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Hi
This is a little off topic, but I don't know of a better place to find someone that would know the answer to my question. Many years ago I used one coax to feed three different inverted V antennas all for different bands. At the time I thought they worked just fine. Worked all kinds of dx with the setup. I have been told lately that the unused antennas on the setup would pick up additional noise. Has anyone ever done any testing with multiple antennas on one feedline to see if they really do pick up extra noise? I'm thinking about putting up new inverted V antennas on 160, 80, and 40 meters and feeding them with one coax. Sure beats antenna switching and it always seem to me that the signal would go to the resonate antenna. I always used a coaxial balun in the feedline. Any ideas would be appreciated. Thanks Scott N5SM _______________________________________________ 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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Yes, you CAN put multiple dipoles on one feedline.
It's commonly done in the government and/or commercial world. It's often referred to as a "fan dipole". The feedline can be either coax or open wire/TV twinlead. Picture two telephone poles (or towers) with the support points for the individual dipoles several feet apart vertically along the two poles/towers. Such an arrangement is sometimes seen at a National Guard armory or Civil Defense center. The dipoles -DO- interact and will need length adjustment, one at a time 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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I happen to have pictures of just such a beast at
http://www.craigr.com/coppermine/thumbnails.php?album=35. It's cut for 40/20/10 meters and works nicely on 15 of course. The KAT100 tuner makes it work on the WARC bands and even on 80m though not very well. Craig NZ0R K2/100 #4941 K1 #1966 KX1 #1499 -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Ken Kopp Sent: Monday, February 19, 2007 4:41 PM To: [hidden email]; [hidden email] Subject: Re: [Elecraft] wire antennas Yes, you CAN put multiple dipoles on one feedline. It's commonly done in the government and/or commercial world. It's often referred to as a "fan dipole". The feedline can be either coax or open wire/TV twinlead. Picture two telephone poles (or towers) with the support points for the individual dipoles several feet apart vertically along the two poles/towers. Such an arrangement is sometimes seen at a National Guard armory or Civil Defense center. The dipoles -DO- interact and will need length adjustment, one at a time 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 _______________________________________________ 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 wsm-3
Scott,
I use 'fanned dipoles' fed with a common coax - yes a balun is highly recommended. The secret to fanned dipoles is to get the ends as far apart as possible so they do not interact. Expect some interaction in any case, and tune them from the lowest band first. I have tried 5 bands - in a word, DON'T, unless you are willing to drive yourself crazy cutting and pruning due to the interaction. 3 bands is about my limit. One other point - do not try to combind bands that are close to the 3rd harmonic of the lower one on the same coax - that too will drive you crazy trying to tune them because the 3rd harminic frequency antenna will also present a low impedance feedpoint. In other words, stay away from combining 80 and 30 meters or 40 meter and 15 meters. I successfully use an 80/40 meter combination, a 20/15/10 combination and a 30/17/12 combination - 3 feedlines to cover 8 bands. Some are dipoles and others are inverted VEE. 73, Don W3FPR > -----Original Message----- > > Hi > This is a little off topic, but I don't know of a better place to > find someone that would know the answer to my question. > Many years ago I used one coax to feed three different inverted V > antennas all for different bands. At the time I thought they worked > just fine. Worked all kinds of dx with the setup. I have been told > lately that the unused antennas on the setup would pick up additional > noise. > Has anyone ever done any testing with multiple antennas on one > feedline to see if they really do pick up extra noise? > I'm thinking about putting up new inverted V antennas on 160, 80, and > 40 meters and feeding them with one coax. Sure beats antenna > switching and it always seem to me that the signal would go to the > resonate antenna. I always used a coaxial balun in the feedline. > Any ideas would be appreciated. > Thanks > Scott N5SM > > _______________________________________________ > 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 > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.441 / Virus Database: 268.18.2/692 - Release Date: > 2/18/2007 4:35 PM > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.2/692 - Release Date: 2/18/2007 4:35 PM _______________________________________________ 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 Ken Kopp-2
On Mon, 19 Feb 2007 22:41:24 -0000, Ken Kopp wrote:
>Picture two telephone poles (or towers) with the support >points for the individual dipoles several feet apart vertically >along the two poles/towers. >Such an arrangement is sometimes seen at a National Guard >armory or Civil Defense center. A lot of them have been replaced by the now-ubiquitous B&W All Band Folded Dipole - the same antenna that I use in an open-V configuration. It works equally flat over the HF (1.8-30 MHz) spectrum. -- 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 _______________________________________________ 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 wsm-3
[hidden email] wrote:
> Has anyone ever done any testing with multiple antennas on one > feedline to see if they really do pick up extra noise? Hm, nobody answered this. My feeling (and it's not based on experiments) is that it would normally not be a problem. For example, if you have an 80 and 160 meter dipole on one feedline, then the unused antenna would be just as likely to pick up additional signals on the desired band as it would noise. So while it might have a tiny bit more gain, the s/n ratio wouldn't change. Having said that, the total signal and noise voltage delivered to the receiver front end would be greater, since the bandwidth of the combination of antennas would be wider. If the receiver's dynamic range characteristics were inadequate, there might be spurious signals generated in the receiver. For example, if you lived in Europe where there are enormous SWBC signals around 40 meters at night, then you probably wouldn't want a 40 meter dipole in parallel with your 80 meter one. -- 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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In reply to this post by wsm-3
In a message dated 2/19/07 4:45:23 PM Eastern Standard Time,
[hidden email] writes: > have been told > lately that the unused antennas on the setup would pick up additional > noise. If so, it will also pick up additional signal. > Has anyone ever done any testing with multiple antennas on one > feedline to see if they really do pick up extra noise? I haven't done any scientific testing, but in actual operation (FD), I have not found any difference from a regular dipole. The principle of multiple parallel dipoles is that the nonresonant dipoles present a high impedance, so almost all of the power goes to the resonant dipole. That principle works the other way, too, when receiving. > I'm thinking about putting up new inverted V antennas on 160, 80, and > 40 meters and feeding them with one coax. Sure beats antenna > switching and it always seem to me that the signal would go to the > resonate antenna. I always used a coaxial balun in the feedline. > Works for me! How high of a center support do you have? 73 de Jim, N2EY _______________________________________________ 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 Ken Kopp-2
If paralleled dipoles for different bands on a single feed line are called a
"fan dipole" it's a misnomer that can cause a lot of confusion. Sometimes folks pick up short-hand term by accident, like assuming that a dipole is always fed at the center to be a "dipole" when, in fact, a dipole is a half-wave radiator and, being exactly 1/2 wave long it has an electrostatic pole at each end, hence it is a "dipole". It's "dipole-ness" has nothing to do with where or how it's fed RF. A "fan dipole" is a single-band affair. It's is a way of broadening the bandwidth of a single-band dipole by simulating a "fat" wire using multiple wires. Typically the wires join at an apex at the center and spread or "fan" out at the far end with cross-wires connecting the ends. That forms larger effective radiator diameter that reduces the "Q" of the antenna; hence the bandwidth is increased. It's not a commonly-used antenna because a simple wire dipole usually has adequate bandwidth on 40 meters and up, and in practice even a large "fan" doesn't broaden the bandwidth all that much; not enough to cover the 3.5 - 4 MHz range with a low SWR, for example. However, like any "fat radiator" dipole, the resonant length is shortened a bit, which can be a help in limited space. Cebik has a good write-up on fan dipoles and their close cousin, the bow tie antenna, at www.cebik.com as part of his discussion of small beams. 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 wsm-3
Scott:
I use several fan dipoles. Both use two elements. One operates on 40 and 30 meters (and I get 15 meters, 3rd harmonic of 40, free into the bargain, but the SWR is a bit above 2 on 15 m, and I must use tuner to match it to the K2. ). The other antenna operates on 80 and 20 meters (and I get 17/12 meters, 3rd and 5th harmonic of 80 meters free into the bargain, but the SWR is a bit above 8 on 12/17 m. I must use tuner to match it to the K2 on 17/12. However, the line losses are acceptable, and the antenna is very effective on all four bands. ) Several gotchas. The elements do interact. The shorter element will be non-trivially off from the "468" formula. The longer element is pulled much less noticeably. However, if you're looking for low SWRs of both bands, be prepared to do a lot of tweaking. I agree with other posted comments. If you use more than 2 elements, be prepared to do a very great deal of very frustrating of tweaking. Very important: Construct your antenna in such a way that the short element cannot wrap around the long one. If it does wrap, it will pull your painstakingly tuned antenna way off the desired resonant frequency. Other caution: Do not suppose that you can simulate a fan dipole on EZNEC. The condition of two parallel elements of unequal length very close together is one place where the computer model departs from reality. I do not use baluns, and it does not seem to have caused me any trouble. Good luck, Steve AA4AK At 04:44 PM 2/19/2007, [hidden email] wrote: >Hi >This is a little off topic, but I don't know of a better place to >find someone that would know the answer to my question. >Many years ago I used one coax to feed three different inverted V >antennas all for different bands. At the time I thought they worked >just fine. Worked all kinds of dx with the setup. I have been told >lately that the unused antennas on the setup would pick up additional >noise. >Has anyone ever done any testing with multiple antennas on one >feedline to see if they really do pick up extra noise? >I'm thinking about putting up new inverted V antennas on 160, 80, and >40 meters and feeding them with one coax. Sure beats antenna >switching and it always seem to me that the signal would go to the >resonate antenna. I always used a coaxial balun in the feedline. >Any ideas would be appreciated. >Thanks >Scott N5SM > >_______________________________________________ >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 N2EY
Jim's another OT like me when all the HF Ham bands were
harmonically-related. Paralleled dipoles worked quite well in that setup although there was a fair bit of interaction, especially from an 80 meter dipole on a paralleled 10 meter dipole. I still recall one summer day running my antenna up and down countless times trying to find the right balance. (I think that may have driven me back to open wire feedline at that QTH <G>). As he pointed out, the lower-frequency antenna tends to offer a very high impedance at the center. For example, on 40 meters, a 120 foot 80 meter dipole in parallel would a two half waves, presenting a voltage loop at the feed point. That means it'd not take (or deliver to the feedline) significant power. Such combinations were used on 80/40/20/10 meters with paralleled 132 foot, 66 foot, 33 foot and 16 foot wires. And 15 meters worked well as a bonus using the 40 meter dipole. On 15 a 66 foot wire is 3/2 waves long, presenting a current loop at the center feedpoint. So one 66 foot long wire did duty as both a 40 meter and 20 meter antenna, presenting a usably-low SWR to a 50 ohm coaxial feedline. It gets a lot more complicated when one tries to use the non-harmonically-related bands. Indeed, I can't imagine how one would pull it off <G>. So your idea is a sound, tried-and-true one for coverage of the bands you listed. And you get 15 meters as a bonus if you want <G>. Ron AC7AC -----Original Message----- In a message dated 2/19/07 4:45:23 PM Eastern Standard Time, [hidden email] writes: > have been told > lately that the unused antennas on the setup would pick up additional > noise. If so, it will also pick up additional signal. > Has anyone ever done any testing with multiple antennas on one > feedline to see if they really do pick up extra noise? I haven't done any scientific testing, but in actual operation (FD), I have not found any difference from a regular dipole. The principle of multiple parallel dipoles is that the nonresonant dipoles present a high impedance, so almost all of the power goes to the resonant dipole. That principle works the other way, too, when receiving. > I'm thinking about putting up new inverted V antennas on 160, 80, and > 40 meters and feeding them with one coax. Sure beats antenna switching > and it always seem to me that the signal would go to the resonate > antenna. I always used a coaxial balun in the feedline. > Works for me! How high of a center support do you have? 73 de Jim, N2EY _______________________________________________ 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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For sheer inginuity, I just love the clothes line dipole in QST a few years
ago. If you have the facility to slide the feed point back and forth using a full loop (folded dipole), perhaps with a remote controlled motor, one feedline and one loop of wire will do a lot of multi-banding for you and be efficient. Sloper mode is the easiest mechanically where one end is easily accessible nearer the ground. David G3UNA _______________________________________________ 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 wsm-3
In a message dated 2/19/07 7:00:22 PM Eastern Standard Time,
[hidden email] writes: > A "fan dipole" is a single-band affair. It's is a way of broadening the > bandwidth of a single-band dipole by simulating a "fat" wire using multiple > wires. Typically the wires join at an apex at the center and spread or "fan" > out at the far end with cross-wires connecting the ends. That forms larger > effective radiator diameter that reduces the "Q" of the antenna; hence the > bandwidth is increased. That's what I think of when someone uses the term "fan dipole". > > It's not a commonly-used antenna because a simple wire dipole usually has > adequate bandwidth on 40 meters and up, and in practice even a large "fan" > doesn't broaden the bandwidth all that much; not enough to cover the 3.5 - 4 > MHz range with a low SWR, for example. > I disagree! Way back in the 1980s, WA3UZI and I did some tests on an 80/75 meter "fan dipole". We used four equal-length wires with spreaders at the ends, making a sort of giant bow tie. The far ends were not connected, they just terminated at the spreaders. The spreaders were horizontal and the whole thing was up about 50 feet, fed with 50 ohm coax. IIRC, if the ends were spread about six feet, the antenna had an SWR well under 2:1 from 3.5 to 4.0 MHz. The wires were a lot shorter than one would expect from the formula - about 57 feet or so. It was built so that one antenna could cover 80 CW and 75 phone on Field Day without need of a tuner, since the rigs we used could handle 2:1 SWR with no problem at all. It took a bit of pruning and testing to get the wire and spreader lengths right. It worked as well as a regular halfwave dipole. > However, like any "fat radiator" dipole, the resonant length is shortened a > bit, which can be a help in limited space. > Yup. Another approach is a cage dipole - multiple wires of the same length all in parallel, spaced around a circle throughout their lengths. I've not tried one because of the mechanical complexity compared to simple fan. Calculations (which I have not tried) predict that a cage of three feet in diameter is needed to get 2:1 SWR from 3.5 to 4.0 MHz. The big problem with such antennas is that they are heavier, more mechanically complex, and have much more wind/ice loading than a regular single wire. We had good supports at the old FD site, and the antenna only had to last a weekend. Even so, we only used it one year. > Cebik has a good write-up on fan dipoles and their close cousin, the bow > tie > antenna, at www.cebik.com as part of his discussion of small beams. > I suppose the best description of our antenna is a bow tie. 73 de Jim, N2EY _______________________________________________ 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 Don Wilhelm-3
On Mon, 19 Feb 2007 17:54:25 -0500, Don Wilhelm wrote:
>3 bands is about my limit. Yes -- beyond that, they get both electrically and mechanically unwieldy. >One other point - do not try to combind bands that are close to the 3rd >harmonic of the lower one on the same coax - that too will drive you crazy >trying to tune them because the 3rd harminic frequency antenna will also >present a low impedance feedpoint. In other words, stay away from combining >80 and 30 meters or 40 meter and 15 meters. This is also very good advice. W2DU has an excellent discussion of this on his website. Google to find it. It's in one of the chapters of his book. >I successfully use an 80/40 meter combination, a 20/15/10 combination Agreed. I also have an 80/40 fan that has loading coils at the ends of the 80 meter element to allow it load on 160 (and, of course, the 40 meter element works fine on 15. That antenna also works quite well (and it's a 4-band antenna!). The loading coils are from HyPower Antenna Co. Google to find them -- they're a good solution for antennas on small lots. I also have a 40/30/20 that works, but is not as well behaved as the harmonically related ones, for the reasons noted. 73, Jim Brown K9YC _______________________________________________ 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 wsm-3
Stuart wrote:
>Even simpler is a 80m dipole fed with balanced line to a tuner for all band >use. The window line is less costly than coax. A good quality tuner is >less lossy in multiband use than coax/ tuner balun, etc.. Balanced antennas >have fewer problems than off center feeds. Balanced line to dipole does not >need a balun at the antenna. That's always seemed the ideal approach to me. You can go anywhere with it with very low resulting losses, which is also very useful for MARS/CAP/SHARES work on those odd HF military frequencies. The only real problem seems to be routing the balanced line from the antenna into the shack without it having much interaction with nearby materials. A second problem is the lack of real balanced-line antenna tuners. Unbalanced tuners with that small output balun are problematic. I bought an old Johnson Matchbox just because it is one of the few true balanced tuners can can still be found. I know that MFJ has a couple of non-balun tuners design for balanced line, but I've never investivated their technical details, nor read reports on how well they perform. Obviously, these would not serve the "gotta swap bands in five seconds" contest crowd, but that's not me. I never trusted those resistor-terminated folding dipoles. Every analysis of them that I've ever read over the past 30 years has been basically unfavorable, as one would expect, with performance at best very much below that of a simple dipole. It is similar to a broad-band antenna design using any length of center-fed non-folded dipole fed with coax, with a hefty 50-ohm resistor across the coax leads at the connection to the dipole. You'd get good VSWR with that from 1.8 to 30 MHz! Come to think of it, about 25 years ago some outfit was hawking something just like that to hams at high cost. Yet, I'm sure you could make some contacts with it, just like you can with a resistor-terminated folded dipole. What these types of antennas show is that, no matter how bad an antenna design is, it'll work sometimes. TANSTAAFL! Mike / KK5F _______________________________________________ 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 always advise using a non-resonant length for a multi-band doublet with
tuner combination. There's a magic figure: multiples of 44ft, 88ft... that Cebik came up with which is a good compromise with impedance matching, ie not horrendously high or low X and R. I notice no-one has mentioned the G5RV and its derivatives, yet. David G3UNA ----- Original Message ----- From: "Mike Morrow" <[hidden email]> To: <[hidden email]> Sent: Tuesday, February 20, 2007 11:50 PM Subject: Re: [Elecraft] wire antennas > Stuart wrote: > >>Even simpler is a 80m dipole fed with balanced line to a tuner for all >>band >>use. The window line is less costly than coax. A good quality tuner is >>less lossy in multiband use than coax/ tuner balun, etc.. Balanced >>antennas >>have fewer problems than off center feeds. Balanced line to dipole does >>not >>need a balun at the antenna. > > That's always seemed the ideal approach to me. You can go anywhere with > it with very low resulting losses, which is also very useful for > MARS/CAP/SHARES work on those odd HF military frequencies. > > The only real problem seems to be routing the balanced line from the > antenna into the shack without it having much interaction with nearby > materials. > > A second problem is the lack of real balanced-line antenna tuners. > Unbalanced tuners with that small output balun are problematic. I bought > an old Johnson Matchbox just because it is one of the few true balanced > tuners can can still be found. I know that MFJ has a couple of non-balun > tuners design for balanced line, but I've never investivated their > technical details, nor read reports on how well they perform. Obviously, > these would not serve the "gotta swap bands in five seconds" contest > crowd, but that's not me. > > I never trusted those resistor-terminated folding dipoles. Every analysis > of them that I've ever read over the past 30 years has been basically > unfavorable, as one would expect, with performance at best very much below > that of a simple dipole. It is similar to a broad-band antenna design > using any length of center-fed non-folded dipole fed with coax, with a > hefty 50-ohm resistor across the coax leads at the connection to the > dipole. You'd get good VSWR with that from 1.8 to 30 MHz! Come to think > of it, about 25 years ago some outfit was hawking something just like that > to hams at high cost. Yet, I'm sure you could make some contacts with it, > just like you can with a resistor-terminated folded dipole. What these > types of antennas show is that, no matter how bad an antenna design is, > it'll work sometimes. TANSTAAFL! > > Mike / KK5F > _______________________________________________ > 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 Mike Morrow-3
Mike Morrow wrote:
> What these types of > antennas show is that, no matter how bad an antenna design is, it'll > work sometimes. TANSTAAFL! Has anyone seen the "Illuminator" from Tom Schiller, N6BT, of Force 12 fame? Fred K6DGW - Northern California Contest Club - CU in the 2007 CQP Oct 6-7 - www.cqp.org _______________________________________________ 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
I use a traditional wide-range balanced tuner - the same circuit Cebik shows
and that has been a Hamshack staple item among some of us since Marconi was around. Center link, split stator variable, and feeders tapped onto the coil. With that tuner feedline length has never been an issue at all. It matches easily values from a few ohms up to several thousand ohms: the highest impedance one might expect with typical antenna geometries. It uses a large coil with heavy wire to avoid ohmic losses at the low impedance end and wide-spaced transmitting cap to handle the very large RF voltages present feeding high impedance loads. It's not automatic, so it's not fast, but I can change bands in about 15 seconds. And it's flexible, handling unbalanced loads like an end fed wire or coax line with equal ease. My normal feedline is high-efficiency open wire line. My open wire line is made of #14 electrical wire separated by high-quality ceramic insulators at long intervals to minimize dielectric and ohmic losses. My antenna of choice has always been the doublet, since I've not had the space for a rhombic or other traveling wave type or the room for a tower and beam. As long as the doublet is at least 1/4 wavelength long, end to end, it's virtually as effective as a half wave. So a 66 foot doublet does a very good job on 80 and a 130 foot doublet does a good job on 160. The big issue on the lower bands is usually height, especially enough height for good low angle radiation from a horizontal antenna. That requires a height of at least 3/8 wave and 1/2 wave is better. On 160 meters it needs to be close to 100 feet up: 130 feet would be ideal <G>. I count myself lucky to get the wire 50 feet up. That provides low angles for DX on 40 meters and up. On 80 or 160 it's an omni-directional NVIS or "short skip" antenna providing excellent coverage out to about 1,000 miles or so on 80; a little less, typically, on 160. Where the wire is well over 1/2 wave long, it shows significant gain as the pattern breaks up into many lobes. In spite of the antenna patterns one finds in books, a real world antenna does not have zero radiation in any direction. It's a matter of having lobes that produce a superior signal in various directions. I've never noticed any deleterious effects from the lobes and long ago quit thinking much about trying to align the antenna for specific coverage. Ron AC7AC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of David Cutter Sent: Tuesday, February 20, 2007 4:14 PM To: Mike Morrow; [hidden email] Subject: Re: [Elecraft] wire antennas I always advise using a non-resonant length for a multi-band doublet with tuner combination. There's a magic figure: multiples of 44ft, 88ft... that Cebik came up with which is a good compromise with impedance matching, ie not horrendously high or low X and R. I notice no-one has mentioned the G5RV and its derivatives, yet. David G3UNA _______________________________________________ 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 am very much enjoying reading the discussions on wire antennas. I
have something I have been trying to figure out how to do for some time, and thought this might be a good place to ask. I have an 80m loop, up about 60 or 70 feet. Currently it is fed with 300 ohm line. All I could find at the time, as what I had left in 450 ohm line (after I helped my elderly neighbor get his antenna back up, and gave him some of the ladder line) was not long enough. Additionally, I went to the local hamfest this weekend and could not find a single vendor selling ladder line, but I digress. I have approximately 290 feet of wire in the air in a horizontal, triangular configuration, fed with (soon to be) ladder line, a balun (1:1) and then coax to the shack. Is it possible to switch this (seems possible from what I have read) to a 160m antenna by taking one side to ground at the balun and feeding the other side? If this is possible, is there a way to do this remotely? David Wilburn [hidden email] K4DGW _______________________________________________ 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,
As far as switching your loop to a 160 top loaded vertical, yes you can do it remotely with relays and a matching network. If your goal is efficiency on 160 meters, the relay switching os only a small part of the equation - you must have a good RF ground for the vertical to work against, and that menas lots of wires in the ground, radiating from the base of the antenna. Some will tell you tht 120 radials will give optimum performance, but 16 or more will give great performance as well. If the radials are buried, the length is not critical, lots of short buried radials will do almost as good as a moderate number of long ones - see the 160 meter antenna simulation results that are outlined on L B Cebik's website www.cebik.com. More information on low band antennas can be found in ON4UN's Low Band DXing book - there are many possibilities. For best results, put the 160 meter matching network at the base of the antenna and match it to your feedline. Since there are many possibilities, make some decision even though it may be a compromise and you too can be successful on 'top-band'. 73, Don W3FPR > -----Original Message----- > > I am very much enjoying reading the discussions on wire antennas. I > have something I have been trying to figure out how to do for some time, > and thought this might be a good place to ask. > > I have an 80m loop, up about 60 or 70 feet. Currently it is fed with > 300 ohm line. All I could find at the time, as what I had left in 450 > ohm line (after I helped my elderly neighbor get his antenna back up, > and gave him some of the ladder line) was not long enough. > Additionally, I went to the local hamfest this weekend and could not > find a single vendor selling ladder line, but I digress. I have > approximately 290 feet of wire in the air in a horizontal, triangular > configuration, fed with (soon to be) ladder line, a balun (1:1) and then > coax to the shack. Is it possible to switch this (seems possible from > what I have read) to a 160m antenna by taking one side to ground at the > balun and feeding the other side? If this is possible, is there a way > to do this remotely? > > David Wilburn > [hidden email] > K4DGW > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/694 - Release Date: 2/20/2007 1:44 PM _______________________________________________ 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
Have you tried using the antenna on 160 through a tuner just as it is?
Chances are you can match it even on 160M and if you do you will not have to worry about the ground losses you would have feeding it against ground (unless using lots of radials). Don K7FJ ----- Original Message ----- From: "David Wilburn" <[hidden email]> To: <[hidden email]> Sent: Tuesday, February 20, 2007 8:07 PM Subject: Re: [Elecraft] wire antennas >I am very much enjoying reading the discussions on wire antennas. I have >something I have been trying to figure out how to do for some time, and >thought this might be a good place to ask. > > I have an 80m loop, up about 60 or 70 feet. Currently it is fed with 300 > ohm line. All I could find at the time, as what I had left in 450 ohm > line (after I helped my elderly neighbor get his antenna back up, and gave > him some of the ladder line) was not long enough. Additionally, I went to > the local hamfest this weekend and could not find a single vendor selling > ladder line, but I digress. I have approximately 290 feet of wire in the > air in a horizontal, triangular configuration, fed with (soon to be) > ladder line, a balun (1:1) and then coax to the shack. Is it possible to > switch this (seems possible from what I have read) to a 160m antenna by > taking one side to ground at the balun and feeding the other side? If > this is possible, is there a way to do this remotely? > > David Wilburn > [hidden email] > K4DGW > > > _______________________________________________ > 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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