Sine Wave Question
- Thread starter Zipper730
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Both.
MIflyer
1st Lieutenant
Sine waves indicate alternating current and there is no negative and positive.
Go to: Technical books online
And Radar circuit analysis : United States. Dept. of the Air Force : Free Download, Borrow, and Streaming : Internet Archive
Go to: Technical books online
And Radar circuit analysis : United States. Dept. of the Air Force : Free Download, Borrow, and Streaming : Internet Archive
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The positives are positive and the negatives are negative, but what is positive and what is negative depends on "stuff".
Since a sine wave represents an alternating current phenomenon, you could say that it is alternately positive and negative. If it helps you understand what's happening you can imagine everything above the axis as positive and below as negative, but understand that is only a visualization tool and not legitimate physics. The sine wave as commonly graphed is generally understood to depict voltage vs time, and in a purely resistive circuit amperage will follow it, but most circuits have capacitive and inductive elements that will cause current to lag or lead voltage, thus introducing a phase shift.
As for out of phase, there are 359 degrees of potential out of phaseness, and they only nullify completely when they are exactly 180° out and of equal amplitude. Unless the two waves are at exactly the same frequency, they will "beat" or "heterodyne", which means they generate an additional wave whose frequency is the difference between the two primary waves.
If you've ever sat in the last row of seats in an airliner with aft mounted engines (DC9, MD80, Embraer145, Canadair CJ50or70) and heard or felt a "zud-zud-zud-zud" sound or vibration as the baggage compartment bulkhead behind your head resonates like a drum, you've experienced a beat frequency. The engines are turning at close to, but not exactly, the same RPM, and try as they might the wrench twisters can never achieve absolute perfect balance on any engine, so there will always be some rotation related vibration. These planes all have electronic engine speed synchronization, but again, nothing's perfect.
The first thing your multi engine flight instructor will teach you is to synch your engines. Learn quickly, because those guys are prone to headaches, and if you give him one he'll be a foul tempered bear for the rest of your training. BTDT!
As for out of phase, there are 359 degrees of potential out of phaseness, and they only nullify completely when they are exactly 180° out and of equal amplitude. Unless the two waves are at exactly the same frequency, they will "beat" or "heterodyne", which means they generate an additional wave whose frequency is the difference between the two primary waves.
If you've ever sat in the last row of seats in an airliner with aft mounted engines (DC9, MD80, Embraer145, Canadair CJ50or70) and heard or felt a "zud-zud-zud-zud" sound or vibration as the baggage compartment bulkhead behind your head resonates like a drum, you've experienced a beat frequency. The engines are turning at close to, but not exactly, the same RPM, and try as they might the wrench twisters can never achieve absolute perfect balance on any engine, so there will always be some rotation related vibration. These planes all have electronic engine speed synchronization, but again, nothing's perfect.
The first thing your multi engine flight instructor will teach you is to synch your engines. Learn quickly, because those guys are prone to headaches, and if you give him one he'll be a foul tempered bear for the rest of your training. BTDT!
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We had one aircraft whose props would wander out of synch, so you were forever having to fiddle with the props to keep it going. Since then, my tolerance for being in an aircraft with the props not synched properly has gone!
Another grouchy bear!
"Nice bear. No beef with you Mr. Bear. Why don't you go your way, Mr. Bear, and I'll go mine. Alright, Mr. Bear? G'bye"!
One of our 1900s kept blowing a transistor in its auto synch box, and there was no way you could keep those four blade Hartzells in synch manually. The props were right behind your shoulder, and you better keep your aspirin handy.
In icing conditions the props were constantly slinging ice against the fuselage right behind the cockpit and it sounded like a nonstop hail storm.
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Crimea_River
Marshal
I don't know how we jumped to the conclusion that the question related to AC current. A sine wave is a trigonometric function that plots the ratios of certain sides of a right angled triangle as the angle rotates through 360 degrees. The sine of an angle is the ratio of the length of the opposite face of the triangle to the hypotenuse. If you center a circle at 0,0 on an x-y axis plot and plot the ratio as the angle increases from 0 to 360 degrees, you will get positive and negative values for the ratio.
MFG The Sine and Cosine Functions
MFG The Sine and Cosine Functions
We all have different takes on Zipper's question. You see it in strictly mathematical terms, pbehn from an engineer's perspective, and I from that of a technician and instructor. Pbehn and I both inferred from the wording of the question that Zipper was talking about electronics, knowing that he's been interested in radar and communications.
I used to work in ultrasonics which is very much like Radar. There are wave effects in the sound waves and also in the electrical system. The mapped side lobes on the chain home system look just like an ultrasonic sound beam and behave in an identical fashion. However there are the pure theories that it is based upon but always some strange effects that also happen. In a storm on the sea, waves can cancel each other out, they can also ride up on each other and produce a brief unstable monster.
An example of how interaction of waves does not follow classic or normal understanding at all times . Stochastic resonance is thought to be why the Chain Home system with experienced operators found incoming aircraft whose signal was below the CRT noise level. I saw this in ultrasonics, after a long time doing it you see patterns in the way signals rise and fall and "roll" across the screen. I cant say whether that was "stochastic resonance" or not, I can say it its a bit complicated, like everything. Stochastic resonance - Wikipedia
ThomasP
Senior Master Sergeant
Hey Zipper730,
Were you asking relative to radio waves?
Were you asking relative to radio waves?
Just like that old Avionics Technician Chief told us in A school, "It ain't the theory or the hardware constructed on the theory that makes it work, it's the operating principle of FM (F_ _king Magic). The engineers design it and build it, but it doesn't work till it's been tweaked out of resemblance to the original device by trial and error!"
Mark Biegert
Recruit
- 9
- Nov 18, 2016
This is an interesting question. Sine waves appear throughout engineering. If you don't want to think about electronics, let's use sound as an example. Pure tones can be described by a sine wave of pressure values about a nominal pressure (often sea level air pressure of 14.7 psi). For convenience, we can think of ambient pressure as our zero-level (see any definition of gauge pressure for more details). Thus, the sound pressure can be plotted as positive and negative excursions about a zero level, but the actual high and low pressure values are really 14.701 psi and 14.699 psi (for example). If you have two sound waves 180° out of phase, the slight positive and slight negative pressure values cancel out.
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Well the theoretical world doesn't have thunderstorms, wind rain and the odd rodent in its laboratory.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Encountered the "FM" principle many times working with two-way telecom.
On one such occasion, a patrol car was in for service: when the deputy keyed the mic, all hell broke loose. The lightbar would go haywire, there was terrible hetrodyne coming from the Nokia hands-free system, his LED maplight would pulsate to his modulation and dispatch (who could hear his transmission) complained that he sounded like he was standing under a waterfall.
So I check the system (Motorola Syntor 100 watt high-band, tuned to 154.690 TX) and come to find that the coax had been severed upstream and the ends were about 2" apart.
My helper was observing when I found the problem and when I said "ah hah!", he asked what it was.
I said: "It's a wicked air-gap".
Looking puzzled, he said: "but it was still working, how?"
Me: "F*****g magic, that's how..."
Damn, those guys in the shop gotta remember to chafe protect them cables when they string 'em through drilled holes!
Had a VOR antenna cable that was strung through an airframe lightening hole with no grommet or chafe protection, vibrating against the sharp edge of the metal. Awkward location, inside vertical stab. Immune to inspection. You know the rest of that story.
Night IFR, dodging thunderbumpers, and suddenly, no NAV, right or left. Those folks in ATC earn their keep!
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