In the world of radiofrequency (RF), a field meter is a device that measures power (in watts) across a frequency range. This range is also called a “spectrum.” Every device that transmits signals, like radios or mobile phones, uses a certain part of the spectrum. Field meters help us measure how strong these signals are in a given area.
Some spectrum analysers have audio and video decoding capabilities:
When we look at a field meter reading, we can see two important parts:
”You have to tell the signal from the noise”
Here is a measurement. You can see the signal (“the mountain”) and all around it is noise. The noise, actually “thermal noise” it is generated by the movement of the atoms in the air.
The spectrum analysis has a weakness: it only shows the present. The waterfall is a special part of the graph located at the bottom. It shows the history of the signal over time, allowing us to see what has happened in the recent seconds.
You all have used oscilloscopes for monitoring time domain signals, but not all of you know about spectrum analysers (frequency analyzers). First of all, you have to know that every complex signal is made of pure tones (sinus signals) just like a lego house is made of bricks. This is called Fourier Theorem.
You can see the translation in the following video:
Complex signal (time) → pure tones (time) → pure tones (frequency)
In Spain, Ministerio de Industria y Turismo plans the mobile network. It has a map for showing all the mobile sites nationwide: Infoantenas. This one is easier to use: AntenasMoviles.
When the installation company finishes the site, a commissioning project is made, which must include 5 measurements of the electric field within a 100-meter radius of the cell tower, among other various measurements and parameters. If there is a sensitive area (playground, school, medical center, etc.) within that 100-meter radius, the company must indicate it and make an RF field measurement at the sensitive point (a measurement must be taken at each sensitive point, even if there are more than 5).
What if we created a heatmap?
And now, with the aid of UAV (unmanned aerial vehicles, “drones”), what if we created a full 3D heatmap?
This is what we try to achieve, along with a full portable mobile site:
The quadcopter will make the measurements.
Launch the Fourier Series Applet and try these signals:
Observe the time and frequency (magnitude) graphs and explain them in a short essay (<100 words). Send it by e-mail.
Underline the stressed syllable: