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Richard Clark wrote:
To this point I have seen no counter demonstrations, nor counter proposals, nor counter argument ... Not unusual since your above deadline for counter demonstrations, counter proposals, and counter arguments was 66 minutes from the time you made the original posting. :-) You are in a room with a 150 ohm (lossless) transmission line coming through a hole in the wall and with a 50+j0 ohm load in the center of the room. Are you telling us that the SWR is not (1+|rho|)/(1-|rho|)? -- 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 80,000 Newsgroups - 16 Different Servers! =----- |
On Tue, 12 Aug 2003 14:13:44 -0500, W5DXP
wrote: Richard Clark wrote: To this point I have seen no counter demonstrations, nor counter proposals, nor counter argument ... Not unusual since your above deadline for counter demonstrations, counter proposals, and counter arguments was 66 minutes from the time you made the original posting. :-) Hi Cecil, I see you still live in a dimensional aberration where you experience 22 days as 66 minutes. You must be oxygen starved by now. 73's Richard Clark, KB7QHC |
Egad.
Given only a line's characteristic impedance and the load impedance, I can tell you exactly what the SWR is for a lossless line. For a lossy line, I only need to know, in addition, the line's length and the amount of loss per unit length. In no case do I need to know the source impedance. If, as you insist, the source impedance affects the SWR on the line, please provide an equation that gives the SWR on the line, with source impedance being one of the variables. It's such a simple thing, surely such an equation appears in one of the several references you cite. I did notice that SWR doesn't appear in any of the titles or the quoted passages, though, so you may have to dig a little. And if Cecil's work leads to the conclusion that the source impedance impacts the line's SWR, then it's wrong. It is, for those who are interested, very easy to see intuitively why the source impedance doesn't affect the SWR. Consider the situation that occurs when the source is first turned on. A forward voltage wave travels down the line toward the load. A reflected wave, whose magnitude and phase are determined by the reflection coefficient at the load end of the line, returns. If we stop time just as the reflected wave is returning, we can calculate the SWR, so far, on the line, solely from the ratio of the forward and reflected waves -- it's the interference between these waves that create the standing waves. Turning time back on again, the returning wave reflects off the source (assuming a source mismatch), producing another forward wave. Let's watch this wave as it travels toward the load, reflects, and returns. Exactly the same proportion of this wave is reflected as for the original forward wave. So, when this new forward wave reflects and its reflected wave returns, we've got a total of two forward waves and two reflected waves. The forward/reflected ratio of the second pair is exactly the same as the forward/reflected ratio of the first pair -- it's the reflection coefficient at the load end. So the ratio of the total forward wave to the total reverse wave is the same for the first pair, the second pair, and the sum of the two pairs. In other words, the second pair of waves hasn't changed the SWR from what we calculated from the original pair of waves. You can continue this observation for each forward-reverse pair, and see that the SWR never changes (at least when observed when each reflected wave just returns) from the original value. And the original value was determined only by the load mismatch, not the source. The source mismatch determines how big the total forward and reflected waves end up being when all the reflections have died out to a negligible value. But it has nothing to do with the forward/reverse ratio, which determines the SWR. Roy Lewallen, W7EL Richard Clark wrote: On Tue, 12 Aug 2003 02:48:49 -0700, Roy Lewallen wrote: Almost correct. The transmitter output impedance has no effect whatsoever on the line's SWR. Roy Lewallen, W7EL Hi Roy, Entirely incorrect. Transmitter output impedance that does not conform to transmission line Z, when presented with a mismatched load through that line, adds mismatch uncertainty in the form of an indeterminate SWR and indeterminate Power to the load. This has already been demonstrated twice. This has long been documented with NBS/NIST references going back 4 decades. There is nothing mysterious about it at all, and it conforms to the rather simple principles of wave interference so poorly presented by Cecil in months past. The authoritative site: http://www.boulder.nist.gov/div813/index.html Direct reference: "Juroshek, J. R.; A Direct Calibration Method for Measuring Equivalent Source Mismatch; Microwave J., pp. 106-118; October 1997 Obscure references: http://www.boulder.nist.gov/div813/r...00S_n2nNet.pdf "With vector measurements of the generator and meter reflection coefficients Ãg and Ãm, respectively, the power of the incident signal am can be related to the power of the source." http://www.boulder.nist.gov/div813/r...FRad_ARFTG.pdf which describes radiometer calibration (perhaps too exotic for this group) "tests are based on two assumptions. First, the network responds linearly to our signal ( no power compression), and second, the radiometer is sufficiently isolated from the source impedance." ... "One of the assumptions made in deriving eq. (2) was that the output from the radiometer is not dependent on the source impedance. In the construction of the radiometer, two isolators are inserted at the input of the radiometer to isolate the radiometer from the source." ... "The mismatch uncertainty depends strongly on the poorly known correlation between uncertainties in the measurements of different reflection coefficients, and so we use the maximum of the uncertainties obtained by assuming either complete correlation or no correlation whatsoever." "Forthcoming Paper: Influence of Impedance Mismatch Effects on Measurements of Unloaded Q Factors of Transmission Mode Dielectric Resonators" IEEE Transaction on Applied Superconductivity "Analysis of Interconnection Network and Mismatch in the Nose-to-Nose Calibration Automatic RF Techniques Group , June 15-16, 2000 , Boston, MA - June 01, 2000 "We analyze the input networks of the samplers used in the nose-to-nose calibration method. Our model demonstrates that the required input network conditions are satisfied in this method and shows the interconnection errors are limited to measurement uncertainties of input reflection coefficients and adapter S-parameters utilized during the calibration procedure. Further, the input network model fully includes the effects of mismatch reflections, and we use the model to reconcile nose-to-nose waveform correction methods with traditional signal power measurement techniques." As I mentioned, obscure references. However, given the impetus of their discussion is long known (and that I have already provided the original references they rely on), NIST presumes the investigators already have that basis of knowledge. 73's Richard Clark, KB7QHC |
Sorry, it's not clear from what you've said just what you're trying to
match to what. Truly, if you connect a 50 ohm load (be it a resistor, or some impedance transformed by a transmission line, tuner, or other means -- makes no difference) to a transmitter, and the transmitter's output impedance isn't 50 ohms, there will be a mismatch at the transmitter output. But who cares? Most transmitters are designed to work properly when terminated with 50 ohms, but that doesn't at all mean that their output impedances are 50 ohms. And it certainly doesn't affect the SWR on any transmission line connected to the transmitter. If you were to discover that your transmitter's output impedance were, say, 10 ohms and you connected it to a 10 ohm load, you'd have a very unhappy transmitter. All you have to worry about is presenting the transmitter with the load it was designed to work into, not what the internal impedance of the transmitter is. Roy Lewallen, W7EL Dr. Slick wrote: Roy Lewallen wrote in message ... Almost correct. The transmitter output impedance has no effect whatsoever on the line's SWR. Roy Lewallen, W7EL My point is that if the output impedance really was at a perfect 50 Ohms, then using a perfect 50 ohms transmission line, you can never match to anything other than 50 ohms. If the S22 is something other than 50 Ohms (usual case), then a transformation via 50 ohm coax about a constant VSWR is possible, for the purposes of matching to a not-quite-perfectly-50 ohms antenna. Slick |
Richard Clark wrote:
I see you still live in a dimensional aberration where you experience 22 days as 66 minutes. I see that you still ignore the technical questions so I will repeat mine: Are you saying that SWR doesn't equal (1+|rho|)/(1-|rho|)? -- 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 80,000 Newsgroups - 16 Different Servers! =----- |
Dr. Slick wrote:
I didn't think you could tell us. I've never seen an SWR meter that you could "calibrate" to 50 or 75 ohms, or less. The calibration of the SWR meter is controlled by the internal sampling load resistor, the 'R' in Peter's V + IR equation. I have a home-brewed SWR meter that measures SWR on both balanced 450 ohm feedlines and on 300 ohm feedlines simply by changing the internal load resistors. -- 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 80,000 Newsgroups - 16 Different Servers! =----- |
Had a look at the refs. I'm curious, did you actually read the
sentence that Roy wrote? Cheers, Tom Richard Clark wrote in message . .. On Tue, 12 Aug 2003 02:48:49 -0700, Roy Lewallen wrote: Almost correct. The transmitter output impedance has no effect whatsoever on the line's SWR. Roy Lewallen, W7EL Hi Roy, Entirely incorrect. Transmitter output impedance that does not conform to transmission line Z, when presented with a mismatched load through that line, adds mismatch uncertainty in the form of an indeterminate SWR and indeterminate Power to the load. This has already been demonstrated twice. This has long been documented with NBS/NIST references going back 4 decades. There is nothing mysterious about it at all, and it conforms to the rather simple principles of wave interference so poorly presented by Cecil in months past. The authoritative site: http://www.boulder.nist.gov/div813/index.html Direct reference: "Juroshek, J. R.; A Direct Calibration Method for Measuring Equivalent Source Mismatch; Microwave J., pp. 106-118; October 1997 Obscure references: http://www.boulder.nist.gov/div813/r...00S_n2nNet.pdf "With vector measurements of the generator and meter reflection coefficients Ãg and Ãm, respectively, the power of the incident signal am can be related to the power of the source." http://www.boulder.nist.gov/div813/r...FRad_ARFTG.pdf which describes radiometer calibration (perhaps too exotic for this group) "tests are based on two assumptions. First, the network responds linearly to our signal ( no power compression), and second, the radiometer is sufficiently isolated from the source impedance." ... "One of the assumptions made in deriving eq. (2) was that the output from the radiometer is not dependent on the source impedance. In the construction of the radiometer, two isolators are inserted at the input of the radiometer to isolate the radiometer from the source." ... "The mismatch uncertainty depends strongly on the poorly known correlation between uncertainties in the measurements of different reflection coefficients, and so we use the maximum of the uncertainties obtained by assuming either complete correlation or no correlation whatsoever." "Forthcoming Paper: Influence of Impedance Mismatch Effects on Measurements of Unloaded Q Factors of Transmission Mode Dielectric Resonators" IEEE Transaction on Applied Superconductivity "Analysis of Interconnection Network and Mismatch in the Nose-to-Nose Calibration Automatic RF Techniques Group , June 15-16, 2000 , Boston, MA - June 01, 2000 "We analyze the input networks of the samplers used in the nose-to-nose calibration method. Our model demonstrates that the required input network conditions are satisfied in this method and shows the interconnection errors are limited to measurement uncertainties of input reflection coefficients and adapter S-parameters utilized during the calibration procedure. Further, the input network model fully includes the effects of mismatch reflections, and we use the model to reconcile nose-to-nose waveform correction methods with traditional signal power measurement techniques." As I mentioned, obscure references. However, given the impetus of their discussion is long known (and that I have already provided the original references they rely on), NIST presumes the investigators already have that basis of knowledge. 73's Richard Clark, KB7QHC |
On Tue, 12 Aug 2003 14:25:47 -0700, Roy Lewallen
wrote: If, as you insist, the source impedance affects the SWR on the line, please provide an equation that gives the SWR on the line, with source impedance being one of the variables. Hi Roy, Your crafted requirement reveals the shortfall inherent in the problem. It is distance based too, and without that discussion there is no way to forecast what SWR or Power reading you would obtain from simply knowing both the load and source's Z's. This is why it is called Mismatch Uncertainty. I have provided NBS and NIST documents both recently and in the past. Recent offerings are obscure, as I have already admitted. The earlier citations I provided were direct and to the point and serve as the basis of the recent work. I have provided data that exhibits the effect. I have provided the test protocol in how to achieve that data. I have also described that this data is also, theoretically, achievable through standard interference math also presented by me in the past. It takes little imagination to observe that there is a zone of confusion that lies between two reflecting interfaces when the path is not fully described. My data showed that path in one foot increments of transmission line over an interval of a quarter wavelength or more. We have been offered evidence of this Mismatch Uncertainty by Dr. Slick if I am to trust his postings - be that as it may, because it requires no further proof. Simply put, bald assertions that SWR is unaffected when read between two discontinuities is wrong without a concomitant description of all paths leading to the SWR meter. This is a commonplace of interference plain and simple. I have observed no one describing this detail (except Dr. Slick). As all this is part of the historical record entitled: "The Cecilian Gambit, a variation on the Galilean Defense revisited" I do not see how its repetition here brings anything new to the mix. None the less, this recent example has been fun. :-) 73's Richard Clark, KB7QHC |
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