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On Apr 30, 11:26*pm, Jim Kelley wrote:
But when there is a change in the amplitude of the standing wave in x, and I max is known, then determining the shift in phase from the equation is a no brainer, Cecil. Jim, I'm still reading, trying to understand the various arguments being put forward! One thing I'm not clear about is your response to Cecil's point about phase measurements along a standing wave. Please correct me if I've got any of this wrong: I'm picturing a half- wave antenna with a current standing wave in the shape of a (half) sine wave. My understanding is that if I could observe the current at a particular point along the antenna its amplitude would vary sinusoidally with time, and its peak amplitude would be determined by its distance from the centre of the antenna (and of course by the peak amplitude of the current at the centre). If I could observe the current at several points along the antenna they would all be in-phase, in the sense that they would all reach peak amplitude at the same time, and cross zero at the same time. The only thing that would distinguish them would be the peak amplitude. Cecil seems to be saying that, in a system like the one I've described, measuring the relative phase of the currents at two points along the antenna tells you nothing about their (electrical) distance apart. If I've misinterpreted him, I'm sure cecil will correct me! Given that the currents all along the antenna are in-phase, Cecil's point seems so obvious - what am I missing? Or do you actually agree this point and I've misunderstood your position? Regards, Steve |
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Jim Kelley wrote:
But when there is a change in the amplitude of the standing wave in x, and I max is known, then determining the shift in phase from the equation is a no brainer, Cecil. Exactly! You and I are agreed that the *amplitude* holds the key to the phase shift *through a straight wire* so you are preaching to the choir. The phase of the total current on a standing-wave antenna is unrelated to the delay through the loading coil. Unfortunately, the current "bulge" through a loading coil causes an error in the simple "no-brainer" calculation that you are suggesting. Some other method of determining the phase-shift/delay through a coil is needed. That other method is to load the loading coil with its characteristic impedance and measure the phase shift in the resulting traveling wave. For instance, in the coil426.EZ file from my web page, the current at the bottom of the coil is 1.0168 amps at 0.00 degrees. The current at the top of the coil is 0.8179 amps at -0.06 degrees. The maximum current in the middle of the coil is 1.1092 amps at -0.04 degrees. The total current equation through a loading coil is not a simple cosine function like it is through a thin-wire. Determining the actual delay through a loading coil is apparently NOT a no brainer. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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On May 1, 12:58*am, wrote:
On Apr 30, 11:26*pm, Jim Kelley wrote: But when there is a change in the amplitude of the standing wave in x, and I max is known, then determining the shift in phase from the equation is a no brainer, Cecil. Jim, I'm still reading, trying to understand the various arguments being put forward! One thing I'm not clear about is your response to Cecil's point about phase measurements along a standing wave. Please correct me if I've got any of this wrong: I'm picturing a half- wave antenna with a current standing wave in the shape of a (half) sine wave. My understanding is that if I could observe the current at a particular point along the antenna its amplitude would vary sinusoidally with time, and its peak amplitude would be determined by its distance from the centre of the antenna (and of course by the peak amplitude of the current at the centre). If I could observe the current at several points along the antenna they would all be in-phase, in the sense that they would all reach peak amplitude at the same time, and cross zero at the same time. The only thing that would distinguish them would be the peak amplitude. Cecil seems to be saying that, in a system like the one I've described, measuring the relative phase of the currents at two points along the antenna tells you nothing about their (electrical) distance apart. If I've misinterpreted him, I'm sure cecil will correct me! Given that the currents all along the antenna are in-phase, Cecil's point seems so obvious - what am I missing? Or do you actually agree this point and I've misunderstood your position? Regards, Steve Hi Steve, Yes, I think you have it right. But there's more to it. Typically we wouldn't measure the amplitude of the standing wave envelope. We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. Cecil seems to believe that he has cornered the market on making such measurements. Although he has proposed an interesting method for making the measurement, others have also made it using conventional techniques. But he lambasts them, unfairly and incorrectly. I guess you had to be there. :-) Thanks, ac6xg |
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Jim Kelley wrote:
Typically we wouldn't measure the amplitude of the standing wave envelope. That is where you are mistaken. The total current on a standing-wave antenna is primarily standing wave current. What you are saying is that we wouldn't typically measure the total current. On the contrary, total current is exactly what we would typically measure and is exactly what w7el measured. That's why he measured a negligible phase shift. We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy on the antenna, is exactly what is the problem. Traveling waves on standing-wave antennas are very hard to separate and measure. Exactly how do you propose to separate the forward wave from the reflected wave while preserving the amplitude and phase of each? Hint: w7el used the total current for his "measurements". -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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Cecil Moore wrote:
I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy on the antenna, is exactly what is the problem. Let me amend that statement which is misleading. The standing wave current on a standing wave antenna, which w7el used for his measurements, accounts for 90+% of the total current. He essentially measured total current, not traveling wave current. I think if you contacted Roy directly, he will admit that fact. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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Cecil Moore wrote:
We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy on the antenna, is exactly what is the problem. Hmmmm. Perhaps I misspoke. I should have said that's what I usually measure when I want to know how much power my antenna is radiating. I guess I don't actually know for sure what other people usually measure. But if they have a Bird wattmeter for example, that's what they usually measure too. ac6xg |
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Jim Kelley wrote:
Cecil Moore wrote: We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy *on the antenna*, is exactly what is the problem. Hmmmm. Perhaps I misspoke. I should have said that's what I usually measure when I want to know how much power my antenna is radiating. I guess I don't actually know for sure what other people usually measure. But if they have a Bird wattmeter for example, that's what they usually measure too. The context, as proved by your first posting above is measurements "along the antenna". Why do you need to divert the issue by changing the context in midstream? Why can't you just discuss things in context? A Bird wattmeter will not work "along the antenna". Contrary to what you assert above, *nobody* uses a Bird wattmeter "along the antenna" to measure anything. A Bird wattmeter is a 4-terminal device requiring a reference which doesn't exist "along the antenna". The only measurements that have been made "along the antenna" are total current measurements. Seems the only way to measure forward traveling waves "along the antenna" is to use a traveling wave antenna like a terminated rhombic. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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On Fri, 01 May 2009 11:15:11 -0700, Jim Kelley
wrote: Cecil Moore wrote: We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy on the antenna, is exactly what is the problem. Hmmmm. Perhaps I misspoke. I should have said that's what I usually measure when I want to know how much power my antenna is radiating. I guess I don't actually know for sure what other people usually measure. But if they have a Bird wattmeter for example, that's what they usually measure too. Hi Jim, For the sake of Steve's interest, it would be fair to point out that no one measures current along the antenna, but many measure the current INTO the antenna (it is/was, in fact, the preferred method for FCC power measurements of AM Band transmitters). And by measuring current INTO the antenna, with it tuned as a resistive load, there is no issue of reflection. Beyond the feed point, conventional teachings inform the FCC of expected performance. Not that Jim has suggested it, but I find it extremely unlikely that anyone uses a Bird Wattmeter to measure current along the length of an antenna (of any size or in any state of match) - however, the electronics of the Bird (and more so the Bruene SWR bridge) could make it achievable.... except. Except the lead making the remote measurement would introduce a significant error as it would inhabit the fields and disturb them. Another method is the in-line current meter with a meter readout. Then that meter is read through binoculars. Years back, such a method was used to kick-start a manufactured controversy which embers now struggle for oxygen in the ashes of this thread. You will recognize the flicker of that spark with one word: phase. Steve, the elements of this discussion you find lacking clarity (in what would seem an ordinary observation to you) are leveraged meanings that are the prelude to a larger proof (sic). To follow it, you would have to suspend your inclination to question odd re-definitions of perfectly understood concepts and invented terms that "supplement" conventional science. If you refuse to suspend your judgment and ask a question along the way, chances are that trolley will jump the tracks. Otherwise, how could something so ordinary take 300 posts to arrive nowhere? 73's Richard Clark, KB7QHC |
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Cecil Moore wrote:
Jim Kelley wrote: Cecil Moore wrote: We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy *on the antenna*, is exactly what is the problem. Hmmmm. Perhaps I misspoke. I should have said that's what I usually measure when I want to know how much power my antenna is radiating. I guess I don't actually know for sure what other people usually measure. But if they have a Bird wattmeter for example, that's what they usually measure too. The context, as proved by your first posting above is measurements "along the antenna". Why do you need to divert the issue by changing the context in midstream? Why can't you just discuss things in context? A Bird wattmeter will not work "along the antenna". Contrary to what you assert above, *nobody* uses a Bird wattmeter "along the antenna" to measure anything. A Bird wattmeter is a 4-terminal device requiring a reference which doesn't exist "along the antenna". The only measurements that have been made "along the antenna" are total current measurements. Seems the only way to measure forward traveling waves "along the antenna" is to use a traveling wave antenna like a terminated rhombic. Yes, bla bla bla, whine, etc. Here is a photograph of a directional wattmeter converted to measure current on W8JI's web page. http://www.w8ji.com/building_a_current_meter.htm ac6xg |
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Jim & Richard,
I guess I'll retire gracefully because I'm not privy to the "history" between individuals on this Forum and I'm now not even sure when answers are to be taken seriously or as a joke. Jim's most recent posting is a good example. We were talking about measuring current along a dipole. I assumed that would mean measuring the standing-wave current, but Jim introduced the notion of measuring travelling wave currents. When challenged as to how we might do that, we got a URL pointing us to a simple standing wave meter - it certainly can't discriminate Forward and Reverse. From other postings I've read I take Jim to be a pretty knowledgeable guy - so this has to be a wind-up, right? Steve |
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Jim Kelley wrote:
Here is a photograph of a directional wattmeter converted to measure current on W8JI's web page. http://www.w8ji.com/building_a_current_meter.htm IT DOES NOT MEASURE FORWARD AND REFLECTED CURRENT! IT ONLY MEASURES TOTAL RF CURRENT! That's exactly why w8ji "measured" a 3 nS delay through a 100 turn, 10 TPI, 2" dia loading coil. Dr. Corum's formulas predicts a velocity factor of 0.033 on 4 MHz for w8ji's coil. That would make it 37 degrees long with a delay of 26 nS. W8JI "measured" a 3 nS delay because the standing wave current that he used for the measurement does not change phase relative to the source phase in a wire or in a coil. Do you really believe that RF current can travel through 53 feet of coiled wire in 3 nS? Doesn't 26 nS make a lot more technical sense? -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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On May 1, 3:55*pm, Cecil Moore wrote:
Jim Kelley wrote: Cecil Moore wrote: We would make a measurement of either the forward or the reflected traveling wave, which are phase delayed along the antenna. I'm sorry, but that is a false statement. Measuring the forward or reflected traveling wave, which is less than 10% of the total energy *on the antenna*, is exactly what is the problem. Hmmmm. *Perhaps I misspoke. *I should have said that's what I usually measure when I want to know how much power my antenna is radiating. *I guess I don't actually know for sure what other people usually measure. But if they have a Bird wattmeter for example, that's what they usually measure too. The context, as proved by your first posting above is measurements "along the antenna". Why do you need to divert the issue by changing the context in midstream? Why can't you just discuss things in context? A Bird wattmeter will not work "along the antenna". Contrary to what you assert above, *nobody* uses a Bird wattmeter "along the antenna" to measure anything. A Bird wattmeter is a 4-terminal device requiring a reference which doesn't exist "along the antenna". The only measurements that have been made "along the antenna" are total current measurements. Seems the only way to measure forward traveling waves "along the antenna" is to use a traveling wave antenna like a terminated rhombic. -- 73, Cecil, IEEE, OOTC, *http://www.w5dxp.com I think that is pretty accurate Cecil. Richard took to argueing with Dr Davis working at MIT where he argued that the Laws of Maxwell do not equate mathematically to the laws of other masters.He was speaking in his normal Olde English term which is talking instead of communicating until he drove the good Doctor away in fraustration. Richard took that as a victory for Shakesphere over the degree in mathematics that Dr Davis earned. Richard now believes he has advanced in the pecking order in matters relating to Radio no less. |
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wrote:
Jim's most recent posting is a good example. We were talking about measuring current along a dipole. I assumed that would mean measuring the standing-wave current, but Jim introduced the notion of measuring travelling wave currents. When challenged as to how we might do that, we got a URL pointing us to a simple standing wave meter - it certainly can't discriminate Forward and Reverse. I just happen to have the answer for anyone with EZNEC. The following EZ files have been modified to run with the free demo version of EZNEC. The following inverted-V antenna is a standing-wave antenna. http://www.w5dxp.com/inv_v.EZ The segment currents in one half of the inverted-v look like this: EZNEC+ ver. 4.0 actual dipole 5/1/2009 5:12:15 PM --------------- CURRENT DATA --------------- Frequency = 3.644 MHz Wire No. 2: Segment Conn Magnitude (A.) Phase (Deg.) 1 W1E2 1 0.00 2 .97807 -0.33 3 .93414 -0.65 4 .86875 -0.94 5 .78291 -1.21 6 .67796 -1.46 7 .55552 -1.70 8 .41724 -1.94 9 .26438 -2.17 10 Open .09505 -2.40 The following inverted-V antenna is a traveling-wave antenna. http://www.w5dxp.com/inv_vT.EZ The segment currents in one half of the terminated inverted-v look like this: EZNEC+ ver. 4.0 actual dipole 5/1/2009 5:22:42 PM --------------- CURRENT DATA --------------- Frequency = 3.644 MHz Wire No. 2: Segment Conn Magnitude (A.) Phase (Deg.) 1 W1E2 1 0.00 2 .99572 -8.77 3 .99064 -18.12 4 .9799 -27.18 5 .96293 -36.30 6 .94055 -45.74 7 .91497 -55.78 8 .8899 -66.70 9 W3E1 .87103 -79.05 Wire No. 3: Segment Conn Magnitude (A.) Phase (Deg.) 1 W2E2 .86769 -87.01 The two antennas are identical except one is terminated in its characteristic impedance and one is not. This is the best way I know of to illustrate the difference between the currents on a standing-wave antenna and the currents on a traveling-wave antenna. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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Jim Kelley wrote:
wrote: Jim's most recent posting is a good example. We were talking about measuring current along a dipole. I assumed that would mean measuring the standing-wave current, but Jim introduced the notion of measuring travelling wave currents. A point of correction here. I believe you will find the notion detailed on Cecil's web page. Yes, the total measured current on a standing wave antenna is primarily standing wave current. The total measured current on a traveling wave antenna is primarily traveling wave current. Please see my last posting. He's a guy with a limited amount of time and patience honestly attempting to subvert the ridiculous by stating the obvious. Obviously, a 100 turn, 10 tpi, 2" dia 75m loading coil cannot have the 3 nS delay that W8JI "measured". Do you disagree? -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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On Fri, 01 May 2009 15:47:41 -0700, Richard Clark
wrote: When challenged as to how we might do that, we got a URL pointing us to a simple standing wave meter - Not really. It is a simple current meter - the page literally shouts that out. it certainly can't discriminate Forward and Reverse. That is correct, but I mentioned such discrimination is possible from the Bruene SWR bridge. As I wrote previously, no one measures forward and reverse currents on antenna elements. Construction examples would be rare. With care and practice as offered at the link, which attends the issues of error (largely dismissed from the greater consideration of "measurement" proofs offered), the Bruene style could similarly be achieved. It is neither a difficult concept, nor a technical hurdle. Hi Steve, I hope you are still following the thread, because as bad as the theory gets, there is always room for instruction - just not in phase. I will expand on my comment of both the meter pointed to, its construction practices, and the topic of accuracy (something everyone offers, but can never prove). First, as to its standing wave meter capacity (in terms of conventional SWR meter usage). The last word, capacity, arises in Tom's (W8JI's linked to) page: The lack of large metallic components minimizes stray capacitance and I did not add a Faraday shield because the shield would increase the capacitance I am now leveraging the word capacity to mean ability in contrast to Tom's literal engineering application - and yet there is something to be said about such a meter having the "capacity" to measure forward or reverse products (as would a conventional SWR meter). Capacitance is required to give the meter the capacity (ability) to measure these currents. The Bruene SWR bridge has one side that is driven by an inductive coupling, and the other side driven by a capactive coupling. Through the combination of the two, the PHASES contribute to either a reverse or forward energy product (conventionally expressed as power). Clearly the link at Tom's page illustrates half of the Bruene SWR bridge, and if that Faraday shield had been tapped (instead of discarded), the meter could have revealed the separate currents. But nobody is interested - it offers nothing new. You will find 0 to no construction examples of this more than rare application. Futher, given its absence of discussion here in all these years, no one is actually interested in "measuring" what they have proven through their measurements.... Sorry Steve, another in-bred joke. Moving beyond the hillarity that ensues from these obvious shortfalls of academic navel gazing; there is still the accuracy to consider. On the face of what is offered at Tom's page, there is an immediate and irrevocable error of 5% built into the instrument as described sitting in its calibration fixture. Under other circumstances, that error could easily eclipse 100%. Suffice it to say it will never achieve better without a small book of charts. As I offered, accuracy is often claimed, but rarely (never) proven. This is a simple counter-proof. Tom expresses it without being aware of the implications: T1 is a current transformer. ... When the single turn primary (a whip or mast) has 1 ampere, the secondary will have .05 amperes (inverse of the turns ratio). all very standard stuff as you may well note. Going on: This type of meter is much more reliable and linear than thermocouple RF ammeters, and perturbs systems much less. This, of course, is related to the "stated but not proven" class of statements that litter the WWW (much less this thread). Here is the literal error: I've applied 50 watts to a precision 50 ohm load, making wire current 1-ampere. Let's assemble these statements. We have a current transformer. It is loaded with 100 Ohms with a lightly coupled linear indicator. It has 50 Watts applied through it to a load. That load is 50 Ohms. What the meter should indicate is a current of 0.9535A if we are to believe that the 50W is absolutely accurate (it is not, but we will skip that for another discussion). The author, Tom, offers to trim the potentiometer for a 1.000A reading - WRONG! How can this be? It is all in the statements offered above. The current transformer is also a RESISTANCE TRANSFORMER. That 100 Ohm load to its secondary is cast into the primary as an in-series 5 Ohm resistor adding to the 50 Ohm nominal load. The instrument is injecting itself into the measurement and this presents the statement: perturbs systems much less. in a new light as it is quite easily demonstrated exactly how much (if we ignore other sources of error) this construction example will perturb the system and nothing is said in comparison to the technology being replaced (thermocouples). Such is poor reporting. What becomes of that error in a short monopole whose radiation resistance is equal to that 5 Ohm insertion loss? FS accuracy is not required in comparison measurements, True enough, but it then ignores what I've offered above: since the meter references against itself. a 5 Ohm instrument load in series with a 5 Ohm radiator (irrespective of phase contributions due to size) will seriously change the fabric of the system. Such is the compounding of poor reporting. If one were to claim to have made ANY current measurements, and then wholly ignore the contribution of errors, then the discussion of phase in a system such as a 5 Ohm radiator with a 5 Ohm instrument loss is going to be absurd. Such are the fruits of poor reporting. 73's Richard Clark, KB7QHC |
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Richard Clark wrote:
. . . On the face of what is offered at Tom's page, there is an immediate and irrevocable error of 5% built into the instrument as described sitting in its calibration fixture. Under other circumstances, that error could easily eclipse 100%. Suffice it to say it will never achieve better without a small book of charts. As I offered, accuracy is often claimed, but rarely (never) proven. This is a simple counter-proof. Tom expresses it without being aware of the implications: T1 is a current transformer. ... When the single turn primary (a whip or mast) has 1 ampere, the secondary will have .05 amperes (inverse of the turns ratio). This means the turns ratio is 1:20. all very standard stuff as you may well note. Going on: This type of meter is much more reliable and linear than thermocouple RF ammeters, and perturbs systems much less. This, of course, is related to the "stated but not proven" class of statements that litter the WWW (much less this thread). Here is the literal error: I've applied 50 watts to a precision 50 ohm load, making wire current 1-ampere. Let's assemble these statements. We have a current transformer. It is loaded with 100 Ohms with a lightly coupled linear indicator. It has 50 Watts applied through it to a load. That load is 50 Ohms. What the meter should indicate is a current of 0.9535A if we are to believe that the 50W is absolutely accurate (it is not, but we will skip that for another discussion). The author, Tom, offers to trim the potentiometer for a 1.000A reading - WRONG! How can this be? It is all in the statements offered above. The current transformer is also a RESISTANCE TRANSFORMER. That 100 Ohm load to its secondary is cast into the primary as an in-series 5 Ohm resistor adding to the 50 Ohm nominal load. The resistance is transformed in the ratio of N^2:1, which is 400:1 for a 20:1 turns ratio. So the insertion resistance is 100/400 = 0.25 ohm, not 5. I'm confident it works as Tom claims. . . . If one were to claim to have made ANY current measurements, and then wholly ignore the contribution of errors, then the discussion of phase in a system such as a 5 Ohm radiator with a 5 Ohm instrument loss is going to be absurd. Such are the fruits of poor reporting. No, this is the fruit of poor reporting. Roy Lewallen, W7EL |
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On Fri, 01 May 2009 18:00:40 -0700, Roy Lewallen
wrote: The resistance is transformed in the ratio of N^2:1, which is 400:1 for a 20:1 turns ratio. So the insertion resistance is 100/400 = 0.25 ohm, Hi Roy, Yes, quite so. not 5. I'm confident it works as Tom claims. It works as it claims is obvious, but not for SWR (neither claimed, nor something you show interest in) - not that it should, but could. We aren't going there either (few would as such an application has no obvious merit). Pursuing the topic of reported phase does not appear to be productive. A curiousity all around. If one were to claim to have made ANY current measurements, and then wholly ignore the contribution of errors, then the discussion of phase in a system such as a 5 Ohm radiator with a 5 Ohm instrument loss is going to be absurd. Such are the fruits of poor reporting. No, this is the fruit of poor reporting. No, that you caught me in a detail with that detail mishandled by me. Complements! The detail was quite accurate; so much so that you accepted it (it was also sourced by Tom) in your reply. That is the value of good reporting. The net result is a very short transaction of point-counter point that doesn't demand 300 posts of careful parsing. My fault was poor application, certainly. You probably stole Art and Cecil's delight at catching me there. ;-0 73's Richard Clark, KB7QHC |
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