- #36
enigma
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Can we please take the hostility down a notch, guys?
4Newton said:Averagesupernova:
As always you seem to get things mixed up. The nature of the device that produces the RF is of no consequences. You only need to be concerned with the process of modulation, the transfer function. As you have pointed out the RF voltage varies in a linear manner with applied voltage. You also agree that the amplitude of the side band also varies in a linear manner with applied audio. If you really don’t understand modulation at this point you must be the only one on this forum that does not.
4Newton said:Of course you know I don’t agree that frequency mixing and amplitude modulation are the same thing. You also know that it is not the same thing.
4Newton said:At this point I can see that you are starting to see this in a whole new light. I also know from what you have posted that you will never state that you are ever wrong.
4Newton said:I have no problem teaching electronics but I don’t care to do it in a confrontational manner. If you whish to know how mixers work or any thing else please change your approach. The approach I recommend is that you state you understanding listen to the other understanding, if different. then pose questions and give replies to the point. If you are confused on any point, resolve the confusion first without confrontation.
I apologize Averagesupernova I should know better, but I did not realize, until now, that I was considered an opponent.having my opponent completely ignore facts”
I am sorry if you have taken offense at my not responding to your quotes but I did not feel that it was necessary. I do not disagree with your quotes. I thought I stated that once before. They are just not relevant to the disagreement about modulation.But I don't see how quoting textbooks and having my opponent completely ignore facts from those books adds anything to this thread.
4Newton said:Averagesupernova;
I am sorry if you have taken offense at my not responding to your quotes but I did not feel that it was necessary. I do not disagree with your quotes. I thought I stated that once before. They are just not relevant to the disagreement about modulation.
4Newton said:I have tried to hold the discussion to the basics of modulation. I did not feel that it was of any use going in any other direction without that basic agreement between us.
4Newton said:I pointed out and you agreed that the voltage out of the RF amp was linear with applied voltage. I also pointing out to you and you agreed that the voltage in the sideband from the modulation was also linear with applied audio, I thought that should have resolved the issue. I still don’t know why it has not. It is axiomatic that a result that is linear is a linear function.
4Newton said:Maybe I should introduce you to the idea of a transfer function. The RF source maybe thought of as a black box. It has only three terminals. Common, supply voltage, and output. The only thing you can change is the supply voltage. The only output you have is the RF. I have shown. And you have agreed, that with any change of supply voltage or supply voltage change at an audio rate the output is always linear. If you disagree all you need to do is show that the output will change in a nonlinear manner with a change of supply voltage.
4Newton said:The black box could be a constant RF source that has a variable resistor the output of the box is linear with the position of the resistor. As you change the resistor, by definition, you modulate the output. This box will produce amplitude modulation with the same waveform of any other AM modulator. There is no nonlinear component. This is why the nature of the RF source is of no importance. Only the transfer function is relevant.
Do you think summing two audio frequencies together with resistors is modulation or mixing?1) To convince you that mixing and amplitude modulation are considered the same thing.
Are you saying that the wave form you see on the scope is or is not the change of voltage with time and what you see is not taking place?2) To convince you that what you call the voltage out of the RF amp
varying linearly with applied audio is nothing more than the carrier and
2 sidebands forming a complex waveform.
Did you follow the concept of transfer function? What is the transfer function of a class C amp with applied voltage? What is the transfer function of a class A amp with voltage?3) To convince you that the source of the RF is in fact relevant and
that the output device is part of the modulator.
4) To convince you that a device running linear mode on the output
would NOT be capable of modulation by superimposing audio onto the power
supply.
What do you think that says? This is a description of a linear function.That the amplitude of the carrier (that is, the value of the carrier’s current or voltage) is made to follow faithfully the instantaneous changes in the audio-frequency voice volttage.
You note the word ADD.They all add together in such a way as to give the
appearance of a single frequency (the carrier) whose amplitude is changing
just the same way that the signal doing the modulating is changing.
Are you aware that you went from voltage to power. How does power vary with a change of voltage in a resistor? Is changing voltage across a resistor a linear function? Look again at you example.Now let's modulate it at a given frequency with a NEAR square wave. I hope you are ok with this method. We will modulate it 100%. So what we have is the 'RF output' going on and off. The voltage NOW swings up to twice the original peak to peak voltage but only half the time. The other half of the time the output is ZERO. Average power dissipated is 2 watts. Now let's modulate at 50%. The envelope peaks up to 15 volts now for a 30 volt peak to peak signal. Incidently, this condition is
defined in the book I quoted as 50% modulation. So now we have power
dissipated in the load at the peak of the envelope of 2.25 watts and the
trough of the envelope of .25 watts for an average of 1.25 watts.
Hmmmmmm. Is this linear? I don't think so.
4Newton said:Averagesupernova
Do you think summing two audio frequencies together with resistors is modulation or mixing?
4Newton said:Are you saying that the wave form you see on the scope is or is not the change of voltage with time and what you see is not taking place?
4Newton said:Did you follow the concept of transfer function? What is the transfer function of a class C amp with applied voltage? What is the transfer function of a class A amp with voltage?
4Newton said:What do you think that says? This is a description of a linear function.
4Newton said:You note the word ADD.
4Newton said:Are you aware that you went from voltage to power. How does power vary with a change of voltage in a resistor? Is changing voltage across a resistor a linear function? Look again at you example.
The transfer function is the behavior of the considered amplifiers. A class A/B amp has a constant output and does not change with any change of voltage. It therefore is irrelevant to the question at hand. You can not modulate it you can not use it for summing. It is a constant output device. The transfer function of a class C amp changes linearly with applied voltage. Just as you show in you chart. The voltage changes linearly with the modulation. Your chart will show the same results if you have no RF at all and you put a step function that has the same differential voltage as you show in col. 2 and 3 into you resistor.Yes I follow the concept of transfer function. However, we cannot agree on the behavior of a class C versus a class A amplifier when superimposing audio onto the power supply. At least I cannot assume we agree because you haven’t answered my question concerning the class A or class A/B amplifier from my last post. So what is the point of talking about transfer function? In order for us to agree on it we have to first agree on the behavior of the considered amplifiers.
Thank you. I don’t know what the other points are that you are talking about. This was the only difference I know of that we hadYes, you are right. The instantaneous voltage on the envelope changes linearly with applied audio.
That is right. It is only important that the transfer function is that same as it is for high level modulation. You can’t take a rock and say that modulation is not linear because the rock can not be modulated. You must have a device that can be amplitude modulated.You said that the source of the RF is irrelevant.
The main reason is to decide on an instrument to prove the question. The oscilloscope will do the complete analysis, only of course if you know how to read an oscilloscope. But at this point the issue is settled. If you wish I will interpret the oscilloscope trace for you and show you how it includes the sidebands.why should we just stick to the oscilloscope
Your last statement.Ummmm, not quite. A mixer or modulator requires a NON-LINEAR device. Using resistors will form an adder which is NOT a mixer.
Nope, a linear circuit is incapable of true modulation. You will not get sum and difference frequencies out of a circuit that you describe. It may be capable of adding 2 signals together to send down the same wire or something but this is not a mixer. I've worked on a lot of RF equipment and I have never seen a mixer/modulator that didn't use some sort of non-linear device.
But the FUNCTION of modulation is not linear. A true linear amplifier will sum two signals and not create new frequencies. A non-linear amplifier will sum them AND create new frequencies. Creating new frequencies is what modulation is all about.
I pointed out to you this function.Yes, you are right. The instantaneous voltage on the envelope changes linearly with applied audio.
This shows that you do not need a nonlinear device and that a linear change produces AM modulation. You did not comment on this statement.The black box could be a constant RF source that has a variable resistor the output of the box is linear with the position of the resistor. As you change the resistor, by definition, you modulate the output. This box will produce amplitude modulation with the same waveform of any other AM modulator. There is no nonlinear component. This is why the nature of the RF source is of no importance. Only the transfer function is relevant.
4Newton said:Everyone here is right to some extent. No one it seems is old enough to remember vacuum tubes...