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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Range of FM and Power

Why is the range of an FM signal shorter than AM signal? I thought it was due to the high frequency of FM signal getting absorbed by physical barriers. Is it so? Does power of a signal has any role to ...
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1answer
41 views

Questions about FM receivers and transmitters?

I have a test tommorrow on phase lock loops, AM/FM receivers along with several other topics. I need to understand this topic clearly before I take the exam to advance to the next schooling in the ...
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2answers
58 views

Why feedback is needed in PLL FM Demodulator?

I am trying to build FM Demodulator in FPGA. The architecture I am trying to use is PLL-based FM Demodulator like the one below. I searched for the working principle of this demodulator but there is ...
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0answers
25 views

Problem with Constant Off-time PWM/Variable Frequency on dsPIC30F2020

I'm using the Microchip dsPIC30F2020. I've been trying for the longest time to get some sort of PFM signal for my project. I see in Section 12.4.7 there is the ability to have constant off-time PWM ...
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2answers
251 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. ...
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2answers
94 views

How to make a RF Choke?

I am a high school student and am making a project on FM receiver for class 11. I am following this circuit diagram: The L2 in this diagram is a 22µH RF Choke. The part listed in the website has ...
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3answers
111 views

There is a missing component in this circuit and couldn't figure out why?

I'm designing a BA1404 Stereo FM transmitter and I found the following source: Source Link You can find the component list, circuit scheme and the other stuff on this page. But when I look at the ...
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1answer
101 views

simple question regarding frequency modulation (FM)

I have a question on frequency modulation. For example, the following signal is frequency modulated: y(n)=sin(2*pi*(400+cos(2*pi*4*t))*t). Since the maximum of cos function is from -1 to 1, so I ...
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1answer
46 views

Will BA1404 circuit work with TEA5591A

For an electronics project I would like to build stereo FM transmitter and receiver circuits. I was just wondering if these two circuits would work together. The BA1404 circuit can be found here. ...
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1answer
69 views

FM and phase/frequency deviation

I have a small understanding issue here, so I would be very glad if someone could help me a bit! We are given this FM modulated signal to volts; ...
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1answer
283 views

FM Radio transmitter and receiver circuits

I'm planning on building a FM transmitter and receiver circuit for an electronics project. I was just wondering if these two circuits would work together. Also would they be suitable for transmitting ...
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1answer
91 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 ...
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1answer
181 views

Why AM is preferred over FM in long distance communication?

In almost all long distance communication AM is preferred over FM. Do type of modulation has anything to do with this or it is just depending on transmitting frequency?
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1answer
147 views

Basic FM circuit

I have been messing around with a basic FM transmitter circuit, and I want to have a better explanation on how it works. I have searched around and found nothing. Can someone please explain how the LC ...
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1answer
79 views

FM Transmitter Amplifier — Maximum output power with non-customized parts?

I would like to build an FM transmitter on my own and I found a nice circuit that acts as a USB sound card to transmit low power FM signals. http://tipok.org.ua/node/35 My plan is to add another ...
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2answers
53 views

Why frequency and coordinatino make sense in FM? [closed]

In FM modulation, the signal changes frequency depending on the amplitude of the original signal. So when you input the coordination frequency how does that makes any sense? For example, you input ...
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1answer
71 views

Radio Receiver IC

I am a Junior EE student that is interested in putting together a small radio receiver project for fun and to get some general practice with design. I have found these receiver chips from Silicon Labs ...
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0answers
98 views

FM tuner/receiver chip with RDS and good audio quality?

I want to rebuild from scratch an old radio and put some modern technology in it. I want to put large (17x5cm) LCD instead of analog scale inside receiver like this: (image from audiofilek.pl) ...
3
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2answers
111 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 ...
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1answer
499 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, ...
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1answer
268 views

Problem solving super heterodyne receiver question

I have two problems which i am trying to solve but i am stuck on the half way. I have the following first question, which i am trying to solve I have solved the problem as following, ...
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1answer
227 views

How does this direct digital synthesis accumulator work?

So, I grabbed some code online and morphed it to work with my DE2-115 board, and now I need some help understanding exactly how it works. ...
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3answers
607 views

Capacitor between emitter and collector

What is the purpose of capacitor C5 ? I know it provides positive feedback to sustain the LC oscillations, but how does this work ?
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1answer
212 views

Streaming UHF/VHF/AM/FM over IP

I am working on a project that can stream TV and Radio signals over IP. I found a device to capture the signals and send them over IP realtek-rtl2832u but I am ...
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1answer
303 views

FM transmitter feedback capacitor [closed]

Why is a capacitor connected across the collector-emitter of the transistor? How does this capacitor prevent decay of LC oscillations?
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1answer
238 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 ...
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0answers
251 views

simple schematic for 10.7MHz crystal-based marker generator

For FM tuner alignment purposes I want to build an outboard 10.7MHz 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 ...
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1answer
113 views

What is the modulation technique used?

I own a Tx/Rx Radio Direction-Finding (RDF) set for a sport called falconry, basically, locating & recovering a pet falcon after flight. The Tx tag is at 218.025MHz from Marshall Radio Telemetry ...
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0answers
71 views

Frequency modulation occurs not in an expected way

I've built this oscillator. Then I gave it a DC bias and connected an mp3 player. Result: I have local fm-stations muted at 90MHz, 90.75MHz and 89.25MHz. However, at 90MHz an mp3 music is very ...
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1answer
705 views

Transmit and receive 433,92MHz signal from the smartphone [closed]

I would like to use my smartphone to send and receive signals from the devices that is working on the 433,92MHz. I assume that it's not possible to communicate directly with this device from the ...
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2answers
95 views

How to increase frequency modulation index?

I'm thinking of making a low power FM transmitter. Here's a diagram. It seems an absolute pull range of a VCXO will limit the modulation index. Is there possibly a way to extend it?
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2answers
173 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 ...
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1answer
112 views

Translate signals amplitude into frequency

I have a sinusoidal signal at 50 Hz, that varies in amplitude, with no offset. The amplitude goes from 0 to 5 V (peak to peak), and the amplitude contains all the information I need. This signal will ...
7
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1answer
256 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 ...
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2answers
2k 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), ...
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1answer
105 views

The primary selection criteria for choosing FM vs. AM is dynamic range

The primary reason for selecting FM over AM is the ability of FM to support a greater dynamic range by spreading the information across a wide range of frequencies, and using more 'horizontal ...
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2answers
90 views

Final RF envelope of FM and AM are the same

https://masi.vuse.vanderbilt.edu/images/0/0b/EECE_252_Final_Project2.pdf Page 2 spectrum plots. Effective RF electromagnetic power profile is effectively the same for baseband audio content ...
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1answer
202 views

Is FM more information density efficient than AM

So here and here, RF power envelope We have determined the information expressed in an AM signal comes from the fact that the amplitude of electromagnetic energy at any given frequency determines ...
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5answers
230 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) ...
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2answers
251 views

Simple way to decoding FSK

I'm trying to build simple fsk transmitter and receiver, the transmitter is just an FPGA with a wire, the logic is quite simple, I mix (with a XOR) the transmission ...
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1answer
185 views

why frequency modulated signal covers small area as compare to am signal [closed]

why frequency modulated signal covers small area as compare to AM signal ?
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2answers
2k views

Using Bessel function graph to finde out side bands

If I am not wrong, using Bessel function we can estimate the side bands of a carrier? Is this correct? If so, what are the steps to find these values from the graph? For example if modulation index ...
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1answer
2k views

Whats the principle of a PLL used as demodulator of a FM signal?

I didnt quite understand te following: A basic PLL consists of the following parts: phase detector low pass filter VCO If you input a 1MHz sine the PLL will try to lock on it by controlling the ...
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2answers
129 views

LEDs in the audio path - linearity? [closed]

I'm repairing an ancient stereo multiplex decoder which has diodes in the signal path for mono/stereo switching. For headroom reasons, I need plenty of Vf on these diodes, which are pulled up by a DC ...
3
votes
1answer
307 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 ...
5
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1answer
835 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. ...
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1answer
225 views

FM Transmitter and transmission

This is an FM transmitter circuit found in Internet Link. Before doing ,I'm simulating in multisim. Since there is no mic input,I have given sine wave generator 1).What is frequency of wave must ...
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3answers
640 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 ...
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1answer
141 views

relationship between modulation index and carrier-suppressed condition in fm

What is the relationship between modulation index and carrier-suppressed condition in FM. What should the modulation index be when the carrier is suppressed in FM?
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2answers
309 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 ...