How to move up/down the frequency wavelength

[Electro132]

Hi,

I am usually asking for help in my circuits but today, i would like to ask you all for help in understanding how to move up and down the frequency wavelength chart. I know that having an LC Tank circuit will define where i am on the chart and also with a tuner i can narrow down the frequency even more. However i can not find any place where i can understand how i can move up and down the frequency chart variably as well as further tune the frequency without having to build more coils for each time i need to move up or down the chart.

Any help is much appreciated. Thanks

 

[(*steve*)]

Look for a mathematical relationship between the values of the components used and the resonant frequency.

Once you have this relationship you can investigate what changes in the values do.

 

[Harald Kapp]

When you use an LC circuit, you'll need an adjustable inductance or capacitance.
Typically you will be able to adjust the resonant frequency within a comparatively small range ("band") only. You will switch between ranges (bands) by using a switch to select different base configurations of L and C.

There are also other means for changing the parameters of an LC circuit, e.g. using varicaps (diodes with voltage controlled capacitance).
Modern tuners typically do not use tunable LC circuits but use PLL circuits to digitally set the receive frequency or use software defined radio to tune in to a station using mainly software.

 

[KrisBlueNZ]

You seem to have forgotten to tell us what you want to move up and down the frequency range. Are you trying to receive RF signals at different frequencies?

 

[Electro132]

You seem to have forgotten to tell us what you want to move up and down the frequency range. Are you trying to receive RF signals at different frequencies?

Well i have this oscillator software (which i would like to learn more about waveforms on) that picks up sounds and other frequencies (pretty much like a music synthesizer) and i would like to try altering the waveform of something (e.g. AM, FM) using log pots to make them long/short and wide/narrow.

I think starting off with just an AM or FM circuit will do but i just can't get my head around a simple circuit where i can place the log pot in. For instance i know that an LC circuit can have a variable cap + cap + coil but i am confused as to whether i should place the log pot before the LC tank where it can control how much current/voltage will go through before it oscillates or whether it is best to place the log pot after the LC tank so it controls the output. However, at this stage i am not quite sure whether placing the log pot afterwards will change the wave so if anyone can guide me through learning this i will be thankful.

Also i need to know where the battery should go. I was thinking it was best placed before the vari cap in the LC tank but i thought otherwise since the LC tank can change polarity and become vice versa. So once again if anyone can help i would be thankful.

Cheers

 

[davenn]

forget your log pot ... no idea why you want that

google this ....

basic am radio receiver circuit

Dave

 

[Electro132]

I had looked at it on google but my main goal is to alter the waveform by making it faster or slower and then viewing the change on an oscilloscope. I have the idea but was wondering if placing a battery + Cap + Coil + potentiometer (which comes off as a tap from the coil and sends out a signal) is correct to make the output waveform faster / slower. The AM / FM circuit was just an idea so i can measure the oscillating frequency but in whole, i am after just altering the waveform from going fast to slow and vice versa. I was experimenting today and didn't get anywhere however, i came to think that the amount of current / voltage being pushed into the log pot would cause the output signal to become either faster or slower. Would this be true?

 

[(*steve*)]

Would this be true?

Not really. You probably need to study how oscillators (especially, it seems) RF oscillators work. You'll find that most have their frequency varied by changing the value of capacitors and inductors.

 

[hevans1944]

If you already have a waveform from your whatever... a software oscillator? What is that? How is it like a music synthesizer? Do you want to make it play faster/slower? What does AM or FM have to do with anything? What does a log potentiometer have to do with anything?

Let's say you have a steady stream of recorded audio (recorded so you can use it over and over again as you experiment) and you want to speed it up or slow it down (is that what you want to do?)... the only way to do that is to digitally sample and store the audio stream on a fast memory device, like a solid state disk or a big chunk of digital memory, and then play back the samples at the speed you desire. Unfortunately this will also shift the frequencies of the audio stream, so if you want to slow the stream down and still have it sound "normal" you will have to restore the original spectrum of frequencies by "filling in the blanks" between samples during playback. OTOH, if you want to speed up the stream and not have it sound like chipmunk speech, you will have to decimate some of the samples so the playback of the faster samples preserves their original spectrum of frequencies.

None of this is particularly easy, but it was worse when attempts were made to do this kind of signal processing with analog electronics, fifty or so years ago, with some success. IIRC, the problem was to synchronize sound with motion picture film when the sound recording was done on a different machine than the picture recording (camera). The two never ran at exactly the same speed, so eventually the sound got "out of sync" with the picture. Recording sound directly on film at the time of picture exposure pretty much solved the problem, at least for monaural recording, but there are other applications where it is desirable to speed up or slow down the sound. For example, fast forwarding without simultaneously up-shifting all the audio frequencies, or slow motion without down-shifting the audio frequencies into an unintelligible rumble. These two examples are at least possible to implement with digital signal processing today, but it isn't exactly easy. Log potentiometers have nothing to do with it.

So, if the above explanation doesn't describe what you want to do... please elaborate. We are all here to help.

 

[Electro132]

Ok cool. Going back to your question - No. What you said is correct but it isn't what i was after. Let's say for example a carrier is made from electricity and on that electricity information is placed on it. However, this information travels with the carrier regardless whether it goes fast or slow. The only thing is, with today's technology, like you said, it is possible but not easy to separate 2 things as both picture and sound must flow together otherwise they will be out of sync.

But what if i wanted to make the wave go faster or slower and not care about what info is on it for educational purposes? The amount of frequencies it would go through would be a large number. However, in my mind this does not matter as the waveform can move faster or slower regardless of which frequency it is on. I understand through my research that as the waveform goes faster or slower it is moving from one frequency to another but it does not mean that it has to move from one frequency to another as in my theory the waveform itself is possible to move faster or slower on its own.

In short, my research states that a waveform that comes out (e.g. like a square wave) of an input can be altered to move faster or slower at the output depending on how much flow of current / voltage is applied (which in this case i have identified as a potentiometer). Is the explanation a bit more clearer now?

Cheers

 

[davenn]

However, this information travels with the carrier regardless whether it goes fast or slow.

that doesn't make sense and is basically wrong

But what if i wanted to make the wave go faster or slower and not care about what info is on it for educational purposes? The amount of frequencies it would go through would be a large number.

this statement also doesn't make any sense

they don't go faster and slower as such ... tho when an RF signal goes via a transmission line there is a change in velocity this is called the Vf Velocity Factor.
But this has noting to do with your misunderstandings

However, in my mind this does not matter as the waveform can move faster or slower regardless of which frequency it is on. I understand through my research that as the waveform goes faster or slower it is moving from one frequency to another but it does not mean that it has to move from one frequency to another as in my theory the waveform itself is possible to move faster or slower on its own

I really don't know where you are doing your research as this is still wrong see my above replies
RF signals travel at the speed of light in a vacuum, ever so slightly slower in air.
because of that with velocity constant, when you change freq, the wavelength changes

In short, my research states that a waveform that comes out (e.g. like a square wave) of an input can be altered to move faster or slower at the output depending on how much flow of current / voltage is applied (which in this case i have identified as a potentiometer). Is the explanation a bit more clearer now?

Sorry, no its not clearer .... you have a total misunderstanding

The principles are similar for audio and RF signal
In fact, what in happening in a circuit, before the oscillator signal is emitter as RF by an antenna or emitted as sound by a speaker is the same. That is, the oscillating energy is carried by an EM ( electromagnetic) wave that oscillates back and forward along the outside of the conductor

Time for you to get back to some basic training .... you should get yourself a copy of the ARRL Amateur Radio Handbook


regards
Dave

 

[hevans1944]

...Time for you to get back to some basic training .... you should get yourself a copy of the ARRL Amateur Radio Handbook


regards
Dave

And maybe a good physics text too. Is Halliday and Resnik "Fundamentals of Physics" still in print? That's what I started with many moons ago.

Edit: Yes it is! Many links available here.

 

[Electro132]

that doesn't make sense and is basically wrong



this statement also doesn't make any sense

they don't go faster and slower as such ... tho when an RF signal goes via a transmission line there is a change in velocity this is called the Vf Velocity Factor.
But this has noting to do with your misunderstandings


I really don't know where you are doing your research as this is still wrong see my above replies
RF signals travel at the speed of light in a vacuum, ever so slightly slower in air.
because of that with velocity constant, when you change freq, the wavelength changes

Actually it does go faster and slower but not as you think. You see when you move up the wavelength chart you basically are making the wavelength smaller and as you move down the chart you are making the wavelength bigger. Of course each frequency has its own wavelength. However, i did say i wanted to alter the wavelength and not stay on one frequency.

Sorry, no its not clearer .... you have a total misunderstanding

The principles are similar for audio and RF signal
In fact, what in happening in a circuit, before the oscillator signal is emitter as RF by an antenna or emitted as sound by a speaker is the same. That is, the oscillating energy is carried by an EM ( electromagnetic) wave that oscillates back and forward along the outside of the conductor

Time for you to get back to some basic training .... you should get yourself a copy of the ARRL Amateur Radio Handbook


regards
Dave

Yep, RF signals, Audio basically anything that has a wavelength i can convert to how i understand them clearly so there really is no misunderstanding on my part.

To break it down so it is more simple, the way i understand how RF works is that they need voltage / current and this acts as the carrier regardless of how many coil turns you do or what frequency you are on. This in turn means that you can place information onto the signal carrier creating a more defined waveform. For some frequencies such as light it may seem impossible but i have found throughout my research that it is well indeed possible to place information on lightwaves as much as radiowaves or soundwaves. Even though these 3 are on different wavelengths the point i am trying to make is that they are all on the same chart meaning i can turn the dial to move from one frequency to another quickly (e.g. from UV lightwaves to Mobile Communications) because they are using the same type of wavelength.

Just imagine a string and the entire chart is on it .... Do you understand?

 

[davenn]

To break it down so it is more simple, the way i understand how RF works is that they need voltage / current and this acts as the carrier regardless of how many coil turns you do or what frequency you are on.

its the parallel inductor and capacitor that sets the frequency of the circuit ... the amount of voltage or current has little to do with it

This in turn means that you can place information onto the signal carrier creating a more defined waveform.

no, it doesn't create a more defined anything

For some frequencies such as light it may seem impossible but i have found throughout my research that it is well indeed possible to place information on light waves as much as radio waves or soundwaves.

of course you can ... how do your think fibre optic transmission occurs ....
but the modulation is just a side issue, there are many, many different types of modulation methods

Even though these 3 are on different wavelengths the point i am trying to make is that they are all on the same chart meaning i can turn the dial to move from one frequency to another quickly (e.g. from UV lightwaves to Mobile Communications) because they are using the same type of wavelength.

no you cannot, there is no piece of gear that covers the whole lot

because they are using the same type of wavelength

what does that even mean ???

PLEASE ......

there are just so many mis-understandings and incorrect stuff in the whole post

If you are not going to listen to what all of us are trying to teach you , I will just close the thread
none of us want to continue to waste our breath if you are not even going to attempt to understand


Dave

 

[duke37]

Electromagnetic waves can indeed have different frequencies. Radios have different wavebands long wave, medium wave, short wave, etc as the frequency rises. The highest frequency in common use is light and fibre optics are used to transmit these signals for large distances.

Sound waves are vibrations in the air and do not have an electromagnetic component.

In order to send information on an EM wave it needs to be modulated, varying its frequency or amplitude. The wave travels at a constant frequency, the same for long wave or light except for a slight slowing down in some materials or cables as has been mentioned.

Putting a resistor into an oscillator will take out energy and likely stop it working altogether.

I suggest that you make a crystal set to get a feel for tuned circuits.

 

[Electro132]

Electromagnetic waves can indeed have different frequencies. Radios have different wavebands long wave, medium wave, short wave, etc as the frequency rises. The highest frequency in common use is light and fibre optics are used to transmit these signals for large distances.

Sound waves are vibrations in the air and do not have an electromagnetic component.

Thank you duke37 for understanding some of what i was saying. However, even though i do agree with you that sound waves are vibrations in the air, they still have a waveform. Why? because it is sound and technically what comes out of your speakers (for e.g. music) has waveforms even though they are vibrations. Check your mp3 music files on 'audacity' - its a program i use for editing and altering music waveforms.

In order to send information on an EM wave it needs to be modulated, varying its frequency or amplitude. The wave travels at a constant frequency, the same for long wave or light except for a slight slowing down in some materials or cables as has been mentioned.

Yes, finally someone can understand what i was trying to say. Modulation is what i was trying to do. Using FM to change and alter the waveform. Maybe using a function generator would do it somehow as i know it sends out a signal usually a square signal, but can also be a triangle and sawtooth. However i also need to know how the wave is changing and need an oscillator circuit just so i can see the wave. Also i was wondering if a multimeter can help.

Cheers

 

[duke37]

A function generator produces lowish frequency signals which can not be used to produce significant EM waves. If you want to see the shape of the waveform you will need an oscilloscope. This will also be needed if you wish to see the shape of the envelope of an AM radio frequency signal.

There is no change of shape of a FM modulated signal. The frequency changes but this will not be easy to see on a 'scope.

 

[davenn]

However, even though i do agree with you that sound waves are vibrations in the air, they still have a waveform. Why? because it is sound and technically what comes out of your speakers (for e.g. music) has waveforms even though they are vibrations.

don't see your point there

Yes, finally someone can understand what i was trying to say. Modulation is what i was trying to do.

I had already told you that

Using FM to change and alter the waveform

no. modulating the carrier in a specific way produces a FM signal
as I have already told you, there are many ways to modulate a signal ( modulation types)

here are some of them .... FM, AM, SSB, typically used for voice
others for digital systems are many and varied .....





Before you worry about modulating a signal, you first need to understand how to
generate a signal and how the values of parallel inductors and capacitors determine the frequency produced

 

[Electro132]

thanks for the info. I'll study some more

Cheers