A small, simple AM receiver project. This AM receiver can pick up medium wave stations in your area
This circuit can use general purpose transistors, and in this example there are 3 BC109C transistors. In this schematic and BOM there is a 200uH inductor and a trimmer 150-500pF capacitor, though these parts can be salvaged from an old AM radio, to preserve the directional nature of a tuning coil, and an adjustment knob (plate capacitor) that work well for radio reception.
The 120k resistor is for regenerative feedback between the Q2 NPN transistor and the input to the tank circuit. The value of this resistor is important to the performance of the entire circuit. In fact, it may be better to replace the fixed value with a variable resistor paired with a fixed resistor to adjust the oscillation and sensitivity of the circuit. All the connections in this circuit should be short to minimize interference.
Performance of the circuit will vary depending on stray capacitance in your layout, the inductor winding/core/length, etc. Changing values of some of the capacitors, or adding them, as well as a potentiometer in the feedback loop can help with the performance of the receiver. With such a small circuit that is affected so much by its construction and its environment, a lot of hand tuning and experimentation will be fun, instructive, and possibly necessary to make it work best.
Simple AM Receiver Project - [Link]
VHF FM Aircraft receiver:
VHF FM Aircraft Receiver is a superregenative receiver developed for listening to FM transmitters but also tunes the aircraft band and the top portion of the FM broadcast band. Receives both AM and FM (107mHz to 135 MHz). You can use this receiver with the any FM transmitter. The receiver is amazingly simple using only one transistor for the receiver section and one IC for the audio section. This circuit is a self-quenching regenerative RF receiver also known as a superregenerative receiver.
VHF FM Aircraft receiver - [Link]
The Si4840 and Si4844 from Silicon Labs are the first CMOS AM/FM/SW radio receiver ICs with analogue tuning and digital display that integrate the complete receiver function from antenna input to audio output. Based on Silicon Labs’ proven and patented digital low intermediate frequency receiver architecture, the Si4840 and Si4844 deliver superior RF performance and interference rejection. The integrated control algorithm provides an easy and reliable control interface while eliminating all of the manually tuned external components used in a traditional receiver. [via]
AM/FM/SW receiver integrated on a single CMOS chip - [Link]
An introduction to AM/FM active antennas: [via]
This article is a reference design (RD) for an automobile AM/FM active antenna. The RD presents the flexibility of the MAX2180 active antenna low-noise amplifier (LNA) and shows how to set the AM and FM gain and the automatic gain control attack point. Single and dual antenna schematics are detailed, including the input and output matching circuits. Using this design together with the data sheet and device’s evaluation (EV) kit, a prototype antenna can easily be developed for a wide range of active antenna requirements.
App note: AM/FM active antenna - [Link]
555 timer based AM radio receiver published on Tube Time is one of many entries for the currently running 555 contest. This project uses a 555 timer as AM demodulator plus amplifier to drive the speaker. The radio signal is tuned with an LC tank circuit. The 555 timer is configured as a PWM where a ramp signal is created with a capacitor and a potentiometer. The radio signal picked by the LC circuit is superimposed on the ramp signal which varies the duty cycle of the output PWM wave. The variation in the duty cycle corresponds to the audio signal in the radio waves.
555 Contest Entry: AM radio – [Link]
So, I needed a small transmitter, which would allow me to transmit good, old music into my AM-only radios. So, one saturday afternoon I got into gear, designed and built a very crude, terribly non-optimized little transmitter. It’s almost a joke expressed in electronics, full of poor design, so please don’t think that this is the best I can do! You must see it as a quick and dirty 5-hour effort, because that’s all the time the transmitter took to design, build, and test
Small AM Transmitter – [Link]
This project shows how to build a simple AM radio transmitter based on 555 timer IC. The circuit parts are: the 555 timer IC, a NPN transistor three caps, three resistors and a potentiometer. The circuit is able to generate an amplitude modulation signal at 600Khz and you are able to receive it using a plain AM receiver. The range is about 30-40 feet. [via]
AM radio transmitter using 555 timer – [Link]
This Crystal Radio is highly selective as to separating stations and tunes in the A.M. band from 570 KHZ up to 1.7 MHZ and the short wave bands up to 2.5 MHZ. It is suggested that crystal earphones be used….. or (preferred) feed the audio output of this tuner into an audio amplifier. A good antenna of at least 50 feet is required along with a good earth ground connection.
High Selectivity Crystal Radio with Short Wave - [Link]
Mike wanted to uniquely identify plants growing in the rows of a field and looked for ways to do that. One way is to measure electrical resistance between stalk base and leaf and thereby uniquely identifying the samples. This proven not to work as there was no way to distinguish measurements taken on the same plant from measurements taken between plants. So he think another way, to measure AC impedance. This technique has actually proven much more interesting. Doing some experiments he found that plants can act as decent antennae. To find out, he decided to build a simple AM radio transmitter. The AM transmitter is build around a ATMega324 8-bit AVR microcontroller and uses embedded timer/counter modules to produce the carrier wave. Check details of this interesting experiment on the link below.
Simple AVR AM Radio Transmitter - [Link]
If a crystal radio is the distilled essence of a radio, this transmitter is the matching distilled essence of transmitters. The transmitter goes together in about 10 minutes, and is small enough to fit in the palm of your hand. Depending on the antenna, the transmitter can send voice and music across the room, or across the street. [via]
Building a very simple AM voice transmitter - [Link]