I would think that you may be referring to, what is called a MIFI. These devices are sold from most internet providers and are wireless access points, much like a phone connected to a major carriers network. They provide wireless internet to as many as 10 other phone, computers and the like. The only thing that actually needs to be connected to these devices is power. They operate on battery, but battery life is greatly reduced when several devices are connected. The other thing that can be connected to the MIFI is an external antenna. You can purchase these from Amazon or even your carried may have them available. If you are actually referring to a “modem” then follow the advice of the first post.
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