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Phase Shift through a 75m Texas Bugcatcher Coil
On Fri, 11 May 2007 20:09:35 GMT, Cecil Moore
wrote: I have been telling Roy for years that his and w8ji's standing-wave current measurements were bogus so he cannot possibly plead ignorance. Now EZNEC agrees with me. Poetic justice? Only if a whore could rhyme. |
Phase Shift through a 75m Texas Bugcatcher Coil
On May 11, 7:44 am, John Smith I wrote:
wrote: do you now how to explain this so normal people can understand? If traveling waves are used to measure phase shift though the coil in question reliable data is obtained on phase shift. If standing waves are used, the data is flawed. Well, you asked for simple now, didn't you? Regards, JS no i didn'tt ask for simple. i asked for an explanation that could be understood. So far i don't see any comparisons of what makes 'bad' data bad, only reasons. everuyone has reasons. reliable? flawed? is this like ~2db? how flawed is ~? |
Phase Shift through a 75m Texas Bugcatcher Coil
facts don't make very good explanations. On May 11, 7:50 am, John Smith I wrote: wrote: do you now how to explain this so normal people can understand? One more simple "fact." Standing waves are really not "standing." They are "moving in place." (well, oscillating, actually) silly-grin JS |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
On Fri, 11 May 2007 19:56:27 -0700, John Smith I
wrote: wrote: facts don't make very good explanations. I found Cecils' .ez files (the excel sheets require the microsoft product which some may not have access to) were an excellent "explanation" of what he proposes. Talk about the gulf between perception and reality. 73's Richard Clark, KB7QHC |
Phase Shift through a 75m Texas Bugcatcher Coil
Herbert wrote:
"Do you know how to explain this so normal people can understand?" I `m not a Guru, but I`ll try. First, there was adispute about delay in an antenna loading coil. That provoked attempts to measure the delay. Then the argument turned to the measurement methods. The antenna signal travels from the transmitter through the coil and through the stinger until it reaches the tip where it is forced to reverse course by the open circuit. All the signal which has not been radiated or lost in waste enroute starts its journey back toward the transmitter. This reflected energy from the antenna tip is of no help in determining delay through the loading coil but the ripples it makes, when it adds and subtracts from the waveform of the forward energy, makes measurements difficult. Frequently a directional coupler is used to measure the energy moving in one direction, while ignoring the energy moving in the opposite direction, to get a meaningful measurement. Cecil proposed a resistor matching the impedance at the tip of the antenna to avoid a reflection. This also eliminates the troublesome ambiguity. Testing is convincing, perhaps, but not really necessary as the delay through a coil has been understood and quantified at least since Ampere who died in 1836. The ARRL Handbook, mine is from 1976, explains inductance on page 25: "Since the induced emf opposes the emf of the source, it tends to prevent the current from rising rapidly when the circuit is closed." Delay is a well known function of inductors. In early times they were often called "retard coils". Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
John Smith I wrote:
Makes you wonder if they bother to download the free trial version of EZNEC and bother to look ... The bugcatcher coil in coil505.EZ has 234 segments. The free demo version of EZNEC is limited to 20 segments. Thus, something like a 2-4 turn helix is all the free demo version will support. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Harrison wrote:
Cecil proposed a resistor matching the impedance at the tip of the antenna to avoid a reflection. This also eliminates the troublesome ambiguity. Actually a little more elementary than that. Take a base-loaded 75m mobile antenna and remove the stinger, leaving only the coil. Install a resistor to ground from the top of the coil and adjust the resistor value equal to the characteristic impedance of the coil. This is the point where the feedpoint impedance at the base of the coil is equal to the value of the resistor in ohms. This is, of course, assuming the coil is less than 1/4WL long which it is for a typical mobile installation. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
What Happens if the Bug Catcher actually catches a Bug. How does that
change things ?? :-) "Cecil Moore" wrote in message t... Richard Harrison wrote: Cecil proposed a resistor matching the impedance at the tip of the antenna to avoid a reflection. This also eliminates the troublesome ambiguity. Actually a little more elementary than that. Take a base-loaded 75m mobile antenna and remove the stinger, leaving only the coil. Install a resistor to ground from the top of the coil and adjust the resistor value equal to the characteristic impedance of the coil. This is the point where the feedpoint impedance at the base of the coil is equal to the value of the resistor in ohms. This is, of course, assuming the coil is less than 1/4WL long which it is for a typical mobile installation. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
"Richard Harrison" wrote in message ... The antenna signal travels from the transmitter through the coil and through the stinger until it reaches the tip where it is forced to reverse course by the open circuit. All the signal which has not been radiated or lost in waste enroute starts its journey back toward the transmitter. This reflected energy from the antenna tip is of no help in determining delay through the loading coil but the ripples it makes, when it adds and subtracts from the waveform of the forward energy, makes measurements difficult. ..... Best regards, Richard Harrison, KB5WZI Which brings me back to my question: How important is the Q and low resistance of the coil and stinger? The subtracted waveform (current) seems to show slight increase at the base of coil, which we are trying to achieve - prolonging the high current portion along the radiator system. If we had traveling wave situation along the radiator - almost uniform distribution (need resistive loading at the tip, just like in Cecil's coil example or Rhombic/Beverage antennas) - how would that affect overall efficiency? When Barry, W9UCW did his experiments and measurements, he was surprised that quality of the loading coil made hardly any difference. Like good Bugcatcher coil vs. bad Hustler type resonator. Do we have the case where some power is being lost for the benefit of stretching the high current portion along the radiator and making up for losses? Normally we always try to minimize the resistive or other loses, but seems that something "fishy" might be going on, or is it insignificant form practical purposes, but I still believe that when involving more loaded elements in an array, things add up and become worthy of considering. (We are talking about quarter wave vertical resonant radiator not the Goosian soup :-) 73 Yuri, K3BU.us |
Phase Shift through a 75m Texas Bugcatcher Coil
Yuri Blanarovich wrote:
Which brings me back to my question: How important is the Q and low resistance of the coil and stinger? As the loading coil is moved from base-loading to top-loading, the average net current through the coil decreases (assuming no top hat loading). The importance of coil Q is related to how much net average current is flowing through the coil. For instance, the net average current through a hamstick coil is enough to burn your hand even after the power has been shut off. I've always had it in the back of my mind to install a 16'x6' piece of hardware cloth at 12.5 ft above ground above my GMC pickup, supported by fiberglass poles. I would mount the loading coil about a foot below the top hat. I'll bet that would win any 75m mobile antenna shootout. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
... For instance, the net average current through a hamstick coil is enough to burn your hand even after the power has been shut off. I've always had it in the back of my mind to install a 16'x6' piece of hardware cloth at 12.5 ft above ground above my GMC pickup, supported by fiberglass poles. I would mount the loading coil about a foot below the top hat. I'll bet that would win any 75m mobile antenna shootout. Cecil: Have you been designing and setting up antennas out at Area 51, again? ROFLOL!!! Regards, JS |
Phase Shift through a 75m Texas Bugcatcher Coil
I undesrtand delay in coils but I don't see anyone arguing delay.
more important is i don't see any differences but everyone is saying this and that is better than something else. coke is better than pepsi = who cares? On May 11, 9:30 pm, (Richard Harrison) wrote: Herbert wrote: "Do you know how to explain this so normal people can understand?" I `m not a Guru, but I`ll try. First, there was adispute about delay in an antenna loading coil. That provoked attempts to measure the delay. Then the argument turned to the measurement methods. The antenna signal travels from the transmitter through the coil and through the stinger until it reaches the tip where it is forced to reverse course by the open circuit. All the signal which has not been radiated or lost in waste enroute starts its journey back toward the transmitter. This reflected energy from the antenna tip is of no help in determining delay through the loading coil but the ripples it makes, when it adds and subtracts from the waveform of the forward energy, makes measurements difficult. Frequently a directional coupler is used to measure the energy moving in one direction, while ignoring the energy moving in the opposite direction, to get a meaningful measurement. Cecil proposed a resistor matching the impedance at the tip of the antenna to avoid a reflection. This also eliminates the troublesome ambiguity. Testing is convincing, perhaps, but not really necessary as the delay through a coil has been understood and quantified at least since Ampere who died in 1836. The ARRL Handbook, mine is from 1976, explains inductance on page 25: "Since the induced emf opposes the emf of the source, it tends to prevent the current from rising rapidly when the circuit is closed." Delay is a well known function of inductors. In early times they were often called "retard coils". Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
what is average net current? is there a peak net current?
On May 12, 7:17 am, Cecil Moore wrote: Yuri Blanarovich wrote: Which brings me back to my question: How important is the Q and low resistance of the coil and stinger? As the loading coil is moved from base-loading to top-loading, the average net current through the coil decreases (assuming no top hat loading). The importance of coil Q is related to how much net average current is flowing through the coil. For instance, the net average current through a hamstick coil is enough to burn your hand even after the power has been shut off. I've always had it in the back of my mind to install a 16'x6' piece of hardware cloth at 12.5 ft above ground above my GMC pickup, supported by fiberglass poles. I would mount the loading coil about a foot below the top hat. I'll bet that would win any 75m mobile antenna shootout. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
wrote:
I undesrtand delay in coils but I don't see anyone arguing delay. The following web page is representative of the side that asserts there is virtually zero delay through a 75m loading coil. But the backers of that argument have grown strangely silent as of late. http://www.w8ji.com/inductor_current_time_delay.htm -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
wrote:
what is average net current? Average net current is the RMS value of the standing-wave current. Here is a graph of such from Kraus: "Antennas" for a 1/2WL dipole: http://www.w5dxp.com/krausdip.jpg Half of that graph would represent a 1/4WL monopole. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, W5DXP wrote:
"Here is a graph of such from Kraus: "Antennas" for a 1/2WL dipole." The Fig. 9-6 that Cecil posted is from an older edition of Kraus. In the new 3rd edition, the same graph is Fig. 14-2 on page 464. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
i see nothing about average or peak net current there a t the link
i see no differences by value only of maytters of taste. Is there someone else here who knows how to explain not fact things so a normal person can understand what this is all about? On May 12, 9:58 am, Cecil Moore wrote: wrote: what is average net current? Average net current is the RMS value of the standing-wave current. Here is a graph of such from Kraus: "Antennas" for a 1/2WL dipole: http://www.w5dxp.com/krausdip.jpg Half of that graph would represent a 1/4WL monopole. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
there is nothing there that shows any difference
virtually zero means anything what does it matter anyway when no one can show simple difference? On May 12, 9:52 am, Cecil Moore wrote: wrote: I undesrtand delay in coils but I don't see anyone arguing delay. The following web page is representative of the side that asserts there is virtually zero delay through a 75m loading coil. But the backers of that argument have grown strangely silent as of late. http://www.w8ji.com/inductor_current_time_delay.htm -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
wrote:
i see nothing about average or peak net current there a t the link i see no differences by value only of maytters of taste. Don't worry, Don, many of the gurus on this newsgroup don't comprehend it either. Maybe when the light dawns upon them, they will explain it better than I can. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
strange
if you dont know average andpeak net current and why use it? On May 12, 4:33 pm, Cecil Moore wrote: wrote: i see nothing about average or peak net current there a t the link i see no differences by value only of maytters of taste. Don't worry, Don, many of the gurus on this newsgroup don't comprehend it either. Maybe when the light dawns upon them, they will explain it better than I can. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, W5DXP wrote:
"The following web page is representative of the side that asserts there is virtually zero delay through a 75m loading coil. But the backers of that argument have grown strangely silent of late." Coils generate counter-emf as a result of forward current and the necessary magnetic field grows no faster than the current grows. Its growth is delayed by the counter-emf. Current does not jump off the rails in a coil. It follows the coil wire as it follows a straight wire elsewhere. Terman says so and here is a quotation from the "Lenkurt Demodulator of August 1965 which describes the operation of a Traveling Wave Tube (TWT). Lenkurt used some of these in heterodyne repeaters operating at 6 GHz because of their wide bandwidth. Lenkurt`s description is very similar to Terman`s description: "The signal to be amplified by the tube is coupled into the gun end of the helix. This RF signal travels as a surface wave around the turns of the helix, toward the collector, at about the velocity of light. The forward movement of the wave is analogous to the travel of a finely threaded screw (I called it a bolt in my analogy) where many turns are required to drive it into position. The signal wave generates an axial electric field which travels*with it along the longitudinal axis of the helix. This alternating electric field interacts or velocity modulates the electrons in the beam." The beam is pencil thin centered inside the helix. The beam is formed and focused much like that inside a cathode ray tube. Its electrons are accelerated by a high positive d-c voltage on the collector and elsewhere in the tube. But that`s not all. Signal voltage on the helix speeds and slows the beam at multiple points along the helix which is many wavelengths long at 6 GHz. This advancement and retardation along the length of the helix bunches up the electrons producing the velocity modulation of the beam. The helix is just a long spiral of wire inside the TWT. There are many cycles of the 6 GHz signal distributed along the wave`s travel route. Terman and Lenkurt say the signal route is along the wire in the coil. I believe them. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Harrison wrote:
Cecil, W5DXP wrote: "The following web page is representative of the side that asserts there is virtually zero delay through a 75m loading coil. But the backers of that argument have grown strangely silent of late." Current does not jump off the rails in a coil. Not disagreeing in general but just fine tuning a bit. In an HF mobile loading coil, the EM waves are photonic in nature so a few photons are capable of migrating to adjacent turns - certainly not enough to cause the 3 nS delay through a 10 inch long 100 turn coil reported by w8ji, but the effect is enough to roughly cut in half the time taken for the current to negotiate the coil wire. I have modeled a 75m Texas Bugcatcher coil at: http://www.w5dxp.com/coil505u.EZ The length of the wire used in that coil is ~48 feet. A wavelength at 3.8 MHz is ~259 feet. So that 48 feet equals about (360)(48/259) = ~67 degrees. Yet EZNEC reports a phase shift of only ~38 degrees. The effect of the interaction between adjacent coils increases the velocity factor of the coil to roughly 1.8 times what it would be if all the current were confined to the coil wire. That's a VF increase from ~0.009 to ~0.016 but certainly still magnitudes short of w8ji's reported value of 0.988 The measured velocity factor as a function of the ratio of coil-circumference/wavelength is presented by Kraus, Figure 8-34 in the 3rd edition. Note that the phase velocity is not a straight line function of circumference. The velocity factor as a function of the ratio of coil-diameter/wavelength has been plotted in Fig. 1 of: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf and is also not a straight-line function. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, W5DXP wrote:
"The measured velocity factor as a function of the ratio of coil-circumference/wavelength is presented by Kraus, Figure 8-34 in the 3rd edition." Yes. The older edition, posted briefly on the web, has a Fig. 7-19 which also has VF`s found by Chu & Jackson, and by Bagby. They also found propagation faster than c for some coil circumferences / wavelength. Photons, massless at rest, can do that. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
... Not disagreeing in general but just fine tuning a bit. In an HF mobile loading coil, the EM waves are photonic in nature so a few photons are capable of migrating to adjacent turns - certainly not enough to cause the 3 nS delay through a 10 inch long 100 turn coil reported by w8ji, but the effect is enough to roughly cut in half the time taken for the current to negotiate the coil wire. ... Cecil: What would you offer as to the "photonic-jump", the capacitance of the adjacent turns with air serving as the dielectric? Since inductance lags and capacitance leads, wouldn't the inductance value between turns serve to offset this? And, the diameter of the wire become a major factor in the phenomenon you propose? What if a spiral wound faraday shield is placed between the turns? Would we still see this "photonic-jump?" Regards, JS |
Phase Shift through a 75m Texas Bugcatcher Coil
John Smith I wrote:
What would you offer as to the "photonic-jump", the capacitance of the adjacent turns with air serving as the dielectric? When electrons are accelerated in a conductor, they emit photons. Some photons are emitted from one turn and migrate to the adjacent turn. One might think of it as a few photons taking a shortcut. Another way of saying the same thing is that the fields couple turn-to-turn. The overall effect is to increase the velocity factor of the coil by something like a factor of two over the "threaded bolt" calculation. However, the effect is still magnitudes too low to explain the 100 turn, 3 nS coil delay described by w8ji. Standing wave current cannot be used to make valid measurements about current amplitude "drops" across or phase shifts through a loading coil. One must instead figure out a way to get a traveling wave flowing through the coil. Then the phase shift becomes perfectly obvious. I have taken Wes's helical coil from: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm and modeled it with EZNEC. I then loaded the coil with a 1250 ohm resistor to minimize reflected current and took a look at the phase shift through the coil. Turns out to be about 37 degrees at 7.15 MHz. That makes it a delay of about 14.4 nS. That coil512.EZ file can be downloaded from: http://www.w5dxp.com/coil512.EZ -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
On Sun, 13 May 2007 11:02:24 -0500, Cecil Moore
wrote: Aside from 100% error (actually more) for Wes' coil, I have taken Wes's helical coil from: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm and modeled it with EZNEC. ... That coil512.EZ file can be downloaded from: is distinctly false. |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote:
On Sun, 13 May 2007 11:02:24 -0500, Cecil Moore wrote: Aside from 100% error (actually more) for Wes' coil, I don't understand but will be glad to correct any error. I have taken Wes's helical coil from: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm and modeled it with EZNEC. ... That coil512.EZ file can be downloaded from: is distinctly false. In what way? -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
On Sun, 13 May 2007 12:49:03 -0500, Cecil Moore
wrote: In what way? Abandon your Xerox ethic and actually read your reference. This advice would work for other citations you copy off too. |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote:
Abandon your Xerox ethic and actually read your reference. This advice would work for other citations you copy off too. Here's what it says: "Case 3 uses a model similar to the other two cases, except the three-segment load wire is replaced by a wire coil ("distributed load") consisting of sixteen turns of 12 AWG wire, spaced 0.5 inch between adjacent turns, for a total height (length) of eight inches. The coil is centered on the length of the monopole and the monopole is brought to resonance by using the resonating function of MultiNEC to adjust the radius of the coil. Eight, single segment wires arranged in octagonal form approximate each turn of the circular coil, for a total of 128 single-segment wires." Exactly what did I miss? -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
... Standing wave current cannot be used to make valid measurements about current amplitude "drops" across or phase shifts through a loading coil. One must instead figure out a way to get a traveling wave flowing through the coil. Then the phase shift becomes perfectly obvious. ... So, "something" roughly related to [speed-of-light - velocity-factor-of-conductor = phase-shift] should be at play (since photons are speed of light and the rf wave is limited by the VF) ??? Regards, JS |
Phase Shift through a 75m Texas Bugcatcher Coil
John Smith I wrote:
So, "something" roughly related to [speed-of-light - velocity-factor-of-conductor = phase-shift] should be at play (since photons are speed of light and the rf wave is limited by the VF) ??? Coherent EM waves traveling in opposite directions can certainly confuse the observer. In order to remain un- confused, one EM wave traveling in one direction should be the wave used for measurements. Otherwise intelligent people have been completely fooled by the two waves traveling in opposite directions. The resultant wave is an illusion and therefore the observations based on standing waves are likewise illusions. How can a standing wave, whose amplitude is dependent upon the the phases of the two traveling waves, be used to determine anything about amplitude? How can the phase, which is essentially fixed and constant at zero degrees, be used to determine phase delay? Standing waves have faked the gurus out of their jockey straps. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
... How can a standing wave, whose amplitude is dependent upon the the phases of the two traveling waves, be used to determine anything about amplitude? How can the phase, which is essentially fixed and constant at zero degrees, be used to determine phase delay? Standing waves have faked the gurus out of their jockey straps. Cecil: Just using logic, an "interference wave" (standing wave) would seem to be a poor choice, alright. But then, my knowledge on this subject makes me dependent upon others, I am listening and attempting to get a grasp on things ... sorry if my ignorance can be taxing at times ... frankly, even to attempt to discern between forward-reflected-standing for the purposes you propose has never entered my mind! Give me a bit, as with others here, this all is taking a bit of time to get ones' mind wrapped around. You have given this quite a bit of thought, I am just beginning down that path ... perhaps when I learn enough, I will agree or disagree. However, you have already given me a bit to play with, such as attempting to "repel photons" from transversing windings. LOL! Regards, JS |
Phase Shift through a 75m Texas Bugcatcher Coil
John Smith I wrote:
... However, you have already given me a bit to play with, such as attempting to "repel photons" from transversing windings. LOL! ... Geesh, everyone must be slow today, sure I would get jumped about using transversing instead of the proper use of traversing ... JS |
Phase Shift through a 75m Texas Bugcatcher Coil
On Sun, 13 May 2007 18:17:29 GMT, Cecil Moore
wrote: Tedious Xerography snipped as being obviously unread by Xerographer. Exactly what did I miss? If you have to be taken by the hand to have it pointed out to you, you shouldn't be doing these kind of things without adult supervision. A I have taken Wes's helical coil from: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm B and modeled it with EZNEC. ... That coil512.EZ file can be downloaded from: is distinctly false. A B Does a symbolic reply nail it down? |
Phase Shift through a 75m Texas Bugcatcher Coil
On May 12, 7:10 am, "Yuri Blanarovich" wrote:
When Barry, W9UCW did his experiments and measurements, he was surprised that quality of the loading coil made hardly any difference. Like good Bugcatcher coil vs. bad Hustler type resonator. Dunno, I don't see too much difference between any of my homebrew coils, but when I compared any of those to a hustler, there was a large noticable difference. The hustler was terrible.. Like a dummy load on a stick. But in comparing any of my usual coils, I don't see a large difference in any of them, including those with heavy gauge wire, vs those with thinner gauge wire. I've found thinner gauge wire is just fine as long as the wires are not wound too close together. If one tried a hustler coil, and a good bugcatcher coil, and saw little or no difference, I would think ground loss was severely overshadowing coil loss. The less ground loss, the more apparant will coil loss become. Of course, the large hustler coils have a fairly well known design defect, and I consider them defective units vs a usual mobile loading coil. Even my cheap homebrew coils are far superior, and I do nothing special.. I once did a side by side test of my mobile vs a friends using a hustler mast and resonator on 75m. No contest.. He was in the noise to many stations, where I was solid copy to most all.. About a 2 S unit ? difference on average. Do we have the case where some power is being lost for the benefit of stretching the high current portion along the radiator and making up for losses? Sorta.. To an extent anyway... The peak point being probably around 75% or so of the total height.. Get too carried away, and excess coil loss will start to offset gains in efficiency from the improved current distribution. In testing all my coils, antennas, etc, I've found Reg's program "vertload" to be fairly accurate. Both in general performance estimates, but also in the estimates on coil loss vs size of wire, etc.. His program said thinner wire should be ok with only slight losses vs thicker wire, with a proper pitch and wire spacing, and in real life it seemed to pan out pretty close. A center load coil, with more turns than a base load, will have more loss. But the overall antenna efficiency is greatly improved, so I know which line I'll be standing in when I pick which one I want to use. :/ If you use a large enough top hat, you can have a base loading coil, and still have good current distribution. But I don't use hats on mobiles.. #1, pretty freaking ugly.. #2, I'll kill them on tree branches fairly quick.. #3, too much wind load at highway speeds.. Tend to flop and whip about with my flexible fibreglass "masts".. I use a center loading coil and a fairly long whip as a decent compromise. In the driving mode, I have 5 ft under the coil, and 5 ft above it.. In the parked mode, I have 8 ft under the coil, and 5 ft over it by adding an extra 3 ft hustler mast at the base. If thats on one of my trucks, my coil is higher than many peoples total antenna height.. :) At this date, I'm still too chicken to drill a hole in my latest car, which is a 2005 corolla... The bad part is thats the one I drive most of the time lately... My honda accord is radioactive, as are both of my trucks, but the trucks burn too much gas, and the accord needs some work.. It doesn't get as good a mpg as the corolla either, although both weigh about the same. I'm lucky to get 30 on the road in the accord, where the corolla gets about 37-40 depending on speed.. But I miss not having a radio on the road at night... I've already been to my lake property up in OK. four times in that car since I got it.. "905 mile round trip" I've put about 8k on that car already, and have had it maybe 3 months or so... The last was a couple of weeks ago. I did install a 80 and 40 single coax fed dipole rig up there last time, so at least the property is radioactive even if my car isn't.. That helps... I strung it up in an old oak tree, and left the coax rolled up by the tree. When I pull up, the coax is long enough to reach about anywhere I'd have the radio, including in the car. I'll probably add 160m legs later.. MK |
Phase Shift through a 75m Texas Bugcatcher Coil
I wrote:
"Current does not jump off the rails in a coil, it follows the coil wire as it follows a straight wire elsewhere." Wikipedia says, electrical conduction is the movement of charged particles through an electrical conductor. The movement forms an electrical current in response to an electric field. Inductance is passive and though it opposes a change in current, nowhere is the inducement to conduct any stronger than it is where the source connects with the coil. The charges at the ends of a coil are going to press on their neighbors to move on and keep the conduction going. Inductance results from the magnetic field that forms around a current carrying conductor. Electrical current through the conductor creates a magnetic flux proportional to the current. When there is an AC sinusoidal source, the phase of the current through a pure inductance lags the voltage by 90 degrees. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
FYI -
Reg Edwards' program produces a VF of .0333 and a delay of 26 degrees for the 75m Bugcatcher coil. ac6xg Cecil Moore wrote: The following web page is representative of the side that asserts there is virtually zero delay through a 75m loading coil. But the backers of that argument have grown strangely silent as of late. http://www.w8ji.com/inductor_current_time_delay.htm |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
Reg Edwards' program produces a VF of .0333 and a delay of 26 degrees for the 75m Bugcatcher coil. Thanks Jim, Dr. Corum's formula indicates a VF of ~0.02 EZNEC indicates a VF of ~0.016 The "threaded bolt" method indicates a VF of ~0.006 w8ji indicates a VF of ~0.42 for his 100 turn, 10 inch long, 2 inch diameter coil. In order to get a valid measurement of the delay through a coil, the coil needs to be loaded with its characteristic impedance to minimize the reflected current. With mostly traveling wave current flowing through the coil, the delay is easy to measure. -- 73, Cecil http://www.w5dxp.com |
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