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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2answers
103 views

Transmit beeps from Arduino through FM transmitter circuit

I am trying to create a simple Arduino parking sensor that sends the warning beeps to the car radio using FM transmitter circuit. I searched different FM circuits and found many of them that use a ...
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1answer
66 views

Frequency Modulation - Why don't we modulate the carrier by multiplying message signal m(t) directly with f_car?

I am master student of computer science and I have got a problem/question from the domain of communication engineering. So: I'm listening to a lecture that's about Layer 1 stuff, and recently we ...
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1answer
116 views

Decoding/Demodulating audio data in Patent US4877027A [closed]

I'm interested in decoding/demodulation audio/voice data sent using microwave pulses as described in this patent: US4877027A - Hearing system In the patent it's shown that voices or any other audio ...
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34 views

How decreasing the effective load impedance in the secondary of a transformer heavily dampens it?

I am reading the operation of the ratio detector for FM demodulation. It works on the principle of diode variable damping (please see the figure here). The capacitor C9 restricts the changes in the ...
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1answer
55 views

Can I use a BC338 in this application?

I want to build this FM transmitter that runs on 1.5-3V. I've got 2 questions so far: Can I use a 2N2222A NPN in this application? (I think I can but want to double check.) How can I calculate (or ...
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83 views

FM receiver With LM386 - Need a Preamplifier

I am building a hoppy FM Receiver and I created the Preamplifier stage 1 and linked it with the LM386 Stage and it goes OK but The output sound from the Speaker is weak so I tried to do some ...
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43 views

Output levels of FM broadcast signals

I wrote an FM mono transmitter with HackRF, and now I'm trying to add stereo and RDS. I'm confused about the levels of the final mono + stereo + RDS mix (after preemphasis, and before the FM modulator)...
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2answers
174 views

I want to build an FM transmitter. How does this circuit work?

I have been tinkering with AM transmitters but now I would like to build and understand FM transmitter circuits. I came across this circuit in a electronics projects book but it does not explain at ...
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1answer
120 views

Arduino accidentally transmitting FM

I was trying to make an FM transmitter and, because I have no mic, I thought I could just use an Arduino (Uno) to generate some tones for testing. It turned out I never got a signal from the circuit ...
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1answer
91 views

Why is frequency spectrum centred at 1 kHz?

This is the circuit that I have built I set the Continuous-Time VCO to a frequency of 1 kHz. Since there is no message signal the modulation index is =0 meaning I would expect one peak and I would ...
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1answer
97 views

What is the equivalent LTSpice diagram of the given varactor diode modulator (FM)

Given below is an example of direct FM generation using varactor diode modulator. What is the equivalent circuit of this in LTspice? Can you explain the given circuit?
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1answer
110 views

How to measure FM deviation for pilot signal?

I'm trying to calibrate my FM signal generator, but don't have the required FM detector. The instructions say: Turn pilot ON, comp OFF Set pilot to 10% deviation Verify detector says 7.5kHz, or ...
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28 views

How Does Varactor AFC Work in This circuit

I have a question about how the varactor on the transistor's emitter can change the frequency of the modified Colpitts oscillator on the collector of this circuit. The junction of the varactor and R30 ...
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2answers
85 views

FM modulation in FM transmitter

I'm using an LM386 for voice amplification. The transmitter transmits the signal from the tank circuit on the correct frequency but without voice. I'm a beginner and a hobbyist and I'm still trying to ...
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147 views

SI4735-D60 chip no FM signal reception

Trying to tune the SI4735 chip to an FM station. Have using this library and example to drive the chip with Arduino UNO and based on the console output from the sketch the control interface works fine:...
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110 views

matrix multiply showing error in dimensions when i am using it for fm demodulation in simulink

I am doing FM modulation and demodulation of audio signal. i have successfully implemented the fm modulation but as i give the output of FM modulation to the matrix display at receiver end, it is ...
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1answer
103 views

Is this a demodulated signal?

1st attempt I have a problem. I built the FM demodulator circuit, but i am not sure if this signal is demodulated. This was my first attempt which following an answer, resulted in a 2nd attempt ...
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1answer
70 views

How do you find the phase lag of the current in this FM demodulation "discriminator" circuit?

I need some help understanding this discriminator circuit for FM demodulation. (L1, C1) is the primary LC tank which resonates with the carrier frequency, whose FM signal is applied at V12. As the FM ...
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1answer
131 views

Spectrum of FM signal?

If a carrier (\$f_c\$) is FM modulated by a single sine wave (\$f_m\$), its spectrum is composed of frequencies at \$f_c + kf_m\$ (\$k \in \mathbb{Z}\$) whose amplitudes are weighted by \$J_n(\beta)\$,...
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178 views

Ratio detector FM demodulator

The aim of the exercise is to design a ratio detector FM demodulator circuit. UPDATE: I changed the circuit: This is my transient analysis in output: I found the information about AC analysis and ...
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1answer
73 views

Reference clock in FM receiver chips (si4735)

The datasheet is mentioning a 32678 Hz "reference clock" (RCLK) input. It appears to be a well known thing in this type of ICs because it's highlighted in the list of features. I guess ...
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1answer
47 views

Bessel function if frequency modulation and modulating index

If amplitude of a message signal is kept fixed and frequency is increased then modulating index will decrease? According to bessel function side tones will be more spaced if frequency increases but if ...
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2answers
61 views

Frequency Modulation with same carrier and message signal of same frequency but different amplitude

How is frequency deviation calculated for a FM wave? Suppose we have a same carrier and a sinusoidal message signal of frequency 5Hz and maximum amplitude of 5V and another sinusoidal message signal ...
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56 views

FM antenna isolation

I want to connect a car antenna (FM radio) to a phone's jack sleeve to provide a good antenna signal to the phone (for its FM radio part). As the car might add some supply DC to the antenna, I decided ...
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2answers
125 views

FM receiver not picking up any stations

I am trying to make an FM receiver. I have a radio transmitter and it's able to pick up and demodulate the signal from that when the transmitter is beside it, but the problem is when I try and pick up ...
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56 views

instataneous frequency in FM

Newbie and trying to understand the concept of instantaneous frequency in FM. Basic equation is \$A\cos(2\pi f_\mathrm{c}t+ 2\pi k\int (\mathrm{message})\,\mathrm{d}t)\$. I wanted to know how the term ...
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1answer
153 views

what are these two fm antenna connectors? How can I join them?

One of these connectors is the type that plugs into my receiver's FM antenna input, and the other is an aftermarket FM antenna output connector. I think the one with threads is called "type F&...
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2answers
128 views

Why can FM be demodulated non-coherently while PM cannot be demodulated non-coherently?

I have read that frequency modulation has the advantage that it can be demodulated non-coherently while phase modulation can only be demodulated coherently. I don't find any reason to support this ...
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1answer
67 views

SIMULINK: The spectrum of the modulated signal remains unchanged despite modification of the modulation index

I try to implement a frequency modulator. From what I know, the more I vary the modulation index (which is set by the gain block here,) the more the spectral lines should increase in number. When I ...
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1answer
68 views

Why is transformer coupling used in a simple slope detector? Can't the FM signal be applied directly in parallel to a tuned circuit?

This is what I mean by simple slope detector: Why can't it be like:
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1answer
105 views

Does satellite radio use AM or FM or both? [closed]

Somehow, I cannot find an answer anywhere... I am guessing both... Several actual satellites had FM in their names, so perhaps that is a clue, but I want to know for sure...
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1answer
117 views

What are some ways I can modulate the duty cycle of SPWM with mixed signals?

I'd like to experiment with SPWM, as used in motor control applications. But instead of modulating the duty cycle with a single frequency, I'd like to use a mix of frequencies. I've been searching for ...
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1answer
90 views

Can the intelligence message of an FM signal be cross-modulated onto another FM signal due to nonlinearities?

Can the intelligence message of an FM signal be cross-modulated onto another FM signal due to non-linearities? Where I work we have several FM two way, repeater radio sites. Over the years I've ...
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1answer
127 views

My FM transmitter never works, Why? [duplicate]

I'm trying to build a FM transmitter, but without sucess. The current schematic I'm using is this one: The alternating current at the (+) of the op amp is the P2 output of my phone. V3 and V4 are 2 ...
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1answer
91 views

How do we tell distance to target at the receiver from frequency modulation?

Was thinking about radar and how to tell distance using FM. If you send a wave with a consistent wavelength of 1 meter, and it hits a target 1000 meters away and then comes back, it will have gone ...
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1answer
193 views

How to add a simple ESD protection to RDA5807M FM tuner antenna pin?

I am using an i2c controlled FM tuner IC (RDA5807M) in a DIY fm radio, but I am a little bit worried about ESD protection on the Antenna line (A headphone lead being used for this). Can i add standard ...
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2answers
56 views

Is the value Vm correct in a FM modulation?

Recently I calculated the Vm and the Vc. However I think the value is ackward and strange. This is the scope image: With the information: This is what I have done:
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2answers
478 views

Increasing range of FM transmitter

What things impact to range of FM signal? If I increse length of antenna would signal range increase? I would like to increase the signal range of this project. Is that possible? Do I need more power ...
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1answer
916 views

FM demodulator LTspice

I am now designing an FM demodulator circuit. And the first step is turning FM into AM, so I could use envelope detector afterwards. Modulator circuit is designed using Colpitts topology. So frequency ...
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1answer
1k views

FM modulator LTspice

I am designing an FM modulator circuit using Colpitts topology. Unfortunately I encountered difficulties and do not know how to solve them as I am new in electronics. Firstly I don't get a clean sine ...
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2answers
95 views

How can picked up FM noise be demodulated?

I have a set of cheap computer speakers, which happens to use a TDA2822M. Its circuit is almost identical to the example circuit from TDA2822M's datasheet. It's USB powered and has no shielding. I ...
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2answers
201 views

Why does a higher bandwidth allow a higher data rate [duplicate]

I have not taken any signals processing classes yet but I am interning at ATnT in the RF department. I do not understand why higher bandwidth increases data rate and the other answers did not make ...
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4answers
363 views

Different antenna lengths for different frequencies?

I just want to understand a few things which I couldn't get clarity from a lot of websites searched through google as I could see differing information. My questions : How does a single FM antenna ...
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1answer
168 views

Collpits FM Receiver

I saw this simple schematic for an FM receiver: https://www.mikroe.com/ebooks/radio-receivers-from-crystal-set-to-stereo/the-simplest-fm-receiver Moreover, I saw some videos online where people have ...
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1answer
97 views

FM broadcasting text

I was listening to a local FM station from my smartphone using a headset. While I was surfing over the available bands I saw that few FM stations can broadcast the name of the song/music details (...
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41 views

How to check for frequencies with stronger signal in FM radio

I'm making a radio player using si4703 IC. I read RDS data to know the radio station name, PI code, etc. I also get the list of alternative frequencies (AF) that the radio station send via RDS. ...
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4answers
282 views

FM Transmitter oscillation problem

I've been trying to get this simple FM transmitter to work over the past few days and I could use some help in a few areas. First iteration was on a breadboard with all parts included. The ...
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0answers
159 views

Uniden BC780XLT Radio scanner, unknown modification

I recently purchased an old Uniden BC780XLT scanner. It has been modified replacing two smd resistor with THT resistors with different values. I am curious about this modification: what does it do? I ...
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218 views

Fm receiver circuit doubt

I was trying to simulate an FM receiver circuit on LTSpice. The circuit is given on this website I want to know how the correct current/voltage will look around the speaker (modelled as 8-ohm ...
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1answer
215 views

Why do I get clear FM signals on my AM crystal radio?

I made a rudimentary radio: long antenna out the window, coil and capacitor (both home-made) in parallel, diode to guitar amp in parallel to LC circuit. It works! Even my calculated L and C ...

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