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#541
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Loading Coils; was : Vincent antenna
On Dec 7, 3:02 pm, wrote:
On Dec 7, 1:00 pm, Cecil Moore wrote: Keith Dysart wrote: If the 100 ohm line was only 5 degrees long, how long would the 600 ohm line have to be to obtain 0 ohms at the input? -jcot(5) = -j11.43 normalized to Z0=100 ohms -j100(11.43) = -j1143 ohms at the junction -j1143/600 = -j1.905 normalized to Z0=600 ohms arctan(1.905) = 62.3 degrees of Z0=600 ohm line Would the phase shift at the junction still be 36.6 degrees? The new phase shift would be 90-5-62.3 = 22.7 deg. 62.3 + 5 + 22.7 = 90 degrees This example would correspond to a larger coil and a shorter stinger in a loaded mobile antenna. -- 73, Cecil http://www.w5dxp.com The smith chart shows this well. If I go up only 5 degrees on the outer circle of open-end (infinite impedance on the 100 ohm line), lower values of electrical angle corresponds to higher reactance, in this case -j1143 for the 5 degree line instead of -j567 for the 10 degree line at the junction. The new phase shift at the junction should be, and is, now lower since the 100 ohm line has a higher capacitive reactance at the junction. As the 100 ohm line is shortened to 0 degrees, we have a 600 ohm transmission line that is open and now the 600 ohm line must be lengthened to the full 90 degrees for 1/4W. This would correspond to a coil with no stinger.- Hide quoted text - - Show quoted text - Ooops, I am posting from the web. This is AI4QJ. |
#542
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Loading Coils; was : Vincent antenna
On Dec 7, 1:00 pm, Cecil Moore wrote:
Keith Dysart wrote: If the 100 ohm line was only 5 degrees long, how long would the 600 ohm line have to be to obtain 0 ohms at the input? -jcot(5) = -j11.43 normalized to Z0=100 ohms -j100(11.43) = -j1143 ohms at the junction -j1143/600 = -j1.905 normalized to Z0=600 ohms arctan(1.905) = 62.3 degrees of Z0=600 ohm line Would the phase shift at the junction still be 36.6 degrees? The new phase shift would be 90-5-62.3 = 22.7 deg. 62.3 + 5 + 22.7 = 90 degrees So sometimes a 600 to 100 ohm discontinuity produces a 36.6 degree phase shift and sometimes it produces a 22.7 degree phase shift (and probably any value in between). I suggest that "work[ing] up the phasor diagrams of the component voltages (or currents) at the junction where rho = (600-100)/(600+100) = 0.7143" will not be useful for predicting the phase shift. ....Keith |
#543
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Loading Coils; was : Vincent antenna
On Dec 7, 12:46 pm, Cecil Moore wrote:
Keith Dysart wrote: You have done this before; postulating explanations that only work in the complexity of the "real" world, but fail when presented with the simplicity of ideal test cases. For Pete's sake, Keith, Ohm's law doesn't even work when R=0. A rather large red herring. Ideal components are the topic, and we mostly use ideal wire with R=0 without difficulty. Then, when the explanations fail on the simple cases, claiming these cases are not of interest because the real world is more complex. I define the boundary conditions within which my ideas work. Whether they work outside those defined conditions is irrelevant. I believe they do work for ideal conditions, but I don't have the need to prove a "theory of everything". Sounds good, but mostly you do not examine ideal conditions because they tend to show that the models fail. With non-ideal conditions, the discussion is easy to drive far from the target and prevent resolution of whether the model works. ....Keith |
#544
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Loading Coils; was : Vincent antenna
Tom Donaly wrote:
Mike Coslo wrote: "Mike Kaliski" wrote in I went along to a couple of meetings many years ago. Full of under achievers with high IQ's complaining how they weren't being recognised or credited in their exams/career/promotion ladder/etc. Intelligence is like talent. It is a gift. What you do with it is what is important. Just because you have one or the other is almost irrelevant if you don't have the other tools needed to be sucessful. I feel like such a piker here - I'm only 150........ - 73 de Mike N3LI - That's o.k. It just means you think less like Terman than some of the others in this group do. I was a little shocked to read his bio. - 73 de Mike N3LI - |
#545
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Loading Coils; was : Vincent antenna
Keith Dysart wrote:
Sounds good, but mostly you do not examine ideal conditions because they tend to show that the models fail. With non-ideal conditions, the discussion is easy to drive far from the target and prevent resolution of whether the model works. My postulate is that Newton was wrong: moving objects come to a rest without any external applied force. Every observation made supports this. There's no need to consider what happens in a frictionless environment, since such a thing doesn't exist. Roy Lewallen, W7EL |
#546
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Loading Coils; was : Vincent antenna
On Dec 7, 3:05 pm, Keith Dysart wrote:
On Dec 7, 1:00 pm, Cecil Moore wrote: Keith Dysart wrote: If the 100 ohm line was only 5 degrees long, how long would the 600 ohm line have to be to obtain 0 ohms at the input? -jcot(5) = -j11.43 normalized to Z0=100 ohms -j100(11.43) = -j1143 ohms at the junction -j1143/600 = -j1.905 normalized to Z0=600 ohms arctan(1.905) = 62.3 degrees of Z0=600 ohm line Would the phase shift at the junction still be 36.6 degrees? The new phase shift would be 90-5-62.3 = 22.7 deg. 62.3 + 5 + 22.7 = 90 degrees So sometimes a 600 to 100 ohm discontinuity produces a 36.6 degree phase shift and sometimes it produces a 22.7 degree phase shift (and probably any value in between). That's right, depending on the electrical (and physical) length of the 100 ohm line, it will have different values of reactance as seen by the 600 ohm line, therefore different phase shifts, all the way to zero when the length of the 100 ohm line is 0 degrees and the reactance is infinite (the 600 ohm line sees an open circuit). Say at 0+ degrees, -jX(C) = 1000000000; this is where you see it headed when you look at the smith chart. At zero degrees of 100 ohm line, you have 90-0-90 = 0 degrees at the discontinuity. AI4QJ |
#547
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Loading Coils; was : Vincent antenna
Dave Heil wrote:
Mike Coslo wrote: "Mike Kaliski" wrote in I went along to a couple of meetings many years ago. Full of under achievers with high IQ's complaining how they weren't being recognised or credited in their exams/career/promotion ladder/etc. Intelligence is like talent. It is a gift. It can be more like a curse. There's nothing quite like a number of teachers telling Junior's parents that Junior is gifted. What you do with it is what is important. Just because you have one or the other is almost irrelevant if you don't have the other tools needed to be sucessful. I feel like such a piker here - I'm only 150........ You don't look that old, Mike. I would be younger, but I was sick a lot as a kid.... - 73 de Mike N3LI - |
#548
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Loading Coils; was : Vincent antenna
Dave Heil wrote:
Mike Coslo wrote: "Mike Kaliski" wrote in I went along to a couple of meetings many years ago. Full of under achievers with high IQ's complaining how they weren't being recognised or credited in their exams/career/promotion ladder/etc. Intelligence is like talent. It is a gift. It can be more like a curse. There's nothing quite like a number of teachers telling Junior's parents that Junior is gifted. Little Mikey just doesn't apply himself..... Little Mikey was bored, but that would mean it was their fault Oops sorry about that - it was a thrid grade flashback 8^) - 73 de Mike N3LI - |
#549
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Loading Coils; was : Vincent antenna
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#550
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Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Dave Heil wrote: Where's the fulfillment in standing around in a room full of folks congratulating each other on how smart they are? It gets the females turned on. It is a well know scientific fact the only true aphrodisiac is a man doing housework. - 73 de Mike N3LI - |
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