Many GSM modems support external antennas to improve the signal strength. If the signal strength is too low you may experience frequent disconnections and performance degradation. Therefore, improving the signal strength can improve the overall modem performance for either Internet or SMS or both.
Does my modem support an external antenna?
Some examples of USB modems supporting external antennas: Huawei E392, Huawei E3276, ZTE MF821, Sierra USB598.
Make sure to check the modem datasheet to check if an external antenna is supported and whether it has a single antenna connector or 2 connectors (MIMO). In the latter case it is recommended to select a MIMO antenna for optimal performance.
Make note of the supported modem frequencies (bands) and the connector type.
Match the appropriate frequencies
First of all check the frequency or frequencies supported by the modem. For example, most industrial modems support just a few frequencies (typically only 2), while consumer USB devices may support a wide range of bands, similar to a mobile phone. Those frequencies must match the bands supported by the carrier. For example, in Latin America most carriers use 850 MHz and 1900 MHz for 2G and 3G. There is aregulation authority in each country providing the exact and up to date information regarding the allocated bands for each carrier.
Check the modem datasheet to make sure the available frequencies are supported. Then look for an antenna, which supports the same frequencies.
For example, a 450 MHz LTE antenna will be inappropriate for a 1700 MHz LTE modem.
The right connector type
There are 3 common connector types: SMA, CRC9 and TS9.
SMA is common in industrial modems. CRC9 is mainly used in Huawei modems. TS9 is mainly used in ZTE modems. However, you can't rely on the modem type and manufacturer to assume the connector type. Moreover, the CRC9 and TS9 look very similar. Therefore, checking the modem datasheet is recommended once again.
If the antenna connector is not the right one, it's possible to use an adaptor.
