Home |
Search |
Today's Posts |
#11
|
|||
|
|||
On Thu, 28 Aug 2003 06:27:40 GMT, "George, W5YR"
wrote: ... "Theory and Problems of Transmission Lines" by Robert A. Chipman. This is a Schaum's Outline book - mine is dated 1968. Many professionals acknowledge that this is one of the most succinct and revealing accounts of t-line theory to be found. Mathematical enough to be rigorous but readable and highly useful. Hi George, I have notice you recommended this author several times, and yet you have casually dismissed his rather straightforward coverage relating to the characteristic Z of a Transmitter: There is no need to know, since its value, whatever it might be, plays no role in the design and implementation of the external portion of the system driven by the transmitter. How do you reconcile this with his coverage entitled "9.10. Return loss, reflection loss, and transmission loss." You may wish to observe the clearly marked figure 9-26 and specifically the paragraph that follows (or the entire section for that matter) that quite clearly reveals what is everywhere else implied: that ALL SWR discussion presumes a Zc matched source. You may observe that Chapman thus refutes your statement above. Further, Chapman goes to some length to describe the Smith Chart's appended line evaluation scales at the bottom to this very matter. To substantiate this from other sources I have offered a very simple example that shows this importance that to date has defied "first principle" analysis (not first principles however, merely the claim of its being practiced analytically in this regard). I will offer it again, lest you missed it. The scenario begins: "A 50-Ohm line is terminated with a load of 200+j0 ohms. The normal attenuation of the line is 2.00 decibels. What is the loss of the line?" Having stated no more, the implication is that the source is matched to the line (source Z = 50+j0 Ohms). This is a half step towards the full blown implementation such that those who are comfortable to this point (and is in fact common experience) will observe their answer and this answer a "A = 1.27 + 2.00 = 3.27dB" "This is the dissipation or heat loss...." we then proceed: "...the generator impedance is 100+0j ohms, and the line is 5.35 wavelengths long." Beware, this stumper has so challenged the elite that I have found it dismissed through obvious embarrassment of either lacking the means to compute it, or the ability to simply set it up and measure it. It takes two resistors and a hank of transmission line, or what has been described by one correspondent as: There is no institutionalized ignorance, just a lot of skepticism regarding the reliability of the analysis methods and the measurement methods. Clearly a low regard for many correspondent's abilities here, and hardly a prejudice original to me. Imagine the incapacity of so many to measure relative power loss - a CFA salesman's dream population. Actually it is quite obvious several recognize that follow-through would dismantle some cherished fantasies. Chapman clearly knocks the underpinnings from beneath them without any further effort on my part. But then, as you offer, they would merely dismiss it by confirming another prejudice: its assumed low station as a Schaum's Outline book I would point out to all, that Chapman's material dovetails with what would have been then current research and teachings of the National Bureau of Standards. Prejudice has "refuted" those findings too. :-) 73's Richard Clark, KB7QHC |
#12
|
|||
|
|||
George, W5YR wrote:
I urge anyone seriously interested in understanding transmission line theory to include Chipman on their bookshelf. It's out of print, George. How much will you take for yours? :-) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#13
|
|||
|
|||
Richard Clark wrote:
"...the generator impedance is 100+0j ohms, and the line is 5.35 wavelengths long." What does the generator impedance have to do with line losses? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#14
|
|||
|
|||
"George, W5YR" wrote in message ... If anyone is interested in really getting to the bottom of this endless jousting, turn to page 136 of "Theory and Problems of Transmission Lines" by Robert A. Chipman. This is a Schaum's Outline book - mine is dated 1968. George, I took a course from Dr Chipman. The text he used was Adler, Chu, and Fano. I bet he references that book. Tam/WB2TT |
#15
|
|||
|
|||
On Thu, 28 Aug 2003 09:02:40 -0400, "Tarmo Tammaru"
wrote: "George, W5YR" wrote in message ... If anyone is interested in really getting to the bottom of this endless jousting, turn to page 136 of "Theory and Problems of Transmission Lines" by Robert A. Chipman. This is a Schaum's Outline book - mine is dated 1968. George, I took a course from Dr Chipman. The text he used was Adler, Chu, and Fano. I bet he references that book. Tam/WB2TT Hi Tam, It is the second reference and it is found on page 8. No doubt those authors also understand that source characteristic Z must be equal to transmission line Z to characterize SWR on the line. Of course, at this point I cannot vouchsafe for that specifically, however, it seems unlikely anyone here will negate the premise. Except to say "t'ain't so." ;-) I said "at this point" as this could be resolved (or from the other 11 references) by my visiting my engineering library at the U. This will not prohibit others from denial however which simply mocks Chapman's work and those he references. I won't put the challenge I have offered others to you. You probably would have answered it by now if you could have. 73's Richard Clark, KB7QHC |
#16
|
|||
|
|||
On Thu, 28 Aug 2003 05:58:09 -0500, W5DXP
wrote: Richard Clark wrote: "...the generator impedance is 100+0j ohms, and the line is 5.35 wavelengths long." What does the generator impedance have to do with line losses? Hi Cecil, From Chapman (you following this George?) page 28: "It is reasonable to ask at this point how, for the circuit of Fig. 3-1(b), page 18, on which the above analysis is based, there can be voltage and current waves traveling in both directions on the transmission line when there is only a single signal source. The answer lies in the phenomenon of reflection, which is very familiar in the case of light waves, sound waves, and water waves. Whenever traveling waves of any of these kinds meet an obstacle, i.e. encounter a discontinuous change from the medium in which they have been traveling, they are partially or totally reflected." ... "The reflected voltage and current waves will travel back along the line to the point z=0, and in general will be partially re-reflected there, depending on the boundary conditions established by the source impedance Zs. The detailed analysis of the resulting infinite series of multiple reflections is given in Chapter 8." The Challenge that I have offered more than several here embody such topics and evidence the exact relations portrayed by Chapman (and others already cited, and more not). The Challenge, of course, dashes many dearly held prejudices of the Transmitter "not" having a characteristic source Z of 50 Ohms. Chapman also clearly reveals that this characteristic Z is of importance - only to those interested in accuracy. Those hopes having been dashed is much evidenced by the paucity of comment here; and displayed elsewhere where babble is most abundant in response to lesser dialog (for the sake of enlightening lurkers no less). Clearly those correspondents hold to the adage to choose fights you can win. I would add so do I! The quality of battle is measured in the stature of the corpses littering the field. :-) So, Cecil (George, Peter, et alii), do you have an answer? Care to take a measure at the bench? As Chapman offers, "just like optics." Shirley a man of your erudition can cope with the physical proof of your statements. ;-) The only thing you and others stand to lose is not being able to replicate decades old work. Two resistors and a hank of line is a monumental challenge. 73's Richard Clark, KB7QHC |
#17
|
|||
|
|||
Richard Clark wrote:
So, Cecil (George, Peter, et alii), do you have an answer? Years ago, I had a discussion with Jeff, WA6AHL, here on this newsgroup. I suggested that the impedance looking back into the source might be Vsource/Isource, i.e. the transformed dynamic load line. However, I have never taken a strong stand on source impedance. If reflections are blocked from being incident upon the source, as they are in most Z0-matched systems, the source impedance doesn't matter since there exists nothing to reflect from the source impedance. My basic approach is to achieve a Z0-match and therefore forget about source impedance. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#18
|
|||
|
|||
|
#19
|
|||
|
|||
On Thu, 28 Aug 2003 12:18:44 -0500, W5DXP
wrote: Richard Clark wrote: So, Cecil (George, Peter, et alii), do you have an answer? Years ago, I had a discussion with Jeff, WA6AHL, here on this newsgroup. I suggested that the impedance looking back into the source might be Vsource/Isource, i.e. the transformed dynamic load line. However, I have never taken a strong stand on source impedance. If reflections are blocked from being incident upon the source, as they are in most Z0-matched systems, the source impedance doesn't matter since there exists nothing to reflect from the source impedance. My basic approach is to achieve a Z0-match and therefore forget about source impedance. Hi Cecil, That's all fine and well. It exhibits a rather standard behavior and confirms conventional expectations. I take by this response that you have no interest in the confirmation of interference in both Optical and RF metaphors being visited at the bench. That is fine too. It is a rather tough example to replicate - except when stumbled upon, then we hear cries for exorcism being needed (my cue). My missives simply offer touchstones of clarity in contrast to the murky sea of un-fettered statements. We are presented with fantastic notions that the characteristic source Z of a transmitter is unknowable, and this statement is usually closely allied to the notion that this same "unknowable" Z is actually responsible for reflecting all power arriving at the antenna terminal. Few of those who utter these witless jokes have any response to the straight line "So what is this Z that does all that reflecting?" In their chagrin, they fail even to repeat "it is unknowable...." Absolutely none can venture a guess that it is either: "much less than 50 Ohms," or it is "much more than 50 Ohms." This would be two obvious rejoinders and yet neither is uttered. Such is faith. The universal silence condemns their specious claims absolutely. These absurd notions deserve a hearty laugh, because it invalidates the need for a tuner which is purposely inserted between the source and load to serve that very purpose (and which you describe as your typical habit which is a nearly universal application). But, again, this discussion is generally reserved only for those interested in accuracy. :-) 73's Richard Clark, KB7QHC |
#20
|
|||
|
|||
On Thu, 28 Aug 2003 12:18:44 -0500, W5DXP
wrote: Richard Clark wrote: So, Cecil (George, Peter, et alii), do you have an answer? Years ago, I had a discussion with Jeff, WA6AHL, here on this newsgroup. I suggested that the impedance looking back into the source might be Vsource/Isource, i.e. the transformed dynamic load line. However, I have never taken a strong stand on source impedance. If reflections are blocked from being incident upon the source, as they are in most Z0-matched systems, the source impedance doesn't matter since there exists nothing to reflect from the source impedance. My basic approach is to achieve a Z0-match and therefore forget about source impedance. Hi Cecil, That's all fine and well. It exhibits a rather standard behavior and confirms conventional expectations. I take by this response that you have no interest in the confirmation of interference in both Optical and RF metaphors being visited at the bench. That is fine too. It is a rather tough example to replicate - except when stumbled upon, then we hear cries for exorcism being needed (my cue). My missives simply offer touchstones of clarity in contrast to the murky sea of un-fettered statements. We are presented with fantastic notions that the characteristic source Z of a transmitter is unknowable, and this statement is usually closely allied to the notion that this same "unknowable" Z is actually responsible for reflecting all power arriving at the antenna terminal. Few of those who utter these witless jokes have any response to the straight line "So what is this Z that does all that reflecting?" In their chagrin, they fail even to repeat "it is unknowable...." Absolutely none can venture a guess that it is either: "much less than 50 Ohms," or it is "much more than 50 Ohms." This would be two obvious rejoinders and yet neither is uttered. Such is faith. The universal silence condemns their specious claims absolutely. These absurd notions deserve a hearty laugh, because it invalidates the need for a tuner which is purposely inserted between the source and load to serve that very purpose (and which you describe as your typical habit which is a nearly universal application). But, again, this discussion is generally reserved only for those interested in accuracy. :-) 73's Richard Clark, KB7QHC |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
A Subtle Detail of Reflection Coefficients (but important to know) | Antenna | |||
Re-Normalizing the Smith Chart (Changing the SWR into the same load) | Antenna | |||
Mother Nature's reflection coefficient... | Antenna |