Mounting the aerial up in the clear should help too. At the turn of the century when I was still at sea, I found that a simple Omni directional magnetic base car phone aerial enabled much better phone and email data from within my cabin - this by putting the aerial as close to the window glass as possible.
However, don't extend the two coax feeders or you will loose more in the coax than you gain by good clear positioning. So in other words the 4G router has to be mounted close to the aerial.
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