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With sufficient accuracy, knowing its maximum value, it is possible to estimate the value of an air-spaced variable capacitor setting just by looking at it. Similarly, the value of a coil can be calculated by counting the number of turns and guessing its length and diameter. The calculation is simple enough. I've done it dozens of times. It gets you into the right ballpark. Which is quite accurate enough for amateur radio purposes. There's no need for rocket science. I can't understand the abysmal state of education in simple arithmetic in our primary schools. We should import the kids who inhabit the sewers of Rio de Janerio and other American cities and employ them as arithmetic teachers. It would be more economic than culling by armed police. ---- Reg, G4FGQ |
On Mon, 01 Aug 2005 21:09:16 GMT, (Robert
Lay) wrote: On Mon, 01 Aug 2005 12:21:59 GMT, chuck wrote: If he has an RF bridge, couldn't he simply terminate the tuner's input with 50 ohms resistive and measure the impedance at the tuner's output? Well, the conjugate, anyway. I'm trying to imagine the benefit of doing it that way, rather than simply measuring the impedance at the transmission line directly. Chuck, NT3G I will break my own rule of not responding to responders and answer your question - otherwise you would assume that I was ignoring you. If I might answer a question with a question - why do you think that a tuner would give up its settings so easily? It's a an interesting speculation. First, let me clarify what I mean by a Tuner's input terminal and its output terminal. Considering that a tuner handles transmitted power in one direction only, we should refer to its "input" side as the port that connects to the transmitter and its "output" port as the one connecting to the antenna or feedline. That agrees with what I interpret your post as suggesting. Therefore, a 50 ohm termination at the "input" side "should" produce a measured impedance at the "output" port that is, as you say, the complex conjugate of the impedance seen looking into the transmission line. I haven't done a rigorous analysis of that configuration, but it certainly seems reasonable and correct. It would, indeed be an optimum way of inferring the impedance that the original poster is trying to measure. I see nothing wrong with your suggestion and would recommend it. Let's pretend that the antenna (load) Z = 49 +j0. Let's also pretend that the "tuner" consists of a series 1 ohm resistor. Looking into the input of the "tuner" we measure 50 +j0. Pretty good, huh? Terminating the input of the tuner with 50 +j0 and looking from the other end we measure 51 +j0. Whoops. Best have a lossless tuner to play this game. I also see no reason to do any of that as it would be just as easy to measure the transmission line input impedance directly - as you said. It's amazing how much good stuff comes out of the woodwork when people are interested in their hobby and interested in learning. Thanks, Bob, W9DMK, Dahlgren, VA Replace "nobody" with my callsign for e-mail w9dmkatcrosslinkdotnet http://www.qsl.net/w9dmk http://zaffora/f2o.org/W9DMK/W9dmk.html |
"Reg Edwards" wrote in message ... With sufficient accuracy, knowing its maximum value, it is possible to estimate the value of an air-spaced variable capacitor setting just by looking at it. Similarly, the value of a coil can be calculated by counting the number of turns and guessing its length and diameter. The calculation is simple enough. I've done it dozens of times. It gets you into the right ballpark. Which is quite accurate enough for amateur radio purposes. There's no need for rocket science. I can't understand the abysmal state of education in simple arithmetic in our primary schools. We should import the kids who inhabit the sewers of Rio de Janerio and other American cities and employ them as arithmetic teachers. It would be more economic than culling by armed police. ---- Reg, G4FGQ I credit the California and Oklahoma Public Schools for my mathematical illiteracy. Went to school in Bakersfield in 1947, got straight A cause the math they taught in the 9th grade was the math I learned in Oklahoma in the 4th grade. Returned to Oklahoma in the middle of the school year and was placed in a 2nd semester Algebra class. Teacher was a coach who spent most of his class time working with (on?) a female student whom he later married. Even if I had been truly interested I'd never have been able to catch up. I was passed on even though I was totally incompetent in Algebra.( this was before social passing became common in the public schools)They should have adjusted my schedule and had me start at the beginning Algebra semester even if it required some class juggling the following year. Perhaps they thought they were doing me a favor, or maybe they just didn't realize how retro the California school math was. Harold KD5SAK |
Good point, Wes. A reminder that a 1:1 swr at the input of a lossy tuner
is not proof of a perfect match at the output! Chuck NT3G Wes Stewart wrote: Let's pretend that the antenna (load) Z = 49 +j0. Let's also pretend that the "tuner" consists of a series 1 ohm resistor. Looking into the input of the "tuner" we measure 50 +j0. Pretty good, huh? Terminating the input of the tuner with 50 +j0 and looking from the other end we measure 51 +j0. Whoops. Best have a lossless tuner to play this game. |
The difference between teaching reading and writing and teaching
arithmetic is that practical uses for reading and writing are immediately apparent to children. Whereas teachers of arithmetic, and then maths, fail to show children the many interesting and practical uses of the subject. It's lack of imagination on the part of teachers - and laziness. They have no interest in the subject themselves. They are themselves victims of poor teaching and of the system which selects them to be teachers. In the UK it can be traced back to ignorance on the part of Ministers of Education. It is a great pity children are not given the opportunity to appreciate the beauty in Mathematics. In England, first year engineering university students have to spend the first 6 months being taught what they should have learned at the age of 14. Including how to read and write. Just prior to a General Election (of Members of Parliament) in the UK I once asked a prospective MP what seven nines were. He didn't know! Yet there was the possibility he could end up as the Chancellor of the Exchequer or even as a Minister of Education. As the meeting was being held in a public house the prospective MP changed the subject and bought me a pint of beer. Presumably in a futile attempt at bribery for a vote. Eventually he lost his deposit (of £500) for failing to collect the necessary small minimum number of votes. ---- Reg. |
Reg Edwards wrote: Just prior to a General Election (of Members of Parliament) in the UK I once asked a prospective MP what seven nines were. He didn't know! He probably thought you were using Cockney rhyming slang, and wasn't familiar with the expression 'seven nines'. The correct answer to your querry was of course: extremely pure. :-) ac6xg |
Reg Edwards wrote:
Just prior to a General Election (of Members of Parliament) in the UK I once asked a prospective MP what seven nines were. He didn't know! Interesting that the same things have very different meanings. In my current business 7 nines would mean roughly 3.16 seconds. Can you tell me why? tom K0TAR |
the square root of seven nines is 3162.27...
if the figure above were microseconds would be ~3.162 seconds. John "Tom Ring" wrote in message . .. Reg Edwards wrote: Just prior to a General Election (of Members of Parliament) in the UK I once asked a prospective MP what seven nines were. He didn't know! Interesting that the same things have very different meanings. In my current business 7 nines would mean roughly 3.16 seconds. Can you tell me why? tom K0TAR |
.... microseconds = milliseconds...
.... even ... frown John "John Smith" wrote in message ... the square root of seven nines is 3162.27... if the figure above were microseconds would be ~3.162 seconds. John "Tom Ring" wrote in message . .. Reg Edwards wrote: Just prior to a General Election (of Members of Parliament) in the UK I once asked a prospective MP what seven nines were. He didn't know! Interesting that the same things have very different meanings. In my current business 7 nines would mean roughly 3.16 seconds. Can you tell me why? tom K0TAR |
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