While ready-to-use 3G and 4G communication modules and USB dongles can be sourced easily from the Internet, the devil rendering them unfit for your application and requiring a system redesign is usually hidden in the details, Some carriers and applications for instance use odd bands not supported by the module (US band 13 being particularly troublesome), while for other systems the addition of a COTS USB dongle is unacceptable. And then there are applications with requirements for uncommon antennas (think SMA) or that need GPS functionality too.It all starts by finding a comms module that suits the communication band(s) you selected and that fits the size and cost criteria. The quality of the field application engineering team of the comms module manufacturer, vendor or distributor is important too as you may need support at some point. The author found Quectel especially welcoming and helpful, Gemalto's distributor YAWiD in Germany and Telit's Polish distributor were okay too, However, the author placed the popular Swiss manufacturer U-blox on the other end of the scale as he did not manage to get responses from them due to their e-mail system, But this is, of course, personal experience. It all depends on the region you're in, and you may have other experiences.
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