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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.

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Datasheet FM Modulator

Hi I want to implement a narrowband FM transmitter and I find all features about power and noise in the FM Modulator datasheet, but nothing about bandwidth. The transmitter will work at center RF ...
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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 ...
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Antenna cable pin-out identification

I am trying to connect a stock car FM/AM antenna with a new aftermarket stereo system, Turns out my car antenna has 2 wires. One is Co-axial cable for signal (Most probably) and there's one more ...
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2answers
235 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, ...
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304 views

What does “a 40 kHz wave modulate with a 1 kHz sound” mean? [closed]

what is mean when say "a 40 kHz wave modulate with a 1 kHz sound"? which of AM or FM Modulation means?
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1answer
67 views

A trio of questions about radio/smartphones [closed]

I know that smartphones can receive FM radio using earbud/built-in antennas, but can they receive amateur radio frequencies (144 MHZ?) and if so, how? Is there a way to sending out radio waves and ...
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1answer
227 views

Why does a foster seeley circuit need transformer coupling?

Having read most of the online references to this circuit and performed some simulations, I still don't have a firm grasp on how this circuit functions. Here's a schematic to refresh (possibly ...
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1answer
325 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 ...
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273 views

Phase Modulator with JFET

At the university we have seen this circuit as a Phase Modulator: simulate this circuit – Schematic created using CircuitLab where \$m(t)\$ is the message at audio frequency and \$v_p(t)\$ is ...
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1answer
5k views

Relation between Signal to Noise Ratio (SNR) and Transmission Bandwidth for FM signal

I was encountered by the below question :: ...
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2answers
2k views

How does the LC circuit work in a FM transmitter circuit

I am using a app called Every Circuit. I dont understand how does the LC circuit function i know that it produces a sine wave but in that case both side of the lC circuit capacitor are connected at ...
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1answer
855 views

How does the frequency increase and decrease in a FM transmitter circuit?

i still dont understand how fm transmitter circuit works, from what i understand the transistor acts like a switch or a valve when the output voltage increases and decreases wont it affect the ...
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1answer
240 views

Simplest FM Radio Spectrum Capture Hardware Without Demodulation [closed]

I am trying to build a FM receiver circuit with simplest elements, transistors, capacitors (an op-amp such as LM 741 would be fine too) for analysis purposes (not real-time radio). The circuit should ...
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1answer
665 views

Is FM index affected by frequency multiplication?

I came across this question which goes An FM signal with modulation index mf is passed through a frequency tripler. What will be the modulation index at the output of the tripler? and according to ...
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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 ...
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1answer
1k views

Spectrum of FM signal [closed]

I've been given a question like Draw the spectrum of FM signal with modulation index beta = 0, 1 ,2,2.5. I know that it is something related to finding bessels values of the given beta but I don't ...
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1answer
2k views

Why it is preferred to have local oscillator frequency larger than carrier frequency in superheterodyne receiver?

So to obtain intermediate frequency Fif, why it is preferred to use Flo > fc So we use this equation Fif = Flo - Fc Instead of Fif = Fc - Flo
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1answer
125 views

I supplied 220 volts to 120 volts FM radio receiver? [closed]

I mistakenly plug an FM radio receiver of 120 volts directly to my home electricity : 220 volts. it worked for almost 5 seconds and then something inside got fried and it stop working. Do you have ...
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1answer
422 views

Is it true that frequency deviation over 2*pi is the phase deviation of an FM/PM signal?

for ∆f frequency deviation if for FM only and PM has Phase deviation. and Kf= ∆f (Hz) of FM? Kf = ∆f (rad/s) for PM? and for th rules: ∆f=(kfmp)/(2p) for FM where mp = mp max-mp min ∆f=(kfmp)/(2p) ...
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1answer
91 views

Does circled transistor or capacitor value cause buffer stage to stop transmitter from working?

I built myself an FM transmitter with an enable option so I can interface it with a micro controller. The Enable line is set through the micro via a 1K resistor (not shown). Once set to enable, the FM ...
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3answers
123 views

Is it possible to “cover up” a FM signal with your one? [closed]

So my question is, if there is a way to use a FM transmitter and send a signal on the same frequency as the local Radio, so that radios only play my signal. Or will it just be interference. In other ...
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1answer
86 views

Audio transmitter - frequency customization from a simple FM transmitter

I am referring the following circuit diagram. Circuit Can I simply change the value of C2 and L1 to transmit at a frequency below commercial FM band say as low as 40 Mhz? I know, I need to make a ...
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1answer
151 views

For which purpose are those resistors on the ANT output?

I've bought a cheap FM transmitter and installed it in my car, but sadly, it gives me too much interference (Too weak signal), even in a totally static signal, so I decided to disassemble the ...
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1answer
153 views

What sort of antenna is this?

Just wanting to learn more about this stuff but can't find any resources based on what i know to ask. This tower has several of these strange looking sets of 2 bent tubes all facing the downtown area....
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Make Si4703 evaluation board Bluetooth capable

While looking for a Bluetooth RDS-TMC receiver which could be queried with FOSS software, and after realizing there’s probably not too much on the market, I stumbled across Si4703 evaluation boards ...
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2answers
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Intermediate Frequency in FM receiver

I have question about specifically FM radio receiver that use the heterodyne principle: How Intermediate Frequency, that's fixed in one frequency (10.7 Mhz), works in FM receivers if FM radios need ...
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113 views

FM Signal Generation

So a few of my buddies and I (all undergraduate Electrical Engineers) were discussing FM signals. We found we all understood the modulation and signal profile itself, but none of us could think of a ...
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1answer
613 views

RDA5807M FM antenna question

I am trying to use RDA5807M to build a radio. My circuit is basically the same as the reference design in data sheet. I know the design uses the GND of earphone as antenna. But I don't understand the ...
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1answer
34 views

Noise floor of a FM duplex

If these 2 signals, that form this duplex, have ranges of 15-30 [kHz] and 30-45 [kHz] using: \$NoiseFloor_{dBm} =10\log _{10}(k\times T_{0}\times 1000)+NF+10\log _{10}(BW)\$ and if \$K,T,F\$ and \$\...
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1answer
366 views

Frequency deviation in VCO chips

I'm trying to do FM modulation on a signal and pass it to the PC and demodulate it using matlab. Matlab requies the frequency deviation in addition to the carrier frequency to do the demodulation. I ...
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3answers
491 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 ...
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6answers
592 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 ...
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2answers
318 views

Separating an FM antenna from a topology which uses headphone ground as antenna

I have a FM radio module with Silicon Labs Si4703 integrated tuner module for Arduino. The module assumes use of headphones and use of ground wire as an antenna (advice is wire length of 1.1-1.45m). ...
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0answers
492 views

Is it possible to make a Raspberry Pi transmit FM on several frequencies at the same time?

I have read a few questions here on transmitting on multiple frequencies at the same time. But all of them was about transmitting the same signal to all frequencies. The PiFM and PiTX projects are ...
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3answers
5k views

Send text data using FM frequencies [closed]

I want to design a device which receives basic text wirelessly, and outputs this text on a display. Using Wi-Fi is not a option. I have an idea that it would be possible to do this using FM ...
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2answers
259 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 ...
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1answer
299 views

Voltage Controlled-Phase Shifting Circuits

Forewarned: I have a somewhat good understanding of signals and systems but electrical engineering circuits aren't my strength. Question: Is there a simple circuit that can introduce a voltage-...
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3answers
226 views

Can a filter circuit be built for the FM broadcast range to only pass the frequencies not bearing a broadcast stream?

I want to build a receiver that constantly sweeps the United States FM broadcast frequencies between 87.8 MHz to 108.0 MHz. However, I want to filter out any frequency that has a radio station ...
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3answers
3k 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:...
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1answer
61 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 ...
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1answer
335 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 ...
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1answer
1k 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 ...
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1answer
3k 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 ...
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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 ...
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1answer
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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:...
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2answers
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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 ...
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5answers
2k views

Building an fm transmitter broadcasting simultaneously to all fm frequencies [closed]

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 ...
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2answers
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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 ...
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1answer
180 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 + \...
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1k 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. ...