Questions tagged [frequency-modulation]

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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Controlling a IR2110 with PFM for Half Bridge Circuit [closed]

I am curious about how to select Cboot for desired control frequency range. https://www.infineon.com/dgdl/Infineon-Bootstrap_Network_Analysis-ApplicationNotes-v01_00-EN.pdf?fileId=...
2 votes
1 answer
121 views

Is it possible to receive an FM signal without a tank circuit?

I was broadcasting FM signals at MHz frequencies in my room. I know that an AM radio will not work to receive FM transmissions. The special issue is that an AM radio can get any AM signal without a ...
1 vote
2 answers
84 views

How to design an RF frontend for an FM receiver

I'm designing a RF receiver for FM Radio. I simulated the circuit in LTspice and got an output as shown below: This is OK, but I would like the gain to be 24 dB across the range of 88-108 MHz. The ...
0 votes
1 answer
200 views

Bessel function of frequency modulation and modulating index

If the amplitude of a message signal is kept fixed, and the frequency is increased, then will the modulating index decrease? According to thr Bessel function the side tones will be more spaced when ...
-1 votes
1 answer
63 views

Frequency demodulation circuit

This is how I designed the frequency modulation circuit, but I cannot perform the demodulation process. It can be done with a PLL but I couldn't install it. How can I demodulate?
3 votes
1 answer
265 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 ...
0 votes
1 answer
792 views

Can telescopic FM/DAB antenna be replaced by Coax?

I tried to search for this prior to asking but with no luck... I have an FM/DAB+ antenna like this: from which a standard 75-Ohm Coax is coming down and I would like to connect it to the radio (...
1 vote
2 answers
109 views

How does this metal detector circuit work with an AM receiver?

I do not understand how this circuit works. From Fun Electronics Projects for the Experimenter by Newton C. Braga. It is described as using the beat-frequency method to detect an object. The ...
1 vote
3 answers
358 views

Frequency upconversion from 1 to 100 MHz for FM transmitter

I'm trying to build an FM transmitter like pifm but using the ESP32. I can generate an FM signal at the DAC output of the ESP32 with a carrier frequency of 1 MHz and a deviation of 25 kHz, but in ...
0 votes
2 answers
38 views

Does the microphone input interfere with the headphone jack input?

In this circuit, there are two inputs to the FM signal. One is from the microphone, another is from the headphone jack. Does the the microphone input interfere with the headphone jack input? Can ...
0 votes
3 answers
3k 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. ...
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0 answers
28 views

Why is it difficult to write the close loop transfer function of a frequency modulated DC-DC converter (for eg - LLC converter)?

I know how to derive and write the transfer function of duty cycle/pulse width modulated DC-DC converter. We need to linearize the switches and then write KVL/KCL equations and then derive the output ...
1 vote
1 answer
121 views

RF signal on Audio/Music/Guitar equipment

It is looking like the standard RF noise from my (new to me) old apartment wiring through my amp to my speakers. Suspected it could be due to poor guitar shielding/grounding, bad cables etc. Started ...
0 votes
1 answer
182 views

Demodulation of FM signal frequency

After playing with homemade AM radios, I noticed that it is boring to broadcast AM signals all alone. I have also noticed that the AM stations around us, are so limited that I had no other chance than ...
0 votes
4 answers
327 views

What is a modulated optical sensor?

I was told to try out a modulated optical sensor as a better and more "robust" option than the usual (unmodulated) optical sensors, saying the modulated ones are less subject to interference....
1 vote
1 answer
592 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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1 answer
806 views

Band selection circuit for SI4825 A10

Following the official schematic and guideline (AN738: Si4825/36-A Antenna, Schematic, Layout, and Design Guidelines), I am building a Si825 A10-based radio receiver. I am getting weak audio output ...
2 votes
1 answer
432 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 ...
1 vote
1 answer
3k views

Which one of these transistors is equivalent to 2N918 NPN?

This is an FM radio receiver. Q1 is 2N918 NPN transistor but it is not available for me. Which one of the following transistors is more equivalent to Q1 ? BC547 TL431 s8550 s9014 2n5401 2n5551 ...
1 vote
0 answers
56 views

What can be done to increase the dynamic range of a FM receiver?

If i have to receive a signal from a far away FM station, nearby stations swamp the receiver if they are both nearby physically or nearby in the spectrum. I believe the AGC in my radio is cutting out ...
1 vote
0 answers
108 views

What could be blocking communication with TDA7706S on a Sony GT520U radio?

I have a Sony GT520U radio which started developing a lot of noise and becoming unresponsive when in tuner mode. Opening it revealed the chipset on the tuner was overheating in less than 3 minutes of ...
0 votes
1 answer
267 views

How to make very low range FM Transmitter?

I am experimenting with building an FM transmitter. I want to make it only have a range of a few meters so I can detect it on my radio at home at a distance of a few meters. The circuit diagram is ...
2 votes
1 answer
52 views

Simple detection of a transient FM frequency shift

I have an application with a 2D array of inductive sensors for position detection of an object on a plane. I have experimented with inductance to digital converters (https://www.ti.com/product/LDC1314)...
2 votes
2 answers
360 views

FM receiver with 2N3904

Please explain how these 2 transistors work. I don't understand how it active an amplify the signal. Source: https://circuitdigest.com/electronic-circuits/simple-diy-fm-receiver-circuit-on-internet
0 votes
2 answers
2k views

FM Receiver, RF Amplifier

In the previous FM receiver, how does the left transistor amplify the input radio signal from the antenna at the collector and output it at the base, from what i know the base always has a smaller ...
0 votes
2 answers
259 views

FM transmitter not giving the intended output of 88MHz to 108MHz

I am trying to build an FM transmitter that outputs 88MHz to 108MHz range using Multisim, but the circuit I constructed gives a lower voltage and lower frequency at the output according to the ...
1 vote
0 answers
74 views

Modern approach of creating VHF FSK (FM) recieeiver

I need to make a narrow band FM receiver for the VHF band. More specifically, not even FM, but FSK. The operating frequency range should include from 35 to 40 MHz. Frequency deviation is around 0.5 to ...
0 votes
1 answer
138 views

Antenna tuner for 1MHz to 150MHz

I am trying to build an antenna tuner for my 2m (1m + 1m) dipole antenna. It has a 1:1 balun and is connected to a coaxial cable which is connected to my radio with an impedance of 50 ohm. I can't ...
2 votes
2 answers
244 views

Broadcast FM: Where is the pre-emphasis applied?

A DSP guy like me should know this, and I think that I do, but I can't seem to find a definitive answer in my Carlson Communications Systems textbook. We know that FM is like phase-modulation (PM) but ...
0 votes
0 answers
45 views

How phase is modulated according to our message signal?

My question: let message signal m(t) be sin(w1t).For frequency modulation (instantaneous phase deviation=phi(t)) d[phi(t)]/dt=kf m(t) so i get that at 90° or π/2 frequency will be max because the ...
2 votes
1 answer
426 views

Why does the frequency deviation of a FM wave have different definitions?

Source 1 defines the modulation index in the expression for FM as follows: As per the expression for frequency modulated wave, isn't the frequency deviation same as Modulation index 'M'? "The ...
1 vote
2 answers
124 views

Why is my LC oscillator PCB design not working?

I'm building a simple FM transmitter to learn more about LC oscillators. I've successfully designed and built the following transmitter on a bread-board and perf-board using standard through hole ...
0 votes
0 answers
124 views

IQ data for analog FM modulation

I am trying to understand how I can produce analog FM modulation using IQ data. So far, I know to generate the FM modulation with an IQ modulator (like the LTC5599.) I have to apply IQ data in ...
1 vote
1 answer
178 views

STM32 FM Transmitter using PWM limitations?

As a learning experiment, I am trying to use PWM to transmit audio in the FM band (80MHZ - 108Mhz). Currently, I have a PWM output with a prescaler of 0, ARR of 1, and pulse width of 1. Since I'm ...
0 votes
4 answers
387 views

AM Receiver Antenna Coil

In almost all the radio receivers whether FM or AM, custom wire-wound coils are used that are wrapped on a ferrite core usually (not always) of 100 mm x 10 mm dimensions. Is it possible to use fixed ...
0 votes
1 answer
165 views

How to adapt a FM reciever circuit to use a varicap diode instead of a trimmer capacitor

My team and I are interested in learning about FM communication and decided to build a simple FM receiver before building a proper transmitter. We looked at some circuits on the web, and they all seem ...
0 votes
4 answers
112 views

Weird component in radio player interferes with FM functionality of the radio itself

I got my hands on an old radio player which has both cassette player and FM/AM functionality. I got constant noises while playing on FM and it turns out to be some weird component on the cassette ...
1 vote
2 answers
274 views

LoRa - Frequency Shift Chirp Modulation - chips in a symbol

I am trying to create a form of FSCM (frequency shift chirp modulation) based on LoRa principle just to learn from it and to obtain a deeper understanding. What I do not get: why is (or must be?) the ...
2 votes
4 answers
6k 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:...
0 votes
2 answers
200 views

FM receiver circuit [closed]

I am doing a college project where I have to build an FM receiver. I didn't have a lot of knowledge about the subject before starting my research. Now, I understand the function of the principal ...
6 votes
2 answers
3k views

Discrete component FM radio receiver circuit - explanation needed

I have built an FM radio receiver from a kit. I'm very happy with the results! It is the Sinclair Micro FM. My goal is to learn about discrete electronics (NO IC's.) The radio works great, but I ...
0 votes
0 answers
84 views

Need help with signal modulation

To capture a mammalian cell, I need to have a constant 4MHz AC signal (coming from a function generator) while sweeping the frequency from the vector network analyzer (VNA) 9kHz to 9GHz to read the ...
1 vote
1 answer
346 views

Why doesn't this FM receiver work in LTspice?

After years, I'm back again to the electronic world. To start off, I just tried to simulate this circuit in LTspice: Source Here is what I've done in LTspice: But it doesn't work. Here is a ...
3 votes
1 answer
1k 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 ...
0 votes
1 answer
834 views

Fm receiver 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 ...
2 votes
1 answer
173 views

Hint for the way a fm receiver works

As far as I know , a simple AM receiver 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 ...
0 votes
1 answer
288 views

FM Circuit Simulation

I tried to simulate a circuit that I found in google. I adjusted some of the values in the tank circuit but the output waveform resembles that of amplitude modulated wave. What could possibly be wrong ...
3 votes
2 answers
795 views

In this Foster Seeley discriminator, what is the purpose of capacitor C3?

I understand the whole circuit, except for the use of capacitor 3. What's its purpose in here?
1 vote
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2k views

Simple schematic for 10.7 MHz crystal-based marker generator

For FM tuner alignment purposes I want to build an outboard 10.7 MHz marker generator to use in association with a piece of gear (ST1000A) that doesn't have one built in. They used to be available in ...
0 votes
2 answers
215 views

FM demodulation circuit

I'm doing an FM demodulator circuit. I am copying the circuit from LTspice in the first image) to Multsim (the second image.) Is what I did in Multisim correct? How can I get a graph from Multisim ...

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