Re: Topband: GAP Vertical Question
Rick N6RK: On 12/16/2012 8:31 AM, Tom W8JI wrote: You likely had an antenna with 1/2 wave of wire spooled up on a short fiberglass rod, which would never behave like a half-wave. You are exactly right. Unfortunately, this myth dies hard. Below is a link to a page on this topic from ANTENNAS, 3rd edition, by John Kraus. Kraus states in the middle of that page that the radiation resistance of such an antenna is the same as a linear conductor of the same overall height/length. http://i62.photobucket.com/albums/h85/rfry-100/Helically-woundVertical.gif RF ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
First, they would be fools or have idiots for engineers to have more than 120 radials. The only real reason they use 90 radials or so is it sometimes gets them out of expensive proof-of-performance measurements. Or, (1) to compensate for field degradation over the course of several decades. In the case of WLS in Chicago, they laid 120 radials on top of an old set of 120 radials. The base Z did not change, nor was it expected to. And (2), to better stabilize a pattern in the case of a DA where soil moisture/content changes with seasons. A typical half-wave BC tower is in the several hundred ohm range because of tower thickness. They are almost never over 1000 ohms. Right, typically a couple hundred ohms. Modeling the base Z of a thick broadcast tower is very difficult with MoM software. Changes in thickness can result in large base Z changes. Paul, W9AC ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
*Half wavelength vertical ground loss* Let's see if we can quantify the conduction losses of a 1.8 MHz half wavelength vertical connected to average earth via a ground rod. This paper by N6LF shows one skin depth at 1.8 MHz to be 6 meters. http://www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf Let's assume the current magnitude in the ground mirrors that of the antenna. Driving the antenna at the base such that the current at the antenna center is 1 amp, the ground current 40 meters away from the antenna is 1 amp. The 1 amp of ground current passes through a section of earth having an effective depth of of 6 meters. For a 1 meter radial length and 40 meters from the antenna the section has dimensions of 1 meter X 6 meters X 250 meters (250 meters is the circumference). Given a resistivity of 200 ohms/meter the resistance of this section is 200/(6 X 250) = 0.13 ohms. The loss in this section is 0.13 watts. Using NEC we see with the base current set to give 1 amp at the antenna center the power into the antenna is 100 watts. Closer to the base of the antenna the effective ground resistance increases due to the smaller circumference. Closer to the antenna the current decreases. Roughly Integrating the ground loss from the base to the 80 meters away gives a total ground loss of 4 watts. The no-radial ground loss is 5 watts and the antenna gain is reduced by 10LOG(100/96) = 0.2 dB from the full radial case. How about ground loss due to the induced E-field in the ground? I believe this is accounted for in the previous calculation. I ran a NEC simulation to explore this. The two cases were a 266' vertical fed against thirty 3' radials and thirty 133' radials. The radials are 0.05' above medium ground. The NEC Average Gain was compared for the two cases and showed a difference of 0.06 dB. Dave WX7G On Sun, Dec 16, 2012 at 6:42 PM, Donald Chester k4...@hotmail.com wrote: Then, why do broadcast stations that use vertical towers at approximately a half wavelength, purchase valuable real estate and spend thousands of dollars for the copper to install from 120 to 240 or more radials, each usually a half wave or more in length? See G. H. Brown: Ground Systems as a Factor in Antenna Efficiency, IRE Proceedings, June 1937 p. 753. Brown demonstrated that the distribution of earth currents and ground losses is such that the region of maximum current and loss occurs at a distance of about 0.35 wavelengths from the base of a ground mounted half wave vertical antenna, which was verified experimentally. There is zero loss at the base of the antenna itself, since there is no base current because the antenna a fed at a current node. An rf ammeter inserted in the ground lead, as well as one inserted in in the antenna lead attached to the insulated base of the radiator will read zero. The ground losses occur farther out from the base of the antenna. Low effective earth resistance provided by a good ground system is ABSOLUTELY NECESSARY for vertical antennas of ANY height if one expects good radiation efficiency. The claim that no ground system is needed for a half wave vertical is nothing more than a long-standing popular misconception. This topic prompted me to dig out and review an anecdote I recall reading in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by USNR Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham who had made the discovery that he could tune and operate a half wave vertical without a ground system, feeding it by a parallel tuned tank circuit whose lower end is grounded. Since an rf ammeter in the ground lead showed no current, he could dispense with the ground system and its loss. He suggested to the Capt. that he should discover the new world of half verticals with no ground system. Quoting from the text (p. 84): The correspondent's claim... is true ONLY IF HE IS CONTENT TO THROW AWAY FROM 40 TO 80 PER CENT OF HIS RADIATED POWER IN THE FORM OF EARTH LOSSES. (the correspondent) stated, 'The ZL's call ME, when I use my half wave vertical!' This is not surprising, in view of the fact that the half wave's vertical pattern has a lower main lobe angle than a quarter wave would have... However, he would hit the ZL's even harder if he would put in a ground system. Of course, the half wave vertical is not dependent on a ground plane, however lossy or efficient, for the condition of RESONANCE, since it is resonant in itself because of its half wave length. However, IT IS DEPENDENT ON A GROUND PLANE FOR ITS EFFICIENCY OF RADIATION, as is any vertical antenna...' Don k4kyv Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to 100% radiation efficiency. Dave WX7G And this statement is based on what? Publications, measurements, modeling? I have built a number of
Re: Topband: GAP Vertical Question
On 12/16/2012 8:31 AM, Tom W8JI wrote: You likely had an antenna with 1/2 wave of wire spooled up on a short fiberglass rod, which would never behave like a half-wave. You are exactly right. Unfortunately, this myth dies hard. Below is a link to a page on this topic from ANTENNAS, 3rd edition, by John Kraus. Kraus states in the middle of that page that the radiation resistance of such an antenna is the same as a linear conductor of the same overall height/length. http://i62.photobucket.com/albums/h85/rfry-100/Helically-woundVertical.gif RF Everyone should know, by now, that radiation resistance in a simple single element is tied directly to ampere-feet of linear spatial area. If we remember this, the E-H antennas, folded monpoles and dipoles, spirals, fractals, CFA's, isotrons, and all the other magically folded, curved, or bent antenna would all become the antennas they actually are. ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Right, typically a couple hundred ohms. Modeling the base Z of a thick broadcast tower is very difficult with MoM software. Changes in thickness can result in large base Z changes. Just to be clear, since the discussion drifted to half-wave radiators, my comment above was specific to the modeling of thick v. thin half-wave radiators, including the 180-195 degree radiators of some well-known 50KW AM stations. The results when modeling the base Z of approx. 1/4-wave radiators is less affected by thickness, probably due to a lower base Z to start with. Paul, W9AC ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
length. For want of a better word its image has to be a perfect conductor for the antenna system as a whole to be 100% efficient. The invocation of image into efficiency or ground losses shows a misunderstanding of antenna basics. We were taught how to use antenna images' in EM theory back in the 1970's, because computers were uncommon and there weren't any modeling programs. The antenna image is nothing but a tool to aid in pattern calculation. It isn't applicable to radial systems, ground losses in verticals, or anything similar. The image, as applied to antenna systems, represents the overall effect of re-radiation from the ground around an antenna. With a vertical, this area extends out for a considerable distance from the antenna. The amplitude and phase of a completely fictitious image is use to calculate field intensity at different points in space, just as if two antennas were being phased in a certain phase and current amplitude relationship. A problem occurred, because people started to think the image was an actual thing that existed at one point or area in the earth, and that allowed them to create false ideas in their heads of what an image is. The image antenna is a fictitious tool for estimating patterns, nothing else. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Just to be clear, since the discussion drifted to half-wave radiators, my comment above was specific to the modeling of thick v. thin half-wave radiators, including the 180-195 degree radiators of some well-known 50KW AM stations. The results when modeling the base Z of approx. 1/4-wave radiators is less affected by thickness, probably due to a lower base Z to start with. The theory (or cause) behind this is twofold: 1.) A thicker radiator at an end has a larger area for the electric field. This results in a less concentrated e-field discontinuity or boundary at the open end of the element. In other words the electric field is not as intense, and that means voltage is less. 2.) Any antenna is also a transmission line. The surge impedance of that transmission line is lower with a larger effective diameter conductor. The mismatch of the open circuit at the far end is transformed through that transmission line, by the standing wave in the antenna, to a new lower impedance at the center, just as the center can be transformed back up to an open end. This means a thicker antenna element doesn't have the low and high impedance extremes at the open end or along the antenna that a thinner antenna has. The standing waves are muted. If the antenna had no radiation or loss, it would have no end current. It would have infinite impedance. This applies to counterpoises also. We can see how difficult it is to have useful things in antennas (antennae are found on insects, and can have zero current) that have no radiation and no loss. :-) 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Tom et al,'this a hobby, pse dont take it that seriously 73 Len SM7BIC -Ursprungligt meddelande- Från: Topband [mailto:topband-boun...@contesting.com] För Tom W8JI Skickat: den 17 december 2012 18:55 Till: topband@contesting.com Ämne: Re: Topband: GAP Vertical Question To work at its maximum efficiency a vertical needs a real ground system and the image is its fictitious counterpart to isotropic. Im oversimplyfing here so no need to pick nits. Besides being untrue, that is confusing or misleading. 1.) Some verticals need no ground. What would also be true is that end-fed antennas always require a counterpoise of some sort, because there always has to be a second terminal of some type for the feedline to push against. 2.) The image is a shortcut tool used to allow longhand pattern calculations. It is not used for efficiency, antenna descripition, or actual operation. 3.) dBi, on the other hand, is a reference condition for a field strength ratio. According to Kraus that image, mirror, or whatever you care to call it occurs at a distance from the base and at a mathematical relationship to where the current peak is on the vertical radiator. In the case of this half wave discussion the reflection occurs around .35 wave out unless you, or others, want to try and discredit Kraus. Thus radials do work with a 1/2 wave and system efficiency is dependent upon the actual ground and how well the radials perform. Since this forum is predominantly DX oriented I prefer to qualify the system efficiency by how well the main lobe extends between its peak and the ground. IOW those low angles needed for DX. There is not wrong with what Kraus teaches. The problem comes when we misunderstand or misapply what he teaches. Using modeling it is easy to realize that significant degradation of the radiated field at the lower angles is very real. I'm not sure models we use are all that meaningful at low angles on low bands. They are OK on extended groundwave, and probably OK on upper HF. They are, however, all we have. Various verticals (mostly VHF/UHF) on tall buildings or towers are not subjected to those ground losses and place a strong signal at the horizon. I'm not going to touch that one, other than to say ground losses for a given soil and condition are dependent of intensity of the electric, magnetic, and electromagnetic fields in a given volume of lossy media. This is why we can have moonbounce, even though losses in the moon's surface are horrible, and why moving an antenna up away from earth or distributing the fields over a wider area by using more radials reduces loss. Where we create a misunderstanding or problem is when we ignore how it works, and pretend all field intensities in a given volume of lossy media are equal at all distances with all antennas. When we do that, we get false ideassuch as half wave verticals have high loss without large radial fields. If that was true, our horizontal half-wave dipoles 1/4 wave or more high would have poor efficiency without large counterpoise fields below the dipole. 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Where is the 40-60% claimed ground loss? I get 4%. On Dec 17, 2012 6:12 AM, DAVID CUTHBERT telegraph...@gmail.com wrote: *Half wavelength vertical ground loss* Let's see if we can quantify the conduction losses of a 1.8 MHz half wavelength vertical connected to average earth via a ground rod. This paper by N6LF shows one skin depth at 1.8 MHz to be 6 meters. http://www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf Let's assume the current magnitude in the ground mirrors that of the antenna. Driving the antenna at the base such that the current at the antenna center is 1 amp, the ground current 40 meters away from the antenna is 1 amp. The 1 amp of ground current passes through a section of earth having an effective depth of of 6 meters. For a 1 meter radial length and 40 meters from the antenna the section has dimensions of 1 meter X 6 meters X 250 meters (250 meters is the circumference). Given a resistivity of 200 ohms/meter the resistance of this section is 200/(6 X 250) = 0.13 ohms. The loss in this section is 0.13 watts. Using NEC we see with the base current set to give 1 amp at the antenna center the power into the antenna is 100 watts. Closer to the base of the antenna the effective ground resistance increases due to the smaller circumference. Closer to the antenna the current decreases. Roughly Integrating the ground loss from the base to the 80 meters away gives a total ground loss of 4 watts. The no-radial ground loss is 5 watts and the antenna gain is reduced by 10LOG(100/96) = 0.2 dB from the full radial case. How about ground loss due to the induced E-field in the ground? I believe this is accounted for in the previous calculation. I ran a NEC simulation to explore this. The two cases were a 266' vertical fed against thirty 3' radials and thirty 133' radials. The radials are 0.05' above medium ground. The NEC Average Gain was compared for the two cases and showed a difference of 0.06 dB. Dave WX7G On Sun, Dec 16, 2012 at 6:42 PM, Donald Chester k4...@hotmail.com wrote: Then, why do broadcast stations that use vertical towers at approximately a half wavelength, purchase valuable real estate and spend thousands of dollars for the copper to install from 120 to 240 or more radials, each usually a half wave or more in length? See G. H. Brown: Ground Systems as a Factor in Antenna Efficiency, IRE Proceedings, June 1937 p. 753. Brown demonstrated that the distribution of earth currents and ground losses is such that the region of maximum current and loss occurs at a distance of about 0.35 wavelengths from the base of a ground mounted half wave vertical antenna, which was verified experimentally. There is zero loss at the base of the antenna itself, since there is no base current because the antenna a fed at a current node. An rf ammeter inserted in the ground lead, as well as one inserted in in the antenna lead attached to the insulated base of the radiator will read zero. The ground losses occur farther out from the base of the antenna. Low effective earth resistance provided by a good ground system is ABSOLUTELY NECESSARY for vertical antennas of ANY height if one expects good radiation efficiency. The claim that no ground system is needed for a half wave vertical is nothing more than a long-standing popular misconception. This topic prompted me to dig out and review an anecdote I recall reading in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by USNR Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham who had made the discovery that he could tune and operate a half wave vertical without a ground system, feeding it by a parallel tuned tank circuit whose lower end is grounded. Since an rf ammeter in the ground lead showed no current, he could dispense with the ground system and its loss. He suggested to the Capt. that he should discover the new world of half verticals with no ground system. Quoting from the text (p. 84): The correspondent's claim... is true ONLY IF HE IS CONTENT TO THROW AWAY FROM 40 TO 80 PER CENT OF HIS RADIATED POWER IN THE FORM OF EARTH LOSSES. (the correspondent) stated, 'The ZL's call ME, when I use my half wave vertical!' This is not surprising, in view of the fact that the half wave's vertical pattern has a lower main lobe angle than a quarter wave would have... However, he would hit the ZL's even harder if he would put in a ground system. Of course, the half wave vertical is not dependent on a ground plane, however lossy or efficient, for the condition of RESONANCE, since it is resonant in itself because of its half wave length. However, IT IS DEPENDENT ON A GROUND PLANE FOR ITS EFFICIENCY OF RADIATION, as is any vertical antenna...' Don k4kyv Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to
Re: Topband: GAP Vertical Question
Yo, Tom, et. al. please do keep taking this seriously! Most of us on this reflector do not have engineering degrees involving the physics of RF. However we do greatly enjoy developing systems to receive and fling RF energy into the ether and try desperately to follow the discussion here in order to improve both our hardware and the understanding of how it works. Exercising the little grey cells in disciplines where I am minimally competent is enjoyable and adds to the operating experience in radio. Minimizing the magic in radio by showing how the tricks are done makes me a better magician.. Thanks to all those who contribute! I hope you all continue to do so in a professional manner. 73 and I remain, Lew W7EW On Mon, Dec 17, 2012 at 10:21 AM, Lennart M lennart.michaels...@telia.comwrote: Tom et al,'this a hobby, pse dont take it that seriously 73 Len SM7BIC -Ursprungligt meddelande- Från: Topband [mailto:topband-boun...@contesting.com] För Tom W8JI Skickat: den 17 december 2012 18:55 Till: topband@contesting.com Ämne: Re: Topband: GAP Vertical Question To work at its maximum efficiency a vertical needs a real ground system and the image is its fictitious counterpart to isotropic. Im oversimplyfing here so no need to pick nits. Besides being untrue, that is confusing or misleading. 1.) Some verticals need no ground. What would also be true is that end-fed antennas always require a counterpoise of some sort, because there always has to be a second terminal of some type for the feedline to push against. 2.) The image is a shortcut tool used to allow longhand pattern calculations. It is not used for efficiency, antenna descripition, or actual operation. 3.) dBi, on the other hand, is a reference condition for a field strength ratio. According to Kraus that image, mirror, or whatever you care to call it occurs at a distance from the base and at a mathematical relationship to where the current peak is on the vertical radiator. In the case of this half wave discussion the reflection occurs around .35 wave out unless you, or others, want to try and discredit Kraus. Thus radials do work with a 1/2 wave and system efficiency is dependent upon the actual ground and how well the radials perform. Since this forum is predominantly DX oriented I prefer to qualify the system efficiency by how well the main lobe extends between its peak and the ground. IOW those low angles needed for DX. There is not wrong with what Kraus teaches. The problem comes when we misunderstand or misapply what he teaches. Using modeling it is easy to realize that significant degradation of the radiated field at the lower angles is very real. I'm not sure models we use are all that meaningful at low angles on low bands. They are OK on extended groundwave, and probably OK on upper HF. They are, however, all we have. Various verticals (mostly VHF/UHF) on tall buildings or towers are not subjected to those ground losses and place a strong signal at the horizon. I'm not going to touch that one, other than to say ground losses for a given soil and condition are dependent of intensity of the electric, magnetic, and electromagnetic fields in a given volume of lossy media. This is why we can have moonbounce, even though losses in the moon's surface are horrible, and why moving an antenna up away from earth or distributing the fields over a wider area by using more radials reduces loss. Where we create a misunderstanding or problem is when we ignore how it works, and pretend all field intensities in a given volume of lossy media are equal at all distances with all antennas. When we do that, we get false ideassuch as half wave verticals have high loss without large radial fields. If that was true, our horizontal half-wave dipoles 1/4 wave or more high would have poor efficiency without large counterpoise fields below the dipole. 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
I, for one, am happy that Tom et al take it seriously, because that's how we learn things to improve our stations. 73, Mike www.w0btu.com On Mon, Dec 17, 2012 at 12:21 PM, Lennart M lennart.michaels...@telia.comwrote: Tom et al,'this a hobby, pse dont take it that seriously 73 Len SM7BIC ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
- Original Message - From: Paul Christensen w...@arrl.net To: topband@contesting.com Sent: Monday, December 17, 2012 9:07 AM Subject: Re: Topband: GAP Vertical Question Right, typically a couple hundred ohms. Modeling the base Z of a thick broadcast tower is very difficult with MoM software. Changes in thickness can result in large base Z changes. Just to be clear, since the discussion drifted to half-wave radiators, my comment above was specific to the modeling of thick v. thin half-wave radiators, including the 180-195 degree radiators of some well-known 50KW AM stations. The results when modeling the base Z of approx. 1/4-wave radiators is less affected by thickness, probably due to a lower base Z to start with. Paul, W9AC In the 1920's several BC towers were half waves without radials on hilltops. Performance was poor due to the height plus the lack of a decent ground on solid rock limiting the ground wave signal to a low value. As a side note tapered towers were also in vogue but that presented other problems. It wasnt until the educated scientific studies of the 30's and published papers/books that resulted that broadcasters began to standardize.along with some push from the FCC. Here we are over 70 years later still arguing the subject and embroiled in myths and some folks are very protective of their alternate beliefs. Did the 100mpg carburetor ever exist? Is this planet only 9000 years old (-; ? Carl KM1H ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
What I can add from personal experience is that a vertical dipole (center fed half wave) without radials, on a rocky cliff top is an absolute killer antenna on the upper HF bands. My vertical dipole works so well that in contests I often just quit using my yagis because of the hassle of rotating or even switching them. The omnidirectional vertical is only maybe 3 dB down on very good directional antennas. Center fed half waves on 160 are a lot harder to set up, so I have no experience there. But if I had a used broadcast tower it sure would be fun to try one. On Dec 17, 2012, at 7:33 AM, Carl k...@jeremy.mv.com wrote: - Original Message - From: Paul Christensen w...@arrl.net To: topband@contesting.com Sent: Monday, December 17, 2012 9:07 AM Subject: Re: Topband: GAP Vertical Question Right, typically a couple hundred ohms. Modeling the base Z of a thick broadcast tower is very difficult with MoM software. Changes in thickness can result in large base Z changes. Just to be clear, since the discussion drifted to half-wave radiators, my comment above was specific to the modeling of thick v. thin half-wave radiators, including the 180-195 degree radiators of some well-known 50KW AM stations. The results when modeling the base Z of approx. 1/4-wave radiators is less affected by thickness, probably due to a lower base Z to start with. Paul, W9AC In the 1920's several BC towers were half waves without radials on hilltops. Performance was poor due to the height plus the lack of a decent ground on solid rock limiting the ground wave signal to a low value. As a side note tapered towers were also in vogue but that presented other problems. It wasnt until the educated scientific studies of the 30's and published papers/books that resulted that broadcasters began to standardize.along with some push from the FCC. Here we are over 70 years later still arguing the subject and embroiled in myths and some folks are very protective of their alternate beliefs. Did the 100mpg carburetor ever exist? Is this planet only 9000 years old (-; ? Carl KM1H ___ Topband reflector - topband@contesting.com ___ It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true. #8212; Bertrand Russell
Re: Topband: GAP Vertical Question
I second this motion. Nearly every day brings some new insights. Thanks, Grant KZ1W On 12/17/2012 11:30 AM, Lew Sayre wrote: Yo, Tom, et. al. please do keep taking this seriously! Most of us on this reflector do not have engineering degrees involving the physics of RF. However we do greatly enjoy developing systems to receive and fling RF energy into the ether and try desperately to follow the discussion here in order to improve both our hardware and the understanding of how it works. Exercising the little grey cells in disciplines where I am minimally competent is enjoyable and adds to the operating experience in radio. Minimizing the magic in radio by showing how the tricks are done makes me a better magician.. Thanks to all those who contribute! I hope you all continue to do so in a professional manner. 73 and I remain, Lew W7EW On Mon, Dec 17, 2012 at 10:21 AM, Lennart M lennart.michaels...@telia.comwrote: Tom et al,'this a hobby, pse dont take it that seriously 73 Len SM7BIC -Ursprungligt meddelande- Från: Topband [mailto:topband-boun...@contesting.com] För Tom W8JI Skickat: den 17 december 2012 18:55 Till: topband@contesting.com Ämne: Re: Topband: GAP Vertical Question To work at its maximum efficiency a vertical needs a real ground system and the image is its fictitious counterpart to isotropic. Im oversimplyfing here so no need to pick nits. Besides being untrue, that is confusing or misleading. 1.) Some verticals need no ground. What would also be true is that end-fed antennas always require a counterpoise of some sort, because there always has to be a second terminal of some type for the feedline to push against. 2.) The image is a shortcut tool used to allow longhand pattern calculations. It is not used for efficiency, antenna descripition, or actual operation. 3.) dBi, on the other hand, is a reference condition for a field strength ratio. According to Kraus that image, mirror, or whatever you care to call it occurs at a distance from the base and at a mathematical relationship to where the current peak is on the vertical radiator. In the case of this half wave discussion the reflection occurs around .35 wave out unless you, or others, want to try and discredit Kraus. Thus radials do work with a 1/2 wave and system efficiency is dependent upon the actual ground and how well the radials perform. Since this forum is predominantly DX oriented I prefer to qualify the system efficiency by how well the main lobe extends between its peak and the ground. IOW those low angles needed for DX. There is not wrong with what Kraus teaches. The problem comes when we misunderstand or misapply what he teaches. Using modeling it is easy to realize that significant degradation of the radiated field at the lower angles is very real. I'm not sure models we use are all that meaningful at low angles on low bands. They are OK on extended groundwave, and probably OK on upper HF. They are, however, all we have. Various verticals (mostly VHF/UHF) on tall buildings or towers are not subjected to those ground losses and place a strong signal at the horizon. I'm not going to touch that one, other than to say ground losses for a given soil and condition are dependent of intensity of the electric, magnetic, and electromagnetic fields in a given volume of lossy media. This is why we can have moonbounce, even though losses in the moon's surface are horrible, and why moving an antenna up away from earth or distributing the fields over a wider area by using more radials reduces loss. Where we create a misunderstanding or problem is when we ignore how it works, and pretend all field intensities in a given volume of lossy media are equal at all distances with all antennas. When we do that, we get false ideassuch as half wave verticals have high loss without large radial fields. If that was true, our horizontal half-wave dipoles 1/4 wave or more high would have poor efficiency without large counterpoise fields below the dipole. 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true. #8212; Bertrand Russell
Re: Topband: GAP Vertical Question
Agreed. Keep going guys, please keep it civil and let the data rip! I for one am learning a LOT. Mark Lunday, WD4ELG ___ It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true. #8212; Bertrand Russell
Re: Topband: GAP Vertical Question
My own experience with 1/2 wave verticals is that they certainly do require a good ground. Maybe a rod in a saltwater marsh is sufficient but not in many other cases. Examples: A Shakespere CB whip in my 66 Corvette which was advervtised for fiberglass cars. It couldnt be heard a mile away with 4W. I added radials from the base on the rear deck to the frame on all 4 corners and then it worked much better. This was back in the late 70's for several years. A 80/40M 6 wire cage vertical, a full quarter wave on 80 and hanging from a tall pine tree branch at a prior QTH. With 60 65-70' radials it was competitive on 80 and on 40. With the radials removed it was a dud on 40. With another phased 1/4 wave on 80 it delivered the gain and F/B expected and 40 was improved with a pair of figure 8's but still not up to expectations. A 4el 40M KLM at 120' fixed that. Carl KM1H - Original Message - From: Richard (Rick) Karlquist rich...@karlquist.com To: Donald Chester k4...@hotmail.com Cc: topband@contesting.com Sent: Saturday, December 15, 2012 3:58 PM Subject: Re: Topband: GAP Vertical Question On 12/15/2012 12:03 PM, Donald Chester wrote: From: charlie-cunning...@nc.rr.com Could you support a vertical 1/2 wave for 160 with aballoon? You could end -feed it at the base through a 1/4 wave of 450 ohm But feeding a half wave vertical with the base near the ground still results in substantial ground losses without a radial system. Don k4kyv And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals with radials. They are indistinguishable in performance and certainly do not exhibit substantial ground losses AFAIK. The PAR electronics 1/2 wave end fed antenna seems to have a good reputation, unlike some GAP verticals. However, I don't recommend feeding it through 1/4 wave of 450 ohm open wire line. I just use an LC matching network. Rick N6RK ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1430 / Virus Database: 2634/5461 - Release Date: 12/15/12 ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
How long did the KLM last before the light boom folded, or the element to boom brackets failed or the linear loaded insulator let go? One good wind storm? Doug Think of all the ways you can hurt yourself laughing. -Original Message- A 4el 40M KLM at 120' fixed that. Carl KM1H ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
A Shakespere CB whip in my 66 Corvette which was advervtised for fiberglass cars. It couldnt be heard a mile away with 4W. I added radials from the base on the rear deck to the frame on all 4 corners and then it worked much better. This was back in the late 70's for several years. CB antenna manufacturers live in a fantasy land, and almost always grossly misrepresent what the sell. A half wave CB whip is about 18 feet long. It is impossible to use a half wave whip on 11 meter mobile on a normal highway or road. You likely had an antenna with 1/2 wave of wire spooled up on a short fiberglass rod, which would never behave like a half-wave. ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
On 12/16/2012 8:31 AM, Tom W8JI wrote: You likely had an antenna with 1/2 wave of wire spooled up on a short fiberglass rod, which would never behave like a half-wave. You are exactly right. Unfortunately, this myth dies hard. A few years ago a ham magazine had a article about a 160 meter vertical that utilized a half wave of wire helically wound on plastic tubing a few dozen feet high. Rick N6RK ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Then, why do broadcast stations that use vertical towers at approximately a half wavelength, purchase valuable real estate and spend thousands of dollars for the copper to install from 120 to 240 or more radials, each usually a half wave or more in length? See G. H. Brown: Ground Systems as a Factor in Antenna Efficiency, IRE Proceedings, June 1937 p. 753. Brown demonstrated that the distribution of earth currents and ground losses is such that the region of maximum current and loss occurs at a distance of about 0.35 wavelengths from the base of a ground mounted half wave vertical antenna, which was verified experimentally. There is zero loss at the base of the antenna itself, since there is no base current because the antenna a fed at a current node. An rf ammeter inserted in the ground lead, as well as one inserted in in the antenna lead attached to the insulated base of the radiator will read zero. The ground losses occur farther out from the base of the antenna. Low effective earth resistance provided by a good ground system is ABSOLUTELY NECESSARY for vertical antennas of ANY height if one expects good radiation efficiency. The claim that no ground system is needed for a half wave vertical is nothing more than a long-standing popular misconception. This topic prompted me to dig out and review an anecdote I recall reading in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by USNR Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham who had made the discovery that he could tune and operate a half wave vertical without a ground system, feeding it by a parallel tuned tank circuit whose lower end is grounded. Since an rf ammeter in the ground lead showed no current, he could dispense with the ground system and its loss. He suggested to the Capt. that he should discover the new world of half verticals with no ground system. Quoting from the text (p. 84): The correspondent's claim... is true ONLY IF HE IS CONTENT TO THROW AWAY FROM 40 TO 80 PER CENT OF HIS RADIATED POWER IN THE FORM OF EARTH LOSSES. (the correspondent) stated, 'The ZL's call ME, when I use my half wave vertical!' This is not surprising, in view of the fact that the half wave's vertical pattern has a lower main lobe angle than a quarter wave would have... However, he would hit the ZL's even harder if he would put in a ground system. Of course, the half wave vertical is not dependent on a ground plane, however lossy or efficient, for the condition of RESONANCE, since it is resonant in itself because of its half wave length. However, IT IS DEPENDENT ON A GROUND PLANE FOR ITS EFFICIENCY OF RADIATION, as is any vertical antenna...' Don k4kyv Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to 100% radiation efficiency. Dave WX7G And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals with radials. They are indistinguishable in performance and certainly do not exhibit substantial ground losses AFAIK... Rick N6RK I can think of NO earthly reason,that makes ANY electromagnetic sense to me, as antenna engineer fo placing a radial system under the end of a vertical 1/2 wave antenna - earth-worms not withstanding! It's CURRENT that warms the earthworms! NOT electric field intensity! ...the ground system does NOT act as a shield from the lossy earth nor protect the earth-worms! There is absolutely NO reason to require a radial system under a 1/2 wave vertical antenna. Such an antenna will operate just fine on its own in free-space. Consider this - to deliver 1000 watts to a 1/4 wave vertical with a REALLY GOOD ground system and a driving point impedance of say 40 ohms would require 5 amps of RF current delivered to the antenna system and ground. Todeliver that same 1000 watts to an end-fed vertical of 2000-4000 ohms real would require an antenna current, at the fed endof 0.5 -0.7 amps! It's the CURRENT that produces the losses in the lossy earth and warms the earth worms. At worst, for the 1/2 wave end fed vertical - a simple ground rodshould be just fine, and the earth worms should be quite comfortable, and the antenna will work VERY well!! Of course it will be 250-260 feet tall! Charlie,K4OTV ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Hi Don, Then, why do broadcast stations that use vertical towers at approximately a half wavelength, purchase valuable real estate and spend thousands of dollars for the copper to install from 120 to 240 or more radials, each usually a half wave or more in length? They almost always do not. First, they would be fools or have idiots for engineers to have more than 120 radials. The only real reason they use 90 radials or so is it sometimes gets them out of expensive proof-of-performance measurements. The exact FCC text is down the page here: http://www.w8ji.com/counterpoise_systems.htm Second, nearly all stations except the old clear channels on the low end use towers around 1/4 wave, often just around 0.2 WL. See G. H. Brown: Ground Systems as a Factor in Antenna Efficiency, IRE Proceedings, June 1937 p. 753. Brown demonstrated that the distribution of earth currents and ground losses is such that the region of maximum current and loss occurs at a distance of about 0.35 wavelengths from the base of a ground mounted half wave vertical antenna, which was verified experimentally. But the field is so weak at that point that there really isn't much to be gained when the radiator is 1/2 wave tall. Plus broadcast stations have a huge investment, and overkill is not an issue for them. That's why the transmitters are so conservative. There is zero loss at the base of the antenna itself, since there is no base current because the antenna a fed at a current node. An rf ammeter inserted in the ground lead, as well as one inserted in in the antenna lead attached to the insulated base of the radiator will read zero. That is absolutely wrong. A typical half-wave BC tower is in the several hundred ohm range because of tower thickness. They are almost never over 1000 ohms. Halfwave BC towers at exact resonance are typically about 1 ampere per kilowatt. There isn't an end-fed half wave in the world with infinite impedance and zero current, even the very thinnest lossless wire would not be zero. The ground losses occur farther out from the base of the antenna. Low effective earth resistance provided by a good ground system is ABSOLUTELY NECESSARY for vertical antennas of ANY height if one expects good radiation efficiency. The claim that no ground system is needed for a half wave vertical is nothing more than a long-standing popular misconception. Actually we do need a ground system, that much is correct, but requirements are much relaxed from very short antennas. With a half wave end fed wire element it is pretty tough to lose more than one or two dB in ground loss, but it certainly needs something there to allow it to be fed. It cannot be fed without some counterpoise. Thick towers are another matter. The surge impedance of the tower is so low that end impedance never gets all that high. This is why thick antennas are wide bandwidth, and why extreme power SWBC stations use thick cage elements. They do that to keep the impedance extremes, even at the open element end, down. This topic prompted me to dig out and review an anecdote I recall reading in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by USNR Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham who had made the discovery that he could tune and operate a half wave vertical without a ground system, feeding it by a parallel tuned tank circuit whose lower end is grounded. Since an rf ammeter in the ground lead showed no current, he could dispense with the ground system and its loss. He suggested to the Capt. that he should discover the new world of half verticals with no ground system. Current is not zero. It cannot be zero at the feedpoint of any end-fed antenna. That is an absolute practical and theoretical impossibility. It is a myth or a pretty gross misconception. While Captain Lee had a lot of good stuff, he was also over the top with some things. It is quite easy, with a thin vertical half-wave element, to get into the 80% efficiency range with a very minimal ground screen. People think of losses as current flow problems, but a significant portion of losses in a half wave ground independent vertical are electric field induced losses at the antenna base. The same would be true for a thin element and no radials, and just a ground rod or several ground rods. Thinner half wave verticals are pretty efficient with a minimal ground. When they get extremely thick the base current increases, and conduction losses can be a significant factor. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Charlie, your starting to sound like the other guy; trying to interpet my posts and spin to your benefit and getting demeaning in the process. Give me a bit more credit than that...OK... I know a bit about antennas. To be a bit more clear the tuner was always connected to a ground.. First to just an 8' rod and then the #6 copper ring around it with the 60 radials. Even the coax was ferrite decoupled as I was far ahead of the pack with their use having worked on the Tempest program as already mentioned. Carl KM1H - Original Message - From: Charlie Cunningham charlie-cunning...@nc.rr.com To: 'Carl' k...@jeremy.mv.com; 'Richard (Rick) Karlquist' rich...@karlquist.com; 'Donald Chester' k4...@hotmail.com; Tom W8JI w...@w8ji.com Cc: topband@contesting.com Sent: Sunday, December 16, 2012 12:06 PM Subject: RE: Topband: GAP Vertical Question Well, Carl Your experience with your 6-wire cage vertical - 1/4 wave on 80 - AND 1/2 wave on 40 was not very enlightening or satisfying and led to some serious misunderstanding!! When you removed the radials - OF COURSE it was a DUD on 40 -if you just left the coax feed in place!! You were trying to end-feed a 1/2 wave resonant antenna on 40m from coax - you must have a heck of a tuner, but the VSWR and mismatch loss were so high that you weren't delivering much of anything to the antenna!! Most of your power was being dissipated in heating the coax operating at very high VSWR!! You could have turned it into an excellent 40m antenna if you had end fed it through a 40m 1/4 wave open wire ladder line or fed it from the top end of a 40 m parallel tuned circuit (cold-end grounded, of course) tapped for a match to your 50 ohm coaxial feed line. If it still worked on 80 without the radials, there must have been a fortuitous length of coaxial shield to supply the missing lower 1/2 of the antenna! But you solved the problem without ANY understanding and put up 4 40m elements at 120 feet! The problem was NOT a GROUND PROBLEM - but was rather one of operator head-spacing! There must have been a hellacious VSWR on that COAX trying to feed that 1/2 wave vertical cage at the end with no radials. Your understanding of antennas, resonance, matching and grounding seems to leave a LOT to be desired! Perhaps some reading and study would help! Regards, Charlie, K4OTV P.S. A 1/2 wave vertical does NOT need a salt water marsh under it to work VERY well! In fact a vertical 1/2 wave in free space also works very well!! -Original Message- From: Charlie Cunningham [mailto:charlie-cunning...@nc.rr.com] Sent: Sunday, December 16, 2012 9:16 AM To: 'Carl'; 'Richard (Rick) Karlquist'; 'Donald Chester' Cc: 'topband@contesting.com' Subject: RE: Topband: GAP Vertical Question Good morning, Carl Well, a 1/4 wave vertical absolutely requires a ground plane!! A vertical 1/2 wave - not really! It seems that, in your observations, you are mixing the two? Any 1/4 wave vertical absolutely does need an image plane to work against! Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Carl Sent: Saturday, December 15, 2012 7:46 PM To: Richard (Rick) Karlquist; Donald Chester Cc: topband@contesting.com Subject: Re: Topband: GAP Vertical Question My own experience with 1/2 wave verticals is that they certainly do require a good ground. Maybe a rod in a saltwater marsh is sufficient but not in many other cases. Examples: A Shakespere CB whip in my 66 Corvette which was advervtised for fiberglass cars. It couldnt be heard a mile away with 4W. I added radials from the base on the rear deck to the frame on all 4 corners and then it worked much better. This was back in the late 70's for several years. A 80/40M 6 wire cage vertical, a full quarter wave on 80 and hanging from a tall pine tree branch at a prior QTH. With 60 65-70' radials it was competitive on 80 and on 40. With the radials removed it was a dud on 40. With another phased 1/4 wave on 80 it delivered the gain and F/B expected and 40 was improved with a pair of figure 8's but still not up to expectations. A 4el 40M KLM at 120' fixed that. Carl KM1H - Original Message - From: Richard (Rick) Karlquist rich...@karlquist.com To: Donald Chester k4...@hotmail.com Cc: topband@contesting.com Sent: Saturday, December 15, 2012 3:58 PM Subject: Re: Topband: GAP Vertical Question On 12/15/2012 12:03 PM, Donald Chester wrote: From: charlie-cunning...@nc.rr.com Could you support a vertical 1/2 wave for 160 with aballoon? You could end -feed it at the base through a 1/4 wave of 450 ohm But feeding a half wave vertical with the base near the ground still results in substantial ground losses without a radial system. Don k4kyv And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals
Re: Topband: GAP Vertical Question
I can think of NO earthly reason,that makes ANY electromagnetic sense to me, as antenna engineer fo placing a radial system under the end of a vertical 1/2 wave antenna - earth-worms not withstanding! ** Another case of not understanding the antenna or the purpose and handling of its current maximum. Some antenna engineer. Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to 100% radiation efficiency. Dave WX7G ** Its not the base that is the problem. The current has to be dealt with no matter where it is located on the vertical conductor or its electrical length. For want of a better word its image has to be a perfect conductor for the antenna system as a whole to be 100% efficient. It is also the current and its efficiency that determine the power radiated at the lowest angles. Excessive losses and that 10db becomes a simple glaring in your face reality. Carl KM1H - Original Message - From: Donald Chester k4...@hotmail.com To: topband@contesting.com Sent: Sunday, December 16, 2012 8:42 PM Subject: Re: Topband: GAP Vertical Question Then, why do broadcast stations that use vertical towers at approximately a half wavelength, purchase valuable real estate and spend thousands of dollars for the copper to install from 120 to 240 or more radials, each usually a half wave or more in length? See G. H. Brown: Ground Systems as a Factor in Antenna Efficiency, IRE Proceedings, June 1937 p. 753. Brown demonstrated that the distribution of earth currents and ground losses is such that the region of maximum current and loss occurs at a distance of about 0.35 wavelengths from the base of a ground mounted half wave vertical antenna, which was verified experimentally. There is zero loss at the base of the antenna itself, since there is no base current because the antenna a fed at a current node. An rf ammeter inserted in the ground lead, as well as one inserted in in the antenna lead attached to the insulated base of the radiator will read zero. The ground losses occur farther out from the base of the antenna. Low effective earth resistance provided by a good ground system is ABSOLUTELY NECESSARY for vertical antennas of ANY height if one expects good radiation efficiency. The claim that no ground system is needed for a half wave vertical is nothing more than a long-standing popular misconception. This topic prompted me to dig out and review an anecdote I recall reading in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by USNR Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham who had made the discovery that he could tune and operate a half wave vertical without a ground system, feeding it by a parallel tuned tank circuit whose lower end is grounded. Since an rf ammeter in the ground lead showed no current, he could dispense with the ground system and its loss. He suggested to the Capt. that he should discover the new world of half verticals with no ground system. Quoting from the text (p. 84): The correspondent's claim... is true ONLY IF HE IS CONTENT TO THROW AWAY FROM 40 TO 80 PER CENT OF HIS RADIATED POWER IN THE FORM OF EARTH LOSSES. (the correspondent) stated, 'The ZL's call ME, when I use my half wave vertical!' This is not surprising, in view of the fact that the half wave's vertical pattern has a lower main lobe angle than a quarter wave would have... However, he would hit the ZL's even harder if he would put in a ground system. Of course, the half wave vertical is not dependent on a ground plane, however lossy or efficient, for the condition of RESONANCE, since it is resonant in itself because of its half wave length. However, IT IS DEPENDENT ON A GROUND PLANE FOR ITS EFFICIENCY OF RADIATION, as is any vertical antenna...' Don k4kyv Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to 100% radiation efficiency. Dave WX7G And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals with radials. They are indistinguishable in performance and certainly do not exhibit substantial ground losses AFAIK... Rick N6RK I can think of NO earthly reason,that makes ANY electromagnetic sense to me, as antenna engineer fo placing a radial system under the end of a vertical 1/2 wave antenna - earth-worms not withstanding! It's CURRENT that warms the earthworms! NOT electric field intensity! ...the ground system does NOT act as a shield from the lossy earth nor protect the earth-worms! There is absolutely NO reason to require a radial system under a 1/2 wave vertical antenna. Such an antenna will operate just fine on its
Re: Topband: GAP Vertical Question
From: charlie-cunning...@nc.rr.com Could you support a vertical 1/2 wave for 160 with aballoon? You could end -feed it at the base through a 1/4 wave of 450 ohm ladder line and it would be a FEARSOME 160 antenna! And the whole radial issue goes away!! I've operated a vertical 1/2 wave for 40m this way with GREAT success!... Probably would be a great antenna as long as the bottom end is elevated well above ground, basically forming a vertically oriented end-fed zepp, something that might actually be feasible with balloon support if the winds are calm. But feeding a half wave vertical with the base near the ground still results in substantial ground losses without a radial system. True, it may be self-resonant and not depend on the ground plane to supply the missing half, but with the presence of lossy earth in the close vicinity of the radiating element, much of the rf power is wasted warming the earthworms, as the earth and its resistive loss provides the majority the return path of rf currents to the antenna base. Another way of looking at it is to think of the ground radial system as a highly conductive shield inserted between the lossy earth and the radiating antenna, carrying the return currents while by-passing most of the ground resistance in the return path. Don k4kyv ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
Don, a 36 helium balloon filled to 32 is enough to lift 130' of #26 wire in no wind. It doesn't take much wind to blow it horizontal. A half wave vertical suffers more as it is blown down so I think it's best to fly 130' at the most. Flying the balloon from a 40' or taller mast would allow the 130' vertical to become an inverted-L as the wind picks up. Mounted 100' out from the shore at the Salt Lake the ground loss is virtually zero. The water depth is 6 at that point. In the ARRL 160 meter 'test this year the balloon blew into a sharp bush and perished. That may be the last balloon I fly at the lake and a 50' base loaded vertical will take its place. Given that a half wave vertical has a base impedance of over 1000 ohms and a single ground rod in dirt is 100 ohms at most not a single radial is needed to obtain close to 100% radiation efficiency. Dave WX7G ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
On 12/15/2012 12:03 PM, Donald Chester wrote: From: charlie-cunning...@nc.rr.com Could you support a vertical 1/2 wave for 160 with aballoon? You could end -feed it at the base through a 1/4 wave of 450 ohm But feeding a half wave vertical with the base near the ground still results in substantial ground losses without a radial system. Don k4kyv And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals with radials. They are indistinguishable in performance and certainly do not exhibit substantial ground losses AFAIK. The PAR electronics 1/2 wave end fed antenna seems to have a good reputation, unlike some GAP verticals. However, I don't recommend feeding it through 1/4 wave of 450 ohm open wire line. I just use an LC matching network. Rick N6RK ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
But feeding a half wave vertical with the base near the ground still results in substantial ground losses without a radial system. Don k4kyv And this statement is based on what? Publications, measurements, modeling? I have built a number of 1/2 wave verticals without radials and compared them to 1/4 wave verticals with radials. They are indistinguishable in performance and certainly do not exhibit substantial ground losses AFAIK. The PAR electronics 1/2 wave end fed antenna seems to have a good reputation, unlike some GAP verticals. I know you already know this Rick, but everyone else should be reminded ***EVERY*** end fed antenna requires some type of ground system. In the PAR antenna, the coax shield is a counterpoise, just like in the end-fed Zepp the ladder line is a counterpoise that radiates. While some seem to have created a new physics that a simple single wire counterpoise can be non-radiating, there always has to be some fairly strong external induction field associated with end feeding an antenna. It can be predominately electric or magnetic, but rest assured there is a return path providing that second terminal for the feedpoint. The PAR antenna gets away with a sloppy feed system because most users run low power, and the shield of the coax becomes the counterpoise. In the real world loss can be all over the place depending on the exact system, including feedline length and grounding. While it is true that I^2 R feedpoint losses are not nearly as bad as a quarter wave Marconi, we exchange the strong current issues of a high current feed with high voltages and a strong electric field. This is why the end-fed Zepp, even in perfect construction form, has terrible local RFI issues even though feeder EM radiation is minimal. If you do a near field measurement of a perfect Zepp, the electric field intensity is off the charts around the feeder. If the feeder is the wrong grounding for common mode, the common mode current can be terrible and the electric field greatly drops. The feeder can radiate as much as the antenna, or more, with a simple ground change! This also applies to the PAR. Even with a half-wave, we have to have some common sense about what we do at the feedpoint and feedline. There are still displacement currents, and if we get rid of that pesky ground current we do that by trading for a pesky electric field. :-) There are enough well-spoken salesmen selling people magic, and they don't need our help. :-) 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: GAP Vertical Question
On 12/15/2012 5:13 PM, Charlie Cunningham wrote: Well, Rick, for me, the 450 ohm line was cheap, available and weatherproof! The trouble with the 450 ohm line is that you have a balanced line with an unbalanced load. You would like to put a balun or common-mode choke at the antenna end, but that is impractical. Thus the line will have substantial radiation and probably will warm the worms. Also, 450 ohm window line is NOT really weatherproof, as has been reported by reliable sources. Maybe you used true OWL which would be. Rick N6RK ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. Jim, Years ago someone purchased and had me measure a GAP vertical. The Gap was terrible on 160 and 80 meters. It was OK on most other bands. On 160 meters, although I have a pretty good mobile antenna, I had about the same field strength from my mobile antenna. The Gap was down about 10 dB from a 1/4 wave on 80 meters, as I recall. My mobile antenna is about 20 dB down from my 1/4 wave 160 meter vertical. The ARRL reviewed one Gap vertical in an on-the-air A-B test, and a small ground mounted trap vertical was equal or better. I'm sure you can search ARRL reviews and find this review. Also, the HF Verticals test by K7LXC and Ward Silver compared many verticals, and had about the same results on 80 meters as I found and the ARRL found. All of these completely independent tests were A-B tests against other reference verticals, and all pretty much agreed with each other. This doesn't mean you can't work DX with a Gap, because I can work VK, JA, and Europe on 160 with my mobile antenna. I've worked several Europeans on 160 SSB while driving down the highway. I can, at times, even beat others in pileups from the mobile on 80 meters. Obviously if the Gap is as good as a better mobile antenna, you can probably work a lot of DX with it. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
K7LXC book review was with the Titan. It was a poor performer against the Challenger, much less my other antennas IMHO of my testing between the two, Junk! de ns9i On 12/11/2012 5:13 PM, Tom W8JI wrote: So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. Jim, Years ago someone purchased and had me measure a GAP vertical. The Gap was terrible on 160 and 80 meters. It was OK on most other bands. On 160 meters, although I have a pretty good mobile antenna, I had about the same field strength from my mobile antenna. The Gap was down about 10 dB from a 1/4 wave on 80 meters, as I recall. My mobile antenna is about 20 dB down from my 1/4 wave 160 meter vertical. The ARRL reviewed one Gap vertical in an on-the-air A-B test, and a small ground mounted trap vertical was equal or better. I'm sure you can search ARRL reviews and find this review. Also, the HF Verticals test by K7LXC and Ward Silver compared many verticals, and had about the same results on 80 meters as I found and the ARRL found. All of these completely independent tests were A-B tests against other reference verticals, and all pretty much agreed with each other. This doesn't mean you can't work DX with a Gap, because I can work VK, JA, and Europe on 160 with my mobile antenna. I've worked several Europeans on 160 SSB while driving down the highway. I can, at times, even beat others in pileups from the mobile on 80 meters. Obviously if the Gap is as good as a better mobile antenna, you can probably work a lot of DX with it. 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
I have a Gap Titan. As the other people indicate it is not as good as a whole variety of other antennas. It is only good for 80 and up. I find that it works fairly well on 40 and 20M. Do I get stomped on in a pile-up - yes I do. Will I eventually make the contact - probably. At times my dipole on 40M does better, at other times it is the Gap Titan. However, I didn't buy this antenna to be the top of the pileup. I bought it to be maintenance free and a low hassle installation. It has been up for 10 years, and it has satisfied the goal of having an antenna in the air with very little maintenance. I make contacts when I want - I just wont be the first one to work the rare DX in a pileup. Scott aka kb0fhp -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of DGB Sent: Tuesday, December 11, 2012 6:27 PM To: topband@contesting.com Subject: Re: Topband: GAP VERTICAL QUESTION K7LXC book review was with the Titan. It was a poor performer against the Challenger, much less my other antennas IMHO of my testing between the two, Junk! de ns9i On 12/11/2012 5:13 PM, Tom W8JI wrote: So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. Jim, Years ago someone purchased and had me measure a GAP vertical. The Gap was terrible on 160 and 80 meters. It was OK on most other bands. On 160 meters, although I have a pretty good mobile antenna, I had about the same field strength from my mobile antenna. The Gap was down about 10 dB from a 1/4 wave on 80 meters, as I recall. My mobile antenna is about 20 dB down from my 1/4 wave 160 meter vertical. The ARRL reviewed one Gap vertical in an on-the-air A-B test, and a small ground mounted trap vertical was equal or better. I'm sure you can search ARRL reviews and find this review. Also, the HF Verticals test by K7LXC and Ward Silver compared many verticals, and had about the same results on 80 meters as I found and the ARRL found. All of these completely independent tests were A-B tests against other reference verticals, and all pretty much agreed with each other. This doesn't mean you can't work DX with a Gap, because I can work VK, JA, and Europe on 160 with my mobile antenna. I've worked several Europeans on 160 SSB while driving down the highway. I can, at times, even beat others in pileups from the mobile on 80 meters. Obviously if the Gap is as good as a better mobile antenna, you can probably work a lot of DX with it. 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
The GAP Voyager is not much better than a dummy load on 160m. On 80m and 40m it received fairly well compared to my other 80 and 40 antennas. Doug Original Message- With the prospect of downsizing and moving into senior housing in the future I am starting to look at vertical antennas that will allow me to continue this wonderful hobby. I have heard some good things about the GAP series of antennas but the company says they do not need radials on most of them and that worries me. Over the years I have become very skeptical about claims and the other BS put out by most companies ( maybe it is a function of age I dunno) so I wonder if these antennas really work. The two antennas that I am interested are the Voyager DX for 160/80/40 and the Eagle DX for the rest of the bands. So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. I sure hope this has not opend another can of worms.. some how I seem to do that .. private emails are ok..especially it the topic gets out of hand and we get a large volume of comments (Tree please dont shoot me before Christmas my wife will miss me.) Jim WA3MEJ Long Live Seal Team VI http://www.qsl.net/wa3mej/index.htm ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
I don't know about the Gaps, but a 43' vertical fed through a 4:1 unun works very well for me on 40-10 meters on a remote hilltop. On 80 and 160 I simply top load it with a long wire. When not in use the wire can either be wrapped around the antenna, or in the summers, removed. Yes there is minor signal loss (some would argue more than minor) due to swr in the feed line, but the unun transformer greatly reduces that, and in return you get some gain on most bands vs a 1/4 wl vertical. I don't use the unun on 80 and 160, but one could with non-resonant top loading. For low visibility at my home QTH in an antenna restricted neighborhood I use a 43' wire up a tree instead of a freestanding vertical… I also have a 23 foot wire which I use above 20 meters, and a longer inverted L for 160. Those three invisible antennas are imperfect but have managed to work almost every DX-pedition in the last 2 years. I believe that they can outperform any commercial vertical. KQ0C On Dec 11, 2012, at 5:47 PM, Doug Renwick ve...@sasktel.net wrote: The GAP Voyager is not much better than a dummy load on 160m. On 80m and 40m it received fairly well compared to my other 80 and 40 antennas. Doug Original Message- With the prospect of downsizing and moving into senior housing in the future I am starting to look at vertical antennas that will allow me to continue this wonderful hobby. I have heard some good things about the GAP series of antennas but the company says they do not need radials on most of them and that worries me. Over the years I have become very skeptical about claims and the other BS put out by most companies ( maybe it is a function of age I dunno) so I wonder if these antennas really work. The two antennas that I am interested are the Voyager DX for 160/80/40 and the Eagle DX for the rest of the bands. So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. I sure hope this has not opend another can of worms.. some how I seem to do that .. private emails are ok..especially it the topic gets out of hand and we get a large volume of comments (Tree please dont shoot me before Christmas my wife will miss me.) Jim WA3MEJ Long Live Seal Team VI http://www.qsl.net/wa3mej/index.htm ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
I had a GAP Voyager when I lived in Albuquerque. My subjective opinion was that it worked well on 80 and 40, was a dud on 20, and was very inefficient on 160, where I was lucky to work east of the Mississippi. 73, Jim N7US -Original Message- The GAP Voyager is not much better than a dummy load on 160m. On 80m and 40m it received fairly well compared to my other 80 and 40 antennas. Doug Original Message- With the prospect of downsizing and moving into senior housing in the future I am starting to look at vertical antennas that will allow me to continue this wonderful hobby. I have heard some good things about the GAP series of antennas but the company says they do not need radials on most of them and that worries me. Over the years I have become very skeptical about claims and the other BS put out by most companies ( maybe it is a function of age I dunno) so I wonder if these antennas really work. The two antennas that I am interested are the Voyager DX for 160/80/40 and the Eagle DX for the rest of the bands. So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. I sure hope this has not opend another can of worms.. some how I seem to do that .. private emails are ok..especially it the topic gets out of hand and we get a large volume of comments (Tree please dont shoot me before Christmas my wife will miss me.) Jim WA3MEJ ___ Topband reflector - topband@contesting.com
Re: Topband: GAP VERTICAL QUESTION
Your question is about the Gap antennae and I have no experience with them. After reading some of the replies you got back I thought I'd mention my antennae system which is both OK some what of a joke. I have a long coax leading to a good location for radials and I have a 5 position remote coax box which leads to a 130' inv-l, an 80M (mostly) vertical, a 40 30 vert and a beater of a butternut I use only for 20M. All the outer braid from the coax coming from the the coax box are grounded to the same radial plate. The 160 inv-L can be used on 160, 15, 12 and 10M with excellent results. The 80M works wonderful on 17M. The 40 also does 15 OK but I hear and get out better with the 160M antenna on 15M. nothing beats the 30M for 30 and the butternut is the only thing that loads up nicely for 20M. All my antennae and radials are 8 wire CAT cable I got off fleabay for around $100 for about a mile of wire. The Ameritron coax switch I've had for many years but it's probably $150. The coax is something you're going to get anyway. But the beauty is I don't need a tuner as the worst SWR is 2:1 and the K3 has an internal tuner for the barefoot times with a SS rig and the amplifier doesn't seem to mind a 2:1 SWR so the amp is no problem. With this el cheapo antenna system I was able to confirm ZL9HR on 17, 30, 40, 80 and 160 (small brag; one of the 185 total 160M QSOs they made!). All that to say, If you can get a few radials down, and some wire in the air (especially the 160 inv-L, you might could save some money over a commercial antenna and do surprisingly well. It won't beat the big dogs but it'll do just fine. Gary KA1J With the prospect of downsizing and moving into senior housing in the future I am starting to look at vertical antennas that will allow me to continue this wonderful hobby. I have heard some good things about the GAP series of antennas but the company says they do not need radials on most of them and that worries me. Over the years I have become very skeptical about claims and the other BS put out by most companies ( maybe it is a function of age I dunno) so I wonder if these antennas really work. The two antennas that I am interested are the Voyager DX for 160/80/40 and the Eagle DX for the rest of the bands. So my question is does anyone have actual experience with these antennas (especially the voyager) as compared to other antennas for a specific frequency. Now guys .. I know you cant really compare a 6 element beam to a vertical of this kind but I am talking about a comparison that is realistic.. like how does it hear, tune, match get out compared to something like another vertical or a dipole up some reasonable distance. I sure hope this has not opend another can of worms.. some how I seem to do that .. private emails are ok..especially it the topic gets out of hand and we get a large volume of comments (Tree please dont shoot me before Christmas my wife will miss me.) Jim WA3MEJ Long Live Seal Team VI http://www.qsl.net/wa3mej/index.htm ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
