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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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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86 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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420 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 ...
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536 views

Is it possible to make a Raspberry Pi transmit FM on several frequencies at the same time?

I have read a few questions here on transmitting on multiple frequencies at the same time. But all of them was about transmitting the same signal to all frequencies. The PiFM and PiTX projects are ...
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1answer
91 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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119 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 ...
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306 views

Superheterodyne receiver with voltage controlled oscillator

I'm new in electronics and I want to create a FM receiver that performs a product of the received RF signal and a local signal (the local signal is also frequency modulated with a Voltage Controlled ...
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1k 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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106 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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307 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 ...
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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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43 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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30 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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47 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
68 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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52 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
84 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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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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3answers
128 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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74 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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138 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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99 views

Antenna cable pin-out identification

I am trying to connect a stock car FM/AM antenna with a new aftermarket stereo system, Turns out my car antenna has 2 wires. One is Co-axial cable for signal (Most probably) and there's one more ...
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487 views

Phase Modulator with JFET

At the university we have seen this circuit as a Phase Modulator: simulate this circuit – Schematic created using CircuitLab where \$m(t)\$ is the message at audio frequency and \$v_p(t)\$ is ...
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1answer
513 views

Is it true that frequency deviation over 2*pi is the phase deviation of an FM/PM signal?

for ∆f frequency deviation if for FM only and PM has Phase deviation. and Kf= ∆f (Hz) of FM? Kf = ∆f (rad/s) for PM? and for th rules: ∆f=(kfmp)/(2p) for FM where mp = mp max-mp min ∆f=(kfmp)/(2p) ...
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63 views

Make Si4703 evaluation board Bluetooth capable

While looking for a Bluetooth RDS-TMC receiver which could be queried with FOSS software, and after realizing there’s probably not too much on the market, I stumbled across Si4703 evaluation boards ...
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1answer
34 views

Noise floor of a FM duplex

If these 2 signals, that form this duplex, have ranges of 15-30 [kHz] and 30-45 [kHz] using: \$NoiseFloor_{dBm} =10\log _{10}(k\times T_{0}\times 1000)+NF+10\log _{10}(BW)\$ and if \$K,T,F\$ and \$\...
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1answer
216 views

For which purpose are those resistors on the ANT output?

I've bought a cheap FM transmitter and installed it in my car, but sadly, it gives me too much interference (Too weak signal), even in a totally static signal, so I decided to disassemble the ...
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2answers
8k views

How to remove the static sound in an fm transmitter

Hi I have a school project and I used the schematics from this website for our FM transmitter. Its actually working but its hard to recognize the music being played because of the static, also does ...