What Does an RF Amplifier Do in an AM Receiver?

Amplifiers give us the technology we need to increase the magnitude of a signal, whether it’s the music from a guitar or the quality of your Bluetooth connection.

But what does an RF amplifier do, and how does it affect your AM radio experience?

Does an RF amplifier in AM radios change the sound quality of your channels, increase volume, or give you access to more channels from a broader range of frequencies?

To answer that question, we need to take a closer look at a few things, from how RF (radio frequency) works, to how amplifiers influence radio signals.

Today, we will take a closer look at the technology behind RF amplifiers and explain how they’re used in radio systems to boost your access to audio content.

What Is Radio Frequency? An Introduction to RF

Radio interface showing an FM station
Radio frequencies are measured in hertz, including kilohertz and gigahertz.

Let’s start by defining radio frequencies, one of the core components of any radio experience.

Radio frequency (RF) represents the oscillation rate of the electromagnetic radiation spectrum measured in units called hertz.

These hertz represent the number of cycles per second when radio waves are transmitted.

One hertz equals one cycle every second.

In the radio landscape, waves can range from thousands of hertz (kilohertz or kHz) to millions of hertz (MHz) and even billions of hertz (Ghz).

Typically, AM frequencies fall within the kHz range, while FM frequencies belong to the GHz landscape.

The wavelength is inversely proportional to the frequency of radio waves. These waves are invisible to the human eye and can come in many forms.

Many types of wireless devices beyond radios use RF fields. Your smartphone, television, Wi-Fi, and Bluetooth all use the same fields.

Even outside the communications space, microwave ovens, garage door openers, and other systems use radio frequencies.

What Is a Radio Frequency Amplifier?

So, now we know what radio frequencies are; what’s an RF amplifier?

An RF amplifier is an electronic device that converts a weaker signal into a radio signal with more power.

Usually, amplifiers are two-port electronic circuits.

They use electronic power from a power supply to boost the amplitude of any signal applied to the input terminal on the amp.

Once the signal is fed into the amplifier, the amp converts it into a much stronger, more significant signal, measured by an increase in gain.

Amplifier gain refers to the ratio of output voltage, current, or power output from an amplifier compared to the same input into the system.

Transistors form the core RF amplifier technology. These solid-state components work as a switch or relay for the movement of electricity.

When a transistor is activated using a low-power signal, it closes the two connections, creating two links that can handle more power than the low-power signal introduced.

The transistors within an RF amplifier can be switched off at the same frequency as a radio signal, resulting in the original signal being replicated at a higher power level.

It’s like flipping a switch multiple times. Transistors can switch at a much faster rate than humans, switching signals millions of times every second.

The Common Types of RF Amplifiers

AM radio numbers in blue on black with high frequencies
Radio amplifiers increase RF spectrum signal, from pulse to solid-state and CW amplifiers.

The term RF amplifier is much broader than most people realize. It’s not just a technology used to increase the signal of an AM channel you’re struggling to access.

An RF amplifier can enhance any signal in the RF spectrum.

There are also many types of RF amplifiers used for various purposes.

The most common forms of amplifiers include:

  • Pulse amplifiers: Pulse amplifiers are a type of RF amplifier used to increase RF pulses generated by electronic devices. They work to boost signal quality without altering the waveform of the RF signal itself. These systems strengthen signals to higher power levels, switching between intense power pulses and zero output at an accelerated rate.
  • Solid-state RF amplifiers: Solid-state amplifiers are particularly popular for enhancing accelerated cavities with RF power in the 100 KW range. They’re often used for testing applications that require less voltage to control and narrow bandwidth. You’ll find these amplifiers in radar, aerospace, medical technology, and communications tools.
  • CW amplifier: A CW amplifier, or continuous wave amplifier, is a form of RF power amplifier used in EMC testing. It amplifies signals while maintaining continuous waveforms. CW amplifiers are often essential for testing devices in the telecom, automotive, antenna, and aerospace environments.
  • Vacuum tube RF power amplifiers: Vacuum tube RF amplifiers have a lower output current and higher voltage power source than other amps. These are the most common amplifiers used for radio transmitters, thanks to their high working voltage. Vacuum tube amplifiers usually boost signal ranges between 20 Hz and 20 kHz.
  • TWT amplifiers: Otherwise known as a traveling wave tube amplifier, the TWT amplifier is a high-power, high-frequency system using traveling wave tubes. It’s another type of vacuum tube used to boost high-frequency signals.

What Does RF Amplifier Do in an AM Receiver?

RF amplifiers can have many use cases.

They use an RF amplifier whenever people need to magnify a radio frequency signal into a signal with a higher degree of power.

Commercial and defense avionics teams, space explorers, and naval groups use this technology.

Notably, RF amplifiers don’t just help to enhance radio signals for AM receivers. They can also increase wireless communications, TV transmissions, and radar signals. There are even amplifiers available that can increase the power of your broadband signal.

These amplifiers are used in AM receivers to enhance a radio message before an antenna transmits it.

Alternatively, an RF amplifier can increase the power of a weaker reception on an AM system. Most amplifiers can be tuned to a specific frequency range, allowing AM receivers to boost specific signals efficiently.

The Power of RF Amplifiers

Ultimately, RF amplifiers are an essential part of the radio experience and crucial in many other walks of life too.

Amplifiers take the relatively weak signal of a radio frequency and turn them up to the next level. This is crucial because most radio waves are diluted when reaching your car or home.

With an RF amplifier, your AM receiver can process a strong signal for conversion into sound.

Your radio receiver combines your antenna, amplifier, tuner, and speaker into a comprehensive system for collecting and processing radio waves.

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