A stud is one option they gave us but at gigeehoitzes that means a custom stainless of whatever strip from bulkhead to stud.
That won't do any good at a few GHz. But one or two small loops will do. Unfortunately they also pick up RF but we can keep them out of the worst.
Well, as John Larkin once said, on some projects packaging can become
Watch out for galvanic corrosion with stainless against pretty much any other metal. Where you develop more than about 0.15V is a potential corrosion problem:
See for example the effect of stainless against aluminum:
Why My Kenmore Washer Died
Mike
Wouldn't you be using a COTS NEMA box? Maybe type 6?
You could simply skip the feedthrough and use a marine grade cable feed? Then the metal is out of the equation.
There are also COTS waterproof cable feeds that I think seal better, but they aren't stainless.
I've examined a lot of NEMA setups, and they tend to pigtail the coax through a connector to avoid this issue. I've seen the feedthrough too, but less often. Think of it this way. That connector is going to need some weather protection on it. Goop, RTV whatever. The pigtail removes one point of contamination.
Leave it painted. Mount the antenna INSULATED, and ground the antenna with a wire, and ground the plate as well. To a ground rod.
Tell me about it, we're packing a 50kW induction heater into the smallest enclosure on the market: tabletop sized, just a little heavy for one person to lift. :)
Tim
r
uld
I had similar anxieties about a nickel under-layer for a gold-plated copper grid to go into a electron microscope - it turned out that there wasn't enough nickel present to make a magnetic field big enough to influence the electrons involved.
Roughly a micron thickness of nickel on top of bulk metal isn't going to see much of a microwave field in the first place, nor radiate much in the way of intermodulation products.
-- Bill Sloman, Nijmegen
With stainless steel studs this client had rather postive experience so far.
[...]
A pigtail connection wire is not such a great thing at several GHz. Too much inductance. It would have to be a metal strip and since nobody makes them it'll be custom :-(
No, a big custom steel box with a steel lid on top.
Ok, but we do not want the metal to be out of the equation. We'd like a low-inductance connection to this steel lid.
Pigtail isn't a great ground at GHz frequencies. Feedthrough without connection will work but results in the coax shield picking up noise from the electronics inside.
There really should not be any RF on the outer surface of the connector if everything is done right. You just need a good DC and low HF path for static and lightning or other external events.
I would mainly think you want to keep out other RF and EMI from entering the enclosure. A large washer should provide capacitance from the connector to the case. maybe use a ferrite core around the cable prior to entry to the case.
Au contraire. They sometimes call those rubber antennas "dipoles" but they aren't. They are ground planes, meaning there must be a ground counterpart. On low frequency antennas that would be a set of radials. On VHF/UHF/SHF stuff that is usually a metal surface. It has to be there.
If you don't provide a GHz-class ground at the base of the antenna the system will seek and find other grounds, inside the enclosure. That is normally not desired for two reasons: RF-wise it's largely uncontrolled and it'll also pick up any inband noise that might be inside the box. Range and RX noise immunity might go to pots.
Well, there is a limit on the size of the washer. Plus those tend to collect all sorts of gunk over time.
epoxy then? or bolt it in before powder coating?
they have some that a 75$ wonder what exotic material they are made of
I'm a bit weary of cheap sma connectors, I have once got some that were a bit too cheap, some of the center connector weren't centered and the isolator it was definitely not Teflon because you had to be fast with the soldering iron or it would melt
-Lasse
Epoxy is a good idea. Although it does add cost because of the curing time during which the panel occupies space in production. Bolt-in before powder-coat, I don't think that'll fly with the guys.
There is a lot of rip-off going on in the world of connectors.
In our case none would be soldered, it's all just screwed together.
Well, you never really completely defined the problem. Maybe you just can't without a NDA.
Without all the information, we are just shooting ducks in the blind. Just for the fun of it.
We have a similar climate here ( coastal Queensland Australia ). Dissimilar metals making contact are always a problem. Conformal coatings, or silicone rubbers, are about the only defense which work reasonably well.
I tried the silver loaded paint, since the version I have is in a very tough, resistant carrier, and hopefully the silver maintains the contact even when the paint gets down into the contact surfaces. So it acts both as a seal and as a conductor. The trick is to coat the surfaces with the paint, then screw them together while the paint is still liquid. When it dries, it should form a conductive layer, and exclude the salt. Whether it works long term remains to be seen.
It's not really any secret. 2.45GHz has to be radiated off the top of a large metal lid, connects to a transceiver inside the box. The bulkhead connector getting the SMA from one side to the other should make contact. Realistically we have about a 2" radius around it available before other stuff gets in the way. Box is plain steel, powder-coated in light gray color. That's about it.
Wish we could do tricks like that. But in our case they'll have a bunch of sheet metal made at a time and it all sits in the stock room until needed. Only then is the hardware mounted into it.
Can you make a 1/4 wave choke joint at 2.45 GHz? Inside or outside the housing? The electronics inside, if exposed to the corrosive atmosphere, would be more of a concern, one would think. Are you using a RpSMA to connect the antenna? Might want to check the rules for a commercial product in the ISM band.
Good luck, hope you figure it out.
tm
Outside, no. Inside, yes. What I am trying to avoid is any RF pickup from the inside. That always costs range.
The electronics are mostly coated, I am not so worried about that. We've got years of experience with that.
Regular SMA. We are legally ok if the antenna is not above a certain gain limit, according to the manufacturer. For the US, that is. The end customer is not allowed to use any other antennas and would typically never touch that area anyhow. Most won't even know what an antenna is because they've all got cable or satellite :-)
This whole reverse connector biz is a joke anyhow, you can buy adapters almost anywhere.
If all else fails well make a custom bracket to bridge over to a stainless stud with the least amount of inductance.
If the frequency is that high, it does not need to be tied to the plate AT ALL. The base of the antenna is 'ground plane' enough for the job. If the transmitter chassis is grounded (and it damn well should be), then the antenna already is as well.
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