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Reg Edwards wrote:
Cecil, when there are several different power levels at different places in a circuit, it is entirely up to you how you reference one to another in dB. Now Reg, that just cannot be true. Otherwise, there would exist no conventions. It's a simple question: When you tell me that the losses in a transmission line with reflections are 2 dB, exactly what power are you referencing those losses against? Reflected volts - yes! Reflected current - yes! Reflected power - NO! Reflected volts and reflected current existing without any associated joules/sec???? I've heard of waves without any trace of energy before, Reg, but I certainly didn't expect to hear miracle metaphysics from you. Whatever happened to V*I*cos(theta) being power? The power companies would be surprised to learn that they are not transferring any joules/sec to their customers. Do you think I can use your argument to get out of paying my electric bill? -- 73, Cecil http://www.qsl.net/w5dxp |
#2
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"Cecil Moore" wrote Reg Edwards wrote: Cecil, when there are several different power levels at different places in a circuit, it is entirely up to you how you reference one to another in dB. Now Reg, that just cannot be true. =============================== That's funny - _I_ don't have any difficulty in believing it! ;o) --- Reg |
#3
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Cecil Moore wrote:
Reg Edwards wrote: Cecil, when there are several different power levels at different places in a circuit, it is entirely up to you how you reference one to another in dB. Now Reg, that just cannot be true. It is true. Otherwise, there would exist no conventions. Multiple conventions exist in all the technical disciplines. A well versed practioneer is familiar with the various conventions commonly in use and will choose the one most appropriate to the problem at hand. General terms such as 'gain' and 'loss' always require the context be carefully established before the term can be used with any precision. For example, dissipative loss in a transmission line is different from transducer loss, but both are often expressed in decibels. One relates to an actual ratio of two physically meaningful power levels, and the other is notional. It's a simple question: When you tell me that the losses in a transmission line with reflections are 2 dB, exactly what power are you referencing those losses against? Reasonable question. Without knowing the context the statement is essentially meaningless. Reflected volts - yes! Reflected current - yes! Reflected power - NO! Reflected volts and reflected current existing without any associated joules/sec???? Reg didn't say any such thing. The wave equation is usually expressed in terms related to the two complementary field quantities associated with energy storage. In the case of TEM transmission lines, the two variables are voltage, and current. The method of reflections (images) used to facilitate solution of the wave equation, utilizes the concept of voltage and current reflection coefficient respectively. These concepts are used to find the v(x,t) and i(x,t) without any reference to to power or energy. Once v(x,t) and i(x,t) are known, the power, v(x,t) * i(x,t) can easily be calculated at any point x and time t. The energy storage density can be calculated as i(x,t)^2 * L/2 + v(x,t)^2 * C/2. As you might expect, the v(x,t)*i(x,t) is the derivative of the energy storage density. I've heard of waves without any trace of energy before, Reg, but I certainly didn't expect to hear miracle metaphysics from you. 'Solving' the wave equation for TEM transmission lines usually means determining the values of the v(x,t) and i(x,t) as a function of place and time. Energy distribution, and it's movement, is easily calculated from the knowledge of v(x,t) and i(x,t). Whatever happened to V*I*cos(theta) being power? Hasn't changed; works for DC out to upper microwave frequencies. The power companies would be surprised to learn that they are not transferring any joules/sec to their customers. Indeed they would. Who do you know who believes they are not transferring energy to their customers? bart wb6hqk |
#4
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Bart Rowlett wrote:
A well versed practioneer is familiar with the various conventions commonly in use and will choose the one most appropriate to the problem at hand. My point exactly, Bart. It is not up to me to define a new standard. Indeed they would. Who do you know who believes they are not transferring energy to their customers? There are people who believe that energy being transferred past a point in the transmission line is not power. However, the IEEE dictionary says that power is the rate of generation, transfer, or consumption of energy. -- 73, Cecil http://www.qsl.net/w5dxp |
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