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Dry goods science popularization | Application of crystal oscillator in AM FM radio.

2024-10-25

Everyone must be familiar with AM radio!

Now that technology is so advanced, why hasn't radio been phased out?

What does such an important radio have to do with crystal oscillators?

In 2023, the US Congress passed a bill (AMRadio for Every Vehicle Act " (S.1669)) requiring new production vehicles to be equipped with AM radios to ensure reliable communication channels in emergency situations. This requirement was introduced primarily for public safety reasons, because AM radio plays an important role in emergency situations, especially in natural disasters, emergencies, etc. AM broadcast signals can cover a wide area and provide critical information.

On September 18, 2024, China's Ministry of Industry and Information Technology issued an exposure draft requiring all vehicles to be equipped with wireless radios, including AM radios. The move is designed to ensure that drivers can receive real-time emergency alerts during natural disasters such as earthquakes and landslides, especially if the internet or other means of communication may fail. The regulation is seen as an important safety measure, especially in areas with weak digital infrastructure.

2024

background reasons

Public safety and emergency communication:
AM radio has much greater coverage than FM radio or digital signals, especially in rural, remote areas or during natural disasters such as hurricanes and earthquakes. AM radio can continue to provide reliable emergency information in the event of network and power outages. Therefore, the US government and emergency management departments believe that maintaining vehicle AM radios is essential for emergency information transmission

Infrastructure stability:
AM broadcasting towers have lower construction and maintenance costs and greater signal coverage, especially in long-distance communication. AM broadcasting can be used as a basic and long-lasting means of communication when the network is unstable or malfunctioning.

The impact of technological change:
In recent years, due to the rise of electric vehicles and autonomous vehicles, many new cars have cancelled AM radios because the electromagnetic interference of electric vehicles affects the reception of AM signals. However, many public safety experts and lawmakers believe that despite technological advancements, there is still a need to ensure the retention of critical emergency communication means.

The frequency of the crystal used by a radio depends on its type (AM or FM) and its internal circuit design. Different types of radios use different crystal oscillators to generate local oscillation frequencies, which are mixed to generate a fixed intermediate frequency signal.

The following are the common crystal frequencies found in radios:

AM radio

Intermediate frequency crystal frequency:
Typically 455 kHz or 450 kHz. This is the most commonly used IF frequency in superheterodyne receiving circuits in AM radios. The local oscillator signal generated by the crystal is mixed with the received AM signal to produce a fixed intermediate frequency signal for demodulation.

FM radio

1、Intermediate frequency crystal frequency:
The intermediate frequency commonly used in FM radio is 10.7 MHz. This means that when the local oscillator signal of an FM radio is mixed with the received FM signal, an intermediate frequency signal of 10.7 MHz is produced.

2、High frequency crystal frequency:
In FM radio, the local oscillator frequency is usually 10.7 MHz higher than the received station frequency. For example, when receiving a 98 MHz FM station, the local oscillator may be tuned to 108.7 MHz.

Other crystal oscillator usage

Some modern digitally tuned radios may use crystals of common frequencies such as 32.768 kHz or 12 MHz to provide a clock source for internal digital processing circuits or microcontrollers.
This type of crystal is used for clock signal generation and digital tuning frequency control, but not directly for signal mixing.

summary

AM radios commonly use 455 kHz as an intermediate frequency crystal.