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Results tagged with frequency-modulation
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user 20218
For questions relating to frequency modulation (FM). This is a scheme where a carrier is modulated by varying its frequency to carry information.
12
votes
If an FM signal has different frequencies, how does the radio receive the signal in a fixed ...
For FM, Carson's bandwidth rule informs you the approximate bandwidth of a transmission. The bandwidth value it calculates contains 98% of the energy of the whole transmission. It is expressed by the …
- 473k
8
votes
Radio Transmitter Circuit
Back-story
Internally to the BJT is a parasite called "Miller capacitance". It can be regarded as a capacitor between collector and base and is typically, for normal transistors, in the region of 10 …
- 473k
8
votes
Accepted
Frequency spacing and the doppler effect
When moving at 1km per second (very fast for anything using a road) a radio wave of carrier frequency 100 MHz will appear to shift to 99.9997MHz if traveling away from the source of the transmission. …
- 473k
7
votes
Accepted
Would you explain the output waveform of this FM transmitter circuit?
Why someone hasn't answered this beats me....
Your sound card input is good for 20 kHz and maybe 80 kHz on a good sound card sampling at 196 kHz. 88 MHz is well over a thousand times too high in freq …
- 473k
7
votes
Identifying an old RF circuit
It looks like an RF transmitter to me, maybe FM
It smells of amplitude modulation rather than FM because of the way 2 modulates the base bias in the oscillator.
Moreover, I'm puzzled by the …
- 473k
7
votes
Accepted
Basic FM circuit
C3 turns the circuit into an oscillator. To understand this you need to think hard about the role of the emitter and the thing you have to think hard about is this - the emitter (as well as the base) …
- 473k
6
votes
Accepted
Simple FM transmitter
All BJTs have what is known as "miller capacitance". It can be "altered" by a greater or lesser reverse bias voltage across the collector-base region. Note that C1 shunts this small capacitance to gro …
- 473k
6
votes
Accepted
How to build an FM transmitter and how does it work?
How am I supposed to learn this stuff?
There are no short cuts and I would learn the following (but there's no guarantee I haven't missed anything from the list because I learnt this stuff decade …
- 473k
5
votes
Accepted
Whats the principle of a PLL used as demodulator of a FM signal?
With FM you get much more than two sideband frequencies. The sidebands you describe sound more like AM (amplitude modulation) sidebands. You may want to supply a link where you get this information fr …
- 473k
4
votes
FM receiver not picking up any stations
I am trying to make an FM receiver. FM receiver not picking up any stations
The circuit you have posted is an AM receiver and it ain't a very good AM receiver either. You need to load the diode dete …
- 473k
4
votes
Accepted
Piece of wire as FM antenna
Have you recently plugged in a phone charger close to the radio?
@andy_aka You were spot on. Moving the USB phone charger to the other
side of the room has eliminated the interference.
I think …
- 473k
4
votes
Send text data using FM frequencies
You can use basic radio modules like these: -
These happen to be from a company called RF solutions but there are plenty of people supplying them.
The tricky part is packaging the data (that you …
- 473k
4
votes
Accepted
FM Transmitter Power and approx Transmission Distance Calculation
I've made a 'powerful FM transmitter' and measured the peak current
across the Amplifying transistor's collector-emmitter. It reads approx
300mA.
You are measuring current incorrectly. Puttin …
- 473k
4
votes
Accepted
Why is transformer coupling used in a simple slope detector? Can't the FM signal be applied ...
Why is transformer coupling used in a simple slope detector?
You don't need a transformer for a simple slope detector. This circuit would work providing you select the centre frequency to be one sid …
- 473k
3
votes
FM transmitter circuit working?
Your understanding is flawed but redeemable. Firstly there is a subtlety in this type of design that is usually missed by beginners. It's called the miller capacitance. That internal transistor capaci …
- 473k