RF design is hard. From designing, prototyping, and testing, to approval, every step of the process is mind-numbingly complex and mistakes are easy to make. For that reason, it’s almost always smarter to use ready-made wireless RF modules instead of building from scratch.

Deciding on which module to use depends on the application. For mass-market IoT devices where compatibility with existing protocols and ecosystems is important, using a standardised protocol such as LoRa or Sigfox often makes the most sense. For devices with more customised requirements, using a generic radio module as a transparent wire replacement can be more suitable.

RF Difficulties

Good radio design is notorious for being complex and difficult to pull off. Radio circuits are difficult to design and subject to EMI problems – which are often difficult to debug. Even once a design has been prototyped and tested successfully, the design process is still not quite finished. RF circuits are very noise-sensitive. Manufacturing at scale can introduce new issues, which have to be debugged, requiring further design iterations. Finally, RF approvals are difficult and expensive to get, and must be applied for each region in which the device is expected to be sold.

For these reasons and more, most wireless devices on the market use ready-made RF modules, rather than custom RF designs. Even for applications with extremely customised requirements, configuring a pre-made, generic RF module can save large amounts of time and money compared to building from scratch.

Standardised IoT-ready RF modules

For applications where use of an existing IoT standard is desirable, RF modules exist which are compatible with major LPWAN protocols. These modules allow for transparent, simple usage of an IoT standard, without designers having to understand the implementation details of each protocol stack.

LoRa and Sigfox are two of the major IoT protocols in the LPWAN space. Both of these low-power, wide-area networks have extremely low power consumption and long range characteristics. Rather than focusing on high bandwidth, they focus on energy-efficient transmission of sensor data over long distances.

The choice of LoRa or Sigfox can be determined by network deployment and cost concerns. LoRa depends on a centralised gateway architecture, and has no subscription costs. This makes it ideal for clustered network deployments. Sigfox has the benefit of not requiring customers to deploy a gateway. Instead, Sigfox devices use a cellular-type network architecture where each device connects with a Sigfox base station in the area. This greatly simplifies deployment; however it comes at a cost for end users, as Sigfox devices attract a small subscription fee to enable them to be used on the network. Just like cellular devices, Sigfox devices only work in areas with network coverage.

Using a standardised, pre-developed IoT protocol will make sense for many devices which are trying to reach a mass audience. LoRa- and Sigfox-compatible devices have the benefit of compatibility with an existing ecosystem of IoT hardware and cloud applications. In addition, pre-certified LoRa and Sigfox modules make these two protocols easy to implement without having to go through lengthy design, testing, and approval processes.

Custom Sub-GHz RF Solutions

Figure 1: This eRA easy radio module from LPRS is highly configurable, making it easy to create custom sub-GHz wireless networks.

Besides standardised IoT solutions, there’s also the custom wireless route. For small-scale deployments, situations where a proprietary protocol is desirable, or to meet certain RF requirements, a configurable sub-GHz radio module provides the flexibility needed.

Custom doesn’t need to mean complex. RF modules from LPRS, for instance, come with easyRadio software that provides a GUI for module configuration, and a simple ASCII-based API to configure and interact with the radio module. With simple UART-mode communication, these modules are easy to use and can act as a transparent wire-replacement between two devices, or can even be configured in multipoint mode to form simple wireless networks.

Operating at sub-GHz frequencies, in license-free ISM bands, means these modules can stay away from the noise of the busy 2.4GHz spectrum. They provide strong penetration even in indoor environments and provide long-range transmissions – much better than Bluetooth or WiFi – while consuming little power. This makes them ideal for many sensor and IoT-type devices.

Their customisability also allows frequency, bandwidth, power output, and data rate to be configured as needed to avoid interference, or to optimise performance.

EasyRadio Modules

Ready-to-use easyRadio sub-GHz RF modules are available from Alpha Micro in eRA and eRIC form factors. eRA modules feature a robust through-hole design great for prototyping and testing. They are integrated radio modules combining a high-performance, low-power RF transceiver, microcontroller, and voltage regulator.

As an SoC design, the presence of a microcontroller allows these to either be used as standalone radio modules, or even to host simple sensor-type applications, in which case a separate application processor is not needed. This saves energy, lowers costs, and speeds up development cycles. 

Figure 2: eRIC modules provide RF simplicity in a compact, SMD package.

eRIC is an SMD version of the easyRadio modules. These compact, affordable radio modules are just as easy to use as the eRA modules, but come in a smaller surface-mount design suitable for high-volume applications.