No matter where you are, you’re almost certain to be near an antenna. You might not know when you’re looking at one—but there are antennas in your phone, laptop, car, etc.

The proliferation of antennas makes sense. After all, over 95% of all data ever created has been generated after 2018. This data informs almost every aspect of modern life: how we relate to ourselves, others, and our world. When you have that much information, you have to have some way of getting it where it needs to go.

The need for antennas is even more obvious when it comes to environmental data. After all, the most important environmental data often comes from the sky, the ground, or a body of water—natural areas where your trusty cellphone signal isn’t readily available. For this reason, it’s useful for anyone concerned with the environment to learn a bit about how antennas work. With a good sensor and the right antenna, you can generate the data you need to understand—and improve—almost any environment!

Signal and Noise

First, it’s important to know what antennas actually do. According to Electronic Design, the simplest explanation is that “[antennas] are transducers that convert the voltage from a transmitter into a radio wave.” This is a rather technical way of saying “antennas take a certain piece of information, and convert it into a signal that can travel through obstacles and across distances.” Let’s look at an example.

Consider a 4-20ma soil moisture sensor, like the one below:

This sensor works by measuring the electrical permittivity of the soil, which is directly dependent on the moisture content of the soil. For instance, when the soil is very moist, a charge sent from one prong of the soil moisture sensor will fully pass through to the other. This is the “piece of information” mentioned in the above description of an antenna. When a reading—say 50% moisture content—is generated, the charge travels up to the attached antenna, where it’s then converted into a radio signal and sent to a receiver.

All About Waves

But what exactly is a radio signal? According to Ham Radio for Dummies, “radio waves are just another form of light that travels at the same speed; 186,000 miles per second”. You can see exactly where radio waves fall on the electromagnetic spectrum through this cool diagram:

You’ll notice that radio waves have the longest wavelengths on the electromagnetic spectrum. This makes them extremely useful for transmitting information.

In general, the shorter the wavelength, the more dangerous to living tissue; radio waves can pass through us and leave us largely unscathed. Radio waves can also travel over vast distances and through numerous obstacles in large part due to their long wavelength; shorter wavelengths encounter more interference. However, that doesn’t mean all antennas send exactly the same radio waves.

First, different antennas send signals in different radiation patterns. These patterns indicate the areas of signal strength and weakness, which is useful when it comes to designing an antenna setup.

While there are a great number of different patterns, which you can read more about here, the most important distinction is between omnidirectional and directional antennas. For instance, WiFi routers typically send out an omnidirectional signal—you wouldn’t want your signal to be very strong in your kitchen and quite weak in your living room! However, omnidirectionality has a drawback: the average signal strength is generally weaker. For an application where an environmental sensor is always sending data to a receiver in a specific location, you might want a highly directional antenna:

Antennas also differ in terms of the exact frequency they use. Certain frequencies are reserved for certain applications; for instance, maritime navigation is commonly done within the 156 and 174 MHz range.

It’s also important to note that different countries have different laws regarding frequencies. After all, you want to ensure that you’re not operating in an unintended range—this can result in picking up signals from other devices, which can make it harder to get high quality data. Many times, websites will have brief explainers detailing the correct frequency for your application and location. You can check out an example of one of these explainers by scrolling down here.

Form Follows Function

Although all antennas send information through radio waves, the variability in the frequency and radiation pattern of antennas mean that many different antenna form factors exist. These form factors are important to consider because not every form factor will be ideal for a certain project—and there are usually a variety of form factors available, even for specific radiation patterns and frequencies.

The simplest antenna is a small dipole antenna, which is essentially a short wire. This type of antenna is often used for environmental applications, because it’s inexpensive, effective at sending basic information (such as a soil moisture percentage), and because it is flexible. This last point is important—oftentimes, environmental applications will need some form of enclosure to keep the electronics of the sensor separated from the elements, and flexibility allows for an antenna to fit into this enclosure.

If you’re interested in a more thorough breakdown of the different types of antennas, this page is an excellent resource. For a cursory overview, the following image serves as a good guide:

When looking at product specifications for antennas, you’ll notice that they almost always contain information about their range. This makes sense, as you’ll want to be sure that the signal can reach its destination. But it’s also important to note that these ranges tend to be generous estimates. In the real world, the range might be at most the range described, but is more likely some lesser distance. 

Many different things impact range in practice. First, the angle of the setup. Particularly for directional antennas, having the antenna pointing towards the receiver is important—you wouldn’t try and throw a football if you were facing the opposite direction from the receiver! Relatedly, antennas which are mounted higher up have better range, because they in effect have a better line-of-sight to the receiver, as discussed here.

Second—and as obvious as it may seem—the actual distance you’re attempting to transmit a signal over has an impact on functionality. Even if an antenna claims to be able to transmit over 2 miles, you can expect the extreme of that range to have worse signal than if you were only transmitting over 100 feet. Both of these factors, set-up and range, are impactful because they influence the number of obstacles that a signal encounters.

Obstacles are important. To a greater or lesser extent, everything a radio signal has to pass through decreases its range. This paper provides a great introduction to this effect (though it talks about infrared waves), and displays how different materials affect signal. As you can see, wood is particularly problematic for signal strength, compounding the challenges of environmental monitoring, which often occurs over wooded areas:

Putting It All Together

While the above might sound like a lot, don’t worry! Most antenna companies have dedicated support staff who can help you figure out what setup to use. And for most problems, there are solutions. For instance, if a range is too far for you to transmit a signal, you may be able to put an additional antenna in between the initial antenna and your receiver, creating what’s called a mesh network. This is akin to the WiFi booster you might use in your house.

Hopefully, you now feel more familiar with some of the basic aspects of antennas. It’s a good thing to be familiar with, especially in the environmental sensor data space—and considering there’s a real environmental data vacuum, knowing the different elements of environmental monitoring is increasingly important. If you feel like further expanding your antenna knowledge, please feel free to check out this excellent Youtube video, or just Google around! 

And of course, we’d love to help you with your environmental monitoring project—please feel free to reach out to us here. Another great way to get involved in the environmental space is to sign up for our Daily Breather email, which gives you regular updates on the air quality where you live.