All About Software-Defined Radios


If you haven’t already heard about software-defined radio, these systems are making a major impact in today’s technology market and are helping to change the way satellites communicate and send messages around the globe.







Let’s start with the basics. Most people have used radios before and understand that different radios are designed to communicate on specific frequencies. Think about the radio in your car. You can tune between 500 kHz - 1700 kHz for AM stations or 88-108 MHz for FM stations in order to listen to the music, broadcast or talk show. 


These frequencies are actually split into channels, where messages can be sent or received using an agreed language. So, if you want to listen to channel 99.9 on your car radio, there is a channel that goes from 99.8-100.0 that is dedicated to that radio station. All radio stations agreed on a language to communicate at so that your radio can translate between the channel information to the sounds you hear. This language is what makes your car radio a “conventional radio”. SDRs are different, and while they still rely upon the right frequencies, they serve a different purpose.


SDRs are distinguished by doing a majority of the language translation in software. 


The components that build up the translator are generally specific to the language you are communicating at. So, if you want to be flexible your options are to either have a lot of different translation modules available in hardware or use software to do the job for you. Simply put, change the software, change the language. And with a powerful enough processor for your software, you can even code up the ability to talk at many channels at the same time.




Above all things, these SDRs are being used to provide flexibility in situations where flexibility previously wasn’t an option. From a regulations perspective, having an SDR makes us more flexible in order to meet spectrum requirements. We can change channels over different locations, vary power depending on direction we are pointing, and adjust our communications capacity so we can avoid interfering with other services.


Also, specifically for Kepler, this SDR allows us to use the same satellite hardware for talking to the gateway at 500 Mbps as it would for talking to 10 simultaneous IOT aggregators at 1 Mbps each. It allowed us to quickly setup hardware for launch and then constantly improve the satellite’s capabilities with software updates—something that would be impossible with hardware radio solutions. Essentially with this radio, Kepler is able to use the same hardware to support different types of customers, from customers that need 1 MB of data a month to those that require 1 GB of data a day.


When it comes to applying SDRs for nanosatellites, this is where Kepler is able to really focus on communication speeds. With the highest capacity throughput SDR available for nanosatellites, this radio comes with over 200 MHz of bandwidth, this means we can easily get 500 Mbps through this device.

The more bandwidth a radio has, the more data it can push. Here’s how to put its power in perspective:

Using our radio we can listen to all the radio stations you have available to your car simultaneously and still have 90% of its capacity empty.




When we were first looking for a radio for our satellite, we had our sights set on some pretty high data rates. More specifically, greater than 100 Mbps, yet we still wanted a product that could fit into a small space (<5cmx10xcmx10cm) and didn’t require a ridiculous amount of power, anything more than 40W means we needed a larger satellite.


The bar was set very high. Since we couldn’t find any radios that met the criteria, we actually made the radio ourselves. We have a custom solution truly designed with our needs in mind.







It took a great deal of research. We chose Ku-band as the most appropriate band to start with radio frequency communications. However, our SDR allows us to iterate on technology every 3 months. We also replace our satellites every three years—meaning we’re not fixed to one piece of technology.

Plus, if there is an advancement in communications, we can put it up in our network in as little as a year. This flexibility not only helped us fill our current needs, but the needs of the future as well.


To summarize, this technology is flexible and able to be used in a variety of places. This includes our intersatellite link as well as IoT aggregation from many devices at the same time. This also means the ability to use the same radio at the ground stations that is used to talk to our satellites. However, the key of this custom-built satellite-defined radio is that new software can be written and new changes can be made as-needed as we look to the future.

Mark Michael
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