Radio Frequency Explained

What is Radio Frequency?

First we need to define what is Electro Magnetic Radiation (EMR): radiation that has both electrical and magnetic properties.

Anytime an electron move, specially in a copper cable,that sends a current in the copper cable. If the electron move inside the copper cable between two batteries, the EMR direction will be at 90 degrees of that.

Note: in 3 dimension, if we see the copper cable in front of us (poking us in the eye), EMR would go in all direction at 90 degrees.

EMR radiation has both electrical and magnetic properties, and requires no medium in order to propagate (even through the vacuum of space, which is why radio telescope was often used to detect non-natural, extraterrestrial EMR).

EMR has a detectable waveform: it oscillates. The cycling of this waveform is measured in Hertz.

In conclusion: radio frequency is the measurement of the oscillation of EMR.

ISM Bands

EMR frequency bands have been given labels. Those assigned by U.S. Federal Communications Commission are called ISM Bands: unlicensed Industrial, Scientific and Medical use.

On a scale from 0 Hz to 3000 EHz (ExaHertz), we can find:

  • Extremely Low (ELF) (Audio)
  • Very Low (Audio)
  • Low
  • Medium (AM Broadcast)
  • High (Shortwave Radio)
  • Very High (Broadcast TV)
  • Ultra High, unlicensed ISM bands are between:
    • 902 - 928 MHz
    • 2.4 - 2.5 GHz
  • Super High, Unlicensed National Information Infrastructure (U-NII) ISM bands are:
    • 5.15 - 5.35 GHz
    • 5.47 - 5.875 GHz
  • Infrared
  • Visible Light
  • Ultra-Violet
  • X-Rays
  • Gamma Rays

As a rule of thumbs, the faster the frequency (faster the oscillation), the more data you can encode. This is why newer Wi-Fi standards are being added on the Super High U-NII/ISM frequency range.

There is a downside though: radio frequency as a tendency to attenuate (encoded data become unrecognizable; like someone speaking closer to you is more audible than someone speaking far away from you). For Wi-Fi, it means that a device need to be closer to the emitter in order to receive information without troubles.

Another downside is as anyone can use ISM bands, they tend to be crowded. This is the case for 2.4 GHz: microwaves would often interfere with Wi-Fi because they would induce noise in this same frequency.

Modulation

Radio Frequency (i.e. EMR) has different properties that can be artificially changed over time to encode data. This process is called modulation.

The following properties can be modulated:

  • Frequency Modulation (FM): the greater the frequency, the more data can be encoded into a Wi-Fi signal
  • Wavelength: the distance between two “positives” or two “negatives”, inversely proportional to frequency
  • Amplitude Modulation: the overall strength (or power) of a signal. Note: RF amplitude weakens greatly over distance and as it passes through objects (this is called attenuation)
  • Phase: a comparison of the waveform between two RF signals. Two identical waveform at comparison time are considered 100% in phase. This phase can be intentionally modified to encode data

For newer Wi-Fi versions, all of the modulation above are used in some form to encode even more data.

Links to this page