linear properties to allow mixing to occur. Silver, gold, tin, etc would be better.

Can you install a dummy connector while the powder coating process is done? At least clean off the inside surface so the lock washer can get a good bite into the steel.

Reply to
tm
[...]

That won't last long. Steel will rust. Other metals will cause galvanic corrosion. See

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Mike

Reply to
Mike

If you can get a lock-washer to bite thru the powder coat on the backside, that gives you DC connection. Then a stainless steel oversize washer on the front side might provide enough capacitance for the GHz frequencies.

I have also experimented with silver-loaded paint around and thru a hole, but results are a bit variable.

Beware any connector exposed to salt spray, the corrosion will kill it.

--
Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
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Reply to
Adrian Jansen

If the inside is exposed to the corrosive atmosphere, so will the electronics. Or maybe something is left out of the description of the requirements.

The gasket on the outside will seal against the powder coat and keep the inside clean and dry, right?

Nickel is not the right coating to use in a corrosive environment.

Reply to
tm

galvanic

the

Any metal in a salt environment is trouble. Any penetration of an enclosure is asking for breakdown of the sealant and capillary wicking into the junction, then galvanic corrosion.

Joerg is an old ham. He understands the difficulty of sealing antenna traps and tuners against the weather. The problem is especially difficult in a salt atmosphere.

This problem is not easy. I'd budget a bit more for the enclosure, and carefully examine the other end of the coax for similar problems.

Mike

Reply to
Mike

you can't put the gasket on the outside and have bare metal under the nut on the inside ? cover every thing in in vaseline or maybe even epoxy before you assemble it to keep the moisture out?

or go crazy, solder it in before powder coating

doesn't seem bad, digikey want 5 times that

-Lasse

Reply to
langwadt

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I second the Nickel plate, mask and then Powder coat. It would be cheaper than any alternative, even if it adds cost.

Cheers

Reply to
Martin Riddle

Philmore/LKG has them for $2 in quantities of 5-500. p/n 11315

Or, roll your own with an 11305, brass nuts, rubber washers for $1.10

Or, leave the powdercoating in place and put a large enough base on the antenna that the couple of dozen pf between base and steel is nearly a short circuit at several Gigs.

THanks,

Jim

Reply to
RST Engineering

That's what I had suggested but they can't do it. For a variety of reasons we have to stay with this shop.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

We don't have a lot of space below, maybe an inch. So we (likely) need to connect to the bulkhead connector with an angled plug. And it should be cheap, low in labor minutes.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Yes, Ni is not ideal but in this case definitely good enough. I have even used it on sensitive equipment in the lower HF range.

We could, but the other issue is that it's bare steel, no plating. In coastal regions having a Ni bulkhead connector on that will look yucky within months.

On thing we were thinking about are PEM nut kind of inserts. Big enough in diameter so its thread don't get in the way, but it'll be tough to find one flat enough. Maybe stainless.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Actually, our electronics fare quite well. And they are coated.

The other option would be to purposely insulate the bulkhead pass-through. Then we'd have no corrosion there as long as nothing crunches through the powder coating. However, then the coax continuin on the inside will become part of the antenna and pick up all sorts of clock harmonics and such. It's a transceiver so this can mess up the RX part of it, IOW we could lose range. We may have to try that though if nothing else pans out.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

And that's just the problem. The lock-washer DC connection would be good enough because it is short. But it'll be eaten away by corrosion. Just the air is enough to do that out there. Imagine a climate where every day massive amounts of humidity condensate onto everything.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

The gasket on the outside would be no problem at all but vaseline would just push corrosion out some more months.

Well, at that price we might just make our own :-)

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Hmm, you'd want to ground the coax to the nearest grounding stud, preferably with a shield covering the section from ground to connector. And probably a ferrite bead or two on the coax between the transceiver and ground point.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Thanks! I'll ask them. Their web site is a train wreck, doesn't even have a search function:

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That's what we'd do if it's too expensive otherwise.

That is what I am trying to avoid because this would have to be fastened to the steel plate again, with screws -> corrosion in four spots instead of one.

[...]
--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

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