# 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.

22 questions with no upvoted or accepted answers
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195 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 ...
73 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 ...
273 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 ...
505 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 ...
66 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 ...
74 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 ...
106 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 ...
289 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 ...
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 ...
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 ...
303 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 ...
57 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 ...
29 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 ...
37 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 ...
128 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 ...
68 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 ...
305 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 ...
434 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) ...
58 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 ...
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 \\$\...