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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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126 views

Why can't we divide the electromagnetic spectrum into arbitrarily many radio frequency bands?

I understand there is concern over the limited amount of wireless spectrum available for allocation but am somewhat confused as to why. Couldn't we just divide the electromagnetic spectrum into as ...
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24 views

Frequency Modulator with sinusoidal output

I am creating a frequency modulator, all the circuits that I have looked so far on the internet are generating a Pulse wave or a Triangular wave output, so if you guys can help me to create a circuit ...
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1answer
51 views

understanding AFSK and FSK

I’d like to understand 1200Hz/2200Hz AFSK in commonly used APRS/Packet/AX.25 applications. When I look at the datasheets for some of the chips existing projects use (e.g the Si446x transceiver-on-a-...
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1answer
93 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?
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2answers
65 views

How does this simple FM slope detector work?

I understand what happens from the diode onwards, it's a rectifying amp and a low pass filter that filters any unwanted frequencies from the carrier, but what is going on in terms of voltage between ...
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0answers
67 views

High SNR FM demodulation

So I need to demodulate the FM signal from a sensor with highest SNR possible, at least 70-75 dB. IF is 10.7 MHz, max. deviation is 200 kHz but I can change those values if needed. Baseband signal ...
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35 views

Connecting an FM radio receiver circuit to a speaker via 3.5 mm audio jack?

As an experiment and for educational purposes, I wanted to build and connect an FM receiver to some old computer speakers via a 3.5 mm audio jack. So I tried building a circuit like this on a bread ...
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2answers
142 views

Direct FM generation using varactor diode

I am trying to generate a constant 1 MHz FM carrier wave. I have achieved it via LC parallel resonance circuit. Initially I let the switch B open and switch A closed, in order to charge the capacitor. ...
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2answers
42 views

Finding required BW with Bessel table

The FM signal (see image 1) is applied to a 50 Ohms antenna, and I am seeking the required bandwith with the Bessel table (image 2). From the FM signal, I deduced that the information frequency is ...
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1answer
301 views

RC transmitter and receiver for Raspberry Pi possible? [closed]

I've got a pet project in which I'm trying to write/build a self learning autopilot for my rc plane. I've got a Raspberry Pi with an IMU and a pitot tube in the plane and it can now control the servos ...
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1answer
139 views

FM Transmitter (Modulator) Circuit Simulation Problem [duplicate]

I've asked my question before, and I am writing this new question with some edits based on my previous problem. I am building a small FM Modulator ( Transmitting ) simulation on (Multisim). I've used ...
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1answer
161 views

What antenna is this?

I just disassembled an external FM antenna designed for an old Asus laptop. I expected to find some circuitry and a monopole or some other simple antenna. However, what I found was the antenna shown ...
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1answer
247 views

FM Transmitter Circuit (range 3 km) on Multisim

I am new to the telecom simulations system specially multisim, which I am having a project that I want to simulate. My project in (Analog Communications) is consisting to have FM Transmitter (...
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2answers
126 views

Need help understanding simple FM transmitter

I made a simple FM transmitter following https://maker.pro/custom/tutorial/how-to-make-an-fm-transmitter and it worked! Now I need some help to understand how. My coil is made of 1 mm copper wire has ...
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1answer
80 views

How do I figure out the ohms of an antenna?

I'm looking at the CZE-05B FM transmitter and in the manual it states the output load is 50 ohm and I need an 50 ohm antenna. So my questions are is this antenna 50 ohms? https://www.ebay.com.au/itm/...
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4answers
132 views

What happens if the frequency of the receiver osc does not match (exactly) the carrier frequency?

I thinking about FM and AM. Theoretically the carrier frequency is perfectly match the demodulation frequency. But what happens if there is a mismatch? I think using AM the frequency of the base-band ...
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3answers
10k views

Are audio cassettes FM or AM?

I know that cassettes store an analog signal, but is the signal Amplitude-Modulated (AM) or Frequency Modulated (FM)?
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2answers
265 views

Is it possible to broadcast FM radio up to 500 metres? [closed]

I'm buying FM transmitter 0.2 watt at Lazada to broadcast for my village community at my area. Not a normal small FM transmitter for car or portable low watt (about 10mW-100mW) which broadcast up to ...
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10answers
7k views

How exactly does AM/FM carry both pitch and loudness of voice?

Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal ...
2
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2answers
102 views

Using audio instrument cable for 1MHz transmission

I'd like to transmit digital data together with an audio signal along an instrument cable. In more detail, I'd like to send MIDI data and the audio signal of a guitar on a single cable. The rationale ...
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3answers
325 views

Radio Transmitter Circuit [closed]

I have seen previous similar answers about radio transmission, but looking at the following scheme I am not sure about the role C3 plays in the circuit. I guess it is needed to remove the DC signal ...
9
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2answers
577 views

Identifying an old RF circuit

I got an old RF circuit (I guess), probably used for pedagogical purposes. Here's the schematic: I chose the positive and ground rails as it seems right to me, looking at transistors and resistor ...
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2answers
125 views

Understanding PLL performance: PFD output bandwidth

For an application I need to FM modulate a signal with a 10 MHz bandwidth. Due to constraints I have no control over, I have to do it in an analog way (so I can't just digitize the signal, IQ modulate,...
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1answer
42 views

Amplitude Spectrum of FM wave from Bessel First order

given the values for \$\beta=5\$, for the Bessel of the first order: \$ J_{0}(5)=-0.26, J_{1}(5)=0.34, J_{2}(5)=0.49...\$ in order to plot the amplitude spectrum of the FM wave, do you treat the ...
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1answer
64 views

how to calculate the maximum radiated power for the FM broadcasting?

I am trying to experiment a fm transmitter project of Raspberry Pi - with a frequency of 88.1 MHz. http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter However, I ...
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0answers
93 views

Phase Locked Loop Gain Design- FM Demodulation

Say I am trying to demodulate a message up to 25kHz in frequency, with a peak frequency deviation of 75kHz and a carrier of 1MHz, implying a 200kHz bandwidth using carsons rule. Would I design the ...
2
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2answers
186 views

Select Phase Detector Cutoff Frequency? Phase Locked Loop FM Demodulation

I'm studying a Phase Locked Loop used for FM demodulation, obviously a phase detector is used in the system. A basic implementation of a phase detector is a multiplier followed by a lowpass filter. I ...
2
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0answers
217 views

Matlab Phase Locked Loop Design : FM Demodulation

EDIT: It seems I've asked too much at once here. I'll do some more studying and come back if I have more specific questions. I'm trying to design an analog phase locked loop in Matlab. I've read ...
2
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2answers
85 views

Does the remote car door keyfob in today's automobiles change its code with every use?

I am just wondering why other keyfobs do not open my car door and thought every signal would have to be unique. So I did some research and they use a rolling code so in fact the code changes with ...
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3answers
490 views

FM transmitter circuit working?

I am trying to understand FM transmitter circuit working basically on how a signal is imposed on to the carrier signal. I would like to get an acknowledgement on whether my understanding is correct or ...
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1answer
305 views

Best mixer for quadrature FM demodulator

I need to demodulate an FM signal and I want to use a quadrature demodulator for this. The signal is 16±0.15 MHz, 3.3V output from CMOS oscillator. I know that Gilbert cell mixers are most commonly ...
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1answer
220 views

Choosing the best FM demodulation technique

I have an FM signal: 200 mVpp, 11.5 MHz carrier, max deviation - 500 kHz, modulating signal frequency range is 40-10000 Hz. And I need to demodulate it with highest SNR possible. The circuit has to ...
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0answers
118 views

Keeping constant bandwidth in tunable quadrature FM demodulator

I need to demodulate an FM signal (4 MHz max deviation) with a strong center frequency drift (550-800 MHz). I've built an AFC circuit to track the drift and now I need to build a tunable quadrature ...
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0answers
43 views

Operation of simple FM transmitter circuit [duplicate]

I found the following little FM transmitter circuit among some old papers and it works pretty well, but I have a tough time understanding how the circuit operates: I understand the trimcap and ...
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1answer
74 views

SA605 input impedance

I am trying to find the associated input impedance to the SA605 mixer RF inputs. I have found several App notes associated with the Chip that discusses the design. On the datasheet they present the ...
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2answers
218 views

FM preselect filter

Hello I am designing an fm receiver and had some questions about the RF front end. To tune into different channels I know I need a tunable oscillator, but does the bandpass filter connected to the ...
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2answers
111 views

FM radio Interference

Near to my location we have IAF(Indian Air Force - Tambaram) training center is there, While hearing FM radio at a at frequency of 106.4MHZ I can hear the cockpit commands/voices daily when these ...
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1answer
84 views

FM folded dipole Antenna

I am designing my personal FM receiver, and I have a question regarding how to design my Antenna, in terms of choosing the wavelength to determine the size of the antenna. To put it as simple as ...
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2answers
195 views

Could a vintage 9 transistor AM/FM implement a phase-locked loop of some form?

A side discussion around an answer to the question How many stations could one hear with an AM/FM radio in front of the ISS' cupola window? has arisen with regard to the possibility that a change in ...
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2answers
1k views

FM Transmitter Power and approx Transmission Distance Calculation [closed]

I am a beginner of electronics and mostly fascinated by hobby circuits right now. I do not have any Electronics Degree. Internet and hobby Electronics books are the only places where I learned lill-...
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2answers
1k views

FM modulation with crystal oscillator [closed]

I have seen many posts where a simple AM transmitter can be made with a crystal oscillator and modulation transformer. Can this idea somehow be modified to FM. I don't want people to misunderstand me. ...
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1answer
339 views

DIY FM Transmitter [closed]

simulate this circuit – Schematic created using CircuitLab I can not find the frequency from an FM receiver... I am not sure for the coils Henries... I tried to make on of my own and I used: 19 ...
2
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1answer
269 views

What is the current status of RDS 2.0?

Radio data system is the standard used for embedding small digital information in FM radio. I am excited for the release of the new RDS 2.0 standard. But I am not really sure if the technical standard ...
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2answers
581 views

“Old FM” vs. Modern FM radio signal. What's the difference and can I adapt?

I have a vintage radio that I managed to get all circuits and tubes back into original spec. The AM stations tune in fine but I get nothing on FM. I am told this is because it's tuning in "Old FM" - ...
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2answers
1k 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 ...
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1answer
264 views

FM Tansmitter - AC Equivalent Circuit - Capacitor Analysis

This is a follow on question from the following two questions: Operation of LC circuit in Frequency Modulation with simulation and linking it to the basic principle of frequency modulation How to ...
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2answers
112 views

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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0answers
104 views

Max Output Voltage Preamplifier Microphone

I'm looking a preamplifier to get 1-2 Volt as Maximum Output Voltage of a microphone with jack 3.5 mm. To get a line-in signal and then modulate in FM. I don't know if this I've found works. Beh­...
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0answers
92 views

FM RDS Sensitivity

I am planning to build a clock based on FM RDS stream. I don't like to have external antennas and furthermore, FM reception in my bedroom is not very good. My hope is that RDS data bitrate is very low ...