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
106 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 ?
0
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1answer
47 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 ...
-1
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1answer
69 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?
1
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1answer
131 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 ...
1
vote
0answers
83 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 ...
1
vote
1answer
74 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 ...
1
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0answers
46 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 ...
1
vote
1answer
127 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 ...
0
votes
2answers
62 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?
3
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2answers
122 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 ...
1
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1answer
96 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 ...
6
votes
1answer
176 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 ...
4
votes
2answers
511 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), ...
0
votes
1answer
88 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 ...
1
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2answers
79 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 ...
-2
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1answer
139 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 ...
4
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5answers
167 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) ...
2
votes
2answers
201 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 ...
-1
votes
1answer
113 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 ?
0
votes
2answers
574 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 ...
1
vote
1answer
612 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 ...
0
votes
2answers
114 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
220 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
votes
1answer
478 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. ...
1
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1answer
170 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 ...
4
votes
3answers
499 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 ...
0
votes
1answer
116 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?
2
votes
1answer
246 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 ...
3
votes
1answer
216 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 ...
5
votes
3answers
258 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 ...
3
votes
1answer
118 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
942 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. ...
3
votes
1answer
210 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
387 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 ...
2
votes
0answers
168 views

Good compact antenna for FM audio transmitter module?

I've been looking at building a short range FM transmitter using this module, the idea is to create a small module that I can integrate into other projects. I'd prefer having the antenna on the same ...
2
votes
1answer
256 views

Audio amplifier kills FM radios signal [closed]

I have a Lepai LP-2020A+ audio amplifier and a K├Ânig FM Pocket Radio. My problem is that the pocket radio works really well on its own, with the headphone plugged in, but when I connect the radio to ...
1
vote
1answer
355 views

FM bug Circuit Issue

I implemented this circuit stripboard layout but when I connected this device to phone, there is no pulse in phone reciever. Please notify me what am I doing wrong!! And here is my implementation ...
0
votes
1answer
171 views

Building a telephone spy

I am implementing the following circuit but I am stuck at one point. How can we input the wires in IN1 , IN2, OUT1, OUT2? I don't know which wire to insert because there are almost 4 or 5 wires ...
-1
votes
2answers
4k views

How do i calculate the frequency of an fm transmitter circuit?

Below is an FM transmitter circuit I found on the web that I would like to build from scratch. How I would calculate the carirer signal frequency so that I know where to tune my FM radio? If I ...
0
votes
2answers
151 views

Limit a radio to a single station

We are organizing a game for students where we are transmitting the daily objectives and hints over from an FM transmitter. Is there a way to limit basic radios to only be able to pick up a certain ...
1
vote
1answer
247 views

Recommendation for si4734 external clock source

The si4734/4735 FM receiver has two options for clock input, one is to use the typical crystal oscillator (a crystal + pair of capacitors to ground), attached to the DCLK+RCLK pins, the other is to ...
2
votes
3answers
468 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 ...
12
votes
4answers
725 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 ...
5
votes
1answer
836 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 ...
1
vote
4answers
2k 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 ...