Understanding the RF Signal and the Carrier Signal

When it comes to wireless electronics, a radio frequency (RF) transmission is a wireless electromagnetic signal used as a means of communication. Radio waves are a type of electromagnetic radiation with radio frequencies ranging from 3 to 300 GHz. The rate of oscillation (of radio waves) is referred to as frequency bands. RF propagation occurs at the speed of light and does not require the use of a medium such as air to travel. RF waves are produced naturally by sun flares, lightning, and stars in space that emit RF waves as they age. Humans communicate via radio waves that have been artificially produced and oscillate at various frequencies.

An RF signal is an electromagnetic wave that communications systems employ to send data from one location to another over the air. For many years, RF signals have been used. They allow music to be broadcast on FM radios and video to be broadcast on televisions. RF waves are, in fact, the most frequent mode of data transmission across a wireless network.


RF technology

RF fields are used in a variety of wireless devices. The RF spectrum is used by cordless and smartphones, radio and television broadcast stations, Wi-Fi and Bluetooth, satellite communications systems, and two-way radios. In addition, microwave ovens and garage door openers, which are not related to communications, use radio frequencies. IR frequencies, which have shorter electromagnetic wavelengths, are used by some wireless devices such as radio and TV stations, remote controls, wireless networks, radio signal, computer keyboards, and computer mice.


RF Signal Pros and Cons

RF Signal Pros

RF Signal Cons

When line-of-sight is possible, the range can be up to 20 miles.

Lower throughput (up to Mbps)

Except for severe rain, which causes poor performance, good operation in a haze, and foggy circumstances.

There is a high risk of RF interference from other RF-based technologies.

Unrestricted operation (only for 802.11-based systems)

Due to radio dispersion beyond the facilities, security is limited.

RF congestion and interference

Radio frequencies in the United States are separated into licensed and unlicensed bands. The Federal Communications Commission (FCC) grants commercial enterprises exclusive use of a frequency band in a specific place by issuing licenses. FM radio, cellular networks, television, military, and satellite communications are examples of entities. Unlicensed frequencies are open to the public but must be shared.

In recent years, internet users’ competition for bandwidth and channels has expanded substantially, resulting in signal difficulties. Furthermore, the distribution of frequencies is unequal. Many regions have broadcasters — radio and television stations — with their own individual frequencies, whereas unlicensed frequencies are crowded with a variety of sources.


Carrier Signal

An electrical oscillator in the transmitter produces a sinusoidal alternating current of radio frequency. Most radio systems in the twentieth century used frequency modulation (FM) or amplitude modulation to add information to the carrier wave (AM).         

The frequency of the initial carrier signal must be retained while adding data to the RF transmission. As a result, there must be a method of modifying some aspects of the carrier signal to discriminate between a 0 and a 1 bit. Whatever technique the transmitter employs must also be employed by the receiver in order for the data bits to be correctly read.

Below shows a carrier signal that has a constant frequency. The data bits 1001 are to be sent over the carrier signal, to toggle the carrier signal on or off, simply utilize the value of each data bit. The ensuing RF is depicted in a Bad Idea 1 plot signal. When a signal is present and has an amplitude, a receiver may be able to detect it. As a result, 1 bit is appropriately interpreted, but there is no signal to receive during 0 bits. If the signal is received, becomes weak, or is unavailable for any reason, the receiver will falsely believe that a long string of 0 bits has been sent.

An alternative approach could be to send only the as demonstrated in the Bad Idea 2 graphic, the upper half of the carrier signal during a 1 bit and the lower half during a 0 bit. This time, the receiver always receives a component of the signal, but the signal becomes hard to receive since key pieces of each cycle are missing. Furthermore, transmitting an RF signal with fragmented alternate cycles is extremely challenging.

Poor Attempts at Sending Data Over an RF Signal


We can modulate a signal to deliver it over a band pass frequency range. We can send numerous signals across a single channel at once if each signal has its own frequency range. They all use different frequency ranges. Another reason to modulate a signal is so that a smaller antenna can be used.

The following are the general goals of RF modulation schemes:

  • Carry data at a set rate.
  • Be somewhat impervious to interference and noise.
  • Be able to transmit and receive data in a practical manner.

A modulation technique can only change the frequency of an RF signal due to its physical characteristics. The qualities are listed below:

  • Phase
  • Amplitude
  • Frequency, but just slightly above or below the carrier frequency.



 Demodulation is the process of recovering the original information or signal from a modified carrier. In the case of amplitude or frequency modulation, a device known as a demodulator or detector generates a signal that corresponds to the instantaneous changes in amplitude or frequency, respectively.


Spread Spectrum

The term “spread spectrum” refers to a type of wireless communication in which the frequency of the transmitted signal is purposefully altered. This gives the signal a far larger bandwidth than it would have if the frequency was not altered.

SPREAD SPECTRUM common categories

  • Used in the 2.4 GHz band, where a limited number of fixed, wide channels allow for complicated phase modulation methods and Data rates that are somewhat scalable.
  • DSSS is a transmission system used in local area wireless network transmissions that combines a data signal at the transmitting station with a high data rate bit sequence that separates user data based on a spreading ratio.
  • Used in both the 2.4 and 5 GHz bands, where data is delivered in parallel across a single 20 MHz channel over a range of frequencies. To move the most data efficiently, each channel is divided into multiple subcarriers (also known as subchannels or tones); both phase and amplitude are modified via quadrature amplitude modulation (QAM).
  • OFDM is a data transmission technology in which a single information stream is distributed across multiple clustered narrowband sub-channel frequencies rather than a single wideband channel frequency.

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