Who’s organizing the air waves; sorting out the frequencies

This column has been exploring the concept of telemetry as a tool for agriculture and defined it as the wireless transmission of data.

Before discussing how to use telemetry in agriculture, here’s a simplified look to appreciate how it works.

Wireless transmission of data is carried on electrical signals of different frequencies. Electrical signals are actually waves or pulses; frequencies are the speed of a wavelength in the electrical signal.

Each frequency has different characteristics, such as how far it will carry, if it goes through objects, if it is absorbed by objects; or if it bounces off objects. These characteristics make certain frequencies useful for specific applications.

Using a nonagricultural example, AM radio stations use a specific range of electrical frequencies that provide long distance transmissions of their signals for music. This range of frequencies is what you see on your radio dial. Country 1600 is actually transmitting their signal on a 1600 khz wavelength.

FM radio stations use a shorter wavelength, which does not travel as far, but is more stable and has fewer interference problems. Most electrical devices use a specific wavelength to transmit data or signals.

You can download a larger version of the frequencies chart here, in PDF format.

It is also important to understand that if a person or company were to use whatever frequency they wanted, there would be a lot of interference. Many signals would likely be blocked or corrupted by interfering signals.

You may have heard of the FCC or Federal Communications Commission in the United States keeping track of radio DJ’s that use inappropriate language. Actually the FCC’s main task is segmenting telecommunication wavelengths frequencies. The commission has a chart that provides an order and standardization for companies and organizations that design, build, and use communication devices.

For example, FCC has reserved a large block of frequencies from 535 to 1705 kHz for AM radio. FM radio stations have a block of frequencies from 88 to 108 Mhz.

Segmented frequency blocks organizes how they are used and helps ensure that signals from one type of device don’t interfere with other devices. If a manufacturer builds a device that uses a signal in the AM or FM frequency zones, the use of that device would interfere with a radio station or visa versa.

Any new device that uses electrical transmission must be registered with the FCC. Look on any device for a FCC number; if it has one it is transmitting some type of signal. Registering with the FCC assures that the signal is compatible with the chart of frequencies and that the device will not interfere with other devices. The good news is that usually the manufacturer does a good job of assuring appropriate signals.

These examples cover all sorts of wireless communications from radios to cellphones. Walkie-talkies, CB radios, and ham radio operators all use available wireless frequencies to transmit communications.

Telemetry is a little different. The way telemetry is defined is the transfer of data, not just voice for communication. In agriculture, there is a lot of data being transmitted through wireless means. But as usage increases, FCC’s chart of available frequencies keeps getting more crowded.

As an example of crowding, we can use GPS NAVSTAR satellites, which transmit navigation data. For awhile there was a conflict between GPS signals and an organization called LightSquared. FCC had sold (yes, segments of frequencies can be sold, though there are not many blocks left and are not affordable for the average person) a segment of frequencies right next to the GPS frequencies.

LightSquared was going to use the frequencies to provide worldwide internet service from a space-based satellite. A good idea, except that after testing, it was found that Lightsquared signals were interfering with GPS accuracy (or actually vice versa). Even though the signals were next to each other, some “bleeding” of signals between the two segments caused interference.

This is where I stop explaining and just say that the distinction between segments is “fuzzy”. The end result is court cases that are still trying to figure it out.

Considering the amount of data that agriculture generates, telemetry can be valuable to growers.

Next week I will examine recent and future uses of telemetry to make precision happen.

Terry A. Brase is an educational consultant, former precision agriculture educator and author. BrASE LLC. Contact him at precision.happens@producer.com

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