We just had an experience with antennae that might interest others. We have a dozen sensor stations in the field measuring water level of lakes in north western Michigan. Each station has an SDI-12 water level sensor connected to a Mayfly with a Digi XBee3 Cellular LTE-M/NB-IoT modem using a $3.00 antenna from Adafruit (https://www.adafruit.com/product/antenna) in a fiberglass enclosure. The system wakes up every 15 minutes to record water levels. At the top of each hour it connects to the tower and sends the collected measurements to our website; Lake-Man.com.
The last station that we installed was in a remote area with very poor LTE coverage. Our modem took minutes to connect and sometimes failed for several hours. Mobile phones have trouble connecting there. Moving the antenna around, shifting the battery position and trying different modems and options had little effect. After reading various posts on EnviroDIY, we decided to try other antennae mentioned there.
For us, the Maximus antenna and other internal-to-enclosure antennae performed similarly – that is to say poorly at this site. As a last resort, we installed a $16 external antenna from Amazon https://www.amazon.com/antenna using an SMB to UFL adapter cable.
The result was a major success – the modem connects within 10 seconds and hasn’t missed a transmission since we installed it. The 10 foot cable did not overly attenuate the signal in our experience.