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#41
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Roy Lewallen wrote:
And if Cecil's work leads to the conclusion that the source impedance impacts the line's SWR, then it's wrong. It doesn't. In fact, just the opposite. My examples do NOT even include a 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 80,000 Newsgroups - 16 Different Servers! =----- |
#42
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On Tue, 12 Aug 2003 17:04:59 -0500, W5DXP
wrote: 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|)? Hi Cecil, Why don't you solve the first problem before presenting your own? 73's Richard Clark, KB7QHC |
#43
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#44
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#45
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"W5DXP" wrote in message ... 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 Cecil, When you do this, does the scale still display the correct SWR for conditions other than 1:1 ? Tam/WB2TT |
#46
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On Tue, 12 Aug 2003 15:52:05 -0700, Roy Lewallen
wrote: It's admittedly hard for me to follow what you've written, but it sounds like you're saying that: Hi Roy, 1. Source impedance affects line SWR, and 2. It's impossible to tell by how much. Did I get that right? No. The sources offered and the data exhibited provide a very clear answer. To state this yet again, it is the lack of knowledge in the distances traversed between reflecting interfaces that introduces the Mismatch Uncertainty. A smart lad might conspire to present any particular Power measurement if he could withhold other details from scrutiny. A lad who considered himself smart may do the same but think he invented a free power amplifier (or dissipationless load). This is simply an account of poor boundary controls that turn some folk into magicians and others into the reincarnation of Galileo. Either outcome is achieved through delusion. Incidentally, you've brought up a new topic, that of an SWR meter. Look at the Subject line. As for the aside about SWR meter reading, I have performed SWR measurements with a variety of NBS methods (many hundreds of times) - none of them described here very often, and some never at all. I doubt any here are so well versed in these methods as to challenge my data by employing them (it would only confirm the results). I would be happy to see as much effort put to it - in that it would represent a technical rebuttal rather than echoed denials. I would be happy to retract my points if someone revealed an error of commission/omission - such has not happened and discussion of that data has been wholly absent. Look Roy, skip the rhetoric (from all sources including me) and explain or refute the data I obtained. If you cannot accept it, reveal the error. If the method is too tedious to replicate - say so. This is not the first time I've broached the subject and I certainly don't expect many to care for one, or follow blithely for another. It only matters in issues of accurate Power determination. 73's Richard Clark, KB7QHC |
#47
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Tarmo Tammaru wrote:
"W5DXP" wrote: 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. When you do this, does the scale still display the correct SWR for conditions other than 1:1 ? The scale is calibrated using known loads so yes, it displays the correct SWR up to 5.83:1. Above 5.83:1 the resolution of the scale is poor because the full scale SWR is infinity. I have marks at 5.83:1 and 10:1. 5.83:1 is where the reflected power equals half the forward power. Incidentally, the Z0 of my '450' ohm ladder- line is closer to 388 ohms. -- 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! =----- |
#48
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W5DXP wrote in message ...
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. BTW, how do you know the accuracy of your homebrew SWR meter? Slick |
#49
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Dr. Slick wrote:
Would these be the termination resistors to ground, one for each directional coupler? Yes I would think that you would have to adjust the width of the traces as well, or the thickness of the dielectric material, or the space between the couplers and the thru-line to use it for an impedance other than 50 Ohms (talking about commercial equipment, that is). I use a toroid to sense the RF current and an R=Z0 resistor to turn it into a voltage. I have a capacitive voltage divider on the RF voltage which is adjustable for calibration purposes. The only real difference between it and a 50 ohm SWR meter is the internal load resistor. It's actually a bridge circuit with a Z0 reference resistor. Unfortunately, it is not very accurate for the relatively high SWRs that I run on my ladder-line, e.g. 4:1 to 16:1 -- 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! =----- |
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