Helix-wound EDP
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Has anyone ever tried/know about winding a w3edp style antenna on a pvc pipe?
I have hardly any space...and every time I manage to get an antenna attach to "Ye Olde Phone Pole","Ye Olde Lineman" arrives and removes it with particular prejudice and dispatch. I recently obtained a 5 foot piece of 4 inch diameter underground pipe that could be used as a form. 73,Thom-k3hrn www.zerobeat.net Home of QRP Web Ring, Drakelist home page,Drake Web Ring, Free Classified Ads for amateur radio, QRP IRC channel, Drake IRC Channel, Elecraft Owners Database www.tlchost.net/hosting/ *** Web Hosting as low as 3.49/month _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Helix-wound EDP
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Morning Thom,
This type of antenna element has been around for a long time, since the late 1930s perhaps before, and bears the family name 'Normal Mode Helix'. Two rules of thumb. For an element that is electrically a quarter wavelength long, the overall physical length of the helix should not be less than 0.05 wavelength e.g. roughly 7ft at 40m. Secondly, the diameter of the 'coil form' must be small - 4 inches would probably be OK below 21MHz, but I would have to check that. When the diameter is very large, the element becomes an 'Axial Mode Helix' with the main radiation lobe off the end of the helix, an antenna often used at VHF and up. As an approximation, the length of wire required for a quarter wavelength element is close to a half wavelength when wound with equal spacing between turns. If you would like I can send you some much more detailed info ( and a little maths!). Which bands do you want to use? 73, Geoff GM4ESD Thom R LaCosta <[hidden email]> wrote: > Has anyone ever tried/know about winding a w3edp style antenna on a pvc > pipe? > > I have hardly any space...and every time I manage to get an antenna attach > to "Ye Olde Phone Pole","Ye Olde Lineman" arrives and removes it with > particular prejudice and dispatch. > > I recently obtained a 5 foot piece of 4 inch diameter underground pipe > that > could be used as a form. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Wed, 14 Dec 2005, Geoffrey Mackenzie-Kennedy wrote:
> Morning Thom, > > This type of antenna element has been around for a long time, since the late > 1930s perhaps before, and bears the family name 'Normal Mode Helix'. Ah...the term "normal" never applies to me (g). > > As an approximation, the length of wire required for a quarter wavelength > element is close to a half wavelength when wound with equal spacing between > turns. OK > > If you would like I can send you some much more detailed info ( and a little > maths!). Which bands do you want to use? What I was hoping to do was have a helix that acted like a w3edp, ie, a multi-band antenna. So, if the edp is 87 to 89 feet, would that mean that a helix might be 174 to 178 feet of wire wound on the form? thanks 73,Thom-k3hrn www.zerobeat.net Home of QRP Web Ring, Drakelist home page,Drake Web Ring, Free Classified Ads for amateur radio, QRP IRC channel, Drake IRC Channel, Elecraft Owners Database www.tlchost.net/hosting/ *** Web Hosting as low as 3.49/month _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Thom, K3HRN wrote:
What I was hoping to do was have a helix that acted like a w3edp, ie, a multi-band antenna. So, if the edp is 87 to 89 feet, would that mean that a helix might be 174 to 178 feet of wire wound on the form? ------------------------------------------------ I did some experiments with a helical antenna wound on a wooden form (2x3" fir, painted). 130 feet (42 meters) No. 16 wire wound on a pole 12 feet long resonates as a 1/4 wave at just 3850 kHz. On my lot where it is a challenge to get 60 feet of wire in the air, my regular antenna is a 50 foot doublet up 30 feet fed with true open wire line, using a link-coupled balanced antenna tuner in the shack. There's nothing unusual about the W3EDP antenna. It's a simple end-fed wire with a single-wire counterpoise. The parallel tuned network means that W3EDP found that it presented a rather high impedance on all bands with the counterpoise arrangement he used. Note that both the counterpoise and radiator are tuned as a system by the network. That's why he disconnects it on some bands to help get a match more easily. Like *all* such antennas, efficiency is highly dependent upon the radiation resistance of the radiator compared to that of the ground system. That means that it is the physical size of the radiator that is important to efficiency, not its resonant frequency. On those bands were the wire is close to 1/2 wavelength long (40 meters) the efficiency will be high because the impedance will be in the thousands of ohms. That will work well even where the ground is very poor. An 85 foot wire will work fairly well even down on 80 meters where it's only a little over a 1/4 wavelength. A 1/4 wave wire has a radiation resistance at resonance of 30-something ohms. Even a poor ground showing close to 300 ohms resistance will permit an efficiency of 10%. Believe me, there's a lot of antennas, especially 80 meter antennas, no where near that efficient. For example, mobile antennas. And that's where your helical design (and the one I've played with) come in. Even though an antenna may be 'resonant', thanks to loading, either with a coil or by making the antenna one huge coil such as you contemplate, it will have a very, very low radiation resistance. In such a short antenna on 80, expect something less than ONE ohm, even though it may be resonant. That means a full sized W3EDP might be as much as 10% efficient with it's minimal ground system on 80 meters but your helical antenna efficiency will be far less than 1%. The full-size W3EDP is longer than 1/2 wavelength on 40 and up, so its efficiency may well exceed 50% or 75% on those bands where the radiation resistance is likely well above 1000 ohms. But that won't happen with a loaded radiator of any sort. The efficiency will stay low, although it does improve somewhat as the frequency increases. For example, my helical antenna starts to look, in terms of efficiency, like a decent 1/4 wave on 20 meters. That's because at 12 feet it IS a decent 1/4 wave on 20 meters, or very close to it! Of course, it's no longer necessary or desirable to wind the helix on that band either. My matching network has to compensate for all that inductance and the ohmic losses in the wire remain! I came to the inescapable conclusion that my short doublet was a far better 80 meter antenna than the helical vertical, even with a full-size 1/4 wave "radial" or "counterpoise". I have a purpose-built high-efficiency tuner designed to match it without baluns. It's the classic balanced tuner design seen in the literature everywhere*. There's a picture of it in my shack above the K2 on QRZ.COM. It's not fast for band-changing but it's versatile and efficient at extreme load impedances. At 100 watts, I work stations out to about 1,000 miles on 80 with consistently excellent reports. That's just about right for the limit on a so-called NVIS (near vertical incidence system) antenna in which all signal goes up to be scattered off of the ionosphere over that range in all directions. Side-by-side comparisons with the helical/counterpoise arrangement show a 2 or more S-unit difference in almost every test, with the doublet the best. Those few situations where the helical was equal to or better were at longer distances - out near 2,000 miles or so on the eastern coast of the USA from Oregon. Such contacts are very rare for me to make, but when I have, the vertical sometimes showed a SLIGHT advantage, or is, at least, considered equal to the low doublet. That fits with the presumption that a vertical has a lower angle of radiation. The reality is that the vertical helical is not much different from the short doublet at long distances without an excellent ground screen, and far inferior at short skip ranges where high-angle radiation is important. Without a large ground screen or radial system, the earth losses are very high, meaning that most of the RF radiated below 20 or 30 degrees above the horizon is attenuated anyway. Some years ago Doug DeMaw, W1FB, published a design that might work for you in a tight situation. I've considered it here, although the short doublet has worked well enough that I've not tried it. He bent a doublet at 90%, like you might for an extreme "inverted V" design, but arranged it so one radiator was horizontal to the earth, making the other one vertical. He used guyed aluminum pipe for the vertical radiator and a simple wire for the horizontal radiator. The system is fed with open wire line and an efficient, balanced ATU. I believe he settled on a compromise 25 feet for the vertical and horizontal segments, producing a radiator with about the same electrical characteristics as mine. The challenge there is to get the whole system up as high as possible. That horizontal wire is an integral part of the radiation system! But if you can put it on a roof at, say, 20 feet, he reported quite good results. I found that it was easier to put up my all-wire doublet with one leg nearly horizontal and the other dropping down to a tie point at about 12 feet above ground. I highly recommend Cebik's excellent web pages for more discussion about antenna and tuner design, especially for those of us with limited space. Ron AC7AC * http://www.cebik.com/link/link.html _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Ron D'Eau Claire wrote:
> Some years ago Doug DeMaw, W1FB, published a design that might work for you > in a tight situation. I've considered it here, although the short doublet > has worked well enough that I've not tried it. He bent a doublet at 90%, > like you might for an extreme "inverted V" design, but arranged it so one > radiator was horizontal to the earth, making the other one vertical. He used > guyed aluminum pipe for the vertical radiator and a simple wire for the > horizontal radiator. The system is fed with open wire line and an efficient, > balanced ATU. I seem to remember this being fed at the bottom, making it a one-radial ground plane. But maybe it was center-fed at the top, as your description suggests. Either way, the idea appealed to me, because it would have high and low-angle components, although both the vertical and horizontal patterns would be skewed. One thing that bothered me about this antenna was that there might (I suspect) be a significant current imbalance in the feedline because of the two legs' unbalanced relationship to ground. That would cause radiation loss from the feedline (and noise pickup). But maybe not -- in which case ths would be a very interesting antenna! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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No, it was center fed like an inverted V, so it was fed at the bottom of the
pole in his arrangement with one side of the feedline going to the pipe and the other going to the horizontal wire. (Otherwise it wouldn't be a 'doublet'). Yes, the arrangement would introduce some unbalance in the feeders. Ron AC7AC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Vic K2VCO Sent: Wednesday, December 14, 2005 10:41 AM To: 'Elecraft Discussion List' Subject: Re: [Elecraft] Helix-wound EDP Ron D'Eau Claire wrote: > Some years ago Doug DeMaw, W1FB, published a design that might work for you > in a tight situation. I've considered it here, although the short doublet > has worked well enough that I've not tried it. He bent a doublet at 90%, > like you might for an extreme "inverted V" design, but arranged it so one > radiator was horizontal to the earth, making the other one vertical. He used > guyed aluminum pipe for the vertical radiator and a simple wire for the > horizontal radiator. The system is fed with open wire line and an efficient, > balanced ATU. I seem to remember this being fed at the bottom, making it a one-radial ground plane. But maybe it was center-fed at the top, as your description suggests. Either way, the idea appealed to me, because it would have high and low-angle components, although both the vertical and horizontal patterns would be skewed. One thing that bothered me about this antenna was that there might (I suspect) be a significant current imbalance in the feedline because of the two legs' unbalanced relationship to ground. That would cause radiation loss from the feedline (and noise pickup). But maybe not -- in which case ths would be a very interesting antenna! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Ron D'Eau Claire wrote:
> No, it was center fed like an inverted V, so it was fed at the bottom of the > pole in his arrangement with one side of the feedline going to the pipe and > the other going to the horizontal wire. (Otherwise it wouldn't be a > 'doublet'). Now I remember that it was as you describe. But you could make a doublet with the horizontal wire coming off the top of the pipe. Sort of an inverted L fed at the top. feed here :---------------- | | | | | | That would have a little lower angle from the horizontal part and less ground loss. I'll have to try these in EZNEC and see what happens. > Yes, the arrangement would introduce some unbalance in the feeders. If it's severe, then the line can be quite lossy. Possibly looking at the element currents computed by EZNEC will give me a clue. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Doublet Antennas (WAS: Helix-wound EDP)
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Vic wrote:
you could make a doublet with the horizontal wire coming off the top of the pipe. Sort of an inverted L fed at the top. feed here :---------------- | | | | | | That would have a little lower angle from the horizontal part and less ground loss. I'll have to try these in EZNEC and see what happens. > Yes, the arrangement would introduce some unbalance in the feeders. If it's severe, then the line can be quite lossy. Possibly looking at the element currents computed by EZNEC will give me a clue. ----------------------------------------- Yes! The challenge with the DeMaw design is getting the whole system up high enough so that the horizontal radiator is at a decent height. The issue of feedline balance is one I've got on my to-do list to investigate. Few "balanced" antennas are really balanced. We tend to tie antennas to trees or buildings, so the part of the antenna that is most sensitive to surrounding objects - the high-impedance ends - is closest to such objects. But what is the real world difference? I can't answer that today. I can tell you that the RF currents in the feeders on my doublet are within 5% of each other, but phase is important too, if we don't want the feeder to radiate. I haven't done phase measurements. Some early ATU designs used an RF voltmeter across the open wire feeders (using large resistors to reduce the voltage and provide isolation) instead of two RF ammeters in series with the feeders. The idea was that maximum voltage meant maximum out-of-phase currents in the lines. Balanced ATU's like I use can be adjusted to alter the phase and balance of currents in the feeders, at least at the shack end where unbalance is the greatest problem. It's done by changing the tap points on the main coil. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Helix-wound EDP
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In reply to this post by Ron D'Eau Claire-2
Was this not the antenna that the Old - Old- Timers used to call the 'Thirty
up thirty out', each leg being thirty feet in length? 73, Geoff GM4ESD ----- Original Message ----- From: "Ron D'Eau Claire" <[hidden email]> To: "'Vic K2VCO'" <[hidden email]>; "'Elecraft Discussion List'" <[hidden email]> Sent: Wednesday, December 14, 2005 6:53 PM Subject: RE: [Elecraft] Helix-wound EDP > No, it was center fed like an inverted V, so it was fed at the bottom of > the > pole in his arrangement with one side of the feedline going to the pipe > and > the other going to the horizontal wire. (Otherwise it wouldn't be a > 'doublet'). > > Yes, the arrangement would introduce some unbalance in the feeders. > > Ron AC7AC > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Doublet Antennas (WAS: Helix-wound EDP)
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In reply to this post by Ron D'Eau Claire-2
A lot of these antenna ideas have been modeled by L. B. Cebik, W4RNL at his
excellent antenna web site: www.cebik.com Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Geoffrey Mackenzie-Kennedy-2
Geoff GM4ESD wrote:
Was this not the antenna that the Old - Old- Timers used to call the 'Thirty up thirty out', each leg being thirty feet in length? --------------------------------- That's a new one to this "Yank" Geoff, but I've learned that over the years what designs are "in fashion" is different here on the states compared to there. That's why I like books like Hey's little tome, "Practical Wire Antennas" so much. It exposes us North Americans to a lot of antenna design ideas that aren't seen in the popular literature here. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Thom LaCosta
At 06:37 AM 2005-12-14, Thom R LaCosta wrote:
>What I was hoping to do was have a helix that acted like a w3edp, >ie, a multi-band antenna. So, if the edp is 87 to 89 feet, would >that mean that a helix might be 174 to 178 feet of wire wound on the form? Thom, The comments you have already received have been excellent. Helical antennas are a great source of confusion to many hams and SWLs. The main thing to keep in mind is that winding an antenna wire onto a relatively small form changes almost every characteristic of the antenna. The harmonic resonances will normally not occur as they would if the wire were straight, the directivity and pattern will usually be different, the feed impedance will be different (usually lower), and the bandwidth and efficiency will be lower (much lower if the length of the helix is much smaller than the straight wire version). To a very rough approximation, a small diameter helix (aka "normal mode") acts much like a straight wire that is the length of the helix form, but with a lumped loading coil in the middle. Hmmm, sounds like a mobile antenna... You can't fool mother nature by winding a 10-wavelength rhombic onto four 0.05 wavelength long coil forms. It would be great if you could! 8-) BTW, the latest version of EZNEC (4.0) has a nice feature that makes it easy to create models of helical antennas (subject to limits on the maximum number of segments.) I can model a helical design if you like. Keep clam, Terry N6RY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Wed, 14 Dec 2005, Terry Conboy wrote:
> At 06:37 AM 2005-12-14, Thom R LaCosta wrote: >> What I was hoping to do was have a helix that acted like a w3edp, ie, a >> multi-band antenna. So, if the edp is 87 to 89 feet, would that mean that >> a helix might be 174 to 178 feet of wire wound on the form? > > Thom, > > The comments you have already received have been excellent. Yep...I am learning a LOT from the expertise of the folks... > > You can't fool mother nature by winding a 10-wavelength rhombic onto four > 0.05 wavelength long coil forms. It would be great if you could! 8-) Yes...but, there is always hope. > > BTW, the latest version of EZNEC (4.0) has a nice feature that makes it easy > to create models of helical antennas (subject to limits on the maximum number > of segments.) I can model a helical design if you like. Don;t want to waste your time and energy....it looks like the Holix is not the way to go....but thanks for the kind offer. Perhaps I need to take "Bribe 101" to convince the pole climbers not to touch my wire. > > Keep clam, Yes, and oysters, mussels, crabs and other goodies. 73,Thom-k3hrn www.zerobeat.net Home of QRP Web Ring, Drakelist home page,Drake Web Ring, Free Classified Ads for amateur radio, QRP IRC channel, Drake IRC Channel, Elecraft Owners Database www.tlchost.net/hosting/ *** Web Hosting as low as 3.49/month _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Thom, the bottom line is to simply put up as much wire as you can wherever you can. You may be very surprised at how well a little bit of an antenna can get out! Just remember that every foot of length and height helps. I've worked from a lot of apartments, some on the ground floor where nothing was more than six feet up, others where I could run a little wire along a wall and some where I could actually put something on the roof as long as it wasn't seen by anyone (landlord didn't want CBers demanding equal rights). In every case I had a lot of very interesting and satisfying operating! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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