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Velocity Factor of Coax
Hello all
What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard |
Velocity Factor of Coax
sorry I should mention the RG-59 is used for impedance matching not feed
line thanks again Howard "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard |
Velocity Factor of Coax
"Howard Kowall" wrote in message
... sorry I should mention the RG-59 is used for impedance matching not feed line thanks again Howard "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard It's principally the relative permittivity of the dielectric that determines the velocity factor. Air alone would yield a value of unity but the presence of a spacer of some sort means practical values are smaller. Foam can get close to air. I wonder why you need a Lindenblad for 2 metres - do you really need good circular polarisation over a range of elevation angles (and omni HRP, of course)? Chris |
Velocity Factor of Coax
On Feb 9, 3:26*pm, "Howard Kowall" wrote:
What determines the *Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters. The velocity of propagation (v.p.) in each branch of the feed harness won't affect the relative field radiation pattern of such an antenna array as long as the same electrical lengths of coax are used between the power divider outputs and the feedpoint of each element of the array. The v.p. of the main transmission line from the tx to the input of of the antenna power divider in this scenario is irrelevant. RF |
Velocity Factor of Coax
"Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard Hi Howard I am interested in reception of CP signals from all points within the upper hemisphere. I am curious about your purpose for this Lindenblad. Jerry KD6JDJ |
Velocity Factor of Coax
"Jerry" wrote in message ... "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard Hi Howard I am interested in reception of CP signals from all points within the upper hemisphere. I am curious about your purpose for this Lindenblad. Jerry KD6JDJ Ever tried crossed 'wilted' dipoles? Chris |
Velocity Factor of Coax
On Mon, 9 Feb 2009 15:30:50 -0600, "Howard Kowall"
wrote: sorry I should mention the RG-59 is used for impedance matching not feed line thanks again Howard "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 You might want to consider using RG-6/u instead of RG-59. These daze, the quality of RG-59 coax is rather marginal. I've seen 80% coverage shielding and cable unsuitable for outdoor use. Meanwhile, the CATV people have switched to RG-6/u for everything. Much of it is quad shielded and UV resistant. Velocity factor is usually 0.66 for solid dielectric and anywhere between 0.7 and 0.9 for various foam dielectric mixes. When you find a suitable piece of cable, grab the manufacturer and full part number. Then, lookup the VF on the mfg data sheet. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
Velocity Factor of Coax
hello all
thanks all who read and emailed back lot of good info came in and I have a good handle on it I am building this antenna for rhcp portable satellite antenna for LEO Ham Radio Sat thanks again Howard "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard |
Velocity Factor of Coax
I've found quite a variation in foamed dielectric cable velocity factor
from lot to lot of the same brand and type, even with major brands. Apparently they don't control the density of the dielectric very well. So if you're planning on using foamed dielectric cable in an application where VF is important, I highly recommend that you measure the VF of a sample from the same piece you'll be using. Roy Lewallen, W7EL |
Velocity Factor of Coax
"Howard Kowall" wrote in message ... hello all thanks all who read and emailed back lot of good info came in and I have a good handle on it I am building this antenna for rhcp portable satellite antenna for LEO Ham Radio Sat thanks again Howard "Howard Kowall" wrote in message ... Hello all What determines the Velocity Factor of a coax cable. Is it the center conductor awg,dielectric,shield or all combined I am building a Lindenblad Antenna for 2 Meters its asked to use RG-59 polyethylene foam coax with stranded center conductor I think the VF is .66 I cant find any stranded center cond where I am,so I want to try it with Solid,but it seems all the solid is VF .88 anyone have any input on this thanx howard Hi Howard The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ |
Velocity Factor of Coax
The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH |
Velocity Factor of Coax
"Roy Lewallen" wrote in message treetonline... I've found quite a variation in foamed dielectric cable velocity factor from lot to lot of the same brand and type, even with major brands. Apparently they don't control the density of the dielectric very well. So if you're planning on using foamed dielectric cable in an application where VF is important, I highly recommend that you measure the VF of a sample from the same piece you'll be using. Roy Lewallen, W7EL I second that Roy, Each time we start a new spool (same mfg) we have to remeasure the V.F.- RG-11U foam. I too believe it is the foam density that is not well controlled. Dale W4OP |
Velocity Factor of Coax
"Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ |
Velocity Factor of Coax
"Jerry" wrote in message
... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ .... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris |
Velocity Factor of Coax
"christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry |
Velocity Factor of Coax
You might want to consider using RG-6/u instead of RG-59. These daze,
the quality of RG-59 coax is rather marginal. I've seen 80% coverage Beware of the Aluminum foil and shields though. Once it gets wet there is no stopping the internal corrosion and will generate broadband noise under power. This includes both RG6 and 9913 and LMR types. They have been banned from all commercial sites around here. Bring a knife with you and inspect before you buy. Tinned Copper braid is better, Silver clad rigid is best. |
Velocity Factor of Coax
On Feb 10, 1:57*am, "Jerry" wrote:
"Harry H" wrote in message ... *The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. *Are you open to trying to build a DCA (which is an antenna that I developed)? * I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. * But, I sure am open to being corrected. *The Feb 2008 QST contains an article on the DCA antenna design concept. *It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. * * * * * * * * * * * *Jerry * KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH * Hi HH * It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. * It is simple. *It is two pairs of crossed dipoles. * Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. * All four dipoles are tilted 30 degtrees from vertical. * One pair is fed 90 degrees later than the other pair. * The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. * But, I have been unable to find anything published related to this simple "Double Cross Antenna" * I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. * Patrik publishes alot of what I send him related to the antenna. *Patrik shows a section of his web page to describe the DCA to anyone interested. * You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his sitehttp://www.poes-weather.com/index.php. * If you have any questions about the DCA concept you are free to E-mail me, anytime. * Or, if you have any facts or data to show where I am wrong about how well this antenna performs, *or know of something that performs better, please set me straight. * * * * * * * Jerry * *KD6JDJ Looked at the URL What this antenna is doing is to aproach equilibrium by taking into account the "weak force" which demands a tilting away from parallelism or the verticle position away from the surface of the earth, without which the radiation pattern will not be balanced. When a U.S.naval base tipped all its verticle antennas at an angle referenced to earth this prior null must have been of great inconvenience with respect to defense alertness. |
Velocity Factor of Coax
"Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris |
Velocity Factor of Coax
"Art Unwin" wrote in message ... On Feb 10, 1:57 am, "Jerry" wrote: "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his sitehttp://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ Looked at the URL What this antenna is doing is to aproach equilibrium by taking into account the "weak force" which demands a tilting away from parallelism or the verticle position away from the surface of the earth, without which the radiation pattern will not be balanced. When a U.S.naval base tipped all its verticle antennas at an angle referenced to earth this prior null must have been of great inconvenience with respect to defense alertness. - - - - A simpler explanation is that the tilt is there to provide a horizontally-polarised component in the radiated field around the antenna, as well as a vertically-polarised component, in order to achieve circular polarisation. The angle of tilt is a design parameter which, along with the radius of the centres of the dipoles and, in this case, the choice of how they are phased, collectively determine the axial ratio. The radiation patterns and match of such an antenna are not affected by its orientation with respect to the surface of the earth! Chris |
Velocity Factor of Coax
"christofire" wrote in message ... "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris Hi Chris I wonder if you have any pictures of a Lindenblad and any radiation plots. I also wonder if an end fire antenna is the same as a broadside antenna when they look the same from a distance. Jerry KD6JDJ |
Velocity Factor of Coax
"Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris Hi Chris I wonder if you have any pictures of a Lindenblad and any radiation plots. I also wonder if an end fire antenna is the same as a broadside antenna when they look the same from a distance. Jerry KD6JDJ You could take a look at www.bbc.co.uk/rd/pubs/reports/1991-15.pdf which on pages 9 and 10 has some details of a Lindenblad for 2.5 GHz, with patterns, that was made from semi-rigid coax and brass tube. The aim in that work was to achieve the best possible axial ratio in order to reject first-order reflections from the ground and nearby objects. If I remember correctly, phase rotation was tried but there really weren't enough variables to get the axial ratio good enough over the whole sphere, so the dipoles were driven in phase and the hole in the vertical radiation pattern at the bottom was 'embraced' as a good thing! In this application, if good axial ratio couldn't be achieved somewhere it was probably better to avoid radiating in that direction. Another Lindenblad, but also arrayed vertically in four tiers, was used at High Hunsley transmitting station for FM radio. The older photos at http://tx.mb21.co.uk/gallery/high-hunsley.php show it (at the top of the structure) but they are rather distant. The modern replacements are basically crossed dipoles in front of reflectors. A significant challenge in the design of these (big) things is to get the horizontal radiation pattern to hand over cleanly from one element to the next around the structure, without lobes or nulls in either the vertical or horizontal component. In UK Band II broadcasting, the polarisation is usually said to be 'mixed' rather than intentionally circular. The Alan Dick company http://www.alandick.com/broadcast_an...roduct_004.htm still offers a Lindenblad array for Band II. Their 'FMAC' looks interesting! As to your question, I'm not certain what you mean so perhaps you could amplify a bit. Certainly if the paths of currents, their relative amplitudes and their relative phases in time, appear the same from different directions then the polarisation should be the same in those directions. A short helix can operate as a broadside and end-fire antenna at the same time and I know the quadrifilar helix is a popular option for small L-Band satellite terminals. However, that radio-camera application imposed stringent demands for axial ratio and, obviously, the requirements for satisfactory reception of CP signals from satellites can be less demanding when CP is used simply to avoid loss on account of mismatched linear polarisations - when the other sense of CP isn't in use at the same frequency by the same satellite. Chris |
Velocity Factor of Coax
"christofire" wrote in message ... "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris Hi Chris I wonder if you have any pictures of a Lindenblad and any radiation plots. I also wonder if an end fire antenna is the same as a broadside antenna when they look the same from a distance. Jerry KD6JDJ You could take a look at www.bbc.co.uk/rd/pubs/reports/1991-15.pdf which on pages 9 and 10 has some details of a Lindenblad for 2.5 GHz, with patterns, that was made from semi-rigid coax and brass tube. The aim in that work was to achieve the best possible axial ratio in order to reject first-order reflections from the ground and nearby objects. If I remember correctly, phase rotation was tried but there really weren't enough variables to get the axial ratio good enough over the whole sphere, so the dipoles were driven in phase and the hole in the vertical radiation pattern at the bottom was 'embraced' as a good thing! In this application, if good axial ratio couldn't be achieved somewhere it was probably better to avoid radiating in that direction. Another Lindenblad, but also arrayed vertically in four tiers, was used at High Hunsley transmitting station for FM radio. The older photos at http://tx.mb21.co.uk/gallery/high-hunsley.php show it (at the top of the structure) but they are rather distant. The modern replacements are basically crossed dipoles in front of reflectors. A significant challenge in the design of these (big) things is to get the horizontal radiation pattern to hand over cleanly from one element to the next around the structure, without lobes or nulls in either the vertical or horizontal component. In UK Band II broadcasting, the polarisation is usually said to be 'mixed' rather than intentionally circular. The Alan Dick company http://www.alandick.com/broadcast_an...roduct_004.htm still offers a Lindenblad array for Band II. Their 'FMAC' looks interesting! As to your question, I'm not certain what you mean so perhaps you could amplify a bit. Certainly if the paths of currents, their relative amplitudes and their relative phases in time, appear the same from different directions then the polarisation should be the same in those directions. A short helix can operate as a broadside and end-fire antenna at the same time and I know the quadrifilar helix is a popular option for small L-Band satellite terminals. However, that radio-camera application imposed stringent demands for axial ratio and, obviously, the requirements for satisfactory reception of CP signals from satellites can be less demanding when CP is used simply to avoid loss on account of mismatched linear polarisations - when the other sense of CP isn't in use at the same frequency by the same satellite. Chris Hi Chris The Lindenblad antenna is fed to produce a null toward zenith. The Lindenblad antenna as defined by Brown and Woodward in the mid 1940s for TV transmission, has an omniazimuth radiation pattern. The DCA has no zenith null. If you consider an antenna with an overhead null to be the same as an antenna with no null to be the same, I have no expectation that you and I will agree. The DCA offers little advantage over a Quad Helix when radiation pattern is considered. The DCA is slightly more sensitive toward the horizon than the Quad Helix. .. The bandwidth of a DCA is far wider than a Quad helix. The DCA is very insensitive to dimensional errors when built by an amateur. The Quad Helix is extreemely demanding of prescission of construction. The original subject of this thread was related to building an antenna for reception of Low Earth Orbiting satellites. I figured the OP could appreciate knowing that a DCA will perform better than a Lindenblad and needs no series matching transformors. Jerry KD6JDJ |
Velocity Factor of Coax
On Tue, 10 Feb 2009 16:04:16 GMT, "JB" wrote:
You might want to consider using RG-6/u instead of RG-59. These daze, the quality of RG-59 coax is rather marginal. I've seen 80% coverage Beware of the Aluminum foil and shields though. Once it gets wet there is no stopping the internal corrosion and will generate broadband noise under power. This includes both RG6 and 9913 and LMR types. They have been banned from all commercial sites around here. Amazing. I can see it's possible to create a diode mixer junction with electrolytic action between the aluminum foil and copper braid. I've never seen broadband noise from coax cable. Usually the foil is mylar or polyester coated and the copper is tinned or silver plated to eliminate any points of contact. Most of the radio sites I've seen are stuffed LMR-400 and LMR-600. Heliax is better, but also far more expensive. Incidentally, if you want to generate RF noise and mixing, there's nothing better than an abraided Heliax outer jacket, with the copper shield touching the zinc galvanized tower. If intermod were really a problem with foil shielded coax, then the common residential CATV distribution system would have a big problem with intermod and mixes. While the buried coax is semi-rigid with a solid aluminum shield, the pole to house drops are usually quad shielded RG-6/u (sometimes with a messenger wire) with foil and braid shields. Bring a knife with you and inspect before you buy. Tinned Copper braid is better, Silver clad rigid is best. Mylar or polyester coated aluminum foil is more important. Scrape the insulation and see if it flakes loose from the foil. I've seen this on very old 9913 and some new LMR-400 of dubious origin. Slight change of topic.... do the commerical sties that ban foil shielded coax also ban nickel plated connectors? Just curious. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
Velocity Factor of Coax
In article ,
Jeff Liebermann wrote: Beware of the Aluminum foil and shields though. Once it gets wet there is no stopping the internal corrosion and will generate broadband noise under power. This includes both RG6 and 9913 and LMR types. They have been banned from all commercial sites around here. Amazing. I can see it's possible to create a diode mixer junction with electrolytic action between the aluminum foil and copper braid. I've never seen broadband noise from coax cable. Usually the foil is mylar or polyester coated and the copper is tinned or silver plated to eliminate any points of contact. Most of the radio sites I've seen are stuffed LMR-400 and LMR-600. Heliax is better, but also far more expensive. Incidentally, if you want to generate RF noise and mixing, there's nothing better than an abraided Heliax outer jacket, with the copper shield touching the zinc galvanized tower. If intermod were really a problem with foil shielded coax, then the common residential CATV distribution system would have a big problem with intermod and mixes. While the buried coax is semi-rigid with a solid aluminum shield, the pole to house drops are usually quad shielded RG-6/u (sometimes with a messenger wire) with foil and braid shields. I don't think those cases (commercial/repeater and CATV) are comparable. As I understand it (anecdotal report and discussions with other repeater owners/builders), the problem with LMR-400 and similar cables occurs when the cable is used in a duplex application, with RF transmit power and the incoming receive signal being carried on the same cable simultaneously. Under these conditions, it doesn't take very much broadband noise generation at all (from the cable, connectors, or nearby metal-on-metal contacts) to cause a problem. The transmitter might be pumping 50 volts RMS of power into the cable, while the receiver is trying to pick off a signal of less than a microvolt at a frequency only 600 kHz away. That's a rather critical environment which really can't tolerate more than a tiny percentage of noise generation in the cables, connectors, or duplexer. I don't think there's any problem with using these sorts of cables in commercial or amateur service in *simplex* applications... they can handle transmitting, or receiving, just fine. It's only when you try to do both, simultaneously, through the same cable. that the noise generation can become a problem. The same can be true of some classes of antenna problems. The repeater system I help maintain developed a serious desensitization problem, due to internal corrosion/oxidation which occurred in the antenna after several years up in the weather. I doubt that the corrosion/oxidation effect would ever have been noticed if the antenna were in service as a normal (simplex) base antenna - it didn't affect the transmit SWR or the receive sensitivity at all, I believe that CATV distribution is a rather easier situation for the cable to handle, since the signals being carried are all of a fairly similar and moderate power level. The downstream carrier levels delivered to the home seem to be around 1 millivolt... that's more than 60 dB higher than what a repeater's receiver has to be able to pick out when it's receiving a just-usable signal from the outer edge of its service area. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Velocity Factor of Coax
"Dave Platt" wrote in message
... In article , Jeff Liebermann wrote: Beware of the Aluminum foil and shields though. Once it gets wet there is no stopping the internal corrosion and will generate broadband noise under power. This includes both RG6 and 9913 and LMR types. They have been banned from all commercial sites around here. Amazing. I can see it's possible to create a diode mixer junction with electrolytic action between the aluminum foil and copper braid. I've never seen broadband noise from coax cable. Usually the foil is mylar or polyester coated and the copper is tinned or silver plated to eliminate any points of contact. Most of the radio sites I've seen are stuffed LMR-400 and LMR-600. Heliax is better, but also far more expensive. Incidentally, if you want to generate RF noise and mixing, there's nothing better than an abraided Heliax outer jacket, with the copper shield touching the zinc galvanized tower. If intermod were really a problem with foil shielded coax, then the common residential CATV distribution system would have a big problem with intermod and mixes. While the buried coax is semi-rigid with a solid aluminum shield, the pole to house drops are usually quad shielded RG-6/u (sometimes with a messenger wire) with foil and braid shields. I don't think those cases (commercial/repeater and CATV) are comparable. As I understand it (anecdotal report and discussions with other repeater owners/builders), the problem with LMR-400 and similar cables occurs when the cable is used in a duplex application, with RF transmit power and the incoming receive signal being carried on the same cable simultaneously. Under these conditions, it doesn't take very much broadband noise generation at all (from the cable, connectors, or nearby metal-on-metal contacts) to cause a problem. The transmitter might be pumping 50 volts RMS of power into the cable, while the receiver is trying to pick off a signal of less than a microvolt at a frequency only 600 kHz away. That's a rather critical environment which really can't tolerate more than a tiny percentage of noise generation in the cables, connectors, or duplexer. I don't think there's any problem with using these sorts of cables in commercial or amateur service in *simplex* applications... they can handle transmitting, or receiving, just fine. It's only when you try to do both, simultaneously, through the same cable. that the noise generation can become a problem. The same can be true of some classes of antenna problems. The repeater system I help maintain developed a serious desensitization problem, due to internal corrosion/oxidation which occurred in the antenna after several years up in the weather. I doubt that the corrosion/oxidation effect would ever have been noticed if the antenna were in service as a normal (simplex) base antenna - it didn't affect the transmit SWR or the receive sensitivity at all, I believe that CATV distribution is a rather easier situation for the cable to handle, since the signals being carried are all of a fairly similar and moderate power level. The downstream carrier levels delivered to the home seem to be around 1 millivolt... that's more than 60 dB higher than what a repeater's receiver has to be able to pick out when it's receiving a just-usable signal from the outer edge of its service area. You got it. Only hardline is authorized on the tower. Hardline doesn't have the problem because it doesn't have a braid to flex in the wind. Braid is less than satisfactory for RF Ground and lightning protection too. Copper ribbons and sheets are preferred for grounds, but regular large copper cable can be substituted in some cases. On a repeater system, corroded or old braided coax hoses your own receiver and others nearby on the tower or the next building with noise. Especially in the wind. You won't hear that on simplex because the receiver is muted when you transmit. I don't know if you have seen CATV hardline with a tank strapped to the utility pole. That keeps water out by pressurizing the hardline. CATV systems DO have problems with corrosion all the time. With all that cable though, the cost to get it up and running is enormous, and they would rather be complaint driven instead. They also use circulators so that the stuff people do in their house doesn't feed back into the system and screw all the other customers up. The 2m people, most business PLMR and the Cops don't get it so they complain about jammers so you get irate service calls. But you can't talk to them because if you talk technical, they cover their ears, scream LALA LALA!! accuse you of lying, and they won't pay for the cure anyway (remember, if you have to think about the answer, you're lying). We do use LMR and 9913 for cheap simplex ground level base station installs because it is cheaper and easier to route. Don't use it around your rotor though. The foil will tear up. |
LEO receiving antennas was Velocity Factor of Coax
Jerry wrote:
Hi Chris The Lindenblad antenna is fed to produce a null toward zenith. The Lindenblad antenna as defined by Brown and Woodward in the mid 1940s for TV transmission, has an omniazimuth radiation pattern. The DCA has no zenith null. If you consider an antenna with an overhead null to be the same as an antenna with no null to be the same, I have no expectation that you and I will agree. The DCA offers little advantage over a Quad Helix when radiation pattern is considered. The DCA is slightly more sensitive toward the horizon than the Quad Helix. . The bandwidth of a DCA is far wider than a Quad helix. The DCA is very insensitive to dimensional errors when built by an amateur. The Quad Helix is extreemely demanding of prescission of construction. The original subject of this thread was related to building an antenna for reception of Low Earth Orbiting satellites. I figured the OP could appreciate knowing that a DCA will perform better than a Lindenblad and needs no series matching transformors. Jerry KD6JDJ Just how good does this antenna have to be. It's not like it's being used as a probe to measure randomly polarized signals, where AR=1 is really important. Quad helix antennas have a reputation for being demanding, but that's where the performance requirements are demanding. Considering that quad helix antennas are made by the millions for GPS and by the thousands for WxSat use on boats, they aren't all that picky, because conventional mass production tolerances are "good enough". Relax the performance requirements and the helix is no more or less difficult than a turnstile or Lindenblad or CP patch. Before the advent of modern modeling tools, *designing* a quad helix was a huge chore, especially if you didn't want to use a quad hybrid in the feed network, but wanted to do the "one a bit long, one a bit short" to get the 90 degrees. But, returning to the original question, why not a turnstile (crossed dipoles fed 90 degrees out of phase)? For LEO satellites, you don't really want a hemispherical pattern anyway. You want something with more gain at the horizon where the slant range is much greater (thousands of km) than at zenith (where the range is hundreds of km). And, for that matter CP is probably not worth worrying about. The loss from a perfect CP to a perfect linear is 3dB. If you're in a situation where 3dB is going to kill you, you've got other problems to worry about. Where CP is really, really nice is when you want to kill multipath from close by reflectors. Or in deep space applications, where you don't know the linear orientation of the transmitter/receiver (and you also ARE worried about eke'ing out the last tenth or hundredth of a dB of performance) Jim, w6rmk |
Velocity Factor of Coax
In article ,
JB wrote: I don't know if you have seen CATV hardline with a tank strapped to the utility pole. That keeps water out by pressurizing the hardline. Shameful. Just *imagine* the effect of all that nitrogen leaking out into the atmosphere! What won't those cable guys try go get away with next? (grin) CATV systems DO have problems with corrosion all the time. With all that cable though, the cost to get it up and running is enormous, and they would rather be complaint driven instead. They also use circulators so that the stuff people do in their house doesn't feed back into the system and screw all the other customers up. The 2m people, most business PLMR and the Cops don't get it so they complain about jammers so you get irate service calls. But you can't talk to them because if you talk technical, they cover their ears, scream LALA LALA!! accuse you of lying, and they won't pay for the cure anyway (remember, if you have to think about the answer, you're lying). Heh. You haven't met the senior hardware guy (Scott N6NXI) on our 2M/220/440 repeater project. He's the staunchest opponent of using foil/braid cable on a repeater that you're ever likely to meet, and insisted on all of our stuff being done to solid commercial-grade standards (circulators, bandpass filters on the auxiliary radios, etc.). Most of the cables inside the rack are custom-cut/routed .25" heliax. It was a lot of work (and more money) but it has paid off in reliability. We've got 3 repeaters and their duplexers in a single rack, right next to one another, and no crosstalk or intermod or desense problems... and we share the site with a powerful paging-service transmitter and a bunch of public-service radio gear. We do use LMR and 9913 for cheap simplex ground level base station installs because it is cheaper and easier to route. Don't use it around your rotor though. The foil will tear up. Good point - thanks - I'll remember to use a braid-cable jumper when I put up a hexbeam later this year. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Velocity Factor of Coax
JB wrote:
I don't know if you have seen CATV hardline with a tank strapped to the utility pole. That keeps water out by pressurizing the hardline. CATV systems DO have problems with corrosion all the time. With all that cable though, the cost to get it up and running is enormous, and they would rather be complaint driven instead. They also use circulators so that the stuff people do in their house doesn't feed back into the system and screw all the other customers up. Ever open up a cable amp that has had leaky (water type leaky) coax dripping into it? Yikes, they usually keep working for a while, with all kinds of electrolyzing going on. It's a pretty sad sight. - 73 de Mike N3LI - |
LEO receiving antennas was Velocity Factor of Coax
"Jim Lux" wrote in message ... Jerry wrote: Hi Chris The Lindenblad antenna is fed to produce a null toward zenith. The Lindenblad antenna as defined by Brown and Woodward in the mid 1940s for TV transmission, has an omniazimuth radiation pattern. The DCA has no zenith null. If you consider an antenna with an overhead null to be the same as an antenna with no null to be the same, I have no expectation that you and I will agree. The DCA offers little advantage over a Quad Helix when radiation pattern is considered. The DCA is slightly more sensitive toward the horizon than the Quad Helix. . The bandwidth of a DCA is far wider than a Quad helix. The DCA is very insensitive to dimensional errors when built by an amateur. The Quad Helix is extreemely demanding of prescission of construction. The original subject of this thread was related to building an antenna for reception of Low Earth Orbiting satellites. I figured the OP could appreciate knowing that a DCA will perform better than a Lindenblad and needs no series matching transformors. Jerry KD6JDJ Just how good does this antenna have to be. It's not like it's being used as a probe to measure randomly polarized signals, where AR=1 is really important. Quad helix antennas have a reputation for being demanding, but that's where the performance requirements are demanding. Considering that quad helix antennas are made by the millions for GPS and by the thousands for WxSat use on boats, they aren't all that picky, because conventional mass production tolerances are "good enough". Relax the performance requirements and the helix is no more or less difficult than a turnstile or Lindenblad or CP patch. Before the advent of modern modeling tools, *designing* a quad helix was a huge chore, especially if you didn't want to use a quad hybrid in the feed network, but wanted to do the "one a bit long, one a bit short" to get the 90 degrees. But, returning to the original question, why not a turnstile (crossed dipoles fed 90 degrees out of phase)? For LEO satellites, you don't really want a hemispherical pattern anyway. You want something with more gain at the horizon where the slant range is much greater (thousands of km) than at zenith (where the range is hundreds of km). And, for that matter CP is probably not worth worrying about. The loss from a perfect CP to a perfect linear is 3dB. If you're in a situation where 3dB is going to kill you, you've got other problems to worry about. Where CP is really, really nice is when you want to kill multipath from close by reflectors. Or in deep space applications, where you don't know the linear orientation of the transmitter/receiver (and you also ARE worried about eke'ing out the last tenth or hundredth of a dB of performance) Jim, w6rmk Hi Jim It isnt clear to me that you read Howard Kowall's original post. He intends to build his own antenna to communicate with low earth orbiting satellites. I have information that will allow Howard to design and build his own antenna that performs better than the design he chose (Lindenblad). Do you disagree that a DCA will perform better than a Lindenblad? I have read many of your post and recognize that you are a smart guy with lots of information about antennas. Thats why I wonder why you'd write something as stupid as " And, for that matter CP is probably not worth worrying about". You know that 3dB *is* normally something to try to achieve while building an antenna. The reason you write that the circular polarization is minimally significant seems to be that you are attempting to minimize the value of the DCA. I wonder if you have any facts or data, measured or calculated, to demonstrate that you know of any antenna that performs better than a DCA for ground based reception from LEOs I agree with you that a Turnstile is a good antenna for LEO satellite communication from Earth. But, I also claim that a DCA will perform better than a Turnstile. Do you disagree? Can you tell me more about why you wrote "For LEO satellites, you don't really want a hemispherical pattern anyway. You want something with more gain at the horizon where the slant range is much greater (thousands of km) than at zenith (where the range is hundreds of km). That is precisely what I tried to address in the QST article. That is precisely why the DCA performs better than all others. Besides, the DCA is relatively easy to build , unlike the Quad helix. Again, do you know of any antenna design that performs better than a DCA for communication with LEOs from earth and doesnt require pointing? Jerry KD6JDJ |
Velocity Factor of Coax
The 2m people, most business PLMR and the Cops don't get it so they
complain about jammers so you get irate service calls. But you can't talk to them because if you talk technical, they cover their ears, scream LALA LALA!! accuse you of lying, and they won't pay for the cure anyway (remember, if you have to think about the answer, you're lying). Heh. You haven't met the senior hardware guy (Scott N6NXI) on our 2M/220/440 repeater project. He's the staunchest opponent of using foil/braid cable on a repeater that you're ever likely to meet, and insisted on all of our stuff being done to solid commercial-grade standards (circulators, bandpass filters on the auxiliary radios, etc.). Most of the cables inside the rack are custom-cut/routed .25" heliax. It was a lot of work (and more money) but it has paid off in reliability. We've got 3 repeaters and their duplexers in a single rack, right next to one another, and no crosstalk or intermod or desense problems... and we share the site with a powerful paging-service transmitter and a bunch of public-service radio gear. Say R56 and it usually covers everything that matters. Check this out. Use to take care of a bunch of UHF Micors he http://eecue.com/images_archive/eecu..._Antennas.html (no i didn't take the picture) |
Velocity Factor of Coax
"Michael Coslo" wrote in message
... JB wrote: I don't know if you have seen CATV hardline with a tank strapped to the utility pole. That keeps water out by pressurizing the hardline. CATV systems DO have problems with corrosion all the time. With all that cable though, the cost to get it up and running is enormous, and they would rather be complaint driven instead. They also use circulators so that the stuff people do in their house doesn't feed back into the system and screw all the other customers up. Ever open up a cable amp that has had leaky (water type leaky) coax dripping into it? Yikes, they usually keep working for a while, with all kinds of electrolyzing going on. It's a pretty sad sight. - 73 de Mike N3LI - I've seen boxes of them. I wish I had pictures of the Micor mobile that was parked in a supervisors car in the middle of a river for 3 days. The battery went dead making green slime. The only money they had in the budget was for repair, so we bid them to replace every board. The Mastr Exec had a Relay and worked fine after drying it out. Things like that are hard to explain. |
Velocity Factor of Coax
Say R56 and it usually covers everything that matters. Check this out.
Use to take care of a bunch of UHF Micors he http://eecue.com/images_archive/eecu..._Antennas.html (no i didn't take the picture) Much better photos he http://www.fybush.com/sites/2005/site-051216.html |
LEO receiving antennas was Velocity Factor of Coax
Jerry wrote:
Hi Jim It isnt clear to me that you read Howard Kowall's original post. He intends to build his own antenna to communicate with low earth orbiting satellites. I have information that will allow Howard to design and build his own antenna that performs better than the design he chose (Lindenblad). Do you disagree that a DCA will perform better than a Lindenblad? Nope.. haven't actually looked at it. BUT.. the thing I was pointing out is looking at the overall system design, (for which design complexity and tolerances are factors that need to be considered), it might not matter. I have read many of your post and recognize that you are a smart guy with lots of information about antennas. Thats why I wonder why you'd write something as stupid as " And, for that matter CP is probably not worth worrying about". You know that 3dB *is* normally something to try to achieve while building an antenna. Not if you've got plenty of link margin already, or if there's an easier way to get the margin (e.g. rather than get 3dB more on the antenna, shorten the feedline from 100 ft, etc.). Howard didn't say which 2m satellite he's looking to listen to, or what kind of receiver he's using. The reason you write that the circular polarization is minimally significant seems to be that you are attempting to minimize the value of the DCA. I wonder if you have any facts or data, measured or calculated, to demonstrate that you know of any antenna that performs better than a DCA for ground based reception from LEOs Nope, that's not what I said. What I said was that sometimes, striving for perfect axial ratio isn't worth it. A linear antenna will have 3dB loss against a perfect CP, and that's a worst case. It might well be that 3dB is ok (for receiving WESAT on 137 MHz, for instance, where they have pretty big EIRP, it wouldn't matter) I agree with you that a Turnstile is a good antenna for LEO satellite communication from Earth. But, I also claim that a DCA will perform better than a Turnstile. Do you disagree? No, I don't disagree or agree. Don't know how well a DCA does or doesn't do. Can you tell me more about why you wrote "For LEO satellites, you don't really want a hemispherical pattern anyway. You want something with more gain at the horizon where the slant range is much greater (thousands of km) than at zenith (where the range is hundreds of km). That is precisely what I tried to address in the QST article. That is precisely why the DCA performs better than all others. Besides, the DCA is relatively easy to build , unlike the Quad helix. My comment was general, on what sorts of patterns one might want for a satellite antenna in a fixed position to communicate with LEO. And, yes, your DCA is easy to build and probably non-critical in dimensions and tolerances (have you checked this? either by modeling or measurement?) But so is a turnstile or a turnstile with reflector or a Lindenblad or even a quad helix, depending on how much variability you're willing to tolerate I will readily concede that building a quad helix for VHF is a mechanical problem, compared to say, 1.5 GHz for GPS. It's going to be a physically large structure (about the size of two gallon paintcans stacked), but if you have a cookbook design (as in, buy X feet of aluminum rod or copper wire, wind it around a plastic trash can, etc.) I've built monofilar and quad helixes (and Lindenblads and turnstiles) using copper foil tape on plastic buckets, rolled up paper, and all sorts of things. Some work better than others, but mostly, it's mechanical issues that are important. The "RF performance" is pretty much the same for a given physical size. After all, for an "omni" sort of antenna close to the ground, there's lots of other factors that probably have a bigger effect. (which was where I started..) Again, do you know of any antenna design that performs better than a DCA for communication with LEOs from earth and doesnt require pointing? How does one define "better"? Is your article in QST posted somewhere? Got a NEC deck? (Can't get it from ARRL because it's too new). Or, heck, rough dimensions and angles, and I can build the NEC model. (googling KD6JDJ DCA doesn't turn up anything useful.) As you know, it's very challenging to get CP with good axial ratio in all directions (sort of an extension of the hairy ball theorem). For that matter, the axial ratio of the signal you're receiving may not be all that hot. Taking GPS as an example, the SVs have a spec that the axial ratio is no worse than 1.2dB within 14.3 degrees of boresight for L1, and 3.2 dB for L2. I couldn't find any convenient data on ham satellite antennas. I think AO51 uses some variant of a turnstile with separate ports for the two transmitters, so one is LHCP the other RHCP. I did find a rough link budget for AO51 (aka Echo) that shows path loss varying by about 8-9 dB from zenith to horizon. If we look at state of the art (at least in the 70s) for deep space exploration, the Low Gain Antenna on Galileo (CP for 2.3GHz) had an axial ratio of 2dB on boresight, and 11dB at 90 degrees off boresight. See Bill Imbriale's book at http://descanso.jpl.nasa.gov/Monogra...rce_external=0 (Volume 8) for more details and lots and lots of measurements. Jim |
LEO receiving antennas was Velocity Factor of Coax
"Jim Lux" wrote in message ... Jerry wrote: Hi Jim It isnt clear to me that you read Howard Kowall's original post. He intends to build his own antenna to communicate with low earth orbiting satellites. I have information that will allow Howard to design and build his own antenna that performs better than the design he chose (Lindenblad). Do you disagree that a DCA will perform better than a Lindenblad? Nope.. haven't actually looked at it. BUT.. the thing I was pointing out is looking at the overall system design, (for which design complexity and tolerances are factors that need to be considered), it might not matter. I have read many of your post and recognize that you are a smart guy with lots of information about antennas. Thats why I wonder why you'd write something as stupid as " And, for that matter CP is probably not worth worrying about". You know that 3dB *is* normally something to try to achieve while building an antenna. Not if you've got plenty of link margin already, or if there's an easier way to get the margin (e.g. rather than get 3dB more on the antenna, shorten the feedline from 100 ft, etc.). Howard didn't say which 2m satellite he's looking to listen to, or what kind of receiver he's using. The reason you write that the circular polarization is minimally significant seems to be that you are attempting to minimize the value of the DCA. I wonder if you have any facts or data, measured or calculated, to demonstrate that you know of any antenna that performs better than a DCA for ground based reception from LEOs Nope, that's not what I said. What I said was that sometimes, striving for perfect axial ratio isn't worth it. A linear antenna will have 3dB loss against a perfect CP, and that's a worst case. It might well be that 3dB is ok (for receiving WESAT on 137 MHz, for instance, where they have pretty big EIRP, it wouldn't matter) I agree with you that a Turnstile is a good antenna for LEO satellite communication from Earth. But, I also claim that a DCA will perform better than a Turnstile. Do you disagree? No, I don't disagree or agree. Don't know how well a DCA does or doesn't do. Can you tell me more about why you wrote "For LEO satellites, you don't really want a hemispherical pattern anyway. You want something with more gain at the horizon where the slant range is much greater (thousands of km) than at zenith (where the range is hundreds of km). That is precisely what I tried to address in the QST article. That is precisely why the DCA performs better than all others. Besides, the DCA is relatively easy to build , unlike the Quad helix. My comment was general, on what sorts of patterns one might want for a satellite antenna in a fixed position to communicate with LEO. And, yes, your DCA is easy to build and probably non-critical in dimensions and tolerances (have you checked this? either by modeling or measurement?) But so is a turnstile or a turnstile with reflector or a Lindenblad or even a quad helix, depending on how much variability you're willing to tolerate I will readily concede that building a quad helix for VHF is a mechanical problem, compared to say, 1.5 GHz for GPS. It's going to be a physically large structure (about the size of two gallon paintcans stacked), but if you have a cookbook design (as in, buy X feet of aluminum rod or copper wire, wind it around a plastic trash can, etc.) I've built monofilar and quad helixes (and Lindenblads and turnstiles) using copper foil tape on plastic buckets, rolled up paper, and all sorts of things. Some work better than others, but mostly, it's mechanical issues that are important. The "RF performance" is pretty much the same for a given physical size. After all, for an "omni" sort of antenna close to the ground, there's lots of other factors that probably have a bigger effect. (which was where I started..) Again, do you know of any antenna design that performs better than a DCA for communication with LEOs from earth and doesnt require pointing? How does one define "better"? Is your article in QST posted somewhere? Got a NEC deck? (Can't get it from ARRL because it's too new). Or, heck, rough dimensions and angles, and I can build the NEC model. (googling KD6JDJ DCA doesn't turn up anything useful.) As you know, it's very challenging to get CP with good axial ratio in all directions (sort of an extension of the hairy ball theorem). For that matter, the axial ratio of the signal you're receiving may not be all that hot. Taking GPS as an example, the SVs have a spec that the axial ratio is no worse than 1.2dB within 14.3 degrees of boresight for L1, and 3.2 dB for L2. I couldn't find any convenient data on ham satellite antennas. I think AO51 uses some variant of a turnstile with separate ports for the two transmitters, so one is LHCP the other RHCP. I did find a rough link budget for AO51 (aka Echo) that shows path loss varying by about 8-9 dB from zenith to horizon. If we look at state of the art (at least in the 70s) for deep space exploration, the Low Gain Antenna on Galileo (CP for 2.3GHz) had an axial ratio of 2dB on boresight, and 11dB at 90 degrees off boresight. See Bill Imbriale's book at http://descanso.jpl.nasa.gov/Monogra...rce_external=0 (Volume 8) for more details and lots and lots of measurements. Jim Hi Jim I wont interlace my reply so that it might be easier for us to read. You wrote that "it might not matter that a DCA performs better than a Lindenblad" Well it does perform better for contact with a LEO satellite and I'd expect that be enough to make the DCA worth considering. Maybe I am missing something. Why would you *not* try making DCA for LEOs?? What (exactly is your point in writing about eliminating line loss when the discussion is antenna sensitivity??? Why is it pertinent what LEO he is interested in or what receiver he uses??? He asked about coax for an antenna harness. I thought I was helping Howard when I pointed him toward the DCA. Jim, if you dont need the DCA design concept there is no need for you to consider it. But, please dont diminish the value of the DCA for LEO use unless you have facts or data to show where I'm wrong about how well the DCA performs. Jim, are you writing that antenna sensitivity "doesnt matter" when receiving NOAA weather satellite signals at 137-138 MHz? If so you are completely wrong. Oh, you personally may have no interest in reception from the NOAA satellites (APT) as low elevations. but, when recording images of the Earth from NOAA satellites (APT) there is *no* antenna that performs better than a DCA. And, that extra sensitivity using the DCA is highly desired by most APT imagers. Yes, I have made lots of measurements of the DCA. I made my own slotted line so I could know the antenna's impedance. I have hundreds of actual (measured) radiation patterns. I have plenty of EZNEC models of the DCA. As I posted earlier, Patrik Tast posts lots of fundamental design information on his Web Site http://www.poes-weather.com/index.php . Clearly, I am proud of the results I have realized with this DCA antenna design project, so I'm always happy to share it with anyone interested. Anyone interested in the DCA has always received answers to any/all questions sent to me. I define better performance as greater sensitivity to signals from LEO satellites. But, the DCA has a much wider impedance match than a Quad Helix. I was pleasantly surprised that the axial ratio of the DCA radiation is exceptionally good at most angles. EZNEC gives good prediction of AR at all angles. Patrik Tast's Signal Plotter records the antenna sensitivity at 1 second intervals while the NOAA satellite is above the horizon. As I remember, you acknowledged that I have developed a method of recording actual radiation patterns using the program Patrik developed for me (SignalPlotter). I submit to you that, if you ever have need to develop a hemispheric coverage antenna for CP signals, you could benefit from learning about the DCA. It works. Jerry KD6JDJ (who sincerely wants to know facts about the flaws in the DCA design) |
Velocity Factor of Coax
"Dave Platt" wrote in message ... snip I don't think there's any problem with using these sorts of cables in commercial or amateur service in *simplex* applications... they can handle transmitting, or receiving, just fine. It's only when you try to do both, simultaneously, through the same cable. that the noise generation can become a problem. The same can be true of some classes of antenna problems. The repeater system I help maintain developed a serious desensitization problem, due to internal corrosion/oxidation which occurred in the antenna after several years up in the weather. I doubt that the corrosion/oxidation effect would ever have been noticed if the antenna were in service as a normal (simplex) base antenna - it didn't affect the transmit SWR or the receive sensitivity at all, All metallic contacts are potential problems. For years I did Navy electronics, including a couple hundred EMI inspections. Where "topside housekeeping" was neglected, broadband noise (BBN) was sure to be a problem. (All topside metallic objects need to be either insulated or firmly connected -- no incidental contact.) As little as a hundred watts would excite some junctions to generate BBN that could be detected throughout the HF band on other antennas. More power would generate BBN up to several hundred MHz. Been there. |
Velocity Factor of Coax
All metallic contacts are potential problems. For years I did Navy electronics, including a couple hundred EMI inspections. Where "topside housekeeping" was neglected, broadband noise (BBN) was sure to be a problem. (All topside metallic objects need to be either insulated or firmly connected -- no incidental contact.) As little as a hundred watts would excite some junctions to generate BBN that could be detected throughout the HF band on other antennas. More power would generate BBN up to several hundred MHz. Been there. Great point! My worst problem was my TV antenna mast, 20' away from my Butternut. Actually generated TVI until I replaced it all, including all brackets and hardware. Most of my neighbors TV antenna systems look far worse for wear. I have offered free labor to replace for surrounding neighbors and was taken up on it by one who had never seen so many stations before. It seems to be something that people don't do right anymore because no one will pay for it. |
Velocity Factor of Coax
On Tue, 10 Feb 2009 07:57:28 GMT, "Jerry"
wrote: "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ I would be interested in seeing what NEC would make of one of these. |
Velocity Factor of Coax
On Tue, 10 Feb 2009 18:12:26 -0000, "christofire"
wrote: "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to E-mail me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris Interesting article, it describes the Lindenblat array as a quartet of coaxial horns. Not the same as a quartet of dipoles at all. |
Velocity Factor of Coax
"JosephKK" wrote in message ... On Tue, 10 Feb 2009 18:12:26 -0000, "christofire" wrote: "Jerry" wrote in message ... "christofire" wrote in message ... "Jerry" wrote in message ... "Harry H" wrote in message ... The Lindenblad has an overhead null that you might find anoying for some high elevation passes of LEOs. Are you open to trying to build a DCA (which is an antenna that I developed)? I make the claim that there is no other hemispheric coverage antenna design that performs better than a DCA. But, I sure am open to being corrected. The Feb 2008 QST contains an article on the DCA antenna design concept. It is my claim that a DCA is extreemely forgiving of construction errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type ferrites as "baluns'. Jerry KD6JDJ Given the fact I don't subscribe to QST, domicile Australia, would you have a copy of the article? HH Hi HH It would be my pleasure to disclose any/all the information I have relating to the DCA antenna design concept. It is simple. It is two pairs of crossed dipoles. Each pair is spaced 1/4 wave apart and fed in phase. One pair is physically mounted 90 degrees from the other pair. All four dipoles are tilted 30 degtrees from vertical. One pair is fed 90 degrees later than the other pair. The concept is so simple and straightfoeward that it is probable that the concept has been developed before I thought of it. But, I have been unable to find anything published related to this simple "Double Cross Antenna" I told my *Internet buddy*, Patrik Tast, in Finland about the concept and he found it to be exactly what he needed for reception of NOAA weather satellite signals. Patrik publishes alot of what I send him related to the antenna. Patrik shows a section of his web page to describe the DCA to anyone interested. You can find the QST article in the section Patrik identifies as ANTENNAS on the first page of his site http://www.poes-weather.com/index.php. If you have any questions about the DCA concept you are free to me, anytime. Or, if you have any facts or data to show where I am wrong about how well this antenna performs, or know of something that performs better, please set me straight. Jerry KD6JDJ ... but surely this is the same as a Lindenblad array? The tilt of the dipoles was always a parameter in the Lindenblad, so I wonder how your DCA differs from what N. E. Lindenblad described in the April 1941 edition of 'Communications'. Chris Hi Chris Several, well educated, antenna experts insist that the DCA is actually a Lindenblad. If you thought the DCA is a Lindenblad, you are not alone. The DCA is not a Lindenblad. The array of four dipoles in a Lindenblad are fed to produce an overhead null. The four dipoles in a DCA are fed to produce no overhead null. The DCA is a hemispheric coverage CP antenna. The Lindenblad is not. Let me know if you have reason to consider the DCA to be the same as a Lindenblad. I knew nothing about Lindenblad until after recognizing the DCA concept. Jerry m KD6JDJ Jerry Perhaps it's a rather fine distinction to say an antenna that has the same physical form as the Lindenblad array is something different because the elements are driven differently. The original version that he patented didn't have rod elements at all (see, for example, http://www.coe.montana.edu/ee/rwolff...B_antennas.pdf ) but it was the configuration of four slanted dipoles around a central pole that appears to have borne his name since 1941. Henry Jasik's 'Antenna Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad array, without being specific about the way the dipoles are driven. However, applying new names to antennas that exploit well known configurations seems fairly commonplace in the professional field, particularly in broadcasting. Of course you can name your antenna as you please, but there might be some value in mentioning that it is a development of the Lindenblad array - you'd certainly need to demonstrate awareness of, and distinction from, the prior art if you were to seek a patent. Chris Interesting article, it describes the Lindenblat array as a quartet of coaxial horns. Not the same as a quartet of dipoles at all. Hi Joseph I sent an E-mail to the address shown as yours in this group. I use EZNEC and have lots of files on various sizes and shapes of the DCA and other OmniAzimuth and Hemispheric coverage antennas. I'd be happy to share them with you if you E-mail me directly. I figure it will benefit me to see the facts and data that shows where I am mistaken about how the DCA better than the other hemispheric coverage antennas for LEO use. It is likely that I have overlooked something. maybe the DCA can be improved. Jerry KD6JDJ Jerry KD6JDJ |
Velocity Factor of Coax
On Mon, 16 Feb 2009 18:49:47 GMT, "Jerry"
wrote: "JosephKK" wrote in message .. . On Tue, 10 Feb 2009 18:12:26 -0000, "christofire" wrote: "Jerry" wrote in message ... snip Chris Interesting article, it describes the Lindenblat array as a quartet of coaxial horns. Not the same as a quartet of dipoles at all. Hi Joseph I sent an E-mail to the address shown as yours in this group. I use EZNEC and have lots of files on various sizes and shapes of the DCA and other OmniAzimuth and Hemispheric coverage antennas. I'd be happy to share them with you if you E-mail me directly. I figure it will benefit me to see the facts and data that shows where I am mistaken about how the DCA better than the other hemispheric coverage antennas for LEO use. It is likely that I have overlooked something. maybe the DCA can be improved. Jerry KD6JDJ Jerry KD6JDJ I can retrieve the email. Thanks for the notice. I have done a bit of gedanken after the slant range issue was raised. A B o H ooo ooooo Let the group of "o" represent a polar view of earth, "A" represent satellite at azimuth (highest point in the sky), "B" represent satellite between azimuth and horizon, "Z" represent satellite very near the horizon, nominal orbital height 1000 miles above mean surface, and mean radius of earth of 4000 miles. Then range to the satellite at A is about 1000 miles, at B may be about 3000 miles and at H would be about 5000 miles. The arithmetic for relative sensitivity versus elevation angle can even be solved analytically, though 4 evenly spaced angles on either side of azimuth would be quite sufficient to plot the most even EIRP curves. Your DCA is notably more hemispherical than that. Can you tinker it up to get about 16 dB more at the horizon than at the azimuth? |
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