dipole antenna efficiency
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Hi all,
if I were to make a dipole, would coiling it round a piece of plastic piping decrease the efficiency of the thing? I intend on making one for 40 meters, one for 80 meters, and one for 10 meters. I've worked out that1 meter of piping will suffice for each leg of each antenna. thanks in advance. shaun _______________________________________________ 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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Shaun, it will decrease the efficiency drastically. A
two meter long 80 meter dipole will be about 10% as efficient as one 40 meters long at the same height. Most texts quote dbi information for a full sized dipole 100 feet high. If you put your antenna near the ground it may not be much more than 1% as efficient as the full sized antenna at 100 feet. You can't cheat the laws of physics, they work the same even if no body is watching. There is no substitute for high and big! If you are trying to run QRP with 5 or 10 watts then you will be doing well to work across the street. In addition, the antenna you are considering will have an impedance of only an ohm or two and be almost impossible to match. Sorry, nice idea, but it will not work well at all. Cookie, K5EWJ, BS Physics, PE/EE, 52 years a ham --- Shaun Oliver <[hidden email]> wrote: > Hi all, > if I were to make a dipole, would coiling it round a > piece of plastic > piping decrease the efficiency of the thing? I > intend on making one for > 40 meters, one for 80 meters, and one for 10 meters. > I've worked out > that1 meter of piping will suffice for each leg of > each antenna. > thanks in advance. > shaun > _______________________________________________ > 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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In reply to this post by Shaun Oliver
Shaun,
For materials needed vs. radio theory, you just can't beat a G5RV antenna. IMHO I've used mine with my K1, K2 and several home brew projs and it works great time and again. Yes, you want to get the center up there a ways. Say around 35-40 feet, but the payoff was good for me. There are a number of sites out there that have good versions of a very old, classic antenna. Very few parts (all of which can be made with junk around the house. Very little investment for a sound payoff. Dohn N8EWY -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Shaun Oliver Sent: Thursday, January 03, 2008 9:20 PM To: [hidden email] Subject: [Elecraft] dipole antenna efficiency Hi all, if I were to make a dipole, would coiling it round a piece of plastic piping decrease the efficiency of the thing? I intend on making one for 40 meters, one for 80 meters, and one for 10 meters. I've worked out that1 meter of piping will suffice for each leg of each antenna. thanks in advance. shaun _______________________________________________ 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 |
Re: dipole antenna efficiency
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In reply to this post by Shaun Oliver
Shaun Oliver <[hidden email]>
> if I were to make a dipole, would coiling it round a piece of plastic > piping decrease the efficiency of the thing? I intend on making one for 40 > meters, one for 80 meters, and one for 10 meters. I've worked out that1 > meter of piping will suffice for each leg of each antenna. > thanks in advance. > shaun Cookie, K5EWJ wrote: > Shaun, it will decrease the efficiency drastically. A > two meter long 80 meter dipole will be about 10% as > efficient as one 40 meters long at the same height. > You > can't cheat the laws of physics, they work the same > even if no body is watching. In > addition, the antenna you are considering will have an > impedance of only an ohm or two and be almost > impossible to match. ----------------------------------------------------------------------------------------------- While Cookie's comments are true, there is a useful type of short antenna known as a Normal Mode Helix, which if built, tuned and matched correctly can work as well as a full size dipole at the same height - although its VSWR (say 2:1 for example) bandwidth is narrower than that of a full size dipole. It consists of wire wound around a fibreglass or plastic rod / pipe with the turns spaced, not closewound. If plastic pipe is used it must have good RF 'Insulating' characteristics i.e if a piece 'cooks' when placed in a microwave oven, when your XYL is not looking, do not use that material. For 80m and 40m a pipe diameter of 2 1/2 inches is about right, for 10m 3/4 inch or thereabouts. The total length of wire in a NM Helix 'dipole' is approximately one wavelength, equations do exist which could be used to calculate the length but I have yet to find an equation which is exact enough to eliminate the need to tweak. The length of pipe for a 40m NM Helical 'dipole' is close to 6 metres, the length could be reduced by increasing the pipe's diameter but there is a limit beyond which the radiation pattern suffers. Very short and effective NM Helix antennas have been built using additional end loading such as hats, but their drive point impedance is very low and difficult to match efficiently and the VSWR bandwidth becomes narrower. The 'Rubber Duck' antenna sometimes used on mobile phones is one type of NM Helix antenna. 73, Geoff GM4ESD _______________________________________________ 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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I seem to remember a 40m beam made this way in one of the old ARRL books.
David G3UNA > > While Cookie's comments are true, there is a useful type of short antenna > known as a Normal Mode Helix, which if built, tuned and matched correctly _______________________________________________ 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: dipole antenna efficiency
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David, the beam was descibed in the 13th (1974) edition of the ARRL
handbook, perhaps in an earlier edition also, it performed well.. 73, Geoff GM4ESD David Cutter <[hidden email]> wrote: >I seem to remember a 40m beam made this way in one of the old ARRL books. > > David > G3UNA >> >> While Cookie's comments are true, there is a useful type of short antenna >> known as a Normal Mode Helix, which if built, tuned and matched correctly _______________________________________________ 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 David Cutter
There are many forms of shortened antennas that work
to varying degrees. Antenna selection and installation is a very complicated situation and the ARRL Antenna Handbook, as large as it is only has a fair sampling of all the information that is available. Any antenna that completed the desired communication worked. Any antenna that could not complete the desired communication did not work. We talk a lot on this reflector about how wonderful the Elecraft products work, but even Elecraft transceivers need to be connected to an effective antenna to achieve the desired result. I have a friend who has a 3 element SteppIR at 70 feet on top of a mountain. He thinks it is a poor antenna because at his previous QTH he had a Hygain 5 element full sized beam at 110 feet which worked much better. Several stations around the world have antenna systems that cover many acres and cost 6 or 7 figures and they work very well. On the other hand, I knew a ham in 1976 who set out to work all states using a Weller Soldering Gun laying on his hamshack floor for an antenna. He was however, driving it with a kilowatt and an expensive antenna tuner. The G5RV antenna and its variations is a clever design and allows working most bands with the assistance of a good antenna tuner. My 160 meter Carolina Windom is a different design that does the same and I have worked DXCC with it in less than a year's time. Both are wire antennas and not very expensive, but not free either. The most expensive thing is ground to install them where antenna restrictions don't bring down the wrath of the taste police. (I have been trying for over 50 years to convince the world that antennas are beautiful, but without success) Neither can compete in a match with a good tri-bander at 60 feet. Helix antennas will work. They will not work as well as a full sized antenna. The Outbacker and the Hamstick come to mind as helix antennas that work. The shorter that you make them, the less efficient they are but we all know that in some instances we can reduce power to a watt or less and still maintain communication. The same goes for antennas. The rubber duck on your hand held will work a repeater if you are close enough. A quarter wave will work the repeater from farther away. Either one will work better if you go to the roof of a 10 story building instead of standing on the ground. Either antenna will work better outside and in the clear than in a building. Antenna selection, like most things in life, requires a lot of compromising. You have to live with your budget, your living circumstances, the XYL and your local taste police. But, there is no free lunch! You can move, you can get a new XYL, but you can't cheat Mother Nature. Cookie, K5EWJ --- David Cutter <[hidden email]> wrote: > I seem to remember a 40m beam made this way in one > of the old ARRL books. > > David > G3UNA > > > > While Cookie's comments are true, there is a > useful type of short antenna > > known as a Normal Mode Helix, which if built, > tuned and matched correctly > > _______________________________________________ > 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 |
Re: dipole antenna efficiency
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In reply to this post by Geoffrey Mackenzie-Kennedy
Shaun Oliver <[hidden email]> wrote: >I was thinking of using 18 mm electrical conduit. with 2 mm spacings for >each turn of the wire. ----------------------------------------------------------------- The diameter is a bit on the small side for the low bands, but NM Helix antennas working as 'quarter wave' radiators on the low bands designed for mobile use, and whose diameter was similar, performed well when evaluated using a proper antenna range, better than a base loaded 8ft whip. The important consideration is that the antenna resonates within the range of frequencies used in the band for which the antenna is designed. I have not tried a single NM Helix with an external tuner for multiband operation nor tried to model one using EZNEC. Good luck! 73, Geoff GM4ESD PS 'Old scribe' --- hmmmpf :-) _______________________________________________ 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 n8ewy
bloody 'ell,,, that was slightly more than I barganned for. oh well,
every little bit helps, and ultimately confuses. shaun. On 4/01/2008 11:58 PM, the old scribe known as Dale Putnam was able to impart this pearl of wisdom: > What is needed is a good effecient, multiband antenna with a general > coverage pattern. > The old saying applies... higher is better. Ok.. now that means up is > good. Low isn't. Unless you are > intent upon working everyone, including the local tv, stereo, and > sometimes even the garage door opener, within a couple hundred miles. > So.. high is good. > Now.. lets take a little bite at a time. A finite amount of power out > of a transmitter.. that doesn't change much, or shouldn't at least. So.. > power out.. now it radiates best from an antenna... ok... now, it seems > to me that the best way to get the power to the antenna is with a > feedline, and the more power that can get into the antenna, the better > it will get radiated. So.. best feedline, under the conditions... > installation restrictions apply. The best feedline in the world... won't > do a lotta good if it isn't installed correctly. Shorts.. poor > connectors... bends too tight,... too close to metal... all apply. > How about asking the feedline to transfer power outside of the > parameters that it was intended? Ok.. so what is best? We ask feedline > to transfer power over a range of freq. into an antenna that is asked to > radiate with high effectiveness over the same range. If you want to do > the math... go for it. There are others that do that rather well... I'd > drather spend time playing radio, but the math still applies. So.. what > works? Everyone has their own "best". Generally speaking, the most > effective is a rather high impedance transmission or feedline. Ok... > open line.. window line.. homebrew... high price... all are > considerations.. even consideration of a single wire feeder known as a > "G" transmission line will do rather well, if the previous > considerations are taken. So.. now we have a feedline. Next the antenna. > Oh boy, here it comes, to where the rope meets leather. The antenna > needs to radiate. Really well.. and that is generally measured at the > other fellow's s meter or ears. Ok, so first, where do you want to talk? > Lets break it down. Inside a 600 mile radius or outside that circle? Now > we all want to talk all over the world... and have the strongest signal > all the time.. That just isn't going to happen. If a good signal is to > be expected within the country.. the antenna needs to be able to radiate > in such a manner as to put a signal to right "there"! Ok, we can all > figure out which antenna has what radiation pattern.... on paper. > And that is a great start. Now... how about the ground effects... the > extra bends and twists? All those can be considered, sure, but the > overriding thought may well be that the antenna needs to accept the > power being brought to it, and radiate it. Resonance, or being "cut to > frequency" works well for the imedance match to the feedline, if that is > a choice to apply. If it is a low impedance feedline.. a small change > will be noticed, because a 5 ohm change referenced to 50, isn't the > same as the same 5 ohm difference referenced to 600 ohm. Bottom line? > Ok.. here it is.. an antenna that works over the range that is needed, > and radiates with the best chosen pattern, with the highest transfer of > power from the feedline to the ether. Pick one... there are many. Many, > many pages of very good information is available to help you choose. > That is applicable.. right now. With the winter weather upon us.. now is > the time for a bit of reading, consideration... and choose. And.. if you > really want that antenna to stay up?... better consider putting it up in > the winter too.. if you put it up in the winter, it will last longer.. > and pretty much work well. Some of the best antennas I've used, have > been put up in the dead of winter, and some during blizzards. Not > necessarily recommended. Which would you rather do? Build it, or maybe > read about it and choose wisely, get everything ready.. and the first > warm day... get ready... get set... then build away! > > See you in the pileups, foxhunts, and most importantly... in the log, > and that's a nice QSL too! > > --... ...-- > Dale - WC7S in Wy > > > > ------------------------------------------------------------------------ > Make distant family not so distant with Windows Vista® + Windows Live™. > Start now! > <http://www.microsoft.com/windows/digitallife/keepintouch.mspx?ocid=TXT_TAGLM_CPC_VideoChat_distantfamily_012008> > > __________ NOD32 2759 (20080101) Information __________ > > This message was checked by NOD32 antivirus system. > http://www.eset.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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In reply to this post by David Cutter
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In reply to this post by n8ewy
Shaun, Dohn, and All,
Your proposal to wrap wire around pipe will probably end up being a "bust". In essence, you would just be loading a coil, and it would be very inefficient as a radiator. Some have tried to use a "helical" approach in order to shorten the overall length, but again that doesn't work all that well either. An example would be using the old "Slinkey" wire toys that we all probably had at one time or another. Those can work, after a fashion, but are generally poor performers. I disagree about the G5RV also. That is not a very good antenna, notwithstanding the huge amount of use those antennas get. The problem is that the G5RV was never intended to be an "all band" antenna, and it is a performer on all but a couple of bands. Unless you use a tuner, you will be very unhappy with the results you get with a G5RV design, particularly with modern rigs that don't have the advantage older tube-type transmitters had with pi-network coupling. The warts that a G5RV has is well documented, and the latest thing I remember reading about it was in a recent issue of Sprat--the Spring 2007 issue. Therein is a discussion by ex-ZS6BKW, who is famous for originating much of the variations for the G5RV that are in use today. Paraphrasing his own words, don't expect much from a G5RV unless you at least use a tuner! Unless you want to put up some sort of trap dipole, or a multi-band vertical, your best option is to get a decent tuner and put up a dipole with balanced line feeders. The 88 foot antenna described by L.B. Cebik on his website (www.cebik.com), is an excellent choice for a simple antenna that will work well on 80 meters through 10 meter. You can shorten that to 44 feet if you want to give up 80 meters. That will fit in just about anyone's backyard, unless you live in a condo. The higher you get it, the better it will work. Just don't use coax, or the losses will eat you alive! You can coax feed an antenna that is resonant with good results. But when you try to use it on a higher frequency (like using an 80 meter coax fed antenna on 40 meters), the results turn to mush. The same antenna fed with balanced line through a tuner will work substantially better at higher frequencies. The resonant antenna (130 feet on 80) works better than the 88 foot antenna does on 80, but the 88 foot version (or the 44 foot version) is intended to standardize your radiation pattern, and is still a decent performer on 80 meters. Another option would be a remotely tuned vertical on your roof. Dr. Megacycle (KK6MC), suggested this to me not long ago when he visited my shack. His advice was to put up a 22 foot vertical, remotely tuned, and using balanced feedline. This would give you pretty decent performance from 40 meters through 10 meters. You would need as many radials (random length) as possible. This was a suggestion as an alternative to my R7 vertical, which is a pretty good performer, but perhaps not as good as the suggested alternative. I haven't tried that yet, but I'd like to. I'm sure the suggestion is a good one. This may be more than you wanted to hear, but it seemed as if you were struggling to come up with a solution. Hopefully it helps some in that process. If wire antennas, or verticals, are just not practical for you, you might want to try a mini-loop. These aren't nearly as efficient as a good wire antenna, but they are quite small, and the results can often surprise you. Besides, they are fun to build! Dave W7AQK ----- Original Message ----- From: "Dohn" <[hidden email]> To: "'Shaun Oliver'" <[hidden email]>; <[hidden email]> Sent: Friday, January 04, 2008 2:50 AM Subject: RE: [Elecraft] dipole antenna efficiency > Shaun, > > For materials needed vs. radio theory, you just can't beat a G5RV antenna. > IMHO I've used mine with my K1, K2 and several home brew projs and it > works > great time and again. Yes, you want to get the center up there a ways. > Say > around 35-40 feet, but the payoff was good for me. There are a number of > sites out there that have good versions of a very old, classic antenna. > Very few parts (all of which can be made with junk around the house. Very > little investment for a sound payoff. > > Dohn N8EWY > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Shaun Oliver > Sent: Thursday, January 03, 2008 9:20 PM > To: [hidden email] > Subject: [Elecraft] dipole antenna efficiency > > Hi all, > if I were to make a dipole, would coiling it round a piece of plastic > piping decrease the efficiency of the thing? I intend on making one for > 40 meters, one for 80 meters, and one for 10 meters. I've worked out > that1 meter of piping will suffice for each leg of each antenna. > thanks in advance. > shaun > _______________________________________________ > 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 > _______________________________________________ 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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Dave's observations are "right on" and good reading.
I've never understood the popularity of the G5RV. It's achieved a sort of "cult" following. The original design was for a 20M -ONLY- antenna, and somehow has morphed into a do everything hoax. I do antenna talks at conventions and hamfests, and I always ask; "How many of you use a G5RV"? The hands go up and it's usually about 50% of the audience. I say; "Gosh, I'm sorry", and try to show them how much easier and more efficient it would be to simply use the open wire feeder portion of the antenna and a balun at/in the (required) tuner. Some years ago the "Carolina Windom" had the same sort of following.... 73! Ken Kopp - K0PP [hidden email] or [hidden email] _______________________________________________ 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 w7aqk
I understand many G5RV's are getting replaced with these antennas. I
have the Grampy version, that is 100' long on each side, for a total of 300' of wire on each side, all in a 100' on each side package. Have had good luck with it. Their shortest is a bit over 70'. http://www.k1jek.com/ - David Wilburn [hidden email] K4DGW K2 S/N 5982 On Fri, 2008-01-04 at 09:33 -0700, David Yarnes wrote: > Shaun, Dohn, and All, > > Your proposal to wrap wire around pipe will probably end up being a "bust". > In essence, you would just be loading a coil, and it would be very > inefficient as a radiator. Some have tried to use a "helical" approach in > order to shorten the overall length, but again that doesn't work all that > well either. An example would be using the old "Slinkey" wire toys that we > all probably had at one time or another. Those can work, after a fashion, > but are generally poor performers. > > I disagree about the G5RV also. That is not a very good antenna, > notwithstanding the huge amount of use those antennas get. The problem is > that the G5RV was never intended to be an "all band" antenna, and it is a > performer on all but a couple of bands. Unless you use a tuner, you will be > very unhappy with the results you get with a G5RV design, particularly with > modern rigs that don't have the advantage older tube-type transmitters had > with pi-network coupling. The warts that a G5RV has is well documented, > and the latest thing I remember reading about it was in a recent issue of > Sprat--the Spring 2007 issue. Therein is a discussion by ex-ZS6BKW, who is > famous for originating much of the variations for the G5RV that are in use > today. Paraphrasing his own words, don't expect much from a G5RV unless you > at least use a tuner! > > Unless you want to put up some sort of trap dipole, or a multi-band > vertical, your best option is to get a decent tuner and put up a dipole with > balanced line feeders. The 88 foot antenna described by L.B. Cebik on his > website (www.cebik.com), is an excellent choice for a simple antenna that > will work well on 80 meters through 10 meter. You can shorten that to 44 > feet if you want to give up 80 meters. That will fit in just about anyone's > backyard, unless you live in a condo. The higher you get it, the better it > will work. Just don't use coax, or the losses will eat you alive! You can > coax feed an antenna that is resonant with good results. But when you try > to use it on a higher frequency (like using an 80 meter coax fed antenna on > 40 meters), the results turn to mush. The same antenna fed with balanced > line through a tuner will work substantially better at higher frequencies. > The resonant antenna (130 feet on 80) works better than the 88 foot antenna > does on 80, but the 88 foot version (or the 44 foot version) is intended to > standardize your radiation pattern, and is still a decent performer on 80 > meters. > > Another option would be a remotely tuned vertical on your roof. Dr. > Megacycle (KK6MC), suggested this to me not long ago when he visited my > shack. His advice was to put up a 22 foot vertical, remotely tuned, and > using balanced feedline. This would give you pretty decent performance from > 40 meters through 10 meters. You would need as many radials (random length) > as possible. This was a suggestion as an alternative to my R7 vertical, > which is a pretty good performer, but perhaps not as good as the suggested > alternative. I haven't tried that yet, but I'd like to. I'm sure the > suggestion is a good one. > > This may be more than you wanted to hear, but it seemed as if you were > struggling to come up with a solution. Hopefully it helps some in that > process. If wire antennas, or verticals, are just not practical for you, > you might want to try a mini-loop. These aren't nearly as efficient as a > good wire antenna, but they are quite small, and the results can often > surprise you. Besides, they are fun to build! > > Dave W7AQK > > > > ----- Original Message ----- > From: "Dohn" <[hidden email]> > To: "'Shaun Oliver'" <[hidden email]>; > <[hidden email]> > Sent: Friday, January 04, 2008 2:50 AM > Subject: RE: [Elecraft] dipole antenna efficiency > > > > Shaun, > > > > For materials needed vs. radio theory, you just can't beat a G5RV antenna. > > IMHO I've used mine with my K1, K2 and several home brew projs and it > > works > > great time and again. Yes, you want to get the center up there a ways. > > Say > > around 35-40 feet, but the payoff was good for me. There are a number of > > sites out there that have good versions of a very old, classic antenna. > > Very few parts (all of which can be made with junk around the house. Very > > little investment for a sound payoff. > > > > Dohn N8EWY > > > > -----Original Message----- > > From: [hidden email] > > [mailto:[hidden email]] On Behalf Of Shaun Oliver > > Sent: Thursday, January 03, 2008 9:20 PM > > To: [hidden email] > > Subject: [Elecraft] dipole antenna efficiency > > > > Hi all, > > if I were to make a dipole, would coiling it round a piece of plastic > > piping decrease the efficiency of the thing? I intend on making one for > > 40 meters, one for 80 meters, and one for 10 meters. I've worked out > > that1 meter of piping will suffice for each leg of each antenna. > > thanks in advance. > > shaun > > _______________________________________________ > > 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 > > > > _______________________________________________ > 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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On Fri, 4 Jan 2008, David Wilburn wrote:
> I understand many G5RV's are getting replaced with these antennas. I > have the Grampy version, that is 100' long on each side, for a total of > 300' of wire on each side, all in a 100' on each side package. Have had > good luck with it. Their shortest is a bit over 70'. And should you want to roll your own: http://www.hamuniverse.com/cobraantenna.html Thom,EIEIO Email, Internet, Electronic Information Officer www.baltimorehon.com/ Home of the Baltimore Lexicon 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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In reply to this post by dave.wilburn
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Re: dipole antenna efficiency
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In reply to this post by WILLIS COOKE
WILLIS COOKE wrote:
> Shaun, it will decrease the efficiency drastically. A > two meter long 80 meter dipole will be about 10% as > efficient as one 40 meters long at the same height. That's only conditionally true, although the conditions are probably going to apply in this case. An antenna that is a long way from the ground (or over a low loss ground) will have a low radiation resistance if it is short, but could be efficient if the loss resistances in the antenna and ATU are small. (I suspect that an antenna that is short compared with its height may also have lower ground losses, but I haven't researched this.) As far as I know, a helically loaded antenna will have a higher radiation resistance than one with all the inductance lumped in the ATU, otherwise they wouldn't be so popular on hand-helds. On the other hand, it may well have rather higher ohmic losses. If <memo.cgu.edu.tw/jui-ching/antenna3.pdf> is correct, one would expect an 80m dipole, constructed from normal mode helices, with a span of 2 metres, to have a radiation resistance of about 200 milli-ohms, whereas <http://memo.cgu.edu.tw/jui-ching/antenna1.pdf> seems to suggest 123 milliohms for lumped loading in the ATU, The radiation resistances scales as the square of the length, providing the antennas are short. I'm also fairly sure that the amount of wire to wind on the helix is significantly different from the amount that would be used in a straight line. My gut feeling is that it should be less, but I haven't researched that, either, although another URL pulled in searching for the above ones suggests one gets the length by pruning back from a quarter wave, although it didn't say whether that allowed for end effects. If this is being used indoors, coupling to the building structures and services may well increase the losses - or they could act as the real radiator! Note that these radiation resistances are over an order of magnitude outside the specification range for the KAT2. I do sympathize with the problem though, as I'm antenna restricted, and haven't really solved the problem yet. -- David Woolley Emails are not formal business letters, whatever businesses may want. RFC1855 says there should be an address here, but, in a world of spam, that is no longer good advice, as archive address hiding may not work. _______________________________________________ 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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Re: dipole antenna efficiency
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In reply to this post by Shaun Oliver
WILLIS COOKE wrote:
>I have a 1973 and a 1977 Handbook and I don't see it in either. What matching method did they use? Sorry my error, I should have said the 13th (1974) edition of the ARRL *Antenna* Handbook - page 219. They used an airwound transformer at the centre of the driven element, 19 turns of B&W 3025 stock connected between the two halves of the helical driven element with a 12 turn tightly coupled link primary. Looking into the link the impedance at antenna resonance was approximately 12 ohms. They used a broadband 1 : 4 balun to raise the impedance to 48 ohms. To reduce antenna Q, short lengths of aluminum welding rod were attached to the free ends of the helical elements. The antenna was a yagi, driven element and director spaced 15ft 8 inches. >I don't think that EZNEC can model a helix very well. EZNEC can only handle straight wires and inductances can be entered either by inductance value or impedance. The closest representation >would be short lengths of wire with several loading coils. I agree, and I am not certain either that an EZNEC model consisting of several loading coils would provide useful answers because the helix could be viewed as a slow wave structure rather than a classic loaded wire. 73, Geoff GM4ESD _______________________________________________ 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 AC7AC
Folks,
Not to dispute the info that Ron has provided, but to add a bit to it --- Let me throw in my $.02 worth in this. Any antenna will radiate if you can feed power to it, and it will radiate all the power that is fed to it, but there is loss to consider too. If the radiator and the transmission line have zero loss, then all your transmitter power will go into the antenna and be radiated - period, but the practical world is not quite so simple, real components have real loss - the challenge is to make the loss a minimum given the circumstances that exist for your installation. OK, so zero loss is the ideal condition. In practice, we have resistive and other losses to contend with. When the load impedance of an antenna falls below 20 ohms or so, I begin to worry about losses because the radiation resistance is a significant fraction of the total resistance. A loss of 10 ohms is insignificant with a radiation resistance of 100 ohms, but a loss of 10 ohms with a radiation resistance of 5 ohms is indeed significant. - that is especially true of verticals where ground loss is a significant factor. A higher feedpoint impedance can be dealt with by using a matching network of some sort, but low feedpoint impednces need to be given special attention so that the line resistance (and the ground resistance in the case of verticals) is minimized. Remember that low impedances mean high currents, and given a fixed resistance, the higher currents mean greater losses - it is all in the physics - you cannot fool Mother Nature. As a side note - window line performs well and with low loss when dry, but when it is wet, the losses in window line can become severe. If you can arrange true open wire feeders, the loss should be low, dry or wet. 73, Don W3FPR . Ron D'Eau Claire wrote: > That's a "linearly loaded" doublet. The zig-zag provides a little more > inductive reactance to help offset the capacitive reactance caused by the > overall length being short. Studies suggest that the resistive losses in the > wire is somewhat less using the "zig zag" than using loading coils each side > of center. So the linear loaded antenna is at least somewhat more efficient. > > > Since that antenna is fed with a ladder line, the length is unimportant > anyway, except to choose a combination of radiator and feeder length that > provides a reasonable impedance on each band. If you have a wide-range > tuner, that's not important either. > > You can skip the linear loading and simply put up a center fed wire fed with > high-impedance (400 to 600 ohm), low loss line. There will be almost no loss > in "gain" over a 1/2 wave radiator as long as the radiator segment is at > least 1/4 wave long, end to end, plus another 1/8 wavelength in the feeders. > That adds up to a total of 1/2 wave of wire counting the two wires in the > feeder and the radiator. > > 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: dipole antenna efficiency
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In reply to this post by Shaun Oliver
The *problem* with ladder line fed antennas is that it's very
difficult to remove common mode noise from them. If that's not an issue for you ... fine. But if it is... 73 de chris K6DBG _______________________________________________ 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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