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Is there a circuit or device that does this?

  1. Jul 9, 2013 #1
    im looking for a circuit with this ability.


    so you have a signal input going into this circuit. and this circuit has an external power supply. this circuit outputs its signal where the input comes in. the thing is, i want the output signal to be 0° out of phase with the input and higher voltage than the input such that the input signal is being pushed back outward. is there by any chance.. any circuit that can do this?

    thanks
     
  2. jcsd
  3. Jul 9, 2013 #2

    Averagesupernova

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    Makes no sense. Exactly how much do you understand about electricity?
     
  4. Jul 9, 2013 #3
    what do you mean by "the circuit outputs its signal where the input comes in"?
    what do you mean by "the input signal being pushed back outward"? like in phase shifted? i that's the case, shifted as compared to the output? then you can't have 0 degrees out of phase.
     
  5. Jul 9, 2013 #4

    Baluncore

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    This does make sense, but only at and above radio frequencies.
    It is easy with microwaves because you can use circulators and directional couplers.
    The specification of zero degrees phase shift depends on where you measure it because the output signal is travelling in the opposite direction to the input signal on the transmission line.
     
  6. Jul 10, 2013 #5

    Averagesupernova

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    Baluncore:
    I have never looked into it to be sure on definitions and etc., but I think typically only POWER has a direction of travel on a transmission line. We don't really consider signals in this manner do we? I would add that what you say about radio frequencies certainly applies, but the physics and theory is the same with lower frequencies, just typically impractical due to the wavelengths and transmission line lengths.
    -
    We need the OP to give us some more info.
     
  7. Jul 10, 2013 #6

    Baluncore

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    Not only do I think about signals in those terms, but I use it every day.

    A linear transmission line propagates signals in both directions quite independently. Each signal has a voltage to current ratio equal to the characteristic impedance of the line. Telecommunications networking has no problem with that. There is a “hybrid” coupler in a line telephone that works quite OK at audio frequencies, but careful adjustment is required to prevent echo. It is more obviously possible when you consider that a submarine optic fibre carries signals in both directions on the one fibre. You can also take a photo, of yourself taking the photo, in a mirror.

    We do need more information from the OP because “zero phase shift at one common terminal” suggests in the first analysis that positive feedback will be a problem. But that is certainly not the case.

    The OP required the amplified signal to be in phase. It did not specify that the carrier of that signal must also be in phase. For example an FM radio receiver that uses it's speaker lead as the antenna.

    Only the OP can refine or expand the question to identify the situation.
     
  8. Jul 10, 2013 #7

    Averagesupernova

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    Baluncore, you have somewhat missed my point. Telephone circuits do indeed have 'signals' flowing in both directions. BUT, I believe they always are working with a specific impedance. So there IS power flowing. The ends of the lines are terminated. The OP implies that he wants to throw a voltage at a port with unspecified input impedance from a source with an unspecified output impedance.
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    What this part means I have no idea:
    The OP's post alone makes NO SENSE, and won't work. To actually make something like this work there needs to be a directional coupler between the generator and said device and a port on this directional coupler that is terminated to absorb the power being reflected back towards the source but not from the source. The magic device he is wondering about will need to have some kind of hybrid circuitry inside to help prevent oscillation.
    -
    If we want to reflect a signal all we need is an unterminated transmission line of the correct length and virtually 100% of the power will be reflected back towards the source. Is the input signal being 'pushed back outward' as the OP says? You tell me. The whole thing is sort of a mind-bender.
     
  9. Jul 10, 2013 #8

    Baluncore

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    Since the characteristic impedance of the line is the same in both directions, the OP requirement that the output signal be “higher voltage than the input” requires some form of power amplification.

    If power gain was not required the answer to the OP question could be as you suggest, “A mirror”.

    We must await refinement of the OP.
     
  10. Jul 11, 2013 #9

    Averagesupernova

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    I just reread my 3rd post in this thread.
    -
    The above comment I made looks somewhat silly. I could have chosen words more carefully.
     
  11. Jul 11, 2013 #10
    Basically that is a Grid Tie Inverter - power source is solar array, the circuit does not operate unless there is a tie to the grid ( V AC present) - and the inverter "pushes" power out, ideally at unity PF.

    Somewhat of a wise-a comment - but technically does the task as I read the OP.
     
  12. Jul 11, 2013 #11

    Baluncore

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    Well identified Windadct.
    Those inverters push out current that is in phase with the voltage on the low impedance supply grid.

    One problem with too many grid connected solar power inverters on any one part of the grid is that if the main supply is lost or disconnected, the inverters can slave off each other and continue to run. Now that is an interesting case of positive community feedback. It becomes even more interesting when trying to reconnect the main supply since there is no immediate control over the phase of either and so the operator must wait for the right instant to throw the switch. I know one dedicated operator who has had nightmares about it.
     
  13. Jul 26, 2013 #12
    hey all, thanks for all the responses, i apologize for the long delay on this thread.

    basically i am looking to see if something like this is possible. where i have a power supply, and this power supply is in phase with the wall power. the voltage of this power supply will always be greater than the wall power.

    first thing's first; will it be possible to put power back into the grid, ie turn my watt meter backwards this way?

    the hypothetical device i was looking for in the beginning of this thread was to get the phases in sync. as baluncore suggested, this device would be like a mirror, except power gain is indeed required.

    i have another general plan of getting the two in phase, but... it's a LOT less reliable.

    will the idea work? (external power supply in sync with wall signal, whose voltage is also always greater than wall power, plug external power supply into wall and make watt meter turn backwards)
     
  14. Jul 26, 2013 #13
    oh, and to:

    i am not an EE major. i do not even have a degree in anything. i'm just a college kid at a mediocre school. go easy :)
     
  15. Jul 26, 2013 #14

    Baluncore

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    Now that you have identified the application it is possible to refine the way you are looking at the problem. You will have no control of the output voltage because you cannot fight the very low impedance network.

    So follow the voltage on the network and then inject a current into the network that is in phase with the voltage. If the injected current comes from an alternative energy source then it should turn your meter backwards. Your system must shut down if there is low voltage on the network, then wait before restarting.

    Now a couple of problems to look out for. If your energy meter is a rotating disk it should run backwards but there are a few that have a one way contact or ratchet installed.

    If your meter is a new digital meter then it will probably measure the average voltage over a cycle and the average current over a cycle. It will then multiply those to get power and accumulate the reading. Unfortunately most metres do not consider the direction of the current so it will cost you to generate power. This way you will also pay for any circulating reactive currents as well as real power.

    Gone are the days when we purchased energy here, we now purchase the change in meter reading.
     
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