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All Band Coax-fed Dipole ??????????
The BuxComm Antenna Company sells what it calls an All Band Coax-fed
Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. |
All Band Coax-fed Dipole ??????????
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All Band Coax-fed Dipole ??????????
I get product not found!!
Is the URL complete? wrote: The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. |
All Band Coax-fed Dipole ??????????
On Sat, 24 Jun 2006 22:19:43 -0400, Dave wrote:
I get product not found!! It is probably one of those clever bits of web technology that use dynamic URLs so that they can't be passed on or linked (probably to frustrate discussion like this)! Search for 8010ABD100 on their home page. Owen Is the URL complete? wrote: The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. -- |
All Band Coax-fed Dipole ??????????
Owen Duffy wrote:
Search for 8010ABD100 on their home page. It says "ready to connect to *your* coax", "RG8X not included)" It's not their fault if *your* coax is lossy. :-) Wonder what kind of balun that is? -- 73, Cecil http://www.qsl.net/w5dxp |
All Band Coax-fed Dipole ??????????
the loss is unacceptable in my opinion. the lobes off the antenna are
unpredictable. an all band antenna like that is just to get on the air. i have met Mr. Rogers several times. Gravity |
All Band Coax-fed Dipole ??????????
"gravity" wrote in message
reenews.net... the loss is unacceptable in my opinion. the lobes off the antenna are unpredictable. an all band antenna like that is just to get on the air. i have met Mr. Rogers several times. Gravity The antenna pattern is highly predictable using modeling software. The transmission line losses are probably not as high as Owen predicts since we do not know the value of the attenuator inside the balun. I have seen at least three antennas that had attenuators in antenna matching networks in order to meet wideband VISOR requirements. These included a 25 ft marine whip, and a military vehicular antenna. All you need is a 3 dB pad for 3:1 VISOR. Giving a power rating to a dipole is suspicious also; although voltage breakdown may be a factor. Note that it is rated at 400 WE "ROMS" -- whatever the heck that is supposed to mean. Regards, Frank |
All Band Coax-fed Dipole ??????????
Sorry I must have clicked spell check for VSWR not "VISOR"! Also
"W" for "WE" and "RMS" for "ROMS". Frank "Frank" wrote in message news:pWxng.91970$S61.1023@edtnps90... "gravity" wrote in message reenews.net... the loss is unacceptable in my opinion. the lobes off the antenna are unpredictable. an all band antenna like that is just to get on the air. i have met Mr. Rogers several times. Gravity The antenna pattern is highly predictable using modeling software. The transmission line losses are probably not as high as Owen predicts since we do not know the value of the attenuator inside the balun. I have seen at least three antennas that had attenuators in antenna matching networks in order to meet wideband VISOR requirements. These included a 25 ft marine whip, and a military vehicular antenna. All you need is a 3 dB pad for 3:1 VISOR. Giving a power rating to a dipole is suspicious also; although voltage breakdown may be a factor. Note that it is rated at 400 WE "ROMS" -- whatever the heck that is supposed to mean. Regards, Frank |
All Band Coax-fed Dipole ??????????
The antenna pattern is highly predictable using modeling software.
he would have to model the antenna, then figure out what beam headings he desires, then find supports for the antenna. this is IMPOSSIBLE on most sububan lots. The transmission line losses are probably not as high as Owen predicts since we do not know the value of the attenuator inside the balun. he might as well use a dummy load. Gravity |
All Band Coax-fed Dipole ??????????
The antenna pattern is highly predictable using modeling software.
oh it's predictable all right, however it's often USELESS. it's a compromise antenna relative to decent dipoles. Gravity |
All Band Coax-fed Dipole ??????????
PHP!
http://www.commparts.com/catalog/ima...ts/8010ABD.gif i'm too lazy to provide more links. Gravity |
All Band Coax-fed Dipole ??????????
These included
a 25 ft marine whip, and a military vehicular antenna. All you need is a 3 dB pad for 3:1 VISOR. you can burn up 6 dB in an antenuator and RG 58. and that's if the SWR is 1 to 1. if someone has interest in 28 mhz, just put up a rotatable dipole too. Gravity |
All Band Coax-fed Dipole ??????????
Giving a power rating to a dipole is suspicious also; although voltage
breakdown may be a factor. Note that it is rated at 400 WE "ROMS" -- whatever the heck that is supposed to mean. 400 w RMS. 750 w peak. Gravity |
All Band Coax-fed Dipole ??????????
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All Band Coax-fed Dipole ??????????
"Frank" wrote in message news:uZxng.91997$S61.76029@edtnps90... Sorry I must have clicked spell check for VSWR not "VISOR"! Also "W" for "WE" and "RMS" for "ROMS". i googled VISOR thinking it was some cool military antenna. Gravity |
All Band Coax-fed Dipole ??????????
Frank, in the absence of information on the balun, I did model it as
ideal, and that the load at the load end of the coax was 4200 ohms. That is probably a reasonable assumption. i dunno it's a 1:1 Balun. i might email them, cause threads like this are pure profit for them. Gravity |
All Band Coax-fed Dipole ??????????
On Sun, 25 Jun 2006 15:26:13 GMT, "Frank"
wrote: The antenna pattern is highly predictable using modeling software. The transmission line losses are probably not as high as Owen predicts since we do not know the value of the attenuator inside the balun. That implies there is an attenuator inside the balun. I don't believe we actually have any information with which to better understand the balun. Frank, in the absence of information on the balun, I did model it as ideal, and that the load at the load end of the coax was 4200 ohms. That is probably a reasonable assumption. A real balun would not perfectly isolate the transmission line from drive so influencing feed point impedance , and would probably transform the real feed point impedance to something different to 4200 ohms, and so the line losses could be different (better or worse). If the balun was built with substantial loss, it would tend to reduce line losses, and yes, 3dB of loss (which would affect performance on all bands), would improve the performance on 7MHz (though that balun doesn't look like it contains a 200W dissipater). All in all, the configuration, although used widely, can be expected to perform poorly. IMHO was right in being suspicious of the product claims. Owen -- |
All Band Coax-fed Dipole ??????????
On Sat, 24 Jun 2006 22:19:43 -0400, Dave wrote:
I get product not found!! Is the URL complete? Googling indicates that several domains are directed to this eCommerce website, including jeanshobbies.com, amateurradio.org, buxomm.com, commparts.com, packetradio.com. Did someone say this guy is an Elmer? Looks like he runs a business with a lot of front doors. Owen -- |
All Band Coax-fed Dipole ??????????
"Owen Duffy" wrote in message
... On Sun, 25 Jun 2006 15:26:13 GMT, "Frank" wrote: The antenna pattern is highly predictable using modeling software. The transmission line losses are probably not as high as Owen predicts since we do not know the value of the attenuator inside the balun. That implies there is an attenuator inside the balun. I don't believe we actually have any information with which to better understand the balun. Frank, in the absence of information on the balun, I did model it as ideal, and that the load at the load end of the coax was 4200 ohms. That is probably a reasonable assumption. A real balun would not perfectly isolate the transmission line from drive so influencing feed point impedance , and would probably transform the real feed point impedance to something different to 4200 ohms, and so the line losses could be different (better or worse). If the balun was built with substantial loss, it would tend to reduce line losses, and yes, 3dB of loss (which would affect performance on all bands), would improve the performance on 7MHz (though that balun doesn't look like it contains a 200W dissipater). All in all, the configuration, although used widely, can be expected to perform poorly. IMHO was right in being suspicious of the product claims. Owen I am inclined to agree with you Owen. I was being a little facetious about the load. I also noticed there is not a single specification on the web site, except for power ratings. (Including the irritating term "RMS power"). Incidentally 750 W into 4200 ohms represents 2.5 kV peak. If the balun is a real transformer it must be well insulated. Frank |
All Band Coax-fed Dipole ??????????
"Owen Duffy" wrote in message ... On Sat, 24 Jun 2006 22:19:43 -0400, Dave wrote: I get product not found!! Is the URL complete? Googling indicates that several domains are directed to this eCommerce website, including jeanshobbies.com, amateurradio.org, buxomm.com, commparts.com, packetradio.com. Did someone say this guy is an Elmer? Looks like he runs a business with a lot of front doors. it appears that buxcomm is owned or operated by K4ABT. i have talked to him several times. he has a lot of history in the ham community. Gravity |
All Band Coax-fed Dipole ??????????
I get product not found!!
Is the URL complete? it uses PHP and a link won't work. Gravity |
All Band Coax-fed Dipole ??????????
On Mon, 26 Jun 2006 00:08:48 GMT, Owen Duffy wrote:
Did someone say this guy is an Elmer? Looks like he runs a business with a lot of front doors. Hi Owen, Buck wrote a column in CQ magazine for awhile a few years back and abruptly left. Don't know the reason, but I did read some of his writings and some were just plain nonsense. For example he advised his readers that they needed to tune their transmission line if they wanted the antenna to work properly. After a few like that I just stopped reading his stuff. By the looks of his antenna advertisements I made the right decision. 73, Danny, K6MHE |
All Band Coax-fed Dipole ??????????
On Mon, 26 Jun 2006 00:49:09 GMT, "Frank's"
wrote: "RMS power"). Incidentally 750 W into 4200 ohms represents 2.5 kV peak. If the balun is a real transformer it must be well insulated. .... and if it is a "voltage balun", a much higher flux level (~1300%) than it would at 50 ohms. Considering the information given in the product data, it leaves one with doubts about the suitability of the recommended coax and the supplied balun, and the performance of the entire system. Owen -- |
All Band Coax-fed Dipole ??????????
wrote:
The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. My opinion would be that you'd be much better off if you want a single wire antenna fed with coax going with one of the off center fed models. the SWR is much better on many bands than the center fed model. But if you must have a center fed model then you'll need to feed it with open wire line of some sort .. coax just is not going to perform well for you in a single wire all band dublet. the Losses on most bands are not good. 73 Dave kc1di |
All Band Coax-fed Dipole ??????????
wrote: The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. A true coax fed "dipole" needs to see a 50 ohm load on any of the bands to be used. Well, unless you like to lose a lot of power on some bands. :/ So it would be better to use an auto tuner at the feedpoint. It would be even better to decide what bands you *really* intend to use, and run dipole legs for each band in parallel. Spread wide apart is better than stacking them on top of each other with spreaders. The antenna as they sell it is pretty micky mouse for an "all band coax fed dipole". As one mentioned, the loss on 40m could be large if you feed with coax to a high Z load. The antenna they sell would be best run using ladder line all the way to a tuner, or tuned by length. Seems like you say they mentioned this, but then why buy the uneeded coax, choke, etc that you would end up discarding. ?? :( MK |
All Band Coax-fed Dipole ??????????
Ooooo Saw the call and had to comment...
I have a 40M inverted Vee up around 35 ft. . I have had out of state contacts on 75, 40(DX), 30(DX), 17, 15, 10 and 6. Is it a "good" antenna? I wish I had better, but it "works". Do I think it is a great antenna? No. Do I think it can be called efficient on the other bands? No. Do I think it has lots of lobes on the higher frequencies? Yes. If I can hear them, I can usually work them. OK by me... Do I have room for better? No. I got much more than what I paid for $0.00. You can probably do better with a "fan-type" dipole. I keep thinking I should at least add 75M wires and 20M wires. When I have time... . . . . . . . . . . . The antenna in question is similar and just as inefficient on some bands and has many lobes on others. It'll get you on the air if this is what you want / can afford. Dave... I used to talk with KC9DI on 2M. We'd say the calls as fast as we could, just to confuse the random listener...(:-) 73, Steve, K9DCI "KC1DI" wrote in message ... wrote: The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. My opinion would be that you'd be much better off if you want a single wire antenna fed with coax going with one of the off center fed models. the SWR is much better on many bands than the center fed model. But if you must have a center fed model then you'll need to feed it with open wire line of some sort .. coax just is not going to perform well for you in a single wire all band dublet. the Losses on most bands are not good. 73 Dave kc1di |
All Band Coax-fed Dipole ??????????
Owen Duffy wrote:
. . . Frank, in the absence of information on the balun, I did model it as ideal, and that the load at the load end of the coax was 4200 ohms. That is probably a reasonable assumption. Perhaps the 4200 ohms is reasonable, but the assumption that the balun is ideal when connected to that load impedance is most definitely not. Any result you get when using that assumption is useless. A real balun would not perfectly isolate the transmission line from drive so influencing feed point impedance , and would probably transform the real feed point impedance to something different to 4200 ohms, and so the line losses could be different (better or worse). A real balun would do all those things, in addition to adding reactance and, at that impedance level, loss. . . . Roy Lewallen, W7EL |
All Band Coax-fed Dipole ??????????
wrote:
The BuxComm Antenna Company sells what it calls an All Band Coax-fed Dipole. http://www.commparts.com/catalog/pro...ffad91005875fb It consists of 135 ft. of wire, a balun at the center feed point, How did you conclude that the feed point is at the center? The lengths of the sides are labeled only "L1" and "L2" on the drawing. and the RG 8X coax transmission line. I don't claim to know a whole lot about antennas, but this configuration is contrary to everything that I have read about feeding mutiband antennas. When I wrote to the company with a question about this, I received a response from K4ABT, Buck Rogers himself. He attached to his note a section from the ARRL Antenna Book, which seems to indicate that coax should not be used with this type of antenna if one wants to use it as a multibander. I have a lot of respect for Buck, based on his years of Elmering a lot of us through his articles. But this one has me stumped. Any input will be appreciated. I believe the antenna will be quite inefficient on some if not all bands, either by accident (a balun which becomes lossy when confronted with extreme impedances) or intent (a resistor inside the "balun" container). If so, it's possible you'll get a reasonable match on all bands, and nearly certain that you'll be able to talk to some people when using it. But it also means that your signal will be considerably weaker than it would be if you were using an efficient antenna. Roy Lewallen, W7EL |
All Band Coax-fed Dipole ??????????
Looking at the thing, I suspect that it is an OCF dipole. It isn't very
clear, but since they have a "L1" and an "L2", that gives us one clue. Most center fed dipoles don't need an L1 and L2, because they assume center fed, inherently 2 equal sides. Notice that they also say "this is not a kit". That is a disclaimer that they put on their other OCF antennas. Finally that 135 foot total length is typical of an OCF dipole. Dis ting is quackin' like a big ol' OCF duck! And as such it should be a serviceable antenna. Funny that some people are dissing BuxComm on technical matters in this case............ ;^) - 73 de Mike KB3EIA - |
All Band Coax-fed Dipole ??????????
"Mike Coslo" wrote in message ... Looking at the thing, I suspect that it is an OCF dipole. It isn't very clear, but since they have a "L1" and an "L2", that gives us one clue. Most center fed dipoles don't need an L1 and L2, because they assume center fed, inherently 2 equal sides. Notice that they also say "this is not a kit". That is a disclaimer that they put on their other OCF antennas. Finally that 135 foot total length is typical of an OCF dipole. OCF = off center fed? i suspect the sides are equal in length. L1 and L2 are just designations used in drawings to denote an element of some length. Buxcomm sells a Windom too. Dis ting is quackin' like a big ol' OCF duck! And as such it should be a serviceable antenna. Funny that some people are dissing BuxComm on technical matters in this case............ ;^) well the coax feed kind of sucks. Gravity - 73 de Mike KB3EIA - |
All Band Coax-fed Dipole ??????????
On Tue, 27 Jun 2006 23:52:02 -0400, Mike Coslo
wrote: Looking at the thing, I suspect that it is an OCF dipole. It isn't very clear, but since they have a "L1" and an "L2", that gives us one clue. Most center fed dipoles don't need an L1 and L2, because they assume center fed, inherently 2 equal sides. Notice that they also say "this is not a kit". That is a disclaimer that they put on their other OCF antennas. Finally that 135 foot total length is typical of an OCF dipole. Dis ting is quackin' like a big ol' OCF duck! And as such it should be a serviceable antenna. Funny that some people are dissing BuxComm on technical matters in this case............ ;^) Mike, we (you and I both) aren't sure of the detail, and that in itself speaks heaps for the product information. Whilst you have drawn a clue that the unspecified L1 and L2 suggest that they are unequal, I drew a clue from the description of a component as "centre insulator with eyehook", and if that product detail is accurate (and we take the ordinary meaning of the word centre to be a point that is equidistant from the extremities) then it suggests centre fed. I still think on balance of the published info, it is represented as an "all-band dipole" on "80 through 10 meters" and appears to be a 135' centre fed dipole with a balun (of unknown type) and recommended RG8/X feedline. Such a configuration will be likely to have high system losses on at least some of the bands with practical lengths of feedline as discussed earlier in the thread by several people. Owen -- |
All Band Coax-fed Dipole ??????????
On Wed, 28 Jun 2006 05:47:18 GMT, Owen Duffy wrote:
Mike, we (you and I both) aren't sure of the detail, and that in itself speaks heaps for the product information. Owen, I found some information for this atnenna at www.stroobandt.com/antennas/windom/windom.html On the design attributed K4BT showing the dimensions to be: L1= 13.4 meters (43.965 ft.) L2= 27.1 meters (88.915 ft.) Regards, Danny, K6MHE |
All Band Coax-fed Dipole ??????????
On Wed, 28 Jun 2006 10:09:55 -0700, Dan Richardson
k6mheatk6mhedotcom wrote: On Wed, 28 Jun 2006 05:47:18 GMT, Owen Duffy wrote: Mike, we (you and I both) aren't sure of the detail, and that in itself speaks heaps for the product information. Owen, I found some information for this atnenna at www.stroobandt.com/antennas/windom/windom.html On the design attributed K4BT showing the dimensions to be: L1= 13.4 meters (43.965 ft.) L2= 27.1 meters (88.915 ft.) Buxcomm's site does list a large number of antennas that are described as "Windom" antennas, but the one that is subject of this thread is not explicitly described in the product information as a Windom of any kind, or as an off-centre fed dipole of any kind. There is an apparent desire on the part of some to construct the case that the subject antenna is a Windom on the basis of: - designation of L1 and L2 on the diagram, although there are no values stated to show that they are unequal; - that elsewhere K4BT has described "coax fed Windoms". There is nothing conclusive on the diagram at http://www.commparts.com/catalog/ima...ts/8010ABD.gif to suggest that this is a "coax fed Windom", though some infer that is the case because of the L1, L2 designation though not values are shown. I argue that designation of a key component separating L1 and L2 as a "center insulatore and eye hook" has more value than the undimensioned L1, L2 designation. What is becoming clearer, is that on the basis of the information published on the commercial web site for this antenna, the buyer cannot be sure of just what he is getting, much less how well it might perform. Owen -- |
All Band Coax-fed Dipole ??????????
Owen Duffy wrote:
On Wed, 28 Jun 2006 10:09:55 -0700, Dan Richardson k6mheatk6mhedotcom wrote: On Wed, 28 Jun 2006 05:47:18 GMT, Owen Duffy wrote: Mike, we (you and I both) aren't sure of the detail, and that in itself speaks heaps for the product information. Owen, I found some information for this atnenna at www.stroobandt.com/antennas/windom/windom.html On the design attributed K4BT showing the dimensions to be: L1= 13.4 meters (43.965 ft.) L2= 27.1 meters (88.915 ft.) Buxcomm's site does list a large number of antennas that are described as "Windom" antennas, but the one that is subject of this thread is not explicitly described in the product information as a Windom of any kind, or as an off-centre fed dipole of any kind. There is an apparent desire on the part of some to construct the case that the subject antenna is a Windom on the basis of: - designation of L1 and L2 on the diagram, although there are no values stated to show that they are unequal; - that elsewhere K4BT has described "coax fed Windoms". There is nothing conclusive on the diagram at http://www.commparts.com/catalog/ima...ts/8010ABD.gif to suggest that this is a "coax fed Windom", though some infer that is the case because of the L1, L2 designation though not values are shown. I argue that designation of a key component separating L1 and L2 as a "center insulatore and eye hook" has more value than the undimensioned L1, L2 designation. What is becoming clearer, is that on the basis of the information published on the commercial web site for this antenna, the buyer cannot be sure of just what he is getting, much less how well it might perform. Of course someone could do an end run around us by just calling BuxComm and getting the real scoop. 8^) I don't doubt that someone might come to a different conclusion, but I think my reasoning is pretty sound. I modeled an equal length version of this in 4nec, and it just doesn't work very well. OTOH, turn it into an OCF dipole, and it is a different story. BuxComm has no need to sell an antenna as "multiband" when it isn't, and when they have other comparably priced models that will work. - 73 de Mike KB3EIA -- |
All Band Coax-fed Dipole ??????????
Mike Coslo wrote:
. . . I don't doubt that someone might come to a different conclusion, but I think my reasoning is pretty sound. I modeled an equal length version of this in 4nec, and it just doesn't work very well. OTOH, turn it into an OCF dipole, and it is a different story. . . How did you possibly determine what the balun input impedance was when terminated with the impedances the antenna presented on the various bands? How did you model the balun? It's almost certainly a "voltage" balun which will force common mode current onto the feedline when terminated with an asymmetrical load. Because of the common mode current, the outside of the feedline must be part of the model. Did you model the antenna with various lengths and orientations of feedlines? I don't believe that a valid model can be made of this type of antenna without knowing and accounting for the major imperfections of the balun, the common mode current it forces, and the feedline length and orientation for the particular installation. Roy Lewallen, W7EL |
All Band Coax-fed Dipole ??????????
Roy Lewallen wrote:
Mike Coslo wrote: . . . I don't doubt that someone might come to a different conclusion, but I think my reasoning is pretty sound. I modeled an equal length version of this in 4nec, and it just doesn't work very well. OTOH, turn it into an OCF dipole, and it is a different story. . . How did you possibly determine what the balun input impedance was when terminated with the impedances the antenna presented on the various bands? You are correct, I couldn't. But what I got was enough to tell me that with the two sides of equal length, there wasn't much need to go any further. Cannot some antenna characteristics be modeled without the entire system in place? I'm no expert, so I'll ask the question: Is there some Balun that will make a 135 foot equal length antenna perform on 80-10 meters? How did you model the balun? It's almost certainly a "voltage" balun which will force common mode current onto the feedline when terminated with an asymmetrical load. Because of the common mode current, the outside of the feedline must be part of the model. Did you model the antenna with various lengths and orientations of feedlines? I don't believe that a valid model can be made of this type of antenna without knowing and accounting for the major imperfections of the balun, the common mode current it forces, and the feedline length and orientation for the particular installation. It isn't whether my model is exceptionally valid. I don't know what the balun is that they use, so that sense it doesn't matter anyhow. You would know much better the balun that would make this antenna work. I'm just looking at what is there, and by looking at both the context of the advertisement, references given for their other antennas and the like, I'm just saying that I suspect that that antenna is a OCF dipole. Their G5RV antennas do *not* have an L1 and L2 to designate length of the sides. If that antenna has an equal length side, it is the only one on the site that does. Yeah, I know they are not really G5RV's. In addition, is BuxCom going to try to sell a product that apparently doesn't work? I don't see any of the hype that tends to go along with the "magic" antennas we sometimes hear about All of the above just about convince me that the antenna in question is an OCF dipole, and that the description and image is a big typo. Others may take it at all at face value, disregard all the evidence to the contrary, and assume that the sellers are just trying to hoodwink a gullible public into buying a non-working product. That doesn't make sense to me. YMMV - 73 de Mike KB3EIA - |
All Band Coax-fed Dipole ??????????
Mike Coslo wrote:
Roy Lewallen wrote: Mike Coslo wrote: . . . I don't doubt that someone might come to a different conclusion, but I think my reasoning is pretty sound. I modeled an equal length version of this in 4nec, and it just doesn't work very well. OTOH, turn it into an OCF dipole, and it is a different story. . . How did you possibly determine what the balun input impedance was when terminated with the impedances the antenna presented on the various bands? You are correct, I couldn't. But what I got was enough to tell me that with the two sides of equal length, there wasn't much need to go any further. Cannot some antenna characteristics be modeled without the entire system in place? Yes, but you have to at least include the whole antenna -- you can't tell much about a two-element array by modeling a single isolated element. In the case of an OCF dipole, unless heroic efforts are made to keep common mode current off the feedline (which the balun doesn't achieve), the feedline is part of the antenna so, like the second element of an array, it can have a major impact on the both the pattern and impedance and has to be included in the model. The balun, feedline length, and feedline orientation all play a role in determining how much current goes down the feedline part of the antenna and where that part is. So you have to know at least that much to get a meaningful result. I'm no expert, so I'll ask the question: Is there some Balun that will make a 135 foot equal length antenna perform on 80-10 meters? "Perform" is one of those binary terms that depend on where you put the dividing line. But the answer is that the only practical way you can achieve a reasonable impedance match to a coax feedline on all bands with a center fed 135 foot antenna is to introduce a fair amount of loss. This could be in the form of a resistor at the feedpoint, for example. Then you'll have an inefficient antenna at least on some bands. Alternatively, you can have low loss at the feedpoint but a lousy impedance match. Then you'd have a lot of loss in the feedline if you fed it with coax. The bottom line is that you'll have poor efficiency on at least some bands if you feed it with coax, no matter what you do -- short of putting either an adjustable or very elaborate fixed matching network at the feedpoint. Nearly any ham can measure the SWR but almost none can measure the efficiency. So many antenna manufacturers have produced lossy antennas which exhibit a low SWR. This is perfectly acceptable to many amateurs, as evidenced by glowing reviews for a number of antennas which can be shown to be quite inefficient such as the B&W T2FD or the Isotron. Those amateurs would positively say that such antennas "perform", and this can't be disputed since the judgment is entirely up to them. . . . Others may take it at all at face value, disregard all the evidence to the contrary, and assume that the sellers are just trying to hoodwink a gullible public into buying a non-working product. That doesn't make sense to me. YMMV "Working" is like "perform" -- the threshold is different for different people. But a quick scan of reviews for the Buckmaster and Alpha-Delta OCF antennas (the latter apparently manufactured by Buckmaster) show high satisfaction from at least the users who have taken the time to post reviews. Whether you or I would be happy with one depends on our personal criteria. Roy Lewallen, W7EL |
All Band Coax-fed Dipole ??????????
Mike Coslo wrote:
I'm just looking at what is there, and by looking at both the context of the advertisement, references given for their other antennas and the like, I'm just saying that I suspect that that antenna is a OCF dipole. At: http://www.commparts.com/catalog/ind...sort=2a&page=2 The OCF's are labeled as Windoms and drawn with unequal elements. The ones drawn with equal elements are not labeled as Windoms. I would infer that they are different but I could be wrong. I sure would like to know what's inside the "balun". -- 73, Cecil http://www.qsl.net/w5dxp |
All Band Coax-fed Dipole ??????????
Roy Lewallen wrote:
Nearly any ham can measure the SWR but almost none can measure the efficiency. How about ten interested parties sending you $5 each so you can buy and test one and review and report back here? -- 73, Cecil http://www.qsl.net/w5dxp |
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