BR-549: As MrAL said, it depends on how you qualify phase. Can I and Q signals be considered in phase?

SLK001: Yes... I and Q are always in phase.

BR-549 said: One signal always starts when another is 15 degrees ahead of it. Are they in phase?

SLK001: If they are the same frequency, then yes.

To me, "in phase" means a zero degree phase angle between two signals. So I and Q are in sync (same freq) but 90 degrees out of phase.

ak

 

I guess that here is the ultimate authority:
"Two waves of the same frequency that pass through
their maximum and minimum values of like polarity
at the same instant are said to be in-phase."

The ultimate authority being Radio Shack's New 1975-76 Unabridged Dictionary of Electronics.

I bow to their authority.

 

I guess that here is the ultimate authority:
"Two waves of the same frequency that pass through
their maximum and minimum values of like polarity
at the same instant are said to be in-phase."

The ultimate authority being Radio Shack's New 1975-76 Unabridged Dictionary of Electronics.

I bow to their authority.

Hi,

Who can argue with a 40 year old publication from a company that is almost out of business

I have one of their 'battery' data books, which is small but a little interesting anyway. Bought it a long time ago when we had a RS in almost every town around here. Now we have one that i know of several miles away and many others closed up, including the one that was in our town.

 

During times of coincidence two signals of the same frequency can be in phase.

Connect two different oscillators set on the same frequency to an oscilloscope to see the coincidence.

Look up Lissajous patterns.

 

I kinda thought the I,Q signals were the components that made the phase of a complete signal.

A constant k just syncs the signal, but they are not in phase......there are locked in a constant out of phase. 3 phase power for instance. Can being locked in a constant out of phase, be considered in phase? Can negative charge flow be considered an inverted positive charge flow?

And I would consider harmonics (if from the same source) as being in phase.

Post #4.....can two cars traveling at different speed be always next to each other?

If the cars represent signals......then all cars travel at the same speed. What changes is the number of rotations per a standard length. That length is 300 million meters. It takes a 1 Hz signal........300 million meters to rotate 1 revolution.
We can equate that length to 1 second of time. c is one second of length.

 

I kinda thought the I,Q signals were the components that made the phase of a complete signal.

As two axes of a polar coordinate system, I and Q are one way of producing, and analyzing, a phase-modulated signal.

ak

 

Hello again,

Here is the graph of a few of the Fourier components of a half wave rectified sine wave.

Note that the 2nd and 4th harmonics appear to start at -90 degrees at t=0 but looking at the whole graph of those two it seems hard to call them "in phase", although the phase shift quantity for both waves is zero because they are both -cosine waves and so their form looks like this:
-A2*cos(2*w*t+0)
-A4*cos(4*w*t+0)

where both phase shifts are zero, and even if we translate the inversion into the phase shift then they both have the same phase shift. It's still hard to say they are in phase though.

So i think the real question is if two waves have the same STARTING phase, can they be considered to be "in phase"?
I dont think so, because if that were true then we could consider two unrelated frequencies that happen to start out at the same phase "in phase" which cant be right.
At the same time though, when talking about harmonics, it might be customary to say that two harmonics are in phase, although i think it would be more accurate to just say they have the same phase starting phase, which gets shortened to "the same phase".

This is just one of those things were we have to be very aware of the context, which usually means we have to know what the application is.

 

MrAl, those are strange signals to me. I am not insulting you, truly, truly I'm not.

But I don't think I want to listen to your music. Not you now. Just your music.

 

Who can argue with a 40 year old publication from a company that is almost out of business

40 years ago, Radio Shack was a technology leader. Their stores, back then, were fun to shop.

 

40 years ago I did repair work for several RS stores. In my home in spare time. They had a great parts department. I could get any part in no time. Good documentation. And they paid their bills promptly.

 

MrAl, those are strange signals to me. I am not insulting you, truly, truly I'm not.

But I don't think I want to listen to your music. Not you now. Just your music.

Hi,

Ha ha, yeah.

Those signals are some of the frequency components of a half wave rectified sine wave which i think we've all seen here at one time or another, as it's just a half wave rectified AC wave.
Those signals are only the fundamental and two harmonics, but if we added them together we'd see a wave that looks like an approximate half wave rectified sine wave. If we computed more harmonics and added them too, we'd get a better and better approximation to the sine wave. In theory, if we did an infinite number, we'd get an exact half wave rectified sine wave out of it.

Yeah i remember the says of ordering from Radio Shack when they had a pretty big catalog of parts, just parts. I was surprised as much as can possibly be when one day the guy at the RS next town over handed me that catalog as i did not know RS would order those parts for us, and there were many many parts to choose from from many manufacturers. I ordered several parts and got them within about week.
Then one day i tried to order parts and they told me they did not do that anymore and no more catalog of parts. That's pretty strange for a place that for a long time dealt with parts and electronic equipment.
Now we are lucky we at least have the internet to order from. RS still has very very limited parts available however, which is still strange. Tells me the management of RS just isnt there anymore.
I was also around to see the fall of Lafayette Electronics, where i purchased my very first current meter after riding my bike several miles when i was very young. It seemed that years later they could not compete with RS. Maybe they should make a comeback now that RS is going downhill faster than a freshly greased roller coaster on a track of wet ice

 

I do remember Lafayette. And of course Heathkit.

But with the web......parts and circuits are no problem.

 

I do remember Lafayette. And of course Heathkit.

But with the web......parts and circuits are no problem.

Hi,

Oh yeah Heathkit, cant forget them, and Eico too.

Yeah we got lucky with the web and parts. I used to have to order through the company or through the snail mail and snail mail orders took as long as orders from China today because the check had to get there first before they ship the stuff. Jameco was around even back then in the 1980's.

 

2 different frequencies signals will be in phase with each other at the "beat frequency":

Measuring this beat frequency is a useful way of accurately measuring very small differences in frequency.

 

Phase difference occurs when there is impedance mismatch i.e coz of capacitive or inductive load, it doesn't matter with the different frequency.

 

In phase? To me that means the wave has the same period and start at the same time reference. It's also possible to have two signals of the same exact frequency but not be in phase. If one signal starts at 0˚ and the other starts at 0.001˚ then the two signals are not in phase. And if they are EXACTLY the same frequency then they will NEVER be in phase. They may be damned close to being in phase, but the aren't truly "In Phase". Same would be true if the second signal were 359.999˚ - again, not in phase.

Harmonics? Well, when the period of one signal is at X time then the second signal is at 2X (or 4X and so on), that's harmonics, the period when both signals are (for reference) zero crossing. However, harmonics is not "In Phase". They ARE in phase for a moment in time that repeats, but so are signals that are NOT harmonic. (i.e. 1.1X) They WILL cross zero point at some point but that does not make them "In Phase".

Someone mentioned amplitude. Has nothing to do with phase.

Think of two clocks. One doesn't run at all while the other one loses a minute every day. Which clock is right more often? The one that doesn't run. It's right twice a day. It may take years (I don't feel like doing the math) before the one that loses a minute every day to be right a second time. HOWEVER, at some point in the future the second clock WILL have the right time again. So in that respect, the two clocks would be "In Phase" for that single moment in time.

[edit]
OK, I did the math. There are 1440 minutes in a day. So if a clock loses a minute every day then it would take 3.945 years before it was right a second time. Half that if you're using a 12 hour clock.

 

In phase? To me that means the wave has the same period and start at the same time reference. It's also possible to have two signals of the same exact frequency but not be in phase. If one signal starts at 0˚ and the other starts at 0.001˚ then the two signals are not in phase. And if they are EXACTLY the same frequency then they will NEVER be in phase. They may be damned close to being in phase, but the aren't truly "In Phase". Same would be true if the second signal were 359.999˚ - again, not in phase.

Harmonics? Well, when the period of one signal is at X time then the second signal is at 2X (or 4X and so on), that's harmonics, the period when both signals are (for reference) zero crossing. However, harmonics is not "In Phase". They ARE in phase for a moment in time that repeats, but so are signals that are NOT harmonic. (i.e. 1.1X) They WILL cross zero point at some point but that does not make them "In Phase".

Someone mentioned amplitude. Has nothing to do with phase.

Think of two clocks. One doesn't run at all while the other one loses a minute every day. Which clock is right more often? The one that doesn't run. It's right twice a day. It may take years (I don't feel like doing the math) before the one that loses a minute every day to be right a second time. HOWEVER, at some point in the future the second clock WILL have the right time again. So in that respect, the two clocks would be "In Phase" for that single moment in time.

[edit]
OK, I did the math. There are 1440 minutes in a day. So if a clock loses a minute every day then it would take 3.945 years before it was right a second time. Half that if you're using a 12 hour clock.

Hello there,

Yes that is why i had trouble calling the harmonics "in phase". However, when we list the phase relationships between some harmonics, we have to state the phase as being the same. For example:
2nd: -90 degrees
4th: -90 degrees.
6th: -90 degrees

See what i mean?
Thus we have to say that the phase is the 'same' even though it might not be proper to say they are 'in phase'.

The general form for a sinusoidal wave is A*sin(wt+ph) where ph is the phase, so the time signals would be something like this:
sin(w*t-90)
sin(2*w*t-90)
sin(4*w*t-90)
sin(6*w*t-90)

where in each case the phase was -90 (the harmonics are actually cosine but that's the main idea).

Yes the amplitude has no effect on the phase.