# Tagged Questions

For questions relating to frequency modulation (FM). This is a scheme where a carrier is modulated by varying its frequency to carry information.

33 views

### FM transmitter circuit calculation [on hold]

Can you help with the calculation of power output and signal to noise ratio , stability ,and range of this circuit..I need to know it for my project ..Thanks in advance!! http://www....
65 views

### Modify Si4703 FM Tuner evaluation board to add an external antenna

I have this Si4703 evaluation board which I would like to modify to attach an external antenna. The board usually uses the plugged in headphone cable as the antenna. Here are the relevant schematics:...
29 views

### Remove microphone from circuit

I found a simple FM Transmiter circuit, which has 2 inputs: microphone and stereojack (JP2). However I want to remove the microphome from the circuit, first idea that came to my mind was to replace ...
45 views

### Minimum threshold fm equation

I have been searching and working to understanding this equation below in relation to FM signals minimum threshold. Pr [dBm]= (Eb/N0)+10∗log10(Rb)+N0 −Gm Eb is the energy per bit to noise power ...
53 views

### XY graph modulating/demodulated signals in FM

I am using Labview to simulate a communication channel using FM modulation/demodulation (with MT Modulate FM VI and MT Demodulate FM VI to be more precise). I made a XY-plot (see below) showing the ...
84 views

### Comparison between FMCW radar modulation techniques

In designing a Frequency modulated continuous wave (FMCW) radar system for target detection, there is a possibility of choosing the modulation technique amongst triangle or saw-tooth modulation. What ...
165 views

### What is the FM threshold effect?

I came across a picture ( shown below ) comparing the SNRs of FM and AM. There was also some explanation of the FM threshold effect and how the threshold effect is the reason as to why the FM graphs ...
423 views

As per this building simple radio it is the simplest AM radio receiver. obviously this is very poor AM receiver.(but it was working for someone in comment) I'm wondering what will happen when ...
181 views

### Would you explain the output waveform of this FM transmitter circuit?

I build this circuit and it works. I wanted to look at the output waveform by my soundcard oscilloscope software. I would expect something like the following picture: But the output waveform was ...
275 views

### Strange op-amp circuit FM radio

I am working on a simple FM radio receiver. Built the circuit and it works very well. Learned few new things, and got some questions, especially the output stage. The Op-amp 2822 is a dual op-amp, but ...
231 views

### Building an fm transmitter broadcasting simultaneously to all fm frequencies

I would like to build an FM transmitter that transmits a signal to all fm frequencies simultaneously, so that any nearby radio tuned to any frequency can receive this signal. Is it possible to do this ...
106 views

### Why do EM waves with longer wavelengths propagate longer distances?

AM radio signals use carrier waves which are quite longer than in FM case. We know that in free space both high and low freq. RF signals should take the same distance in same period of time. There ...
54 views

### Bessel Differential Equation and Angle Modulation

I'm trying to undestand the role of the Bessel differential equation in calculating the side bands of a phase modulated signal. I started out with the textbook example u_{PM} = cos(w_C \cdot t + \...
221 views

### Improve output quality of FM receiver TEA5767

I have connected a TEA5767 to my Arduino board using I2C and can tune it fine (see instructable.com). As antenna a ~70cm long simple cable is connected. I've connected a cheap 5V amplifier. ...
54 views

### Questions about FM Mic Kit Schematic

I'm currently building an FM Microphone kit and I'd like to understand its operation before physically putting it together. The documentation only provides an overview of some aspects and provides no ...
130 views

### How do PPM FM channels work? [closed]

I know the difference between AM and FM. What I don't get clearly is how the transmitter with a single antenna can transmit up to nine different channels with almost no interference between channels. ...
62 views

### Calculated result for inductance seems wrong?

I'm building an FM radio transmitter kit which includes an LC tank, where C is a tuner capacitor of ~30pF and the resonant frequency is ~100Mhz. The value of the PCB trace inductor, however, is not ...
164 views

### How is FM modulation is achieved using a single BJT

I want to understand how this circuit achieve frequency modulation. The BJT is a 2N3904. I found that millers effect comes into play and varies the frequency of the tank circuit about a center ...
149 views

### Is there anyother way to construct an FM transmitter

I recently built an FM transmitter that uses a combination of coil and capacitor as an oscillator to generate the carrier frequency. I built this transmitter: Now my problem is that I find it ...
168 views

### Is it illegal to transmit in the FM range for personal use

I am building an FM transmitter. It is going to be designed to transmit only for a short range of around 50 to 100 meters. My question is whether it is illegal to transmit signals in the FM band over ...
119 views

### Can an inductor be substituted for a coil

I am designing this FM receiver circuit. I have a few questions related to the circuit. Buying coil in my locality is a little expensive. So would it be alright to substitute an inductor in its ...
96 views

### College Computer/Electrical Engineering Circuits - Modulating Signal DC offset based of modulating index question

Here is an image of the question. I am stuck at part a, which asks to find the DC Offset based of a modulating index of 0.7, or 70%. So essentially, you will transform the maximum and minimum, yes? ...
225 views

### Found a part on an old FM transmitter used for tuning. What is it?

This is an old transmitter from the early nineties. The part is the white block with the screw through it. I'm assuming it's a capacitor of some sort, but other than that I don't know much. I don't ...
98 views

### Fm reciever local VFO sa615

I'm building a FM receiver based on a SA615. But when I test the VFO (variable frequency oscillator) with a spectrum analyzer and a sniffer probe I don't see any frequency showing up. So the ...
45 views

### Describing FM inductors

Why, when providing FM radio designs, do people use physical parameters instead of electrical? I.E. 2 turns, 20awg, 2cm dia.
101 views

### Hint for the way a fm reciever works

As far as I know , a simple AM reciever can consist of a LC filter(connected at antenna) which amplifies the selected frequency, a demodulator( a diode for example) which rectifies the signal,an amp ...
82 views

### What's the next logical step in applying input to this FM transmitter circuit?

Last year, I posted this question about a very simple RF transmitter circuit: Does this simple RF transmitter circuit actually work? I built it myself, and actually remade it after I posted an answer ...
125 views

### How to send analog data using FM/FM Telemetry

I am measuring the strain a bicyclist is placing on a bicycle crank arm throughout riding, using strain gages. I would like to send this data (after amplification) off of the bicycle crank arm and to ...
757 views

### FM transmitter design?

I stumbled across a relatively simple FM radio transmitter online. Credit: makezine.com I wanted to understand how it works (it is called "super simple" on the website), but several hours I have ...
613 views

### FM Carrier Wave Generation

I'm trying to understand how the following FM radio schematic works. Specifically, I want to know how the carrier wave is generated. I understand the concept of an LC tank and I think I see it ...
3k views

### If an FM signal has different frequencies, how does the radio receive the signal in a fixed frequency?

If an FM signal has different frequencies according to the modulation, how does the radio receive the signal in a fixed frequency like 103.2 MHz?
328 views

### Can we send text data over FM radio? [closed]

Can we able to broadcast text data over the FM radio.If yes, how can I implement this.
534 views

### USB to 3v converter to power a battery powered FM transmitter?

I have a SCOSCHE FM Transmitter which practically eats up 2xAAA batteries, I was thinking of using my TV's USB power for the transmitter. My search lead me to this 3 in 1 DC-DC USB 5V to 3.3V Step-...
338 views

### What is this type of radio fm antenna connector called?

I'm looking for an antenna replacement for my dad's busted radio (iHome IH8) and I'm having some trouble finding the name of this type of plug. The only things I find when searching online are coaxial ...
120 views

### Objections to use an RCA connector for antenna in broadcast FM receiver

Due to budget & space restrictions, I am thinking about replacing a PCB BNC connector used to attach an external FM antenna. It seems to me an RCA connector could be an option, given its good ...
113 views

### Triangulation with Single Tone FM TX and Three RX using Phase Detection [closed]

I'm looking for some IC and frequency suggestions to accomplish the following task. Modulate a tone onto a carrier and continuously broadcast this signal toward an array of three receiving antennas(...
474 views

### Video Home System (VHS) bandwidth

Standard play VHS video cassette recorders offered only about 3 MHz luminance bandwidth by recording the signal on an FM carrier. What is that carrier frequency? Is it possible to confirm the carrier ...
104 views

### what is the function of pre-emphasizer and dee-emphasizer in Stereophonic FM Receiver?

what is the purpose of theses two block ? I know that pre-emphasizer will boost the high frequencies before transmission and dee-emphasizer will reducing them by a corresponding amount in the ...
101 views

### Detection of FM transmitter carrier phase

I would like to detect the phase (only) of a standard FM transmitter carrier over the air while it is modulated, while at the same time avoiding receiver threshold effect. Typical commercial FM ...
85 views

### FM Antenna Question

I am a swim coach trying to play music for my swimmers while they swim. I am currently using this transmitter with this antenna . I have no issues with the transmitter as it is more than powerful ...
659 views

### Use Potentiometer to change frequency in FM Radio Transmitter

I know that in most circuits you use a tank circuit consisting of an inductor and variable capacitor in parallel to generate different frequencies like this one. However since most cheap trimmer caps ...
325 views

### Use Preformed inductor instead of coil for FM Transmitter

I want to build this transmitter: The inductor in the schematic says 0.1uh so I figured I could get some of these and use them instead of making my own like it describes in the picture. I would be ...
519 views

### 555 timer as FM transmitter vs. Tank Circuit

This site seems to suggest the use of the 555 timer in astable mode to generate frequency modulation from a source. The typical transmitter uses a tank circuit with an inductor and trimmer capacitor ...
2k views

### How to remove the static sound in an fm transmitter

Hi I have a school project and I used the schematics from this website for our FM transmitter. Its actually working but its hard to recognize the music being played because of the static, also does ...
143 views

### Superheterodyne receiver with voltage controlled oscillator

I'm new in electronics and I want to create a FM receiver that performs a product of the received RF signal and a local signal (the local signal is also frequency modulated with a Voltage Controlled ...
537 views

### Frequency spacing and the doppler effect

Suppose that I'm working on a system which needs to use a transceiver with an FM signal. If that system moves very fast (i.e. it is a satellite or whatever) in which the maximum doppler effect can be ...
1k views

### Using a Dipole Antenna on a 50 ohm FM transmitter

First of all, while I'm not new to electronics, I'm new to the radio world. I am helping a friend overseas set up a community radio, and am getting everything set up over here before I ship it. I ...
78 views

### FM signal example

Sorry if this question is too basic, but I'm a software engineer student who must study communication systems. I try to represent a FM signal in a graphing calculator, but I don't know why the result ...