There are two main types of narrowband modems available in the IOT space and these are CAT-M1 and NB-IoT and there has been considerable industry debate as to which is the best system.
The normal 4G / LTE modems which are in standard cell phones have a very large bandwidth, perhaps 25 Mhz for web surfing and streaming. The CAT-M1 bandwidth is a much smaller 1.4 Mhz bandwidth and the NB-Iot is even smaller at 0.2 Mhz bandwidth.
For Neon Telemetry / IOT applications we usually do not need high bandwidth. These modems suit us very well. There is also the promise that with the lower bandwidth standards, power consumption will be less, and that is very important for our applications as IOT sensors and telemetry may be able to survive on a single lithium battery for perhaps 10 years.
Unidata are providing modems with CAT-M1 as these are the first to become available. Our modems also cover 2G, 3G and 4G so we are covering all the bases, no need to worry if a 2G or 3G network will be shut down in the future.
We also expect to also offer the NB-IoT modems when they become available. The table below shows some of the key differences.
As the electronics becomes smaller, so do the connectors.
Unidata uses the following connector types for cell phone and satellite modem connections:
SMA (SubMiniature version A) connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw-type coupling mechanism. The connector has a 50 Ω impedance.
SMB (SubMiniature version B) connectors are coaxial RF connectors developed in the 1960s. SMB connectors are smaller than SMA connectors. They feature a snap-on coupling and are available in either 50 Ω or 75 Ω impedance. They offer excellent electrical performance from DC to 4 GHz.
MCX (micro coaxial connector) are coaxial RF connectors developed in the 1980s. They have the same inner contact and insulator dimensions as the SMB connector but are 30% smaller. MCX is standardized in European CECC 22220.
With this miniaturisation also comes risk, as the smaller connectors are less robust that the much larger TNC or N Type connectors.
As these cables carry high frequency radio signals care needs to be taken to allow gentle curves in the routing, not right angles, as right angles cause reflections which degrade the signal. The measurement of how much reflection occurs is called Voltage Standing Wave Ratio, or VSWR for short.