Hi Costas -
An external antenna for your 4G modem is a good idea, if not two! We’ll have a guide eventually, but in the meantime I’ve been testing with these antennas and this router, but depending on where you are in the world you may need different hardware, based on the cellular bands in use. hese anntenas work great with the larger 14mm deck holes. I like using this router style because then you have the additional benefit of an ethernet switch (and ethernet connection to Pi), but all the Pi USB ports are available and so one could be used with a USB 4g modem.
Zero tier is truly amazing, and once setup as an extension it punches through the NATS of cellular networks with ease. It will connect quicker if you configure your cellular device to use ipv6 only.
Best of luck!
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