|
A little more on missing degrees
I havn't much idea on what the present argument is all about. And I
have no wish to take sides. But - If Line-1 has impedance Zo1 and is a fractional wavelength L1 long, and Line-2 has impedance Zo2 and is a fractional wavelength L2 long, then when both lines are connected together and are brought into so-called 1/4-wave resonance by pruning the length of one of the lines, it is IMPOSSIBLE for L1 + L2 to equal 1/4-wavelength or 90 degrees. There are ALWAYS some degrees "missing" - depending on the ratio Zo1/Zo2. Except only when Zo1 = Zo2 will L1 + L2 total 90 degrees. Can be proved mathematically without invoking standing or reflected waves. You just have to believe in mathematics. Line-1, of course, is a loading coil and Line-2 is a whip. I hope this settles an argument. For a demonstration download program TWOLINES from website below. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
A little more on missing degrees
Reg Edwards wrote:
I havn't much idea on what the present argument is all about. And I have no wish to take sides. But - If Line-1 has impedance Zo1 and is a fractional wavelength L1 long, and Line-2 has impedance Zo2 and is a fractional wavelength L2 long, then when both lines are connected together and are brought into so-called 1/4-wave resonance by pruning the length of one of the lines, it is IMPOSSIBLE for L1 + L2 to equal 1/4-wavelength or 90 degrees. There are ALWAYS some degrees "missing" - depending on the ratio Zo1/Zo2. Except only when Zo1 = Zo2 will L1 + L2 total 90 degrees. Can be proved mathematically without invoking standing or reflected waves. You just have to believe in mathematics. Line-1, of course, is a loading coil and Line-2 is a whip. I hope this settles an argument. For a demonstration download program TWOLINES from website below. ---- .................................................. ......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. ......... And what is line three and line four? 73, Tom Donaly, KA6RUH |
A little more on missing degrees
Reg Edwards wrote:
If Line-1 has impedance Zo1 and is a fractional wavelength L1 long, and Line-2 has impedance Zo2 and is a fractional wavelength L2 long, then when both lines are connected together and are brought into so-called 1/4-wave resonance by pruning the length of one of the lines, it is IMPOSSIBLE for L1 + L2 to equal 1/4-wavelength or 90 degrees. If we have three sections and Z02 Z01, ---Z01---+---Z02---+---Z01--- the first impedance discontinuity causes a phase shift in the *opposite* direction from the second impedance discontinuity. That's why moving a loading coil from a base-loaded position to a center-loaded position requires more degrees of coil. W8JI has been trying to make a big deal out of that fact but it is just simple physics. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
"Reg Edwards" wrote in message
... I havn't much idea on what the present argument is all about. And I have no wish to take sides. But - If Line-1 has impedance Zo1 and is a fractional wavelength L1 long, and Line-2 has impedance Zo2 and is a fractional wavelength L2 long, then when both lines are connected together and are brought into so-called 1/4-wave resonance by pruning the length of one of the lines, it is IMPOSSIBLE for L1 + L2 to equal 1/4-wavelength or 90 degrees. There are ALWAYS some degrees "missing" - depending on the ratio Zo1/Zo2. Except only when Zo1 = Zo2 will L1 + L2 total 90 degrees. Can be proved mathematically without invoking standing or reflected waves. You just have to believe in mathematics. Line-1, of course, is a loading coil and Line-2 is a whip. I hope this settles an argument. For a demonstration download program TWOLINES from website below. I don't understand the argument either. Why would anyone care how many degrees an antenna has; it radiates all the power whatever its length. Frank |
A little more on missing degrees
Frank's wrote:
I don't understand the argument either. Why would anyone care how many degrees an antenna has; it radiates all the power whatever its length. Some of us care whether that radiation is heat or RF. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
"Cecil Moore" wrote in message
. com... Frank's wrote: I don't understand the argument either. Why would anyone care how many degrees an antenna has; it radiates all the power whatever its length. Some of us care whether that radiation is heat or RF. :-) -- 73, Cecil http://www.qsl.net/w5dxp A 15 ft long horizontal dipole, #14 AWG, on 3.8 MHz, has a radiation efficiency of 90.17%. The loss due to heat is 0.45 dB. Designing an efficient matching network may be difficult. Even with 100 W delivered to the antenna the 52 kV at the feedpoint may pose a problem. Frank |
A little more on missing degrees
Frank's wrote:
"Reg Edwards" wrote in message ... I havn't much idea on what the present argument is all about. And I have no wish to take sides. But - If Line-1 has impedance Zo1 and is a fractional wavelength L1 long, and Line-2 has impedance Zo2 and is a fractional wavelength L2 long, then when both lines are connected together and are brought into so-called 1/4-wave resonance by pruning the length of one of the lines, it is IMPOSSIBLE for L1 + L2 to equal 1/4-wavelength or 90 degrees. There are ALWAYS some degrees "missing" - depending on the ratio Zo1/Zo2. Except only when Zo1 = Zo2 will L1 + L2 total 90 degrees. Can be proved mathematically without invoking standing or reflected waves. You just have to believe in mathematics. Line-1, of course, is a loading coil and Line-2 is a whip. I hope this settles an argument. For a demonstration download program TWOLINES from website below. I don't understand the argument either. Why would anyone care how many degrees an antenna has; it radiates all the power whatever its length. I personally wouldn't use an antenna with any less than a Master's degree..... - 73 de Mike KB3EIA - |
A little more on missing degrees
For those of you who may be unfamiliar with the mathematics of
transmission lines, download program TWOLINES and enter the following practical values - Line-1 represents the loading coil. Line-2 represents the whip to be pruned for 1/4-wave resonance. Enter Zo1 = 6000 ohms, a practical value. Enter electrical length L1 = 0.15 wavelengths. Enter attenuation = 0.1 dB for wire loss in coil. Enter Zo2 = 400 ohms, a practical value. Enter electrical length L2 = 0.0077 wavelengths. Enter attenuation = 0.001 dB Enter open-circuit load resistance = 100 Megohms and load reactance = 100 Megohms. To check that the circuit is in 1/4-wave resonance, vary plus or minus length of Line-2 for zero or minimum input reactance. The input resistance of the coil or Line-1 is about 16 ohms, a typical value. But L1 + L2 = 0.1577 wavelengths = only 57 degrees. The missing 90 - 57 = 33 degrees are just not needed for resonance. So why is everybody making such a fuss about it? ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
A little more on missing degrees
Reg Edwards wrote:
For those of you who may be unfamiliar with the mathematics of transmission lines, download program TWOLINES and enter the following practical values - Line-1 represents the loading coil. Line-2 represents the whip to be pruned for 1/4-wave resonance. Enter Zo1 = 6000 ohms, a practical value. Enter electrical length L1 = 0.15 wavelengths. Enter attenuation = 0.1 dB for wire loss in coil. Ignoring losses and starting at 0-j0, plotting this value on a Smith Chart normalized to 6000 ohms, the normalized value is -j1.38 -j1.38 * 6000 = -j8280 ohms Enter Zo2 = 400 ohms, a practical value. Enter electrical length L2 = 0.0077 wavelengths. Enter attenuation = 0.001 dB Starting at 0-j*infinity and plotting backwards, this value on a Smith Chart normalized to 400 ohms is -j20.7 -j20.7 * 400 = -j8280 ohms But L1 + L2 = 0.1577 wavelengths = only 57 degrees. The abrupt jump from -j1.38 to -j20.7 provides a 66 degree phase shift in the angle of the reflection coefficient as read off the Smith Chart. The missing 90 - 57 = 33 degrees are just not needed for resonance. So why is everybody making such a fuss about it? The missing 33 degrees are there, provided by the phase shift in the reflection coefficient. The angle of the reflection coefficient in the stinger at the impedance discontinuity is ~6 degrees. The angle of the reflection coefficient in the coil at the impedance discontinuity is ~72 degrees. 72 - 6 = a 66 degree jump in the angle of the reflection coefficient. That equates to the missing 33 degrees of antenna. The wave that is only 3 degrees back from the tip reflection point is suddenly only 54 degrees from the current maximum point. It appears to me that the interference of the forward and reflected waves at the impedance discontinuity causes an actual 33 degree phase shift. How to analyze what happens at such an impedance discontinuity is covered in my energy analysis article at: http://www.qsl.net/w5dxp/energy.htm I will try to do that analysis sometime today. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
"Reg Edwards"
The missing 90 - 57 = 33 degrees are just not needed for resonance. So why is everybody making such a fuss about it? _____________ An antenna * system * does not need to have X number of degrees to be resonant. It only needs to have ~zero reactance at its feedpoint -- which, for electrically short AND long radiators can be achieved by use of a suitable matching network. Such networks don't add or subtract electrical degrees, however. They only reduce/cancel the natural reactance of the physical radiator in use. RF |
A little more on missing degrees
"Richard Fry" wrote in message ... An antenna * system * does not need to have X number of degrees to be resonant. It only needs to have ~zero reactance at its feedpoint -- which, for electrically short AND long radiators can be achieved by use of a suitable matching network. Such networks don't add or subtract electrical degrees, however. They only reduce/cancel the natural reactance of the physical radiator in use. RF The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. Something that is so obviously missing from 99 percent plus of the bulk of posts on the subject! Dean -- W4IHK |
A little more on missing degrees
Dean Craft wrote:
The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. A self-resonant coil is obviously 90 degrees long. If one removes 5% of the turns and replaces them with a stinger to bring the system back to resonance at the same frequency, do you really believe the coil has magically changed from 90 degrees long to zero degrees long? -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
"Cecil Moore"
A self-resonant coil is obviously 90 degrees long. _____________ A coil is not the electrical equivalent of a linear, physical, ~90-degree, self-resonant radiator. How well do you expect your self-resonant coil to radiate? When you add a stinger to a coil, it is the stinger that radiates the great majority of the applied power. The coil just makes it possible/practical for the tx to supply r-f power to that antenna system that the stinger CAN radiate, by improving the Z match between the source and the feedpoint. RF |
A little more on missing degrees
Dean Craft wrote:
SNIPPED The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. Something that is so obviously missing from 99 percent plus of the bulk of posts on the subject! Dean -- W4IHK Dean, maybe we can start a discussion about the missing 1% "Something that is so obviously missing from 99 percent..." |
A little more on missing degrees
"Dave" wrote in message . .. Dean Craft wrote: SNIPPED The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. Something that is so obviously missing from 99 percent plus of the bulk of posts on the subject! Dean -- W4IHK Dean, maybe we can start a discussion about the missing 1% "Something that is so obviously missing from 99 percent..." I have all but given up on that possibility. If its not heated immature school yard rhetoric driven by obvious professional jealousy, then its mind playing games just as has appeared since my earlier post. The troll effect all too frequently takes over and destroys any serious chain of thought. Dean -- W4IHK |
A little more on missing degrees
I gave up on the 'missing degrees' and all variations topic about 1
month ago. Hit the KILL Button and read on! Dean Craft wrote: "Dave" wrote in message . .. Dean Craft wrote: SNIPPED The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. Something that is so obviously missing from 99 percent plus of the bulk of posts on the subject! Dean -- W4IHK Dean, maybe we can start a discussion about the missing 1% "Something that is so obviously missing from 99 percent..." I have all but given up on that possibility. If its not heated immature school yard rhetoric driven by obvious professional jealousy, then its mind playing games just as has appeared since my earlier post. The troll effect all too frequently takes over and destroys any serious chain of thought. Dean -- W4IHK |
A little more on missing degrees
Richard Fry wrote:
"Such networks don`t add or subtract electrical degrees, however. They only reduce/cancel the natural reactance of the physical radiator in use." True if the only mismatch is reactance. A too-long antenna can be electrically shortened for matching purposes by tuning it to resonance with the proper series capacitance. A too-short antenna can be electrically lengthened for matching purposes by tuning it to resonance with the proper series inductance. Reactance varies quickly near the resonant length. Radiation resistance varies more slowly tending to increase at a steady rate as the antenna is lengthened. What radiates is current in a length of antenna. What gets current into an antenna is a conjugate match. Reactance is zeroed out, and source and load resistances are matched. That`s what`s needed for maximum power transfer between generator and antenna. Analysis may have been more abundant than needed for practical purposes. The velocity of current through a coil has been disputed. Some said it was almost instantaneous. That was new to me. The nature of inductance is to produce counter emf which by Lenz`s law opposes current into an inductance and temporarily delays current changes in an inductance. Only in a pure resistance is there instantaneous correlation between voltage and current. It is believed that the speed of light "c" is a speed limit on electromagnetic waves. An action in one place must have a delayed response elsewhere depending on distance. I can imagine a wave launched at one of an inductor sweeping across its length and ignoring the round and round path of the wire, but I don`t know of any of the old authors in my collection who say that such a short-cut happens. Conductors are the source of free electrons which permit current flow and my experience is that electricity goes where it is wired. Best regards, Richard Harrison, KB5WZI |
A little more on missing degrees
Richard Fry wrote:
"Cecil Moore" A self-resonant coil is obviously 90 degrees long. A coil is not the electrical equivalent of a linear, physical, ~90-degree, self-resonant radiator. How well do you expect your self-resonant coil to radiate? Not very well. Nobody is saying that a coil is a good radiator. It probably radiates about as much RF as a piece of wire of the same axial length as the coil. Nothing about the discussion of phase shift through a coil has had anything to do with radiation. In fact, I have ignored radiation from the coil in all of my calculations since I consider it to be negligible. We have a phase shift in a transmission line with negligible radiation. The same is true of a loading coil. When you add a stinger to a coil, it is the stinger that radiates the great majority of the applied power. Absolutely no question about that. The round and round design of a coil makes it more akin to a piece of transmission line than it does to a radiator. But like a transmission line stub, it contributes a phase shift to the system. The stub on a properly designed J-Pole doesn't radiate much either. But one can certainly calculate the phase shift from the feedpoint to bottom of the radiating element. Again, the phase shift in the coil has virtually nothing to do with how much the coil radiates. Looking at just one turn on the coil, the current on each side of the turn is approximately equal magnitude and flowing in opposite directions (just as in a transmission line). So virtually all the radiation is canceled by the opposite near fields (just as in a transmission line). -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
Richard Harrison wrote:
I can imagine a wave launched at one of an inductor sweeping across its length and ignoring the round and round path of the wire, but I don`t know of any of the old authors in my collection who say that such a short-cut happens. Conductors are the source of free electrons which permit current flow and my experience is that electricity goes where it is wired. Consider a tank circuit link coupled to the outside world. There are probably negligible free electrons flowing from primary to secondary. Yet efficient energy transfer occurs when the coils are tightly coupled. In a loading coil, each turn is tightly coupled to the adjacent turn causing part of the current to be the result of the fields rather than wire path. That's why the VF of the loading coil is roughly double what it would be for "round and round the coil" calculations. The VF for a 75m bugcatcher coil appears to be in the ballpark of 0.04 which is a far cry from the straight across 1.0 or even 0.5 -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
Dave wrote:
I gave up on the 'missing degrees' and all variations topic about 1 month ago. Hit the KILL Button and read on! For those who didn't give up, here is a summary of what I was able to do with EZNEC. This exercise should be able to be repeated in the real world. 1. Using the helix feature of EZNEC, I created a 100 turn octagonal coil, 6 inches in diameter, 4 turns per inch. 2. I installed it as a base loading coil over a mininec ground plane and removed turns until it was self-resonant on 4 MHz. That left a total of 69 turns on a 1.435 foot long coil. Give that the coil is 90 degrees at the self- resonant frequency, I calculated a velocity factor of 0.023 for the coil. 3. The coil was then trimmed to half size, i.e. 34.5 turns. Assuming it was then 45 degrees long, the Z0 was determined to be approximately 2200 ohms by looking at the feedpoint impedance reported by EZNEC. 45 degrees from 0-j0 on the Smith Chart is at -j1.0. 4. A stinger was added to the above 45 degrees of coil to bring the antenna back to resonance on 4 MHz. It took 7 ft. of stinger, or 10.2 degrees. 10.2 degrees from 0-j*infinity on the Smith Chart is at -j4.8. 5. The ratio of -j4.8/-j1.0 is the ratio of the Z0 of the coil to the Z0 of the stinger. If the Z0 of the coil is indeed 2200 ohms, the Z0 of the stinger is 458 ohms, just about where it should be. The impedance discontinuity provides the "missing" ~35 degrees of the antenna. 6. Using Dr. Corum's equation for velocity factor yields 0.02 for that coil, a value 13% lower than the one predicted by EZNEC, well within the ballpark for expectations. My conclusions: The delay through a loading coil is in the tens of degrees. The delay through the elements of the antenna do not add up to 90 degrees. In the above EZNEC example, the delay from feedpoint to the tip of the antenna is only 55 degrees. The "missing" degrees are provided by the impedance discontinuity between the coil and the stinger. There is no real- time delay associated with those "missing" degrees. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
In item 2 you make an unsupported statement: "Give that the coil is 90
degrees at the self-resonant frequency,..." Self resonance only means that the capacitive and inductive reactances, both distributed, are equal. That does not validate a 90 degree assumption. Without that validation, IMO, the subsequent discussion is questionable. Cecil Moore wrote: Dave wrote: I gave up on the 'missing degrees' and all variations topic about 1 month ago. Hit the KILL Button and read on! For those who didn't give up, here is a summary of what I was able to do with EZNEC. This exercise should be able to be repeated in the real world. 1. Using the helix feature of EZNEC, I created a 100 turn octagonal coil, 6 inches in diameter, 4 turns per inch. 2. I installed it as a base loading coil over a mininec ground plane and removed turns until it was self-resonant on 4 MHz. That left a total of 69 turns on a 1.435 foot long coil. Give that the coil is 90 degrees at the self- resonant frequency, I calculated a velocity factor of 0.023 for the coil. 3. The coil was then trimmed to half size, i.e. 34.5 turns. Assuming it was then 45 degrees long, the Z0 was determined to be approximately 2200 ohms by looking at the feedpoint impedance reported by EZNEC. 45 degrees from 0-j0 on the Smith Chart is at -j1.0. 4. A stinger was added to the above 45 degrees of coil to bring the antenna back to resonance on 4 MHz. It took 7 ft. of stinger, or 10.2 degrees. 10.2 degrees from 0-j*infinity on the Smith Chart is at -j4.8. 5. The ratio of -j4.8/-j1.0 is the ratio of the Z0 of the coil to the Z0 of the stinger. If the Z0 of the coil is indeed 2200 ohms, the Z0 of the stinger is 458 ohms, just about where it should be. The impedance discontinuity provides the "missing" ~35 degrees of the antenna. 6. Using Dr. Corum's equation for velocity factor yields 0.02 for that coil, a value 13% lower than the one predicted by EZNEC, well within the ballpark for expectations. My conclusions: The delay through a loading coil is in the tens of degrees. The delay through the elements of the antenna do not add up to 90 degrees. In the above EZNEC example, the delay from feedpoint to the tip of the antenna is only 55 degrees. The "missing" degrees are provided by the impedance discontinuity between the coil and the stinger. There is no real- time delay associated with those "missing" degrees. |
A little more on missing degrees
|
A little more on missing degrees
Dave wrote:
In item 2 you make an unsupported statement: "Give that the coil is 90 degrees at the self-resonant frequency,..." Self resonance only means that the capacitive and inductive reactances, both distributed, are equal. That does not validate a 90 degree assumption. Without that validation, IMO, the subsequent discussion is questionable. Quoting from the Corum paper concerning self resonance of a coil: "The forward and backward traveling waves have superposed to give this voltage standing wave distribution along the resonator. There is a voltage null at the base, a voltage maximum at the top, and a sine wave envelope along the structure." That defines 90 degrees of coil. For the standing wave, there are 90 degrees between a voltage null and a voltage maximum. The voltage maximum at the top of the coil corresponds to the current null existing there because the current has no place to go. The voltage null at the base corresponds to the current maximum there which is a necessary condition for self resonance. There's 90 degrees between a voltage null and a voltage maximum. There's 90 degrees between a current null and a current maximum. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
Cecil Moore wrote:
SNIPPED Quoting from the Corum paper concerning self resonance of a coil: "The forward and backward traveling waves have superposed to give this voltage standing wave distribution along the resonator. There is a voltage null at the base, a voltage maximum at the top, and a sine wave envelope along the structure." That defines 90 degrees of coil. For the standing wave, there are 90 degrees between a voltage null and a voltage maximum. The voltage maximum at the top of the coil corresponds to the current null existing there because the current has no place to go. The voltage null at the base corresponds to the current maximum there which is a necessary condition for self resonance. There's 90 degrees between a voltage null and a voltage maximum. There's 90 degrees between a current null and a current maximum. Under that definition my 8 foot high mobile antenna has a voltage maximum at the top and a current maximum at the base and must, therefore, be 90 degrees long. But, it is physically only 16 degrees long [8/43.5 @ 5.37 MHz]. Now it is 5 degrees long above the top of the coil and 10 degrees long below the coil ... ad nauseum [ for another 2 months ] ... Where is the other 74 degrees?? This is the question that started this 2 month discussion. Is there a fallacy in Corum's paper? Does Corum's paper apply to a combination of a loading coil and radiating elements? My reasoning is as follows: if I draw a phasor diagram, I have +10 degrees phase shift from the feed point to the base of the coil. I can then assume a +90 degree phase shift in the coil, classical inductive response; then, the 'stinger', from the top of the coil to the tip of the antenna produces a net -10 degree phase shift from both inductive[+] and capacitive[-] effects resulting in a net 90 degree phase shift for the full eight foot antenna. Am I being too simplistic? I conclude that I have a 16 degree long antenna with a feedpoint resistance of ~13 ohms [ Rr = ~1.0 ohm and Rloss = ~12 ohms] with zero ohms reactance [resonant]. [And that the phase shifts stated above are fundamentally correct.] |
A little more on missing degrees
Dave wrote:
Where is the other 74 degrees?? Please reference my other postings. It is all explained there. 1. There are tens of degrees in the coil. That phase shift is not instantaneous and obeys the VF of the coil. 2. There are tens of degrees in the impedance discontinuity between the coil and stinger. That phase shift is instantaneous and requires no delay. 3. There are tens of degrees in the stinger. That phase shift is not instantaneous and obeys the VF of the stinger. 4. They all add up to 90 degrees. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
Dave wrote:
Where is the other 74 degrees?? This is the question that started this 2 month discussion. Is there a fallacy in Corum's paper? Does Corum's paper apply to a combination of a loading coil and radiating elements? My reasoning is as follows: if I draw a phasor diagram, I have +10 degrees phase shift from the feed point to the base of the coil. I can then assume a +90 degree phase shift in the coil, classical inductive response; then, the 'stinger', from the top of the coil to the tip of the antenna produces a net -10 degree phase shift from both inductive[+] and capacitive[-] effects resulting in a net 90 degree phase shift for the full eight foot antenna. Am I being too simplistic? I conclude that I have a 16 degree long antenna with a feedpoint resistance of ~13 ohms [ Rr = ~1.0 ohm and Rloss = ~12 ohms] with zero ohms reactance [resonant]. [And that the phase shifts stated above are fundamentally correct.] You don't need to go to anywhere near that much trouble. If you replace the stinger with a lumped series RC to ground with the same impedance as the stinger, you'll get nearly the same currents, both magnitude and phase, at the top and bottom of the coil as you did with the stinger. No "missing degrees" -- no "degrees" at all, in fact. No forward and reverse traveling waves, no standing waves. No smoke and mirrors, no bafflegab. Just plain old circuit analysis. Roy Lewallen, W7EL |
A little more on missing degrees
Roy Lewallen wrote:
You don't need to go to anywhere near that much trouble. If you replace the stinger with a lumped series RC to ground with the same impedance as the stinger, you'll get nearly the same currents, both magnitude and phase, at the top and bottom of the coil as you did with the stinger. No "missing degrees" -- no "degrees" at all, in fact. No forward and reverse traveling waves, no standing waves. No understanding of the laws of physics - just 1001 shortcuts and rules of thumb - consistent with the dumbing down of the US educational system and amateur radio. -- 73, Cecil http://www.qsl.net/w5dxp |
A little more on missing degrees
"Dave" wrote in message . .. Under that definition my 8 foot high mobile antenna has a voltage maximum at the top and a current maximum at the base and must, therefore, be 90 degrees long. But, it is physically only 16 degrees long [8/43.5 @ 5.37 MHz]. Now it is 5 degrees long above the top of the coil and 10 degrees long below the coil ... ad nauseum [ for another 2 months ] ... Where is the other 74 degrees?? This is the question that started this 2 month discussion. Dave, your 8 ft mobile antenna is not 90 degrees long, you don't have zero reactance at the feedpoint. You will have to insert the loading coil or matching network to do that and that adds the missing degrees. (You might have maximum current as far as the whip is concerned, but not maximum current corresponding to the base of resonated whip, just fraction corresponding what standing wave would supply for that tip o'antenna.) Then you have drop of current along the coil, (missing degrees) and rest in the stinger at corresponding degreed to the straight radiator. (Worst efficiency of that length of antenna.). As you start moving the loading coil up the antenna, you start increasing the high current in bottom part of antenna, then drop along the coil, then rest of the drop towards the stinger, down to zero. As you move coil higher, you will have to add the turns in order to maintain resonance (90 degrees overall, zero reactance at the feedpoint). Looks like my idea about the role of impedance has some merit, Cecil is hitting it with idea of "losing" some degrees at the impedance "bumps" completing the picture of them mysteriously missing degrees, to dismay of same current believers. So looks like degrees of mast, plus degrees of impedance bump between the mast and coil, plus degrees of coil, plus degrees of impedance bump between the coil and stinger, plus degrees of stinger should add up to 90 degrees in resonant monopole or resonator, as some antenna pioneers called it. Do we get it now more precisely? Or there are still some "missing" degrees floating around? 73 Yuri, K3BU/m |
A little more on missing degrees
We haven't been missing any degrees around here.
We hit the low 90's , while even still in late April. It's May now, and still no obvious loss of degrees. Feels like summer, the grass is green, and I feel quite warm most every day. It's those people up far north that miss degrees. :) MK |
| All times are GMT +1. The time now is 07:35 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com