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The Dark Side of the Conjugate Match

Discussion in 'General Technical Questions and Answers' started by KL7AJ, Mar 12, 2010.

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  1. W5DXP

    W5DXP Ham Member QRZ Page

    On the contrary, a single photon can pass through two slits and interfere with itself on the other side. That's a characteristic of a wave even though it is a single photon. Even single photons exhibit the wave/particle duality. EM fields consist of photons. It is the choice of detector built by humans that collapses the probability function into a particle or a wave and it can be either - your choice.

    The EM wave surrounding the wire consists of a cloud of quantized photons progressing from free electron carrier to free electron carrier at the speed of light in the medium.

    Perhaps a quote from Feynman would help:

    "So now, I present to you the three basic actions, from which all the phenomena of light and electrons arise:

    -Action #1: A photon goes from place to place.
    -Action #2: An electron goes from place to place.
    -Action #3: An electron emits or absorbs a photon."


    When Feynman says "light", he is including radio frequencies.
     
  2. W5DXP

    W5DXP Ham Member QRZ Page

    No, there are two mechanisms for generating photons and EM fields/waves. But photons and EM fields/waves are the same quantized phenomena and are both generated by the two mechanisms.

    1. An atomic orbital change generates photons/fields at fixed quantized energy levels, i.e. at fixed frequencies. A laser is an example.

    2. A free electron does NOT change atomic orbits and mimics the frequency of the applied energy. Conductors, like copper and aluminum, contain free electrons. A ham antenna is an example.
     
  3. W8JI

    W8JI Ham Member QRZ Page

    http://www.w8ji.com/Vacuum_tube_amps.htm

    73 Tom
     
  4. W5DXP

    W5DXP Ham Member QRZ Page

    There is a grain of truth there. It must have the same physical reflection coefficient and opposite sign. But, as Walt says, it has a virtual reflection coefficient of 1.0 looking back from the load. For the sake of simplicity, let's replace the tuner with a simple Z0-match. Here's a lossless example:

    100w
    source---50 ohm coax---+---1/2WL 300 ohm twinlead---50 ohm load

    The voltage reflection coefficient at the load is -0.7143. The power reflection coefficient at the load is 0.51. The forward power is 204 watts and the reflected power is 104 watts.

    The physical power reflection coefficient at point '+' is 0.51, same as at the load. The virtual power reflection coefficient at point '+' is zero looking from the source and 1.0 looking back from the load.

    What most people don't understand is that there are two phenomena for redistributing energy back toward the load from the Z0-match at point '+'. One is an ordinary reflection from a physical impedance discontinuity which is what you are talking about above.

    The second mechanism is associated with interference. This mechanism is described in Reflections II under - "Sec 4.3 Reflection Mechanics of Stub Matching". Here's the URL:

    http://w2du.com/Chapter04.pdf

    In my above Z0-matched example, 0.51 of the 104 watts of reflected power (53w) is re-reflected by the physical impedance discontinuity. What happens to the other 51 watts of reflected power that is not re-reflected by the physical impedance discontinuity? As Walt describes in Chapter 4, it undergoes destructive interference with a complimentary part of the source wave. The destructive interference between 51 watts of the reflected power wave and 51 watts of the source wave redistributes all of the reflected power back toward the load.

    Apparently, in order to try to simplify things for his readers, Walt lumps both physical re-reflection and interference effects into a single virtual power reflection coefficient of 1.0 at point '+' looking back from the load. But it is readily apparent from section 4.3 in Reflections II that Walt understands that second step roll played by interference effects. He says in Chapter 4: "The destructive interference causes mutual cancellation of two complementary reflected waves generated by two complementary mismatches".

    In a paper I wrote for Worldradio, I explained the two-step process of re-reflection/interference at a Z0-match which also applies to a tuner. That paper is reproduced at:

    http://www.w5dxp.com/energy.htm

    What we are discussing is the same phenomena involved in the 1/4WL thin-film coating on non-reflective glass which is covered in the references.
     
  5. KD0CAC

    KD0CAC Ham Member QRZ Page

    Just a simple question the conservation law , as I understand it .
    If we can not create / or destroy .
    How does a 100 watts onto an RF system , feedline , antenna etc become more than a 100 watts ?
    If we are talking about the reflected power added to the next moment of power [ seems like time is being left out ] , the current = now transmission is mixing with the reflected , past transmission " time " , then become noise on the now signal ?
    I hope that can be a coherent idea to some , maybe wrong idea , just trying to calibrate / tune the mind ?
    This is one of the biggest parts of Ham Radio that I like , the learning of applied science to communication .
     
  6. KA5S

    KA5S Ham Member QRZ Page

  7. W5DXP

    W5DXP Ham Member QRZ Page

    There is no conservation of power law. There is a conservation of energy law. Joules are conserved - watts are not conserved. The forward power can be greater than the source power because, during the key-down transient state, enough joules were loaded and stored in the transmission line (and not delivered to the load) to support the forward power and reflected power values.

    Assume a one-second long lossless transmission line with an SWR of 5.87:1, i.e. a power reflection coefficient of 0.5 at the load. Steady-state source power is 100 watts. Steady-state forward power is 200 watts. Steady-state reflected power is 100 watts. In a lossless system:

    Source power = load power = forward power minus reflected power

    During steady-state, there are 300 joules of energy contained in the transmission line that have not been delivered to the load. If you iterate the reflections on a second by second basis, you will see the total joules of energy converging to 300 joules in the transmission line. RF joules cannot stand still so there are 300 total joules/sec passing a point in the transmission line during steady-state. That does not violate the conservation of energy principle.

    Take a look at a plot of instantaneous power. Power is created and destroyed during every RF cycle.
     
  8. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Hi Walt:

    My email address is: kl7aj@arrl.net.

    Sorry I haven't been in the conversation too much; I've been deep in the throes of the Opus. Just signed up Jim Massara, N2EST, to to most of the illustrations for the tome! Jim illustrated my very first QST article back in 1983, and it's only right that I recruit him for this project. As they say, "Dance with who brung ya."

    By the way, I'd be most honored if you'd be interested in writing a sidebar for the Opus. Any topic of your choice would be great!

    How are sales of "Reflections III" going? I hope you make a killing on this revision!

    73,

    Eric
     
  9. KC8VWM

    KC8VWM Ham Member QRZ Page

    Hi Walt,

    I am just popping in here to say I use your well designed products, appreciate your work and I enjoy reading your well written publications. It would be a pleasure to meet you in person sometime.

    Thank you.
     
    Last edited: Sep 13, 2010
  10. K9AAN

    K9AAN XML Subscriber QRZ Page

    We may be saying the same thing. Here is my take without the use of complex variables...

    A coaxial transmission line may be modeled with lumped components by an inductance in series as the center conductor, to represent the inductance of the cable, and a capacitor in between the center conductor and shield, to represent the capacitance between the two conductors. [BTW, this is, essentially, an LC low pass filter.]
    A tuner works to introduce reactance in the cable-antenna system that nullifies the reactance induced by the non-resonant antenna. This is why, mathematically, we need to consider the complex conjugate. If there is too much capacitance from an antenna that is too short, we introduce inductance at the tuner. If there is too much inductance from an antenna that is too long, we introduce capacitance at the tuner.
    The net effect of all the reactances in the tuner-cable-antenna system is, we hope, to null the reactances and produce a “resistance” that is equal to the transmitter’s resistance for maximum power transfer.
    By introducing inductance or capacitance or, usually, both to the tuner-cable-antenna system we change the characteristics of the wave travelling down the transmission line. That is, we alter the phase relationship between the voltage and current. The alteration made at the tuner compensates the alteration made at the antenna so that when the wave reaches the antenna, it is at the proper phase relationship with respect to the antenna and all of the forward power is transmitted.
    As we know, the impedance in a cable changes with its length. Back in the old days, engineers would use a device called a Smith Chart to determine how long a cable had to be so its impedance would match that of the antenna. Another way of looking at the tuner is that the tuner, by introducing series inductance and parallel capacitance, makes the cable electrically longer or shorter so that the appropriate electrical cable length is produced.
    Since the cable impedance now, electrically, matches the antenna impedance, there is no reflected power, it is all transmitted.
    So why then can higher power be measured between the tuner and the antenna than that produced by the transmitter? Probably because the altered phase angle between the voltage and current is not taken into consideration. This is known as the Apparent Power in Electrical circles. Apparent Power is always higher than Real Power. When power is measured by standard methods, it is Apparent Power that is measured not Real Power.
    If, there were no reactances in the transmitter-cable-antenna circuit, the Apparent Power and the Real Power would be the same. However, with reactances we have phase shifting which creates Apparent Power and misleading measurements.
    Since all the power is transmitted, does this make the antenna as efficient a radiator of power as a properly tuned antenna? No, but it helps. Once “tuned” by the antenna tuner, there is a total match of system impedances but there is still that phase relationship between the voltage and current in the antenna. The more out of phase (out of tune) the antenna is the more out of phase the electric and magnetic fields coming off the antenna will be and that will effect the Apparent Power transmitted.
     
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