FM Modulators

Introduction

This article elaborates on the various FM Modulators used nowadays to modulate a signal. It will tell you the working of frequency modulation and applications of FM. Frequency modulation is one type of wireless data transmission. 

What is frequency demodulation? 

FM demodulation is sometimes known as FM detection and by several other names. This circuit was used with older technology. This is an important step in receiving a frequency modulated signal. Frequency demodulation is important to recover the carrier signal after the signal has been received, filtered, and amplified. 

FM demodulator circuits are found in FM receivers, which include broadcast receivers and two-way radios which can be found in devices like radios, or any receiver that uses frequency modulation. This frequency will vary according to the value of the baseband signal. 

Prerequisites of frequency modulation 

There are a few things that are required for modulation. 

Firstly, transmitters in the system should meet the following modulation requirements: 

• If the sideband emission is doubled, you should maintain the peak modulation between 75 and 100 percent. 
• But when the system uses the phase modulation in the 156 – 162 MHz bands, you should maintain the band up to 75 and 100 percent. 
• If there is a single sideband, your upper sideband must be used for transmission. These sidebands should limit the peak envelope power to their permitted operating system. 

Secondly, a modulation limiter is required on radiotelephone transmitters using A3E, F3E, and G3E emissions to prevent any modulation above 100%. Survival craft transmitters, transmitters that do not require a licence, and transmitters with an output power of fewer than 3 watts are exempt from this requirement.

Thirdly, an audio low-pass filter is required on transmitters operating in the 72.0-73.0 MHz and 75.4-76.0 MHz bands. The filter must be inserted between the modulation limiter and the modulated radio frequency stage. It must have attenuation at more than 1 kHz by at least 40log10 (f/3) dB at frequencies between 3 and 15 kHz, where “f” is the frequency in kilohertz. Attenuation at frequencies over 15 kHz should be at a limited 28 dB more substantial than at 1 kHz. 

What is the application of frequency modulation? 

You can use frequency modulation if the frequency of the radio wave is slightly poor or low or less vulnerable to the noise as compared to the amplitude. Frequency modulation was created to be used for this purpose. It was meant to reduce the noise, thus improving the quality of radio receptions. 

Low noise FM reception is used in many communication technologies, such as high fidelity audio broadcasts. These broadcasts heavily rely on noise resistance. It also implies that changes in signal and fading issues due to mobility are lessened for mobile radio or portable radio communications due to the use of demodulators. 

How can you define frequency modulation via a mathematical equation? 

You can distinguish frequency modulation as the proportion of frequency deviation of the carrier divided by the frequency of the modulating signals. 

Mf = modulation index of FM = ∆f / fm 

What are some categories of FM Modulators?

According to FM Modulators notes, there are many kinds of FM detectors and demodulators available today. Among these types, some were used when radios were made from discrete devices. PLL based detectors and quadrature,  sometimes called coincidence detectors,  replaced these systems and are used currently. They have been replaced because they are easy to interlink into integrated circuits and need very few requirements. This IF stage may process in a way that the IF amplifier is driven into limiting and can improve the FM receiver’s noise interference problems. The process helps to reduce or eliminate variations in amplitude that may result in noise and allows the frequency to pass. 

You can find the frequency demodulators in broadcast receivers, portable radios, two-way radios and other applications:

Slope detection

A general way of using FM demodulation is slope detection. Slope detection uses the selectivity of receivers to provide demodulation. It isn’t very useful in the long run. This type of FM demodulator has many disadvantages. If the radio’s selectivity curve is not linear, there can be distortion. It means the receiver is more reactive to changes in amplitude among other things. 

Ratio detector

In this detector, the demodulation requires a ratio detector that uses a transformer with a third winding which will generate a phase-shifted extra signal. 

Foster Seeley FM

Foster Seeley FM was the main competitor against FM demodulators in radios, back when they started using discrete components. In many ways, the Foster Seeley FM demodulator and the ratio detector are extremely similar. But this type did not use any winding on the transformer, instead, they used a separate choke. 

Demodulator with phase-locked loop

A phase-locked loop can be used to demodulate FM. This FM detector has outstanding performance and requires few changes and modifications in manufacturing. The PLL FM demodulator also has the advantage as it can easily integrate within a circuit. This demodulator allows you to add an entire receiver chip. 

Conclusion 

In this article, we learnt about frequency modulation or FM. Frequency modulation is used in several applications such as communications and broadcasting stations. Frequency modulation is the process of encoding information in a carrier wave by modifying a carrier wave by changing the instantaneous frequency of waves.