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Questions tagged [fm]

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

28
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3answers
10k views

Are audio cassettes FM or AM?

I know that cassettes store an analog signal, but is the signal Amplitude-Modulated (AM) or Frequency Modulated (FM)?
20
votes
10answers
7k views

How exactly does AM/FM carry both pitch and loudness of voice?

Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal ...
16
votes
4answers
6k 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?
15
votes
4answers
3k views

Receive several fm-radio stations at the same time (~10-20 MHz wide summary at 90MHz radiofrequency)

What is a cheap way to receive and record on PC several (tens) of fm-radios (public, e.g. news, music, etc)? Such radios uses frequencies like 90.4 MHz or 102.7 MHz, sends a stereo (sometimes with ...
12
votes
1answer
2k views

How can this FM transmitter modulate?

simulate this circuit – Schematic created using CircuitLab This is a minimalist FM transmitter I've found from http://www.talkingelectronics.com/projects/Spy%20Circuits/SpyCircuits-1.html I'm ...
10
votes
4answers
2k 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 ...
9
votes
2answers
579 views

Identifying an old RF circuit

I got an old RF circuit (I guess), probably used for pedagogical purposes. Here's the schematic: I chose the positive and ground rails as it seems right to me, looking at transistors and resistor ...
7
votes
1answer
2k views

Why do FM radio signals occupy greater bandwidth than AM?

If a 5kHz baseband signal is modulating an AM carrier wave, the sidebands will be centered around the carrier wave and the the signal will occupy 10kHz bandwidth. AM radio limits the upper modulating ...
6
votes
3answers
1k 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 ...
6
votes
3answers
1k 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 ...
6
votes
5answers
1k views

What decides the range of FM band?

I read that the frequencies over which FM signals can be transmitted is limited between 88 MHz and 108 MHz. Why is it confined to a particular range and why specifically to this (88 MHz to 108 MHz) ...
6
votes
1answer
4k views

Variable Capacitor?

I am working on a simple FM radio transmitter and I was looking for a variable capacitor to help tune the circuit. I rummaged around and took apart an old Sony radio that had this component in it. ...
6
votes
2answers
1k 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 ...
5
votes
3answers
2k views

simplest FM radio receiver?

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 this ...
5
votes
2answers
9k views

How does Frequency Modulation work with radio frequencies?

Inspired by this question: What is the basic difference between AM and FM radio? I got to wondering: If I put my FM radio on some radio channel (Let's just say 100 MHz to pick some number), shouldn'...
5
votes
3answers
5k views

Capacitor between emitter and collector

Considering the circuit below.: What is the purpose of capacitor C5? I know it provides positive feedback to sustain the LC oscillations, but how does this work ?
5
votes
3answers
881 views

FM Receiver's Oscillator resonating to a frequency, but its modulated?

In an FM, the frequency is modulated. So whatever reaches the receiver is not a constant frequency. This being the case, at Receiving an AM/FM Signal: "In an FM radio, the detector is different, but ...
5
votes
1answer
4k views

FM Transmitter Modulation

I am designing an FM transmitter as a learning experience and for fun, but I am having some difficulty with FM modulation. I am using a VCO with a Colpitts topology and common emitter configuration. ...
5
votes
2answers
231 views

Can AM and FM signals at the same frequency be separated?

Suppose one radio station emits an amplitude modulated (AM) signal at 100 MHz, and a nearby station emits a frequency modulated (FM) signal at 100 MHz. Is it possible to separate these two signals, ...
5
votes
1answer
2k views

Good ICs for receiving and decoding FM RDS

I'm interested in doing a project to read FM RDS data. Can anyone recommend good chips for both the FM receiver and RDS decoder? For an FM receiver, I'd like to be able to control FM frequency (...
4
votes
3answers
2k 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 ...
4
votes
2answers
1k 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 ...
4
votes
2answers
252 views

FM Receiver, how it works?

Im working on a Visible light communication project. Its a simplex transmitter receiver setup using an LED to send data to a photodiode receiver. Im thinking of ways to encode the data for ...
4
votes
3answers
1k views

FM Quadrature detector - is it the best choice

My input is an FM carrier of 80.00MHz. It is FM modulated with 625kbpsec data. The deviation from carrier is about +/-700kHz. The data never spends more than about 38us in a low state or high state i....
4
votes
1answer
1k 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 ...
4
votes
3answers
1k views

Question about FM and PM and Angle Modulation

I am having a bit of trouble understanding how FM works mathematically. I fully understand the conceptual basics regarding how information is transfered by modulating the frequency, but what I don't ...
4
votes
1answer
887 views

How do I determine the proper FM transmitter strength?

I want to build an FM transmitter that will transmit (on an unused frequency) from my laptop (near my video projector) to my receiver (about 20' away on the other side of the room). Then, I thought ...
4
votes
1answer
166 views

What antenna is this?

I just disassembled an external FM antenna designed for an old Asus laptop. I expected to find some circuitry and a monopole or some other simple antenna. However, what I found was the antenna shown ...
3
votes
4answers
4k views

Does this simple RF transmitter circuit actually work?

I've come across this circuit a few times while searching for simple transmitter circuits, and decided to try it. According to this site, it should be transmitting at around 90Mhz. http://www....
3
votes
2answers
9k views

Why did my FM transmitter mysteriously die?

I made a little FM transmitter project a few months ago. I used an Arduino, a litle 4-digit serial LED display, a couple of buttons and an FM transmitter component with breakout board I had this put ...
3
votes
1answer
1k 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 this:...
3
votes
1answer
148 views

Why can't we divide the electromagnetic spectrum into arbitrarily many radio frequency bands?

I understand there is concern over the limited amount of wireless spectrum available for allocation but am somewhat confused as to why. Couldn't we just divide the electromagnetic spectrum into as ...
3
votes
1answer
5k views

How to build an FM transmitter and how does it work?

I have become interested in radio transmission and would like to know how to build an FM radio transmitter. When I search for information I either get a block diagram or a video of someone putting it ...
3
votes
1answer
2k views

Simple FM transmitter [duplicate]

How does this circuit perform Frequency modulation. I know the LC generates the carrier frequency. How does the transistor act as a varicap to perform FM. Which part of the circuit acts as a varicap ...
3
votes
1answer
883 views

Generating 19kHz and 38kHz phase-locked sine waves

As a personal project, I'm designing a stereo FM transmitter from scratch. Part of this entails design of a stereo multiplexer. Using this description, I've worked out how I'm going to implement most ...
3
votes
1answer
954 views

What is the energy efficiency between FM radio tower broadcasting over an area vs point to point streaming via Internet?

Doing some research, it seems that an FM radio tower in a densely popoulated area can maximally transmit about 50kW of power. If you assume a certain amount of people tuning into the station, is that ...
3
votes
2answers
681 views

Determining type of modulation

The circuit below is a radio transmitter circuit of a typical RC car. The circuit makes use of IC TX2 encoder. The output of IC ("SO" pin) is a series of pulses at low speed (84 Hz). This signal will ...
3
votes
1answer
1k views

Single-station FM radio

I'd like to build an FM radio that is pre-tuned to a specific station. I could use something like the Si4703 FM tuner chip, but they're expensive and difficult to solder by hand (and require a ...
3
votes
1answer
208 views

Building radios using RLC Meter

I'm interested in building AM and FM radios from discrete components. Has anyone ever used an RLC meter to precisely create the inductors and other elements used in these radios? I know cheaper RLC ...
3
votes
1answer
172 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(...
3
votes
2answers
747 views

Identify discriminator circuit?

The Dynaco FM-3 tuner uses what appears to be a Foster-Seeley discriminator with one diode reversed, or, if you prefer, a ratio detector without the third coil and stabilizing capacitor. The Dynaco ...
2
votes
1answer
1k views

Does amplitude of FM signal even matter?

Thinking about FM modulated signals that store information only in frequency so that their amplitude has no effect on the sound, I began to wonder: Does the amplitude even matter in the end? Well, ...
2
votes
6answers
583 views

Can we transmit FM signal using AM band and AM signal using FM band?

What I am asking is if it is possible to transmit a frequency modulated wave in AM range(550-1650 Khz) and similarly to transmit an Amplitude modulated wave in FM band (88-108 Mhz). I would like to ...
2
votes
4answers
3k views

Controlling DC (Pager) Motor with Audio Signal

I'm trying to control a DC (pager) motor with a sound signal so that I can use an audio synthesizer to control the speed of the motor. I'm hoping to modulate the speed of the motor at audio rate (1-...
2
votes
2answers
287 views

Is it possible to broadcast FM radio up to 500 metres? [closed]

I'm buying FM transmitter 0.2 watt at Lazada to broadcast for my village community at my area. Not a normal small FM transmitter for car or portable low watt (about 10mW-100mW) which broadcast up to ...
2
votes
2answers
207 views

Select Phase Detector Cutoff Frequency? Phase Locked Loop FM Demodulation

I'm studying a Phase Locked Loop used for FM demodulation, obviously a phase detector is used in the system. A basic implementation of a phase detector is a multiplier followed by a lowpass filter. I ...
2
votes
3answers
486 views

Piece of wire as FM antenna

OK, this is really annoying me. I have an old bedside radio/alarm clock that's been fine for a couple of decades, and which still works perfectly well at night. Its crude FM antenna is a simple ...
2
votes
2answers
286 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 ...
2
votes
3answers
793 views

Part for VHF/FM booster?

I'm needing to create a booster and the easiest schematic I've found is this: http://electronics-diy.com/500mW_FM_VHF_Transmitter_Amplifier_Booster.php however, they do not document what part they use ...
2
votes
1answer
323 views

Frequency changing element in an FM transmitter

In a simple FM transmitter such as this What element does the frequency modulation? I don't mean the oscillation itself, since it's clearly created by tuned tank circuit, but the modulation. There ...