Waveform Definition

[Tony Stewart]

As already mentioned in post #13

OK then I agree but it is not a variable pulse width ,
hence not a subcategory of PWM.

Many ICs now support both PWM and PFM to better support a wide range of dynamic loads with less overshoot.

 

[Nigel Goodwin]

OK then I agree but it is not a variable pulse width ,
hence not a subcategory of PWM.

It varies the width of one of the pulses (either mark or space), and is thus a varient of variable pulse width.

 

[BR-549]

As long as everyone understands the difference, there's no need to disagree about the definitions. We change classifications and definitions all the time.
We have different contexts, for the same thing.......in different fields.

For instance, chemistry and electronics are the exact same thing, but no one looks at it that way. We give them a different context.

 

[Tony Stewart]

It varies the width of one of the pulses (either mark or space), and is thus a varient of variable pulse width.

You may be thinking of something else. BR-549 said this "vary the off time only" That means fixed pulse variable frequency, or PFM or "pulse rate"

 

[Nigel Goodwin]

You may be thinking of something else. BR-549 said this "vary the off time only" That means fixed pulse variable frequency, or PFM or "pulse rate"

The off time is just a negative going pulse? - which you're width of.

 

[BR-549]

I have a problem defining frequency as an asymmetrical alternation. But I know you fellows work with what you have.

If the duration of the alternations is not equal, I personally would not call that a frequency. That's why I asked you guys what is was called.

But evidently you do term that as frequency. The alternation of ANY two states, no matter the durations. Which is new and foreign to me.

It's my education(or lack of), training and work experience bias.

I figured the dynamic I described would be some form of duty cycle terminology.

 

[AnalogKid]

PFM, PPM, and PWM all are duty cycle terminologies. They are three *different* ways that a frequency is modulated by varying one or both halves of the duty cycle. AND - they are not the only ones.

ak

 

[AnalogKid]

I figured the dynamic I described would be some form of duty cycle terminology.

PFM, PPM, and PWM all are duty cycle terminologies. They are three *different* ways that a frequency is modulated by varying one or both halves of the duty cycle. AND - they are not the only ones.

ak

 

[ChrisP58]

I have a problem defining frequency as an asymmetrical alternation. But I know you fellows work with what you have.

If the duration of the alternations is not equal, I personally would not call that a frequency. That's why I asked you guys what is was called.

But evidently you do term that as frequency. The alternation of ANY two states, no matter the durations. Which is new and foreign to me.

It's my education(or lack of), training and work experience bias.

I figured the dynamic I described would be some form of duty cycle terminology.

The frequency (in Hertz) of a periodic waveform is the reciprocal of the time (in seconds) it takes for that waveform to repeat itself.

It does not matter what the shape of the waveform is, as long as there is a repeating pattern with a definable beginning and end points, and that the next, equal waveform begins at the end of the first.

If the time between the start of that waveform and the beginning of the next waveform is 1 millisecond, then the the frequency of that waveform is 1 KHz.

 

[BR-549]

My problem with this frequency definition is allowing the absence of a signal, to be included as part of a waveform, when there is nothing there. But I'm sure they have related this as IF something was there. Let's say that the light switch was off for 23 hrs. and one for one, then the period is 24 hrs. And then off for 22 hrs. on for two. The period remains the same, but that is not a repetitive action, the pattern has changed. But keeps the period. And classified as the same frequency.

Very confusing to me. So frequency can contain a series of unique patterns. As long as you keep the period? I have never thought of frequency in such a manner. It seems it would be hard to encode information with this dynamic. I assume all here is in reference to power transfer, not information.

I was going to set my generator up to a speaker, to get a better feel for it, but forgot it's loaned out.

 

[BR-549]

We have amplitude, frequency and phase modulation. Could the dynamic that I explained, using the terms just explained to me, be termed or called, period modulation? In reference to my first post, not the last one.

 

[AnalogKid]

My problem with this frequency definition is allowing the absence of a signal, to be included as part of a waveform, when there is nothing there.

This is an incorrect way of thinking about a frequency. In electronics, and especially in signals and communications, the "off" part of the signal is relative to what the signal is and what it is doing. If a square wave signal is going to a transistor that is turning on an LED, then either the high part or the low part (called phases) of the signal can turn on the LED depending on what type of transistor is used.

Anything that repeats has a frequency. This can be as simple as a complete cycle of a sine wave, square wave, etc, or a more complex waveform such as the audio signal for one note of a piano.

Let's say that the light switch was off for 23 hrs. and one for one, then the period is 24 hrs. And then off for 22 hrs. on for two. The period remains the same, but that is not a repetitive action, the pattern has changed. But keeps the period.

Correct. The periods of each phase of the signal have changed, but the period of the waveform (the sum of the periods of the phases) and the frequency - how often the entire cycle repeats - is the same. In the case of your example, the frequency is 0.00001157 Hz, or 11.57 uHz.

If you look at the lifetime ratings of lightbulbs, you will see that they are stated in terms of how many hours per day the light is on. For example, 24,000 hours at 6 hours per day. The assumption here is that the bulb is on continuously for the 6 hours, so the frequency is one cycle per day, the on period is 6 hours, and the duty cycle is 25%.

ak

A totally unnecessary aside: The vast majority of LED bulb failures happen at power-on. A better way to rate the expected lifetime is the total number of turn-on cycles. Back in the 80/90's, people noticed that switching power supply reliability was more a function of how often a PC was turned on and off that how long it was running. This actually showed up in the reliability ratings of some power supplies, and large corporations instructed their PC users to leave them on overnight.

 

[BR-549]

Thanks ak,

My 24 hr. example and point in post #30, was that the same period could not have a repeated pattern. And the term frequency was still appropriate. Which was confusing to me.

With this new understanding of frequency, then the dynamic of my first post, with a changing off time, would be considered a change in frequency. I had been thinking in terns of duty cycle, not frequency.

This seems to have happened when digital came to be. And equating with analog.

To me, if there is a break in signal, the term frequency became invalid, and it would be referred to as duty cycle. There are no breaks in a wave function in a media. A vibration rings. But for engineers working with intermittent power, frequency has a different context to what I was use to. I always thought of frequency applied to continuous change. And referred to switching states, as duty cycle......to denote the difference.

It's fine, I see the logic of what you fellows have explained to me. It allows intermittence to be likened to frequency. And I can see how a 50% duty cycle can be a frequency. But it was hard to see it, when both the duty cycle is changing, and the period is changing, to use the term frequency with intermittence. I just needed to expand my understanding of the term.

Anyhow, back to my first post, could that dynamic be referred to, as a period modulation of an intermittence? I guess I was trying to get an electrical description of a mechanical dynamic. Trying to relate a motion in common terms with the expertise here.

I never thought of phase, as a state change, or a polarity change, during a period. I always thought of phase, as the start time(and therefore the peak time) of the period. Arrival time. The phase of current is the arrival time, compared to the voltage arrival time. I thought of amplitude mod as a level change. FM mod was a contracting and expansion of period. And PM mod as a + and - of arrival time. i.e., sliding(in time) the peak of the period.

If flipping or inverting the period is PM mod, then would that indicate, that a space wave does not need to serially alternate to propagate thru space? As Maxwell stated.

I believe that a wave function in a circuit is very different than a wave function thru space. Space can not support a wave function. Only an intermittence, a duty cycle. Blinking. Never a continuous stream. A flux(light) of intermittence only appears as continuous.

But now know, that an intermittence is considered a wave function. I always assumed that a wave function needed a media TO function in. And only applied to media environments. Not space.

With a wave function thru media, the shift in frequency is reciprocal with an inversion of location. In other words, we can switch locations of train whistle and listener at station....and the shift is the same. One location is moving, the other is not. But I don't believe that happens with EM radiation. We will not get the same shift, if we invert locations. The duration of the emission, propagation length and detection are all the same durations with media functions. Making it reciprocal. But with EM propagation, the dynamic of emission and the dynamic of detection are completely different and not reciprocal. The motion of the detector is sensitive to shift, but the motion of emitter is not. Only the phase(start time) changes with emitter motion. Because of distance time. The detector motion, changes both the duration of on time and off time by the same amount, giving that shift. A symmetric period change with detector motion. The emitter gives a asymmetric period change with motion. Only the off time varies. The on time is always emitted as a constant length chunk. And takes no time to emit, it's instant.

Apply a 180 degree precision one shot into a dipole feedpoint. No feed lines. Generator at feedpoint. A one shot will not pump up a feedline. You get one "wave". Every 180, an instant emission happens. Twice(two emissions) per cycle. Install a precision rectifier at feedpoint of dipole and transmit. Tune in with receiver. See any difference? Now AM modulate it. Do you hear any difference?

Wave velocity.....phase velocity....group velocity.....it's all trying to describe intermittence. With a wave function....and with no media to function in.

A wave is a constant change to the present. A duty cycle is the alternation of the present.

I know, I know, twilight zone, right?

 

[rjenkinsgb]

Whatever the waveform may be, you can take a Fourier transform of it and see the component frequencies that make up the waveform.

The modulation you refer to could possibly be called pulse position modulation, or even a type of frequency modulation.

 

[BR-549]

Yes rjenkinsgb, ak gave me the formal definition, thanks. And an example with that wide sweeping power supply.

And the FFT does makes signals much easier to see and understand. The digital revolution has enabled all to study electronics at reasonable cost these days. It would have been nice 50 yrs. ago.

Does the FFT come from the influence or the reaction to the influence?

When we detect and measure rf power, I believe that half of that power comes from the detector......detecting that power. Reacting to that influence power. It reacts with the same amount of power.

But no one believes that.

 

[rjenkinsgb]

When we detect and measure rf power, I believe that half of that power comes from the detector......detecting that power. Reacting to that influence power. It reacts with the same amount of power.

Measuring power in a properly impedance-matched transmission line is just a matter of measuring the signal RMS voltage anywhere along the transmission line.
The power passing through the transmission line is whatever power that voltage will equate to at the load end.
eg. On a matched 50 Ohm system, an RMS signal voltage of 100V will result 2A current flow in the load, so 2A x 100V = 200W power in the load.

Other than the impedance matching, it's the same principle as measuring a supply voltage and load resistance and being able to calculate the power the load will dissipate at that voltage.

(A mismatch can result in meaningless readings and reflected power, which is why impedance matching (low SWR) is so important).

No "power" as such is drawn by the power meter or multimeter, the measuring device will general have vastly higher impedance than the circuit being tested so no noticeable influence on it.

 

[BR-549]

Pardon me, I should have stated space propagated power.

 

[rjenkinsgb]

I should have stated space propagated power.

You can only measure field strength then, which has many possible influences.

It may be given as voltage resulting at the load on a specific antenna, or the required antenna voltage to get a specific signal-to-noise or demodulated signal quality in a receiver.

 

[BR-549]

I believe a dipole in transmission mode, has a completely different dynamic than a dipole in detector mode. In transmission mode, the dipole is anti-resonant and breaks/cuts the field around it. The cut is instant. leaving a neutral dipole for the next inducement feed. The dipole cuts the field, every 180 degrees. Preventing resonance. The dipole is charged, but never discharged, only cut. The discharge goes out in space. Not back into dipole, like it does in RX mode.

In detector mode, the dipole is resonant and rings. Like a tank circuit. This is because of the two different feeding dynamics. In TX mode the dipole is end fed. In RX mode the dipole is broadside fed.

The received propagation has a duration of 1/2 period, not a full period. This charges the dipole. The other half period comes from the dipole discharging. The discharge time equals the charge time...i.e...resonance. A ringing. This discharge happens during the dead space of the emission. Emission is intermittent.

So, if we put a resistor across the feedpoint, we will measure the inducement(charging) and the reaction(discharging).

A doubling of the inducement. We measure 1watt, but only 1/2 watt was induced.

What do you think of my eureka moment?

 

[rjenkinsgb]

A dipole is most definitely resonant in "transmit mode", as you call it. The resonance and impedance changes with frequency are very easily measured with the appropriate equipment.

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Antenna tuning and matching are part of setting up any good antenna, and the adjustments have exactly the same effect on receive as on transmit.

(I've been a licenced radio ham, designing and building gear and antennas since the 70s).