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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81 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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69 views

Short range FM transmitter

I made this FM transmitter from this video (https://youtu.be/joFourugXvs) but it has a very short range (30 cm). Where's my mistake?
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65 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
67 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
96 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
109 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
56 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
68 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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34 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
70 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
50 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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52 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
91 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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31 views

Loop Filter in an ADPLL

I am implementing an ADPLL in an FPGA with VHDL, and I am encountering a problem in correctly implementing the loop filter. The code that I currently have for the loop filter is the following : ...
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3answers
53 views

Frequency demodulation with a spectrum analyzer

In my university lectures I have generated an FM signal (for instance with carrier frequency of 2GHz, frequency deviation equal to 100kHz, and modulating frequency equal to 100kHz.) In order to ...
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49 views

Increasing Locking range of ADPLL in VHDL on FPGA for FM Demodulation?

I am trying to implement an all digital PLL so as to demodulate an FM signal from the input. The centre frequency of the test signal is that of 140kHz. The system works fine upto a deviation of +-...
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3answers
71 views

Loop Filter in all digital PLL cutoff?

I am implementing an all digital PLL system on an FPGA using VHDL. Now, I have not yet closed the loop, instead I have modelled a sinwave(simulating an input) at 22kHz and also modelled a cosine wave(...
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54 views

Loop Filter cutoff frequency of an all-digital PLL

I am trying to implement an all digital PLL for FM demodulation on an FPGA using VHDL. I built all the blocks needed, i.e the NCO centered at 100kHz, the phase detector(simple multiplier) but now I am ...
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1answer
537 views

Understanding this simple FM receiver

I know the theory of FM, but I just can't understand how this simple circuit works. So let's say a radio station is transmitted on 100 MHz, as I understand in this case the oscillator should also ...
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1answer
87 views

FM demodulation (not!) using PLL?

I have to demodulate a square wave FM+PWM modulated signal, so for the FM demod I'm using a PLL with a positive edge sensitive comparator to lock on frequency only (CD4046BE). Carrier frequency is ...
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4answers
76 views

Clarifications about up and down converting mixers

Let's look at this definition of mixers (reference): A real mixer cannot be driven by arbitrary inputs. Instead one port, the "LO" port, is driven by a Local Oscillator with a fixed amplitude ...
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2answers
354 views

Simple FM Radio Receiver project

I've been making my own simple FM radio. I know it's not quite appropriate to make this stuff on breadboard, but if it works, I'll move in on the board and solder it. I wanted to ask why my radio is ...
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2answers
82 views

Can I transmit to several FM radio channels concurrently using one digital transmitter?

I have an Si4720 that can transmit at one FM radio frequency at a time, and if I use several of them on my board, I would be able to transmit at several FM radio frequencies at the same time. This ...
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1answer
49 views

Estimate data transmission rate on a given frequency using FM

How can I estimate how much data can I transmit on a given radio frequency range using FM? My goal is to consider using radio to transmit data packages, and I want to evaluate bandwidth. Plus ...
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47 views

FM modulation using sine wave

I've learned that to analyze the spectrum of frequency modified carrier with a sinusoid wave, it needs to be expressed as the following: $$m(t) = A_m\cos(2\pi f_mt) $$ $$s(t) = A_c \sum_{n=-\infty}^{...
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70 views

Can long-range radio waves from an RTV tower penetrate thin plastic composite material next to its source?

We are currently developing a conceptual design for the renovation of Croatia's main RTV tower located on 1033 meter tall peak Sljeme at the Medvednica mountain north of Zagreb. The idea is to ...
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1answer
573 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 ...
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1answer
798 views

Can someone explain how this Ratio detector circuit works?

I understand how a Foster Seeley discriminator works, but in this Ratio detector, which is a modified version of the former, I don't understand the purpose of having three transformer windings, or ...
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3answers
147 views

Frequency/amplitude modulation and SNR

I read (for instance here) that FM modulation is less affected by noise than AM modulation. But I don't understand conceptually the reason for that: why is the SNR with frequency modulation higher ...
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2answers
149 views

Is a coil FM transmitter frequency affected by my body static?

I've built this coil FM transmitter following these guides which are essentially the same: https://maker.pro/custom/tutorial/how-to-make-an-fm-transmitter https://www.instructables.com/id/The-...
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1answer
166 views

FM Demodulation

I'm using a demodulation fm circuit in multisim. it takes 1 minute on the oscilloscope to complete a full waveform, and every waveform the amplitude is decreasing. I want to know why is the amplitude ...
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1answer
78 views

How frequency is modulated in FM transmitter circuit [duplicate]

I am new to looking at FM transmitter and have a few questions regarding the FM Transmitter circuit below. Please break down your answers as simple as possible as I am not as well versed in circuits ...
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1answer
166 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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53 views
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181 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
279 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
731 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
87 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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84 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
571 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
107 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
1k 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
368 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
300 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
1k 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
404 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
337 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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219 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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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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627 views

Broadcast range of an FM radio station with given transmit power [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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