A transmitter is an electronic device in electronics & telecommunications, with the help of an antenna it generates radio waves. The TX generates an RF alternating current, which is applied to the antenna. When the antenna is excited by this AC then it radiates radio waves.Transmitters are used in broadcasting as well as electronic devices which communicate by radio like garage door openers, wireless computer networks, mobile phones, Bluetooth enabled devices, ships, aircraft, spacecraft, etc. This article gives an overview of what is a transmitter, AM transmitter and simple AM transmitter circuit using two transistors.
What is a Transmitter?
The short form of the term transmitter is TX. The main purpose of the transmitter is for radio communication of data over a distance. The information which is given to the transmitter is in the form of electronic signal such as an audio signal or video signal. The TX combines the information signal which is carried by the RF signal, that generates the carrier signal. This procedure is called modulation.There are different ways to add the information to the carrier. In AM transmitter, the amplitude varies by adding the information to the radio signal. In an FM transmitter, the information is added by varying the frequency of the radio signal. Different types of modulation are used.
An amplitude modulation transmitter or AM transmitter can be defined as, when the transmitter transmits the AM signals then it is called as AM transmitter. These transmitters are used in different frequency bands for amplitude broadcast such as short wave frequency bands and medium wave frequency bands.The frequency range of the medium wave is in between 550KHz-1650KHz whereas the short wave band frequency range is in between 3MHz-30MHz. AM transmitters are classified into two types based on the transmitting power. They are
- High Level Transmitters
- Low Level Transmitters
High level transmitters use high level modulation whereas low level transmitters use low level modulation. The selection of these modulations depends on the transmitting power of the amplitude modulation transmitters. When the order of the transmitting power is in KW, then high level modulation is used. Where a few watts of power is required, then low level modulation is used.
The field of applications of AM transmitter is mainly involved in military, entertainment, government, business and personal.
Simple Two Transistors AM Transmitter Circuit
The circuit diagram of the simple two transistor based AM transmitter circuit is shown below. The Simplest AM transmitter circuit include of many parts. In this circuit the values of the resistors R2-10K, R5-4.7K and Q1, Q2 transistors are 2N3644. Here, the Q1 transistor is used to increase the audio signal from the crystal microphone. A R3 resistor limits the sound signal’s amplitude which is increased by Q1 transistor.
The Q2 transistor generates an RF signal in the form of the Colpitts oscillator circuit. The two capacitors C4, C5 and L1 inductor are used to set the output of the radio frequency. The audio signal of the Q1 transistor is sent to the Q2 transistor. It makes the amplitude of the radio frequency signal from the Q2 transistor to change the height of the sound signal. The RF signal has lower peak height as well as the sound signal will be sent to the radiating broadcast antenna.
The frequency of the broadcast transmitter can be changed by tuning the capacitance of C4 The frequency range of the TX in the broadcast system is AM range, and this AM TX can be spread out over a distance of 100 feet long.
AM Transmitter Module (QAM TX3)
The QAM TX3 is a one type of AM transmitter module gives a complete radio frequency transmitter. This AM transmitter is used to transmit the data up to 3KHz from any standard source like CMOS/TTL. The functioning of this wireless module is very easy and provides a wide range of operating voltage. When the voltage level is applied to the module then the o/p of the RF power increases in line. The data can be transferred from an encoding device or microprocessor.
The main features are
- It is a SAW resonator
- Transmit range is up to 50meters
- The input of this modem is CMOS or TTL
- The operating frequency is stable
- The wide operating voltage is 3-12volts
- It is available as 315MHz or 433 MHz applications
The applications of this model are mainly involved in various fields like wireless security systems, controlling of garage door and remote gate, data capture and remote sensing.
Thus, this is all about what is a transmitter, AM transmitter, simple two transistors AM transmitter circuit and AM transmitter module (QAM TX3). We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or electronics and electrical engineering projects, please give your feedback by commenting in the comment section below. Please refer the below link for free E-book on communication systems