GSM Antenna for Cargo Container

[VistaListener]

Anyone have any experience in mounting a GSM antenna onto a cargo container. I'm told this cargo container has electricity installed for lighting and I'm to install a low voltage alarm system with a cellular module for alarm reporting. I'll need to get an antenna outside the container, which really makes it vulnerable to tamper, but there will be an outdoor bell on the container as well.

Depending on signal strength, I may not need to go too high up, so I'm thinking about a small mast attached to the side of the container. Hopefully, a grounding rod has been installed by whoever installed the electrical and I'll mount the mast near that so I can run a ground wire to that.

 

[mmckenna]

The steel on these things is pretty thick. We've got a few at work.
You're going to have to drill through either the top or the side. They usually have some vents, but getting something through them is going to be difficult.

To avoid tampering, take a look at doing a NMO think mount somewhere near the center of the roof. A gain GSM cellular antenna should be pretty short and will essentially be hidden.

If signal strength is an issue, you could do a pole mount on the side and install a directional antenna pointed towards your closest cell site. Use a cable feed through or weather head designed for keeping water out.

If this is going to be on a mountain top, make sure everything is grounded. Also, make sure the coax feed line is grounded with a proper protector. If this is a radio site, they won't like your alarm system being a path into their container for lightning.

Lots of good antennas out there to do what you want.

 

[W8RMH]

I was going to suggest an antenna mounted in the center of the roof as well to prevent tampering.

They make Thick Surface Antenna Mounts for thicker materials.

 

[VistaListener]

Thanks for the replies. I'm not sure what type of mount, whether on top or side. I think these containers are low enough it really doesn't matter where to mount the antenna. If someone wants to disable it, there's not much that can be done. Maybe a tamper loop running along with the coax would trigger the alarm and sound the outdoor bell.

I was thinking of running a bare ground wire from a ground rod up to the mast where the antenna connects to the bracket, which will serve to ground the shield. This way I can enclosed the coax, along with a tamper loop, in armored liquid tight, which may give it some protection from wire cutters. Also, I can use weather proof, tampered, L fitting for a side mount.

 

[mmckenna]

Thanks for the replies. I'm not sure what type of mount, whether on top or side. I think these containers are low enough it really doesn't matter where to mount the antenna. If someone wants to disable it, there's not much that can be done. Maybe a tamper loop running along with the coax would trigger the alarm and sound the outdoor bell.

I was thinking of running a bare ground wire from a ground rod up to the mast where the antenna connects to the bracket, which will serve to ground the shield. This way I can enclosed the coax, along with a tamper loop, in armored liquid tight, which may give it some protection from wire cutters. Also, I can use weather proof, tampered, L fitting for a side mount.

Sounds like a good idea. Some radio sites are starting to do this with their grounding systems due to the theft of copper.

Grounding the outer shield of the coax is not sufficient. You should install a Poly-Phaser type unit designed to cover the frequencies in use by the antenna. This takes care of the center conductor also.

As you stated, if they want it, they'll find a way to steal it. Most you can do is make it difficult for them.

 

[VistaListener]

McKenna, a NMO mount for a structure would be nice as it looks small enough to hide on top of the container. It may go unnoticed by someone walking around on the ground. It might have to be a GSM mobile NMO antenna and mount. Grounding may take some thought.

 

[VistaListener]

I just looked at poly-phaser lightning arrestor and it looks simple enough. I wonder if that could go inside the container with the ground wire exiting to a rod?

 

[mmckenna]

You don't say where you are located, but here in the USA you'd have to meet the National Electric Code rules. Not sure about a shipping container as it may be considered a "portable" structure, but you'd probably do well by following the code.

All grounds, even for your cellular radio and antenna need to be bonded to the electrical ground. What that means is that whatever you install, even if it's a dedicated ground rod just for radio, it -must- be bonded (connected) to the electrical ground for the "structure". What that prevents is from one of the grounds being at a different potential from the other. This would be a very bad thing if the electrical grounding system was damaged or disconnected.

I'd take a look at what's already there and plan accordingly. You didn't mention what the container was going to be used for. I may have incorrectly assumed it was for other radio equipment. Either way, you do need to follow code.

A "thick" NMO mount would be a good start. They can either have coaxial cable coming directly out of the mount or they can be purchased with a type "N" connector and you install your own coax. Thread a mobile antenna on to it and you'd be good to go. Might want to consider some silicone around the base. While this isn't necessary for a vehicle install, these containers can be sometimes a little beat up. That means the roof could be bowed slightly and allow water to pool. Ideally, you'd want to put your antenna in a place where water won't pool. The NMO antennas usually come with really good seals, but they are designed for mobile use, not submersion in a puddle.

 

[prcguy]

I would use a GSM hockey puck antenna model with no mount, just drill a hole and a hollow threaded stud sticks through the roof with the coax and you put a big nut on the inside of the ceiling. These are small, flat and will probably fit down in the corragations of the container and disappear. No lightning protection would be needed.
prcguy

 

[VistaListener]

prcguy, would you have a link to the antenna you're suggesting. I'd like to take a look at it.

Also, I'm probably over thinking this about running a separate ground. If the signal strength is strong enough to get by with a low profile antenna, or something like a mobile antenna, then the install would be similar to a mobile install where the antenna gets grounded to the metal structure of the car. Right?

I can see a separate ground if there is a mast involved and the antenna projects much higher than the container.

 

[popnokick]

Are we all correct in assuming this cargo container is NOT in service as an active shipping container? If it is being actively used for shipping it may mean rethinking everything, e.g. what if another container is stacked above it, what if other obstructions develop, etc?

 

[VistaListener]

This cargo container is used for storage only. You can buy these for all sorts of uses. So, now it's a permanent fixture.

 

[VistaListener]

Follow-up to this post.

I installed the system and used an older multiband 3dB antenna by Antennex, which I've had for several years, and appears to be a OEM by Laird. This antenna is temporary and is about 2.75" tall with a threaded permanent stud mount. I don't have a photo of it but it looks similar to a Laird TRA6927M3PB-001, which I ordered and will replace the temporary one.

I drilled a 3/4" hole in the top of the cargo container, inserted it from the outside and secured it with a locking nut. The cargo container will act as a ground plane, much like installing in a mobile situation. Silicone will seal it up to prevent water leakage.

Using LMR-240 coax with a Type-N male connector I attached to the antenna stud and ran the coax, about 4', to the radio that took a SMA male.

Since it's not in an area where lightning is a problem, I did not use a separate ground.

Results are -89dB, which is quite good for this cellular application and I expect better with the new replacement.