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#11
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Carolina Windom without a balun: go figure
Owen Duffy wrote:
jawod wrote in : I've attached the original article that describes the CW in question. As you now know, that didn't work. You need to put the article on a web site somewhere, or give the URL of an existing copy. Owen Thank you SO much Owen here ya go www.w5fc.org/files/QRP%20Expressions.pdf John AB8O |
#12
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Carolina Windom without a balun: go figure
On Wed, 29 Oct 2008, jawod wrote:
here ya go www.w5fc.org/files/QRP%20Expressions.pdf John AB8O This was the article that convinced me to build a NCW. (The 3rd option) I scaled mine up to the 132 ft version so I could have 80m. When I finally have a QTH to support its size, I will string it up permanently. Till then, it is my field-day antenna of choice. My 706IIg with AT180 autotuner have no trouble getting a clean match on 6m thru 80m. |
#13
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Carolina Windom without a balun: go figure
jawod wrote in :
.... Thank you SO much Owen here ya go www.w5fc.org/files/QRP%20Expressions.pdf There are a host of issues with the content of the article. I don't intend to red pen the article, but the issues sound a warning about credibility. There is no doubt it describes a Ruthroff 4:1 balun in its "new Carolina Windom" configuration. Such a balun will have a very low common mode impedance. Factors of your implementation that are / may be different include: The DXE balun you used appears to be described as a current balun on the DXE web site. If it is, it may work differently. (I have already commented on the lack of clarity of the product information, perhaps they might clarify it if you email them with a support question - "what did I buy?".) DXE also warn us that 'tuner' style baluns such as the one you used are more likely to be reactive an higher frequencies... presumably a consequence of thicker wire insulation which increases the Zo of the TL sections which results in less ideal impedance transformation with increasing frequency. Owen |
#14
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Carolina Windom without a balun: go figure
DXE also warn us that 'tuner' style baluns such as the one you used are more likely to be reactive an higher frequencies... presumably a consequence of thicker wire insulation which increases the Zo of the TL sections which results in less ideal impedance transformation with increasing frequency. Thanks for the input. The strange thing is that the system failed at ALL freq's. The original use of the balun was with a folded dipole and a feedline of 300 ohm twinlead cut to an odd multiple of the lowest freq desired...which I did and it worked reasonably well. I cannot understand how this application (the CW OCF) is significantly different from the original one, at least in terms of using a 4:1 balun. Allow me to put this to rest. I can live with it as it is, theoretical considerations notwithstanding. I don't want to go over to the dark side, but, hey, it works. Maybe I have a new "Magic" Antenna. John AB8O |
#15
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Carolina Windom without a balun: go figure
jawod wrote in :
... Maybe I have a new "Magic" Antenna. Instead of the "perfect antenna" as claimed in the article! Owen |
#16
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Carolina Windom without a balun: go figure
jawod wrote:
Three versions of the Carolina Windom are presented: Original single wire feed, Actually, not a Carolina Windom - simply a traditional Windom, the grandfather of all Windoms - named after Major General Loren G. Windom, W8GZ, (Windy) (QST, Sep 1929, pp 19-22, 84). www.geocities.com/w8jyz/8GZ.pdf OCF with twinlead and balun, Don't know if it was ever a commercially available antenna called a "Carolina Windom" but this is just a traditional "Off-Center-Fed Dipole" labeled as such in my 1957 ARRL Handbook. http://www.w8ji.com/windom_off_center_fed.htm and OCF with 10' length of coax This is what most people think about when someone says "Carolina Windom" and the reason that some people were confused. http://www.hamuniverse.com/k4iwlnewwindom.html I guess I'll conclude that the balun has failed. At least hang a 200 ohm non-inductive resistor on the output and measure the input impedance. I don't know how you can assume the balun has failed if you don't know what impedances the balun was having to deal with. -- 73, Cecil http://www.w5dxp.com |
#17
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Carolina Windom without a balun: go figure
On 2008-10-29, jawod wrote:
I've attached the original article that describes the CW in question. Three versions of the Carolina Windom are presented: Original single wire feed, OCF with twinlead and balun, and OCF with 10' length of coax to a choke balun (1:1). Mine is the middle one. Please see Fig 3A. The balun is at the bottom of the twin lead (I think I mistakenly referred to it as ladder line). I added large ferrite beads just below the balun on the coax as discussed here in the group earlier. If I'm reading this correctly, you put the balun at the bottom of the twin lead and the ferrite bead balun just under it. Many 'Carolina Windoms' use the balun at the feed point, the ladder line or twin lead under that, and the ferrite bead balun at the bottom of the ladder line, to which is attached the coax. Placing the balun (4:1 or whatever) under the twin lead would really do strange things to the impedance and probably cause the problems you mentioned. 73 ...Edwin, KD5ZLB -- __________________________________________________ __________ "Once you have flown, you will walk the earth with your eyes turned skyward, for there you have been, there you long to return."-da Vinci http://bellsouthpwp2.net/e/d/edwinljohnson |
#18
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Carolina Windom without a balun: go figure
When trying to understand off center fed antennas, it's important to
realize a few key facts: 1. A properly working "voltage" or "Ruthroff" balun will force common mode current to exist on the feedline in its attempt to cause equal voltages on the unequal length sides relative to the feedline shield. 2. Even if an effective "current" or "Guanella" balun is used, feedline current will still be induced by the uneven coupling between the two antenna sides. 3. A transforming balun is very unlikely to effect the expected transformation ratio, and is likely to add a significant amount of series and/or shunt reactance except at those spot frequencies where the match is close to perfect. This isn't to say that off center fed antennas can't sometimes be made to "work", i.e., provide a reasonable impedance match on some bands. But when they do, it's not for the reasons you think from an analysis assuming a perfect transformer and balun. It usually involves a complex relationship among the particular imperfections of the balun/transformer, feedline, and path to the Earth taken by the feedline shield. Roy Lewallen, W7EL |
#19
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Carolina Windom without a balun: go figure
Edwin Johnson wrote:
... Placing the balun (4:1 or whatever) under the twin lead would really do strange things to the impedance and probably cause the problems you mentioned. 73 ...Edwin, KD5ZLB Actually, I would expect placing a 4:1 balun under the 300 ohm balanced line and before the 50 ohm unbalanced to provide a step-up(or step-down, depending on the "direction" you view it from) of 50:200 or 4:1, as it properly should. However, as someone presented in a paper a little while back, some antennas "filled with errors" are able to function in some manner and end up gaining their supporters ... If you were to place a 1:1 balun at this same point, I would expect little difference, but a difference (and, since you are mismatched at this point, simply maintaining this mismatch with a component introducing some loss and "redirecting" CM currents, not a good difference!) It seems the "misunderstood/mystical/magical balun" lives on ... Regards, JS |
#20
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Carolina Windom without a balun: go figure
Roy Lewallen wrote in
treetonline: When trying to understand off center fed antennas, it's important to realize a few key facts: .... Yes, I thing you are quite correct Roy. The advertising hype that goes along with many of these commercially popularised antennas gives the impression that deployment of multi-band wire antennas for the lower HF bands is a very standardised thing, a no- brainer. One buys the product, installs it in their own environment in their own way, and it just "works" out of the box... whatever "works" means. The real world doesn't work that simply. But to a buyer with faith in the promotional claims, they can buy a lot of satisfaction for only $69.99 or whatever, and not have any untidy left over materials to clutter up their home, or residual technical issues to clutter up their mind. Today, the growth opportunity in the US is selling attic antennas for low HF bands to new hams. Not as popular here because restrictive covenants on residential properties aren't as common. But, hey, a simple wire antenna with published performance figures from 160m to 2m is attractive to *our* new six hour hams. Which antenna is that? The W5GI Mystery Antenna, you know, the one "that performs exceptionally well even though it confounds antenna modeling software". Owen |
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