4g towers transmit downward to users in the city below them. They do not transmit upward.
That is why if you leave you phone turned on during a commercial flight, it will stop working after take off anyway. The towers don't send signal upward. You might still collect some residual signal for a little bit if you are near a tower and directly above it for a thousand feet or so, but not at 14,000 ft.
4g towers transmit downward to users in the city below them. They do not transmit upward.
That is why if you leave you phone turned on during a commercial flight, it will stop working after take off anyway. The towers don't send signal upward. You might still collect some residual signal for a little bit if you are near a tower and directly above it for a thousand feet or so, but not at 14,000 ft.
This couldn't be done with a 3g/4g/5g/LTE modem.