question about radio

[joe0311]

When amplifying a sound wave, what does the current actually do to the wave to make it louder? As in, how do the electrons of the current actually interact with the audio wave mechanistically?

[Strange]

I'm not sure what context you are thinking of here. But there isn't really a place where electric current interacts directly with the sound wave.

 

There are two three main components for amplifying sound: a transducer to convert mechanical movement to changes in electric current or voltage (a microphone), an electronic circuit that will use those small changes to control a larger voltage or current change (an amplifier), and a transducer to convert that back to mechanical movement (speaker or headphones).

 

There are many types of microphone. They can operate by, for example, changing resistance and hence the current through a circuit. Or it can move a coil in a magnetic field, or change the spacing in a capacitor.

 

The amplifier consists, at the simplest level, of a transistor where the changing input current on the "base" terminal controls how much current flows through the "collector" and "emitter" terminals. The transistor has a gain which defines how much larger the output current change is that the input. Real amplifiers are much more complex for reasons of efficiency and accuracy.

 

The speaker is typically a coil in a magnetic field: the changing current through the coil causes the speaker to move. The current is larger than that from the microphone and so the movement of the speaker is greater and, therefore, louder.

 

 

Edit: Just saw "radio" in the title. Not sure what part of the question relates to radio ...

 

Radio is transmitted as electromagnetic waves. You end with two systems like I described above. At the transmitter, instead of the speaker, you have an antenna (crudely speaking). And then you have a receiver where, instead of the microphone, you have another antenna which picks up the weak radio signal from the air.

 

(This is all horribly simplified but I hope it helps. Or, at least, allows you to ask some more questions!)

Edited May 18, 2016 by Strange

[studiot]

 

When amplifying a sound wave, what does the current actually do to the wave to make it louder? As in, how do the electrons of the current actually interact with the audio wave mechanistically?

 

 

The microphone in the studio converts the sound wave to an electrical wave.

 

This electrical wave copy of the sound wave is superimposed on a radio carrier wave and received at the radio receiver.

 

The loudspeaker in the receiver is a form of electric motor that moves backwards and forwards (rather than going round and round) when driven by an electric current.

 

The backwards and forwards motion pushes the air to create a sound.

 

So if the speaker is driven by an electrical copy of the original sound wave it pushes the air in the receiving room to create an audible copy in the air.

 

Like any motor the greater the drive current the stronger the motion and in this case the louder the sound.

 

So the reciever contains electrical amplification circuitry to make the driving electrical signal larger or smaller.

That is make the whole of the electrical copy large (or smaller) in the same proportion.

 

This is controlled by the volume control.

Edited May 18, 2016 by studiot

[Sensei]

what does the current actually do to the wave to make it louder? As in, how do the electrons of the current actually interact with the audio wave mechanistically?

Typical speaker is stationary magnet with moving electromagnet attached to membrane (or reverse set up with stationary electromagnet and moving magnet),

when current is flowing in one direction, electromagnet creates magnetic field, and membrane attracts to magnet,

when current is flowing in opposite direction, electromagnet creates opposite magnetic field, and membrane repels from magnet.

 

 

The larger current is flowing through wire, the more powerful electromagnet's magnetic field, attracting and repelling it more powerfully.

This pushes air around membrane thousands times per second.

 

You can very easily verify it by taking speaker and connecting it to battery, without resistor, then with resistor, or variable resistor. Change polarization +- of battery and you will see it's moving in opposite direction.

[joe0311]

Thank you very much for all your replies! I think I understand a little better now! So the audio wave goes through a transistor which adds more electrons/current to the vibrations, making them louder?

 

Now how exactly would the microphone work if it was a coil in a magnetic field? Is there a constant current in the coil, and when a sound causes the diaphragm to vibrate it alters that constant current somehow? How exactly is the vibration of the diaphragm causing the fluctuations of the current which create the audio wave peaks and troughs?

 

For one of the other microphone types, what would be the mechanism for changing the resistance to make an audiowave?

Edited May 19, 2016 by joe0311

[Externet]

It is difficult to express what happens until you study and understand more of the principles involved in electronics.

 

Meanwhile, do a couple of unusual things...

- Connect the two terminals of your stereo speaker wired to the other stereo speaker and to nothing else.

Tap with your fingers the cone of one speaker and observe the other speaker cone.

One behaves as a microphone, the other as speaker.

 

-Grab between thumb and index the antenna of your automobile just an inch above its base and shake it. Observe how much the base moves and how much the tip moves. Sort of mechanical amplification.

 

Radio as in the posted title and audio are similar electrically but with different behaviors. Radio frequencies have the ability of electrically traveling over the air; audio hardly travels electrically over the air.

 

If you have seen the discotheque lights that flash and change intensity at the rhythm of music... The light you see is the carrier signal as a radiowave; the flashing cadence is the audio or information carried (modulation). Your eyes are the receiving antenna, your brain discerns the rhythm.

 

There is a loooong path of learning in front of you, with many things to discover.

 

Keep this link ----> http://www.williamson-labs.com/ for hopefully a near future.

[rangerx]

RF signals are collected from the air using a variable capacitor. This is amplified and applied to the oscillator, which converts any tuned signal to 10.7 MHz. This is called the intermediate frequency (IF). A modulated signal is then passed through a potentiometer (volume control) at the input side of a circuit otherwise known as the pre-amp. The signal is then passed to the power amp for output.

Edited May 19, 2016 by rangerx

[Strange]

RF signals are collected from the air using a variable capacitor.

 

They are "collected" by an antenna. In older (analog) receivers a variable capacitor is one way of filtering out the frequencies of interest.

 

This is amplified and applied to the oscillator, which converts any tuned signal to 10.7 MHz. This is called the intermediate frequency (IF)

 

That is a common frequency for FM but it is not used by all receivers.

 

A modulated signal is then passed through a potentiometer (volume control) at the input side of a circuit otherwise known as the pre-amp.

 

You have missed out the entire demodulation stage

 

Which, for digital and spread spectrum signals, can be pretty complex!

[swansont]

Thank you very much for all your replies! I think I understand a little better now! So the audio wave goes through a transistor which adds more electrons/current to the vibrations, making them louder?

 

 

 

Transducer, not transistor. They are different things. A transducer is a component that converts a mechanical input into an electrical one, or vice-versa.

[Sensei]

Transducer, not transistor. They are different things. A transducer is a component that converts a mechanical input into an electrical one, or vice-versa.

Not necessarily mechanical.

On the list of transducers there is also f.e. antenna, photodiode.

https://en.wikipedia.org/wiki/Transducer

Edited May 20, 2016 by Sensei

[joe0311]

And the oscillator runs at a specific frequency to be used as a 'carrier wave'? How does it create this frequency? It's sending out pulses of current at a constant value? How exactly does it do this? Also, how is the electrical signal (after it's amplified) actually added to the carrier wave?

Edited May 20, 2016 by joe0311

[Strange]

I think you have too many questions for this to be an effective way of learning. It might be better for you to go and read up about how radios work and then come back with specific questions about bits you don't understand. But ...

 

The carrier wave is a sine wave (not pulses) generated by an oscillator.

 

The signal is used to added to the carrier either by a modulator. This changes either the amplitude of the carrier (AM) or the frequency of the carrier (FM). How "exactly" it does this is pretty complicated.

 

(Keywords for searching in bold.)

[Externet]

And the oscillator runs at a specific frequency to be used as a 'carrier wave'? How does it create this frequency? It's sending out pulses of current at a constant value? How exactly does it do this? Also, how is the electrical signal (after it's amplified) actually added to the carrier wave?

 

Yes. An oscillator runs at an specific frequency and when its electrical signal is applied to an antenna, it travels over the air. If that carrier signal has another superimposed signal to it, both are propagated; the carrier and the signal. The process to 'merge' both is called modulation. At the receiver end, the carrier is discarded and the signal of interest (audio) is extracted by another circuit called demodulator or detector.

 

Tutorials show schematic diagrams. There, lines are interconnecting wires between components expressed as symbols. Better print this :

----> http://web.gps.caltech.edu/~als/IRMS/course-materials/lecture-1---electricity/circuit_symbols.pdf

 

There is several flavors of oscillators and of modulators.

----> http://www.electronics-tutorials.com/oscillators/oscillator-basics.htm

 

The electrical signal is actually added by a modulator circuit, also there is several flavors.

Watch this. (I have not fully) and should help ---->

 

Another site for your future is :

----> http://www.discovercircuits.com/resources/tutorials.html

 

But my number one suggestion is start by obtaining a kit like these and read carefully its manual, that should be basic and good:

 

----> http://www.ebay.com/itm/Science-Experiment-Kit-Dangerous-Book-Essential-Electronics-from-Brookstone-/151384016052?hash=item233f30c4b4:g:~24AAOSwiylXBYe3

 

----> http://www.ebay.com/itm/NEW-RadioShack-Make-It-Electronics-Component-Kit-1-250-Pieces-Experiments-1-11-/371594888159?hash=item5684c803df:g:m~UAAOSwy5ZXBsxF

 

And do not expect to learn/do it all on the web. Books are important. Very important.

[joe0311]

Yeah I've been reading about how radios work (I'm just doing this for fun btw, not school), and the problem is that it seems like all the articles I read tell simplified versions of how it works. Like I don't see anything about how an oscillator can make the current go at a steady frequency or how a modulator actually puts the audio signal and carrier wave together. I hate walking away from google articles feeling like they just told me vague descriptions. But thanks guys I'll take a look at this stuff, appreciate it. : )

[Strange]

An oscillator generates a constant frequency because it is a "tuned circuit". To understand this, think about a capacitor that has a certain charge on it: if you discharge it through a resistor then it will take a fixed time to discharge. The time is a function of the capacitance and resistance values.

 

Then think about the feedback you get when a microphone gets too close to a speaker. The frequency of that feedback depends on the time it takes for the signal to go round the loop. In an electronic circuit you can use the R and C values with an amplifier and feedback to generate a specific frequency.

[joe0311]

Oh ok thanks, I'll do some more reading and I may be back with some questions later. Thanks again for all your help! That goes to all you guys in the thread as well!

[studiot]

Two suggestions to help.

 

Firstly a good textbook at introductory level is the TEC level 2 book

 

Radio Systems level2 by DC Green.

 

Followed by the level 3 Book strangely enough called

 

Radio Systems level3 by DC Green.

 

Secondly get used to reading and understanding Block diagrams

They are really useful.

I wanted to draw one to go with my original reply, but I am sorry I did not have time and the moment has now passed.

 

https://www.google.co.uk/search?q=block+diagrams&hl=en-GB&gbv=2&source=lnms&sa=X&ved=0ahUKEwjehvPRw-7MAhXGD8AKHQGXDlEQ_AUIBA

 

Some good examples come from this site

 

http://ukradio.info/Degen/

 

such as this one for a radio receiver.

Ask anything about it.

 

 

Edited May 22, 2016 by studiot

[joe0311]

Ok cool I'll look into that stuff thanks for the suggestions : )