How exactly do radio sine-waves work?

Question

Ok so I was looking for a hobby not long ago. And it struck me, electronics. Long story short, I wanted to learn about and produce radio waves and an actual working radio. Ok so contrary to the title, I get some of the main, bare concepts of sine but How exactly are pure sine waves produced in pure way. In such a way that the crest is curved. And how accurate do sine waves have to be to work with broadcast. I'd like to learn the maths so that I don't have to "guesstimate" everything. And how does the x axis move synonymously to the y?. Please help, thanks everyone.

Answer 1

Well, it depends....



There are several ways to create a sine wave.



First you should appreciate that a sine wave is a very natural shape. It is a single frequency of vibration. You can see it in the vibration of a string, the swaying of a tree or ripples on water. So basically if you can create a single frequency you automatically have a sine wave.



Sine wave oscillator. There are various designs of oscillator circuit that produce pure or nearly pure sine waves. What they have in common is that there is an amplifier with its output fed back to its input through some components that cause a phase shift of 180 degrees at a particular frequency. Also, the gain of the amplifier must be >=1 at that frequency. Once those conditions are fulfilled the circuit will oscillate and you will get a sine wave.

In fact it is so easy to fulfil these conditions that it is very common for amplifier circuits to oscillate when they are not supposed to, especially if there is some unplanned feedback from output to input.

You will be familiar with the high pitched howl you get when you put a microphone too close to a loudspeaker. That's the amplifer oscillating and creating a sine wave. Here the phase shift is provided by the delay that the sound experiences from speaker to microphone.

To get a pure sine wave from an oscillator it is usually necessary to limit the gain of the amplifier somehow, otherwise you get clipping, which adds extra harmonic frequencies to the signal (also known as distortion).



Oscillator & filter. You can make a simple oscillator that produces a non-sinusoidal waveform, such as a square wave. If you then pass this through a narrow band-pass filter tuned to the fundamental frequency you will get a sine wave out. This is quite a common method in radio, because at radio frequencies you can make a very sharp bandpass filter using small inductors and capacitors.



Sine shaping. This is the method traditionally used by audio waveform generators, although with the rise of cheap digital technology it has largely been superseded.

It relies on the fact that you can make an oscillator that creates a very stable linear triangle wave. You then pass this through a network of diodes and/or transistors that rounds off the peaks and troughs of the waveform, creating a reasonable approximation to a sine wave.



I don't know the figures, and they will vary depending on the transmission band being used and the national regulations, but the allowable harmonics in a transmitted signal will be very small indeed, which means you need a very pure sine wave. You can achieve that by using bandpass filters without too much difficulty.

Answer 2

As a hobby, the fastest and cheapest way to bring you up to speed, is to find the nearest amateur radio club, and take a course leading towards a radio license.



The club probably has a recommended textbook, or "study guide", which will explain all the basics, as well as local laws governing the hobby, so that neither you nor your listeners or fellow broadcasters experience unpleasant interference.



In general, a nice clean sine wave can be created by energizing a "tank circuit" - an inductor and capacitor in parallel.



The tank circuit will naturally resonate at one specific frequency, where f = 1 / ( 2 pi root (L * C) )



where f is in Hertz, L is in Henries, and C is in Farads.



To keep the circuit oscillating, you'll need to create some feedback, with a simple transistor amplifier.



If the amplifier design is not done properly, you'll end up with either a sine wave that decays to nothing, or a sine wave that grows until it distorts.



The math here starts to get pretty complicated, pretty quick. Best to google "Hartley" or "Colpitts" oscillator schematics, and adjust the values as necessary.



Once you've got a working oscillator, to make AM, you'll need to "mix" the oscillator (carrier) signal with your intelligence (audio) signal - one method is to amplify the oscillator with a variable gain amplifier, where the gain is controlled by the incoming audio.



If you find the book "Electronic Principles" by Malvino, you'll find a mixer near the end of the book.



You could also consider purchashing an AM transmitter kit... likely legal if only using a 9V battery, and 1 foot of antenna wire.



Or, buy the book "ARRL Handbook for Radio Amateurs" - over a 1000 pages of circuits, theory, application, antennas, etc.

Answer 3

"synonymously to the y"

subfluxually?

Your question shows that you have so much to learn, it is very difficult to form an answer.

The most basic answer is that some circuits naturally form nice smooth sine waves because of the physics involved.

Looks like you need to check out a good basic electronics and radio textbook and perhaps take a class.

Answer 4

As a interest, the quickest and optimum low fee thank you to hold you as much as velocity, is to locate the closest beginner radio club, and take a path optimum in path of a radio license. The club in all threat has a cautioned textbook, or "learn coaching manual", which will make clean each and all the basics, as nicely as community regulations governing the interest, so as that neither you nor your listeners or fellow broadcasters adventure grotesque interference. usually, an superb clean sine wave must be created with the aid of way of energizing a "tank circuit" - an inductor and capacitor in parallel. The tank circuit will for sure resonate at one specific frequency, the area f = a million / ( 2 pi root (L * C) ) the area f is in Hertz, L is in Henries, and C is in Farads. to maintain the circuit oscillating, you will would desire to create some comments, with an subject-loose transistor amplifier. If the amplifier format isn't executed astonishing, you will ultimately finally end up with the two a sine wave that decays to not something, or a sine wave that grows till ultimately it distorts. the mathematics superb right here starts to get particularly complicated, particularly rapid. superb to google "Hartley" or "Colpitts" oscillator schematics, and alter the values as necessary. as today as you have have been given a working oscillator, to make AM, you will would desire to "mixture" the oscillator (service) sign with your intelligence (audio) sign - one mindset is to augment the oscillator with a variable earnings amplifier, the area the convenience is controlled with the aid of way of the incoming audio. in case you discover the e book "digital suggestions" with the aid of way of Malvino, you will discover a mixer on the brink of the top of the e book. you additionally can evaluate purchashing an AM transmitter kit... probably criminal if in undemanding words utilising a 9V battery, and a million foot of antenna twine. Or, purchase the e book "ARRL coaching handbook for Radio Amateurs" - over a one thousand pages of circuits, theory, utility, antennas, and so on.