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On Mon, 6 Oct 2003 14:38:48 -0400, "Tarmo Tammaru" wrote:
"Walter Maxwell" wrote in message .. . This concept is foreign to me, so if I'm wrong I'd like to have some proof that the source impedance can have any influence on SWR. Walt Walt, I don't think the source impedance has any effect on SWR. In fact I have changed the source impedance and saw no change in SWR. But Since tha SWR meter is a really dumb bunny, I wonder of the meter can be mislead by a reactive source impedance that forces the current to be out of phase with the voltage. Perhaps a case where the source and load both are reactive? Tam/WB2TT Tam, I totally disagree with those who say SWR appearing on a mismatched transmission line is dependent on the source impedance. If I understand Richard C correctly, he claims with 'bullet-poof' certainty that SWR is dependent on the source impedance. And if I understand Reg's earlier statement correctly, he shares Richard's position. I asked Reg for clarification, but he has not yet responded. Richard C, you suggest we step up to the bench and perform your experiment that will prove you are correct. If you described this experiment to me earlier I invoke my Alzheimer's excuse for not remembering it. So would you please repeat it for my benefit? I'll be back at my Florida lab by Oct 22, and am anxious to perform it. And Richard H, thanks for the support. More than 50 years of lab and professional work on transmission lines have never shown the source impedance to have any effect on propagation along the line, other than to influence the magnitude of the signal as it enters and propagates along the line. Walt, W2DU |
"Cecil Moore" wrote in message ... Richard Harrison wrote: In the usual h-f transmission line, Zo appears as an Ro. RG-174 has about 6dB loss per 100ft on 12m. Its Z0 is equal to Sqrt[(R+jXL)/(G+jXC)]. Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs say the Z0 of RG-174 is a nominal 50 ohms. of course its not exactly 2500, otherwise there would be no loss. but its close, maybe 2500+j10 or something like that. and even the resistive part may not be exact, the nominal 50 ohms could be 45 to 55 depending on the tolerances of the manufacturer. |
On Mon, 06 Oct 2003 14:37:18 -0500, Cecil Moore
wrote: I offered an experiment that might prove you right ... I suspect the above condition is representative of what you are seeing in your measurements. Hi Cecil, Your memory of those measurements alternately gains clarity and fades by the passage of each moment. I need no further examples, as flawed or superlative as they may be, to support my thesis that stands by simple resistive loads. Your gilding of the Lily and painting the Rose is performed off the bench as a means to yet again force the world into a speculation that your xeroxed page of Chipman responds to. No further analysis is required, it has been performed and data taken has demonstrated it. If you choose to put forward a variant employing reactance, you could at least step up to the bench to offer confirmatory or rejecting evidence as I did. This is a simple example of offering a complete analysis to peers for study and review. Some problems defy such completeness, others defy analysis at the bench. This issue that I have presented, and to which you toss in a variant are wholly germane and within the capacity of any Ham to attempt to support or refute through scientific method. It is equally obvious that such methods and manners are an alien concept competing with sneer review. As such, this disregard constitutes the kulture of institutionalized ignorance that dominates "debate." Cecil, I seriously doubt your protestations of effusive gushing I offered an experiment that might prove you right, Richard in that of your crafted "might" (which certainly offers no prospect of you actually performing any deed) is weighed with condescension. Such passivity merely conforms to the existing kulture and hardly rises to the effort and reportage I have already offered. 73's Richard Clark, KB7QHC |
On Mon, 06 Oct 2003 21:10:25 GMT, Walter Maxwell wrote:
Richard C, you suggest we step up to the bench and perform your experiment that will prove you are correct. Hi Walt, This is a misrepresentation of my work. I responded here that the appearance of poor criticism suggests that my work is bulletproof (among a spectrum of equal likelihoods) and my statement is a critique of that shoddy work being offered as rebut to my data. Further, I make no pretense that such an experiment will prove me correct and I have offered on more than one occasion that someone with care equal to mine could easily find data that refutes mine. I have no illusions to being "correct" and have freely admitted that everything I do contains error. However, I do, by training and experience, exhibit those bounds of accuracy where others simply caterwaul on that they need no lessons in the matter and further would never "change their mind." Now, if this appears to be backtracking, it is evident only to those who will never attempt anything at the bench and have no capacity to weigh their own sources of error - either of judgement or demonstrable skill. In conclusion, it is certainly an illusion to imagine that anything is ever concluded. The best I can achieve is a confluence of thought with one or several in educating rather exotic issues that lie outside of the experience of many. There is nothing inherently common about this, and is of interest to only those who aspire to accuracy, a very limited audience. The larger point that is germane to the whole of the audience is found in the conduct of analysis, its support or its refutation. The scientific community does not brook simple nay-saying and the shotgun approach to cut-and-paste arguments offered as rebuttal. I have described methods and results. My methods can be challenged, my results can be shown irreproducible. I have offered tangible, testable propositions, means, and results to which absolutely nothing of equal merit has been put forward to provide a meaningful assault. It is in that context that the appearance of a bulletproof presentation has been suggested by me. :-) The irony of my comments lies in the simple observation that this only takes two resistors and a hank of line for one such test. The magnitude of effort, as evidenced by those simple constraints suggests that my critics are seriously skill impaired to offer honest testing. I am content to stand above such midgets even if I have to stoop so as to not make it so overwhelmingly and embarrassingly obvious. 73's Richard Clark, KB7QHC |
"Walter Maxwell" wrote in message ... Tam, I totally disagree with those who say SWR appearing on a mismatched transmission line is dependent on the source impedance. Walter, I agree with you. But I am making a distinction between SWR and *measured* SWR. People who think an SWR meter possesses magic properties should look inside one. It takes one instantaneous sample of the NET voltage V, and one instantaneous sample of the NET current I. It displays the vector sum of K(V + k2I) and K(V- k2I) where K is the sensitivity, and k2 is chosen to make the second equation equal to 0 for a 50 Ohm load. The approximations made in coming up with what is printed on the meter scale assumes that for the forward wave the voltage and current are in phase. I have seen descriptions of how these things work, but no equations to back these up. I suspect one would start with the two equations that I listed, but express I in terms of V and deltaZ, where deltaZ is the deviation from 50 Ohms. K can arbitrarily be 1. I also suspect that Bird, etc don't really want us to know that. Tam/WB2TT |
Walt wrote -
Well, Reg, the reason I asked for an expression that includes the source resistance in measuring SWR is that you said above that the internal impedance of the transmitter is ASSUMED to be 50 ohms. This implies that the SWR is dependent on the internal impedance of the source, does it not ? =============================== Walt, there's just a slight misunderstanding. It is not I who makes that silly assumption - it is the stupid so-called SWR + |rho| meter! The meter indication is linearly proportional to |Rho|, from 0-to-1, from zero to full-scale. In effect, by means of its scale-calibration, it calculates SWR and Refl power from |Rho|. I understand conversion tables even appear in the handbooks. The number 50-ohms appears in meter design calculations, and therefore affects the meter indication of |Rho|. One expression involved is |Rho| = (50-ZL)/(50+ZL) - The meter therefore ASSUMES the impedance seen looking back towards the transmitter from the meter is exactly 50 ohms. But, as you well know, in the usual amateur situation, this assumption can be, and often is, is wildly incorrect. There are only a few remaining old-wives who still think it's true. But the biased arguments still habitually remain. As I have been saying for years, the solution is to change the name of the undoubtably useful meter to TLI (Transmitter Loading Indicator). Forget about SWR on an imaginary, non-existent transmission line and get into the real world. Don't shoot the messenger of apple-cart-upsetting news. It's not new to the rigid old-wives Establishment. Walt, please direct any criticism towards the education-disrupting meter indications. For design of so-called HF SWR meters download in a few seconds and run immediately program SWRMETER from website below. Copious design notes are included. I have just re-read them. After 3 years their readability could be improved and updated but I have no intention of doing so. ----------------------------------------------------- Walt sez, This concept is foreign to me, so if I'm wrong I'd like to have some proof that the source impedance can have any influence on SWR. ---------------------------------------------------- Walt, you must have been familiar with the incorrect concept for years. As we both know, changing the internal impedance of the transmitter cannot possibly have any effect on SWR on the imaginary transmission line, if there is one between transmitter and the meter. It is the meter itself which gives silly answers because it, and its users, assumes a line of exactly 50-ohms, longer than 1/2-wavelength actually exists. It doesn't! ---- ======================= Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.g4fgq.com ======================= |
On Mon, 6 Oct 2003 20:52:24 -0400, "Tarmo Tammaru" wrote:
"Walter Maxwell" wrote in message .. . Tam, I totally disagree with those who say SWR appearing on a mismatched transmission line is dependent on the source impedance. Walter, I agree with you. But I am making a distinction between SWR and *measured* SWR. People who think an SWR meter possesses magic properties should look inside one. It takes one instantaneous sample of the NET voltage V, and one instantaneous sample of the NET current I. It displays the vector sum of K(V + k2I) and K(V- k2I) where K is the sensitivity, and k2 is chosen to make the second equation equal to 0 for a 50 Ohm load. The approximations made in coming up with what is printed on the meter scale assumes that for the forward wave the voltage and current are in phase. I have seen descriptions of how these things work, but no equations to back these up. I suspect one would start with the two equations that I listed, but express I in terms of V and deltaZ, where deltaZ is the deviation from 50 Ohms. K can arbitrarily be 1. I also suspect that Bird, etc don't really want us to know that. Tam/WB2TT Well, Tam, I agree with you also, but your comments only relate to accuracy, not whether the internal resistance of the source has any influence on the SWR. I'm well acquainted with the various types of swr meters, the Bruene lumped-constant directional coupler, for instance, or for a more professional example, the HP-778D dual directional coupler that I use with an HP-8405A Vector Voltmeter in my own lab. The value of the source resistance can be any value, and its reflection coefficient rho seen looking into the output can be any value from zero to one. If the value is zero it simply means any reflected power reaching the output is absorbed and if rho = 1all reflected power is re-reflected. With any combination of the above the SWR on a mismatched line is the same. The only effect these parameters have on the line is the magnitude of the signal being propagated. I know this from years of experience, beginning with slotted lines, and from the engineering literature. For example, Walter C. Johnson on Page 100 spells it out specifically. What I'd like to see is for those who say SWR is dependent on the source impedance to show how and why this what I call 'misconception' can occur. Walt, W2DU |
Richard Clark wrote:
On Mon, 06 Oct 2003 15:16:04 -0500, Cecil Moore wrote: None of my statements has any meaning outside of the context in which they are offered Well, as this all thread started from one context: everything can be explained by achieving a conjugate match being so encompassing as to enlarge beyond your capacity to explain, we find ourselves with shortfalls of example to any context. But that's not what I said, Richard. Everything within the original context can be explained by achieving a conjugate match but you deleted the context and therefore misquoted me. If I say, "It is always daylight at 12 noon." and you quote me as saying "It is always daylight ", you have turned my true statement into a false statement which is not an ethical thing to do. -- 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! =----- |
David Robbins wrote:
"Cecil Moore" wrote: Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs say the Z0 of RG-174 is a nominal 50 ohms. of course its not exactly 2500, otherwise there would be no loss. but its close, maybe 2500+j10 or something like that. and even the resistive part may not be exact, the nominal 50 ohms could be 45 to 55 depending on the tolerances of the manufacturer. Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline - is all that extra loss accounted for in the +j10 term? -- 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! =----- |
On Tue, 7 Oct 2003 01:29:43 +0000 (UTC), "Reg Edwards"
wrote: Walt wrote - Well, Reg, the reason I asked for an expression that includes the source resistance in measuring SWR is that you said above that the internal impedance of the transmitter is ASSUMED to be 50 ohms. This implies that the SWR is dependent on the internal impedance of the source, does it not ? =============================== Walt, there's just a slight misunderstanding. It is not I who makes that silly assumption - it is the stupid so-called SWR + |rho| meter! The meter indication is linearly proportional to |Rho|, from 0-to-1, from zero to full-scale. In effect, by means of its scale-calibration, it calculates SWR and Refl power from |Rho|. I understand conversion tables even appear in the handbooks. The number 50-ohms appears in meter design calculations, and therefore affects the meter indication of |Rho|. One expression involved is |Rho| = (50-ZL)/(50+ZL) - The meter therefore ASSUMES the impedance seen looking back towards the transmitter from the meter is exactly 50 ohms. But, as you well know, in the usual amateur situation, this assumption can be, and often is, is wildly incorrect. There are only a few remaining old-wives who still think it's true. But the biased arguments still habitually remain. As I have been saying for years, the solution is to change the name of the undoubtably useful meter to TLI (Transmitter Loading Indicator). Forget about SWR on an imaginary, non-existent transmission line and get into the real world. Don't shoot the messenger of apple-cart-upsetting news. It's not new to the rigid old-wives Establishment. Walt, please direct any criticism towards the education-disrupting meter indications. For design of so-called HF SWR meters download in a few seconds and run immediately program SWRMETER from website below. Copious design notes are included. I have just re-read them. After 3 years their readability could be improved and updated but I have no intention of doing so. ----------------------------------------------------- Walt sez, This concept is foreign to me, so if I'm wrong I'd like to have some proof that the source impedance can have any influence on SWR. ---------------------------------------------------- Walt, you must have been familiar with the incorrect concept for years. As we both know, changing the internal impedance of the transmitter cannot possibly have any effect on SWR on the imaginary transmission line, if there is one between transmitter and the meter. It is the meter itself which gives silly answers because it, and its users, assumes a line of exactly 50-ohms, longer than 1/2-wavelength actually exists. It doesn't! ---- ======================= Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.g4fgq.com ======================= No Reg, I've never been familiar with the incorrect concept. I had never thought anyone was that uninformed until you and Richard C brought it up here. I was flabbergasted to think you held that position, so I'm relieved to know that you aren't among the uninformed. And Richard's last two posts seemed contradictory--I haven't yet totally understood what his position really is. I'm sure you're aware that the voltage applied to the meter movement of the SWR meter is actually making the indicator hand respond to the value of rho, but with the scale graduated in units of SWR. To verify this we adjust the forward reading for full scale for the reference reading. We then switch to the reflected reading. Let's say the mismatch is 3:1 for rho = 0.5. If the SWR indicator is accurate a voltmeter will now read 0.5. exactly half scale, where the full-scale reading is 1.0. Reg, I'm not lecturing you, because I know that you know this--this is my way of telling you that I also know it. Walt, W2DU |
Richard Clark wrote:
No further analysis is required, it has been performed and data taken has demonstrated it. Nuff said! Guess that settles it - and you don't want or need to understand the underlying physics. Why do you keep posting? If you choose to put forward a variant employing reactance, you could at least step up to the bench to offer confirmatory or rejecting evidence as I did. I don't understand how to set up your experiment. Your verbal description was extremely confusing. How about a decent diagram? -- 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! =----- |
On Mon, 06 Oct 2003 22:33:17 -0500, Cecil Moore
wrote: If I say, "It is always daylight at 12 noon." and you quote me as saying "It is always daylight ", you have turned my true statement into a false statement which is not an ethical thing to do. Hi Cecil, I don't know why you bother with discussion of ethics when you cannot respond to the technical enquiry. This is your 12th entry in this side thread that was NOT addressed to you and you have nothing to offer but the squishy touchy problem of your perception of a moral dilemma whose discussion is best left to a democrat running for office. And this silliness about "true statements" is absurd in its own right and easily an example of a moral rigidity that brooks no contrary evidence. Unlike you, I am fully aware of my errors, their source, and their contribution or benign influence upon other discussion. You have spent to much time in a binary world, a womb that has insulated you from the reality of uneven edges and impure solutions. You are out of your element trying to force fit nature into the only solution you have from a xeroxed page. 73's Richard Clark, KB7QHC |
On Mon, 06 Oct 2003 22:56:18 -0500, Cecil Moore
wrote: I don't understand how to set up your experiment. Your verbal description was extremely confusing. How about a decent diagram? Hi Cecil, Then argue what constitutes a decent diagram? Cecil, you are a goldbrick. Frankly, I have no interest in explaining it to you. That is why I offered it only once. All that need be said was said, and I responded to every technical enquiry you put to me. That you are confused is your own problem and not my responsibility. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
You are out of your element trying to force fit nature into the only solution you have from a xeroxed page. Maybe so, but that xeroxed page is what you offered as a reference. That's why I xeroxed it. Nothing on that page has changed since I xeroxed it. It still talks about a "resonant rise of voltage" in series resonant circuits, the most probable cause of a variation in SWR and the very thing that you refuse to accept or acknowledge. -- 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! =----- |
Richard Clark wrote:
wrote: I don't understand how to set up your experiment. Your verbal description was extremely confusing. How about a decent diagram? Then argue what constitutes a decent diagram? No, you have presented absolutely no diagram at all - just a set of unintelligible words. You have a web page. Why are you afraid to publish a schematic? -- 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! =----- |
You've got to be careful with cause and effect. There's not a direct
correspondence between loss and characteristic reactance. A transmission line can be very lossy, yet have a completely real characteristic impedance. Such a line doesn't have any reactance term in its characteristic impedance to "account for" its loss. To learn more about these, look up "distortionless line" in the index of your favorite transmission line text. The converse, however, isn't true. Any line which has a reactive Z0 does have loss. You can find the equations needed to calculate Z0 and loss coefficient alpha from R, G, L, and C in _Reference Data for Radio Engineers_. Deriving from them an equation directly relating alpha and Z0 should give you something to do for a number of long winter evenings. Maybe even give you a break from thinking about waves of average power bouncing about. Roy Lewallen, W7EL Cecil Moore wrote: David Robbins wrote: "Cecil Moore" wrote: Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs say the Z0 of RG-174 is a nominal 50 ohms. of course its not exactly 2500, otherwise there would be no loss. but its close, maybe 2500+j10 or something like that. and even the resistive part may not be exact, the nominal 50 ohms could be 45 to 55 depending on the tolerances of the manufacturer. Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline - is all that extra loss accounted for in the +j10 term? |
Roy Lewallen wrote:
A transmission line can be very lossy, yet have a completely real characteristic impedance. That's what I thought. Is RG-174 one of those transmission lines? Maybe even give you a break from thinking about waves of average power bouncing about. At least with average power, one cannot violate the conservation of energy principle by creating instantaneous energy in a passive load. :-) -- 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! =----- |
Cecil wrote:
Is a simple "yes" or "no" too much to ask? From Richard, yes. |
Richard Clark wrote:
If you choose to put forward a variant employing reactance, you could at least step up to the bench to offer confirmatory or rejecting evidence as I did. OK, here's an interesting data point. I adjusted my IC-756PRO for 5W output on 7.2 MHz using the following circuit. 7.2MHz 5W source---(+j442)---(-j442)---50 ohm dummy load SWR meter at the dummy load read 5W forward with an SWR of 1:1 Then I installed the SWR meter between the coil and the cap. With 5W supplied by the source, the forward power read 150 watts. Indicated SWR was 3:1 -- 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 100,000 Newsgroups - 19 Different Servers! =----- |
Reg Edwards wrote:
But where have you hidden this remarkable transmission line which is long enough to mug and hoodwink so-called SWR meters? It does not exist! Your argument falls flat at the start. Reg, I asked the question over on sci.phisics.electromag and got the following answer: So unless almost all the power diverts into an undesireable mode (by a factor of more than a million to one), one foot of (RG-213) cable should see pure TEM at the end. So according to a pretty smart guy, one foot of RG-213 on each side of a 50 ohm SWR meter will ensure that the SWR meter is in the 50 ohm environment for which it was designed. I have three feet of RG-400 on each side of mine. -- 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! =----- |
Roy Lewallen wrote:
Cecil Moore wrote: Roy Lewallen wrote: A transmission line can be very lossy, yet have a completely real characteristic impedance. That's what I thought. Is RG-174 one of those transmission lines? No. Distortionless lines are specially made, or periodically loaded with fixed components to achieve distortionless characteristics. Incidentally, I recently carefully measured the Z0 of nine pieces of RG-58 type cables at 10 MHz. R varied from 48.1 to 57.2 ohms, and X from -0.67 to -2.32 ohms. Assuming 57.2 - j2.32 ohms Z0, our 50 ohm SWR meters may be off by 15%? Could this be the answer to Richard C's SWR readings? I suggested that as a possibility early on but he dismissed it. -- 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! =----- |
On Tue, 07 Oct 2003 10:49:50 -0500, Cecil Moore
wrote: Richard Clark wrote: If you choose to put forward a variant employing reactance, you could at least step up to the bench to offer confirmatory or rejecting evidence as I did. OK, here's an interesting data point. I adjusted my IC-756PRO for 5W output on 7.2 MHz using the following circuit. 7.2MHz 5W source---(+j442)---(-j442)---50 ohm dummy load SWR meter at the dummy load read 5W forward with an SWR of 1:1 Then I installed the SWR meter between the coil and the cap. With 5W supplied by the source, the forward power read 150 watts. Indicated SWR was 3:1 Hi Cecil, And so? 73's Richard Clark, KB7QHC |
|
Cecil Moore wrote:
Roy Lewallen wrote: A transmission line can be very lossy, yet have a completely real characteristic impedance. That's what I thought. Is RG-174 one of those transmission lines? No. Distortionless lines are specially made, or periodically loaded with fixed components to achieve distortionless characteristics. Incidentally, I recently carefully measured the Z0 of nine pieces of RG-58 type cables at 10 MHz. R varied from 48.1 to 57.2 ohms, and X from -0.67 to -2.32 ohms. I made one measurement at 1 MHz, on a cable whose Z0 at 10 MHz was 49.0 - j0.69 at 10 MHz. That cable's Z0 at 1 MHz was 50.7 - j2.05 ohms. I wasn't able to make good measurements below 1 MHz with my setup. . . . Roy Lewallen, W7EL |
Richard Clark wrote:
wrote: OK, here's an interesting data point. I adjusted my IC-756PRO for 5W output on 7.2 MHz using the following circuit. 7.2MHz 5W source---(+j442)---(-j442)---50 ohm dummy load SWR meter at the dummy load read 5W forward with an SWR of 1:1 Then I installed the SWR meter between the coil and the cap. With 5W supplied by the source, the forward power read 150 watts. Indicated SWR was 3:1 Hi Cecil, And so? And so it seems to support your variable SWR observations. -- 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! =----- |
Cecil,
Very interesting. Can you take one more reading. Leave the meter between the coil and cap, and then short out the coil. If shorting out the coil makes any difference, you are seeing the imperfection due to the meter. This is what I was alluding to in my response to Walter. Tam/WB2TT "Cecil Moore" wrote in message ... Richard Clark wrote: If you choose to put forward a variant employing reactance, you could at least step up to the bench to offer confirmatory or rejecting evidence as I did. OK, here's an interesting data point. I adjusted my IC-756PRO for 5W output on 7.2 MHz using the following circuit. 7.2MHz 5W source---(+j442)---(-j442)---50 ohm dummy load SWR meter at the dummy load read 5W forward with an SWR of 1:1 Then I installed the SWR meter between the coil and the cap. With 5W supplied by the source, the forward power read 150 watts. Indicated SWR was 3:1 -- 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 100,000 Newsgroups - 19 Different Servers! =----- |
Tarmo Tammaru wrote:
Very interesting. Can you take one more reading. Leave the meter between the coil and cap, and then short out the coil. If shorting out the coil makes any difference, you are seeing the imperfection due to the meter. This is what I was alluding to in my response to Walter. Shorting out the coil will leave the load at 50-j442 ohms, a very high SWR. -- 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! =----- |
There could be quite a number of reasons Richard's readings aren't
indicating what he thinks, and this is certainly one of them. Of one thing I'm certain -- the reason is something other than actual SWR being modified by source impedance. And yes, our SWR meters can easily be that far off when attempting to measure the real SWR on real cables. Good thing it doesn't matter, huh? Roy Lewallen, W7EL Cecil Moore wrote: Assuming 57.2 - j2.32 ohms Z0, our 50 ohm SWR meters may be off by 15%? Could this be the answer to Richard C's SWR readings? I suggested that as a possibility early on but he dismissed it. |
"Cecil Moore" wrote in message ... David Robbins wrote: "Cecil Moore" wrote: Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs say the Z0 of RG-174 is a nominal 50 ohms. of course its not exactly 2500, otherwise there would be no loss. but its close, maybe 2500+j10 or something like that. and even the resistive part may not be exact, the nominal 50 ohms could be 45 to 55 depending on the tolerances of the manufacturer. Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline - is all that extra loss accounted for in the +j10 term? no, its more complicated than that. the attenuation constant (usually alpha) = Re(gamma) where gamma is sqrt((R+jwL)(G+jwC)) Zo is sqrt((R+jwL)/(G+jwC)) so there is not a simple way to relate the characterisitic impedance to loss. for a low loss line the approximation for alpha is (R/2Zo)+(GZo/2) which can probalby be applied for most normal cases, but again, you have to get the R and G values of the line which can not be directly calculated from Zo. |
On Tue, 07 Oct 2003 13:54:34 -0500, Cecil Moore
wrote: Richard Clark wrote: wrote: OK, here's an interesting data point. I adjusted my IC-756PRO for 5W output on 7.2 MHz using the following circuit. 7.2MHz 5W source---(+j442)---(-j442)---50 ohm dummy load SWR meter at the dummy load read 5W forward with an SWR of 1:1 Then I installed the SWR meter between the coil and the cap. With 5W supplied by the source, the forward power read 150 watts. Indicated SWR was 3:1 Hi Cecil, And so? And so it seems to support your variable SWR observations. Hi Cecil, With 5W supplied you read 150W forward? Well that aside, it is not very remarkable to see 1:1 into a dummy load. It is also not very remarkable to see 3:1 into a complex load. You do not state you have any transmission line between the two reactances until you dropped in the SWR meter, that isn't particularly meaningful either. So, in the end, you demonstrate nothing of my examples that have always been premised with a transmission line being integral to the concept. The short of it: I have always described this as a problem involving two resistors and a hank of line. The long of it: You have merely demonstrated your own invention of two conjugated reactances and one resistor - not the same thing at all, not even conceptually. Now, if you added a 1foot length between the two reactances, and then replaced that with a two foot length, and then replaced that with a three foot length, and then replaced that with a four foot length.... out to at least half a wave of electrical length. And all the while taking forward and reverse power readings (or SWR, take your choice) and specified the frequency THEN and ONLY THEN would you be able to make a first pass comparison. To take an observation from Metrology: one measurement tells you nothing of any accuracy, two measurements only confuse, three begins to reveal a true measure, more improves matters. Your two readings say nothing to the matter (Mismatch Uncertainty) and actually confirm expectations that lie outside of my examples. 73's Richard Clark, KB7QHC |
On Tue, 07 Oct 2003 14:25:26 -0500, Cecil Moore
wrote: Shorting out the coil will leave the load at 50-j442 ohms, a very high SWR. Hi Cecil, That's the point.... 73's Richard Clark, KB7QHC |
"Cecil Moore" wrote in message ... Tarmo Tammaru wrote: Very interesting. Can you take one more reading. Leave the meter between the coil and cap, and then short out the coil. If shorting out the coil makes any difference, you are seeing the imperfection due to the meter. This is what I was alluding to in my response to Walter. Shorting out the coil will leave the load at 50-j442 ohms, a very high SWR. -- 73, Cecil http://www.qsl.net/w5dxp Hi Cecil, I think what you did was to force the current to be in phase with the voltage and fooled the meter into thinking it was all forward power. That is sort of the experiment I was going to do, but you beat me to it. Note that in the case where you moved the meter, you actually changed the load, but you know that. Tam/WB2TT |
Richard Clark wrote:
The long of it: You have merely demonstrated your own invention of two conjugated reactances and one resistor - not the same thing at all, not even conceptually. But it is what Chipman discusses. -- 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! =----- |
Tarmo Tammaru wrote:
I think what you did was to force the current to be in phase with the voltage and fooled the meter into thinking it was all forward power. That is sort of the experiment I was going to do, but you beat me to it. Note that in the case where you moved the meter, you actually changed the load, but you know that. I didn't appreciably change the load on the transmitter. All I did was change the position of the SWR meter in the serial component chain. This is essentially what Chipman discusses in his book. Now comes the big question. Does the same thing happen on a line with reflections when the impedance looking one direction is 100+j100 ohms and the impedance looking the other direction is 100-j100 ohms? Is there a localized energy exchange between that +j100 ohms and that -j100 ohms that affects the SWR meter? -- 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! =----- |
On Tue, 07 Oct 2003 20:27:58 -0500, Cecil Moore
wrote: Richard Clark wrote: The long of it: You have merely demonstrated your own invention of two conjugated reactances and one resistor - not the same thing at all, not even conceptually. But it is what Chipman discusses. Hi Cecil, OK, so you are not up to the issues I am discussing. I'm not interested in debating the single page you have xeroxed. You asked for any reference that bore upon the Source Z and I noted it was on the page facing the first page you xeroxed for other discussion. If you find some interest in it, that's fine, but you are operating under a very slim lead of a single citation I offered to answer your question that covers far more territory. Chipman offers many pages of discussion (basically an entire chapter that goes unread by his "disciples" here) describing the action of the Source upon the system's SWR and that one page you inappropriately treasure as an icon is hardly the beginning and certainly not the end. 73's Richard Clark, KB7QHC |
However, if you have coax with good dielectric (polyethylene or
Teflon), at HF and below the loss is strongly dominated by the R term. You can verify through measurements, if you are careful, that G can be assumed zero unless you've done something to degrade your line's dielectric. BUT...it's much easier to measure the line's attenuation directly than to measure (accurately) the impedance's real and imaginary parts anyway, so why would one try to do it that way? Cheers, Tom (Example: RG174 at f=30MHz will have a bit more than 3.4dB/100 feet loss because of R, and probably well under .025dB/100 feet loss because of G. See Roy's suggested reading for the source of those numbers.) "David Robbins" wrote in message ... "Cecil Moore" wrote in message ... David Robbins wrote: "Cecil Moore" wrote: Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs say the Z0 of RG-174 is a nominal 50 ohms. of course its not exactly 2500, otherwise there would be no loss. but its close, maybe 2500+j10 or something like that. and even the resistive part may not be exact, the nominal 50 ohms could be 45 to 55 depending on the tolerances of the manufacturer. Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline - is all that extra loss accounted for in the +j10 term? no, its more complicated than that. the attenuation constant (usually alpha) = Re(gamma) where gamma is sqrt((R+jwL)(G+jwC)) Zo is sqrt((R+jwL)/(G+jwC)) so there is not a simple way to relate the characterisitic impedance to loss. for a low loss line the approximation for alpha is (R/2Zo)+(GZo/2) which can probalby be applied for most normal cases, but again, you have to get the R and G values of the line which can not be directly calculated from Zo. |
Cecil,
You changed the load the SWR meter saw. In the first instance it was 50 Ohms. Then you changed it to 50 - j442. I think what you want to calculate is the phase of the current flowing through the SWR meter relative to the phase of the voltage. I wonder if anybody on this newsgroup has a contact at Bird who could shed additional light on this. Tam/WB2TT "Cecil Moore" wrote in message ... Tarmo Tammaru wrote: I think what you did was to force the current to be in phase with the voltage and fooled the meter into thinking it was all forward power. That is sort of the experiment I was going to do, but you beat me to it. Note that in the case where you moved the meter, you actually changed the load, but you know that. I didn't appreciably change the load on the transmitter. All I did was change the position of the SWR meter in the serial component chain. This is essentially what Chipman discusses in his book. Now comes the big question. Does the same thing happen on a line with reflections when the impedance looking one direction is 100+j100 ohms and the impedance looking the other direction is 100-j100 ohms? Is there a localized energy exchange between that +j100 ohms and that -j100 ohms that affects the SWR meter? -- 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! =----- |
Tarmo Tammaru wrote:
You changed the load the SWR meter saw. Exactly! Now the question is: In a conjugately matched system where 100+j100 is seen looking back toward the source and 100-j100 is seen looking toward the load, have we "changed the load the SWR meter sees" by installing it at a 100 +/- j100 point? -- 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! =----- |
I guess I'm not surprised by the 150W fwd power reading, but there
should be a correspondingly large ref power and a high SWR, if the meter is accurate. Assuming a perfect 50-j442 load and a meter calibrated perfectly to 50 ohms and perfectly accurate, I'd expect to see 102.7W going out and 97.7W coming back. But I also do NOT expect a typical meter to read very accurately at high SWR. Another thing to remember: the meter will disturb the resonance significantly, when inserted between the cap and coil. The capacitor is only about 50pF, and the meter is likely going to look like more than 5pF at that high impedance point between the inductor and capacitor. It's easy enough to look at in RFSim99, for example. When you move the SWR meter, the load on the transmitter does NOT stay the same! I simulated the meter as 7cm of 50 ohm air-dielectric line, and the return loss seen at the transmitter (at 7.2MHz) went from very high (theoretically infinite) without the line/meter inserted, to only 8.14dB (~2.3:1 SWR) with the line/meter between the coil and cap. It's important to understand the limitations of your test equipment, and also to realize how that equipment may affect operating conditions of the circuit. (Tam: my recommendation is to do the test yourself. It will be a lot easier to play with "what-ifs" and to check out things that don't at first make sense if you have direct control of the experiment.) Cheers, Tom "Tarmo Tammaru" wrote in message ... Cecil, You changed the load the SWR meter saw. In the first instance it was 50 Ohms. Then you changed it to 50 - j442. I think what you want to calculate is the phase of the current flowing through the SWR meter relative to the phase of the voltage. I wonder if anybody on this newsgroup has a contact at Bird who could shed additional light on this. Tam/WB2TT "Cecil Moore" wrote in message ... Tarmo Tammaru wrote: I think what you did was to force the current to be in phase with the voltage and fooled the meter into thinking it was all forward power. That is sort of the experiment I was going to do, but you beat me to it. Note that in the case where you moved the meter, you actually changed the load, but you know that. I didn't appreciably change the load on the transmitter. All I did was change the position of the SWR meter in the serial component chain. This is essentially what Chipman discusses in his book. Now comes the big question. Does the same thing happen on a line with reflections when the impedance looking one direction is 100+j100 ohms and the impedance looking the other direction is 100-j100 ohms? Is there a localized energy exchange between that +j100 ohms and that -j100 ohms that affects the SWR meter? -- 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! =----- |
"Tom Bruhns" wrote in message m... (Tam: my recommendation is to do the test yourself. It will be a lot easier to play with "what-ifs" and to check out things that don't at first make sense if you have direct control of the experiment.) Cheers, Tom Tom, I read you, but first I have to paint the kitchen. I was going to use 50 +/& -j50. I also want to get inside the meter and look at the voltage and current separately. It's a Kenwood, no sealed slugs. Good point about the meter changing the reactance; 160 m might be a good place to do this, or I might use a variable capacitor. Tam/WB2TT |
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