Navigating the Radio Spectrum: Frequencies, Uses, and Behaviors

The radio spectrum is a large and varied place.  Technically, it even includes visible light.  So what do all those frequencies get used for, and what determines which ones are used for each application?  The details are pretty complex, but the main principle is simple:  Radio waves act differently at different frequencies, and so frequencies are selected to take advantage of those different behaviors. In other words, different strokes for different folks.

There are several attributes that affect the choice of frequencies for a particular application.  For example, higher frequencies tend to have less range than lower frequencies.  When Ham Radio operators want to talk to friends in a distant country, they use frequencies that are much lower than those used for cellular phones, which only need to connect with a nearby cellular tower.  On the other hand, higher frequencies, such as those used for cellphones, tend to penetrate buildings better than lower frequencies, an advantage for portable cellular users inside homes and offices.

Tailoring Frequencies for Specific Applications

Another consideration is bandwidth, or the amount of spectrum needed to send the information.  While simple voice calls don’t need a large amount of bandwidth, streaming video and large data downloads, from gaming for example, require lots of spectrum to carry the load.  The higher you go in frequency, the more bandwidth is available.  For example: one percent of a megahertz is 10 kilohertz, which will barely support one voice channel, but one percent of a gigahertz is 10 MHz, which would support several streams of video!

Antenna size is also a consideration.  The lower the frequency, the larger the antenna.  Cellular handsets don’t generally use frequencies below 650 MHz, and a big reason for this is the size of the antenna.  Even at 650 MHz, the antenna can be a challenge for smaller handsets.  At lower frequencies, the problem becomes even more severe.  Years ago, we had a client who wanted us to design a wireless modem for laptop computers that would operate in spectrum near 40 MHz.   We explained that while we could design the wireless modem, then antenna would have to be several feet long.  That requirement immediately made the project a no-go.

There is one other consideration in the selection of frequencies that is frequently overlooked, but is very, very important:  History.  A lot of frequencies are used for specific applications because they have been used that way for decades.  AM and FM radios, as well as television channels, all use the frequencies they use because those frequencies were selected long ago, mainly based on the technology available at the time.  Even though there may be better frequencies for those applications now, they stay “stuck” where they are because changing them would be too disruptive to existing users.

Consult the Experts: Radio Design Group Can Help!

What does all this mean for companies looking to design new radio and wireless products?  First, when considering a new design, it’s important to look at what frequencies can be used for the application, and how practical will they be for that application.  The example of the several foot long antenna shows how important this is.  In addition, the availability of components is also a consideration.  Parts used in applications with a large consumer base, such as automotive radios, cellphones and television sets, are likely to be more available, and have a lower price point, than parts that are more specialized, so picking frequencies that are close, or at least compatible with those parts is an advantage.  Finally, it’s important to look at how crowded the spectrum is when making strategic decisions.  Your product will be a complete failure if it can never get a channel to work with.

So, while selecting which chunk of radio spectrum to use looks simple, it is much more complex than it seems, and it’s a good idea to let the experts help guide your decision. Fortunately, this is where our expertise lies! Radio Design Group can help you determine the best path forward with your RF project. Contact us today for your no-cost, no-obligation consultation.