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Horizontal loop antenna
I am considering a horizontal loop antenna that would be "squarish"
(depending on tree locations) and about 400' in circumference. My (automatic) tuner is located in my garage (with 100' of coax going to the shack in the house). The lead wires for the antenna and ground are short and direct through the garage wall - I don't envision any feedline from tuner to the wire loop. I don't want to use a balun since there isn't really any feedline to balance and the impedances presented to the balun would be all over the (Smith) chart. Would it make sense to feed one end of the loop from the tuner and connect the other loop end to the ground connection near the tuner or just leave it open (essentially a square longwire antenna)? I would also have three counterpoise wires following the loop lying on the surface of the ground. The articles that I can find all use openwire feedlines and balanced tuners (or baluns) but that arrangement doesn't fit my situation. Thanks W0BF |
Horizontal loop antenna
On Sat, 09 Feb 2008 17:16:07 -0600, Bruce W. Ellis
wrote: I am considering a horizontal loop antenna that would be "squarish" (depending on tree locations) and about 400' in circumference. My (automatic) tuner is located in my garage (with 100' of coax going to the shack in the house). The lead wires for the antenna and ground are short and direct through the garage wall - I don't envision any feedline from tuner to the wire loop. I don't want to use a balun since there isn't really any feedline to balance and the impedances presented to the balun would be all over the (Smith) chart. Hi Bruce, Well, in fact you have described a feedline - the one going to the automatic tuner. This one has every need for choking as any line that left the tuner (which is, by and large, not recommended by most automatic tuner vendors). You probably also have DC power or control lines going to that tuner as well. They need choking too. However, given you also mention a 100 run, then this presumably means along or under ground. Ground proximity would probably snub any Common Mode currents which would then reduce your specific need for choking. Would it make sense to feed one end of the loop from the tuner and connect the other loop end to the ground connection near the tuner or just leave it open (essentially a square longwire antenna)? You might want to make it switchable. I would also have three counterpoise wires following the loop lying on the surface of the ground. This technique falls outside of the canon of most lore, but not without its benefits. However, three wires will not provide much efficiency gain. On the plus side, it could make a difference for NVIS. You don't mention much about frequencies of operation nor about directionality. The articles that I can find all use openwire feedlines and balanced tuners (or baluns) but that arrangement doesn't fit my situation. Thanks W0BF You have enough to work with as it is. As for openwire or coax feedlines; to my knowledge, autotuners are built to feed unbalanced antennas directly (at the feedpoint) rather than as traditional hand adjusted tuners being used away from the antenna. This is, perhaps, a bias from seeing too many SGCs. Anyway, I don't see a downside to your plan. 73's Richard Clark, KB7QHC |
Horizontal loop antenna
Try it...
Maybe you will like it... And if you don't, THEN we will say you should have known better in the first place :) denny / k8do |
Horizontal loop antenna
On Feb 9, 5:16*pm, Bruce W. Ellis wrote:
I am considering a horizontal loop antenna that would be "squarish" (depending on tree locations) and about 400' in circumference. *My (automatic) tuner is located in my garage (with 100' of coax going to the shack in the house). *The lead wires for the antenna and ground are short and direct through the garage wall - I don't envision any feedline from tuner to the wire loop. *I don't want to use a balun since there isn't really any feedline *to balance and the impedances presented to the balun would be all over the (Smith) chart. *Would it make sense to feed one end of the loop from the tuner and connect the other loop end to the ground connection near the tuner or just leave it open (essentially a square longwire antenna)? *I would also have three counterpoise wires following the loop lying on the surface of the ground. *The articles that I can find all use openwire feedlines and balanced tuners (or baluns) but that arrangement doesn't fit my situation. *Thanks * W0BF Greetings, I had a horizontal loop antenna up for several years prior to my moving to Texas. It was cut for 80 meters and was about 30 feet up in a square configuration. I fed it with coax to one corner, however I had a homebrew choke at the connection point. I used a 10" long piece of 6 inch pvc pipe with about 10 turns of coax around it. The antenna worked fairly well and by virtue of the design loops are pretty quiet. You mention 400 feet on your loop. The formula I used was 1005/ frequency = feet in loop. There is a yahoo group devoted to skywire loop antennas and some good info can be found there. At the present time I'm getting ready to erect an 80 meter loop, but this one will be fed with 600 ohm homebrewed ladder line into a Palstar balanced wire tuner. I'm anxious to get this on the air. 73 KI4BUN / AAV6TP TX |
Horizontal loop antenna
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Horizontal loop antenna
Sum Ting Wong wrote:
On Mon, 18 Feb 2008 13:47:22 -0800 (PST), wrote: There is a yahoo group devoted to skywire loop antennas and some good info can be found there. There is also an article on pg. 56 of the March 2008 QST on this topic. The author used ferrite on the coax/power cable to the auto tuner to isolate it an make it act as a balanced tuner. The loop in the article was fed directly and not with a feedline from the tuner to the loop. S.T.W. I once thought that would work, and even helped a little with an Antenna Compendium article promoting it a long time ago. But I came to realize that it doesn't matter at all whether the balun is at the input or output of the tuner -- the balun is just as effective one place as the other. The reason is that what counts is the common mode impedance, which is the impedance to ground seen looking along the outside of the coax toward the antenna, and this is the same on both sides of the tuner (except, of course, for the difference due to the short distance between the two points). Putting the balun the input has the disadvantage of making the tuner chassis hot. I'm sorry to see that QST's article review process still isn't working. Roy Lewallen, W7EL |
Horizontal loop antenna
I'm sorry to see that QST's article review process still isn't working. Roy Lewallen, W7EL Heck Roy, if it worked, Nov-Dec QEX would have been 14 pages shorter. (And a better rag for it as well!) W4ZCB |
Horizontal loop antenna
Bruce W. Ellis wrote:
"I am considering a horizontal loop antenna that would be "squarish" (depending on the tree locations) and about 400` in circumference." If you had more trees (octagonalish) would enclose more area with the same wire. Radiation is a function of loop area. Tesonant loops are often one wavelength in perimeter. 400` is about 122 meters. 160 meters = 525 feet. 80 meters = 262 meters. What band do you prefer? If a loop`s perimewter is a little too short for resonance, it`s inductive and can be tuned with a low-loss variable capacitor. The 20th edition of the ARRL Antenna Book has a horizontal loop "skywire" (squarish) on page 5-20. A 7 MHz loop at 40 ft. elevation has about the same radiation as a 7 MHz dipole at 30 ft. elevation for various azimuths. It might be worthwhile reading the Antenna Book article before construction. Best regards, Richard Harrison, KB5WZI |
Horizontal loop antenna
Richard Harrison wrote:
If you had more trees (octagonalish) would enclose more area with the same wire. Radiation is a function of loop area. Can you please explain that a little more? If you put 100 watts into a 400 foot circumference loop and it radiates 95 watts, will an 800 foot loop radiate four times that, or 380 watts? Then can you feed back 100 to put back into the loop, and have 280 left over to run your refrigerator to keep your beer cold? Or if the 800 foot loop radiates 95 of your 100 watts, does the 400 foot loop radiate only 23.75 watts? If that's what happens, where does the rest of the power go? Is the radiation pattern the same for a long skinny loop as for a round one, as long as the enclosed area is the same? . . . Puzzled, Roy Lewallen, W7EL |
Horizontal loop antenna
Roy Lewallen, W7EL wrote:
"Can you please explain that a little more? (Radiation is a function of loop area.)" Not being a typist, I`ll refer you to "TV And Other Receiving Antennas" by Arnold Bailey. On pages 407 and 408 Bailey gives two formulas for computing the antenna resistance for a loop antenna. On page 408, Bailey has Fig. 8-14 which plots radiation resistance (the stuff we build antennas for) versus the loop perimeter in wavelengths. For a square closed loop of one wavelength perimeter, the graph indicates about 50 ohms. Bill Orr, W6SAI in "All About Cubical Quad Antennas" gives the full-wave vertical loop antenna an impedance of 125 ohms on page 15. On page 14, Orr writes: "For purposes of illustration, the two wire folded dipole may be "pulled open" to a diamond-shaped loop fed at the bottom point. If this distortion of the loop is continued the antenna will become a shorted transmission line." A perfect circle is the geometric shape enclosing the most area for a given perimeter. The more corners a closed figure has, the more closely it usually approximates a circle. That is why I commented on an octagon versus a square. Best regards, Richard Harrison, KB5WZI |
Horizontal loop antenna
I'm missing something here. I don't see anywhere in the response which
explains how "radiation is a function of loop area" and why increasing the loop circumference would be advantageous. Richard Harrison wrote: Roy Lewallen, W7EL wrote: "Can you please explain that a little more? (Radiation is a function of loop area.)" Not being a typist, I`ll refer you to "TV And Other Receiving Antennas" by Arnold Bailey. On pages 407 and 408 Bailey gives two formulas for computing the antenna resistance for a loop antenna. On page 408, Bailey has Fig. 8-14 which plots radiation resistance (the stuff we build antennas for) versus the loop perimeter in wavelengths. For a square closed loop of one wavelength perimeter, the graph indicates about 50 ohms. Perhaps you build antennas for radiation resistance, but I think most people build them to maximize radiation in some direction. In any case, please exclude me from the "we" in your statement about what "we" build antennas for. You said "radiation is a function of loop area" and recommended a larger circumference. Equations are useless unless you understand how to apply them. So can you use those equations to show us how much more a loop of 800 foot circumference will radiate than one with a 400 foot circumference? You can assume 100 watts applied to each, and either zero wire resistance or any reasonable value. Bill Orr, W6SAI in "All About Cubical Quad Antennas" gives the full-wave vertical loop antenna an impedance of 125 ohms on page 15. On page 14, Orr writes: "For purposes of illustration, the two wire folded dipole may be "pulled open" to a diamond-shaped loop fed at the bottom point. If this distortion of the loop is continued the antenna will become a shorted transmission line." A perfect circle is the geometric shape enclosing the most area for a given perimeter. The more corners a closed figure has, the more closely it usually approximates a circle. That is why I commented on an octagon versus a square. Which brings me back to the question I asked, Is the radiation pattern the same for a long skinny loop as for a round one, as long as the enclosed area is the same? Roy Lewallen, W7EL |
Horizontal loop antenna
Roy Lewallen wrote:
I'm missing something here. I don't see anywhere in the response which explains how "radiation is a function of loop area" and why increasing the loop circumference would be advantageous. What you seem to be missing is that Richard H. said absolutely nothing about radiated *power*. The radiation *pattern* is certainly a function of loop area. -- 73, Cecil http://www.w5dxp.com |
Horizontal loop antenna
On Mon, 18 Feb 2008 19:31:00 -0800, Roy Lewallen
wrote: Putting the balun the input has the disadvantage of making the tuner chassis hot. Roy, Thanks for ANOTHER lesson. I have a SGC-230 tuner in the RV that I use to tune a wire when we go camping. I think the metal mounting brackets are isolated from the floating tuner chassis and that you have to use a grounding lug on the bottom. Never verified that since I have always used the ground lug anyway. I was thinking of adding ferrites to the input side of the tuner and then using it to tune a dipole fed with 450 ohm window line. Maybe I'll just stick with the longwire. I noticed the guy who wrote that article mounted his tuner on an el cheapo cutting board, probably just for that reason. S.T.W. |
Horizontal loop antenna
Sum Ting Wong wrote:
I have a SGC-230 tuner in the RV ... I was thinking of adding ferrites to the input side of the tuner and then using it to tune a dipole fed with 450 ohm window line. My SG-230 tuner manual says that is a no-no. It says: "The coupler must be located *at the antenna*. Never use a feed line or coaxial cable at the output of the antenna coupler." -- 73, Cecil http://www.w5dxp.com |
Horizontal loop antenna
On Tue, 19 Feb 2008 23:18:14 GMT, Cecil Moore
wrote: Sum Ting Wong wrote: I have a SGC-230 tuner in the RV ... I was thinking of adding ferrites to the input side of the tuner and then using it to tune a dipole fed with 450 ohm window line. My SG-230 tuner manual says that is a no-no. It says: "The coupler must be located *at the antenna*. Never use a feed line or coaxial cable at the output of the antenna coupler." Cecil, Saw that and wondered about isolating the coax and DC power with the ferrite and maybe changing the rules about doing that. Since you're a whole lot sharper than I am on this stuff, what do you figure the reason is for not tuning a balanced feeder with it? That would make things sooooooooo much easier if it worked. Thanks. S.T.W. |
Horizontal loop antenna
I have a SGC-230 tuner in the RV ... I was thinking of adding
ferrites to the input side of the tuner and then using it to tune a dipole fed with 450 ohm window line. My SG-230 tuner manual says that is a no-no. It says: "The coupler must be located *at the antenna*. Never use a feed line or coaxial cable at the output of the antenna coupler." On the other hand, page 16 of the SGC-230 manual PDF specifically shows a balanced dipole, being fed through "balanced line feeders, 300-600 ohms, up to 40 feet". The ladder line is shown as being connected to the antenna "hot" terminal, and to the case of the coupler. The manual is quite clear about not using a coax feedline above the antenna, or having a feedline out to a longwire antenna which has more than a very small amount of capacitance to ground. The information shown on page 16 suggests that you may be able to bend this restriction if you're using a balanced feedline, although I suspect that you'll still want to make sure that you've got low capacitance between ground and the hot side of the line (keep the feedline well away from metal, and use high-quality feedthrough insulators). I don't know about using a balun at the base of the feedline... this will (almost of necessity) require the use of a length of low-impedance feedline of some sort, and this could be exactly the sort of thing that prevents the SGC from matching the line properly. Using a choke on the coax-and-control side might work better, although this too seems to be something that SGC discourages. I haven't been terribly happy with the SGC tuner I picked up (admittedly for cheap, at a ham swap-meet). It's an early-model SGC 230, and its tuning algorithm seems very finicky. In particular, it won't tune into any but the easiest loads when fed by my Kenwood TS-2000. I suspect that the reason is that the TS-2000's high-SWR foldback circuit is rather aggressive, and chops the power down to well under 10 watts anytime the rig sees an SWR of more than 2:1 or so. The fluctuating transmitter power seems to confuse the coupler's matching algorithm... no big surprise there. Seems to work better when fed from a simple TenTec Scout, which has a different high-SWR- protection mechanism that doesn't cause the power to flop around as much. Anyhow... my impression is that the SGC tuners are best suited for their original application - feeding a whip or longwire, whilst being securely bolted and multiply-grounded to a Big Metal Vehicle Chassis. They also seem to do OK feeding verticals over a big bed of radials. I just don't think they're all that well suited to feeding balanced antennas. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Horizontal loop antenna
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Horizontal loop antenna
Sum Ting Wong wrote:
On Mon, 18 Feb 2008 19:31:00 -0800, Roy Lewallen wrote: Putting the balun the input has the disadvantage of making the tuner chassis hot. Roy, Thanks for ANOTHER lesson. I have a SGC-230 tuner in the RV that I use to tune a wire when we go camping. I think the metal mounting brackets are isolated from the floating tuner chassis and that you have to use a grounding lug on the bottom. Never verified that since I have always used the ground lug anyway. I was thinking of adding ferrites to the input side of the tuner and then using it to tune a dipole fed with 450 ohm window line. Maybe I'll just stick with the longwire. I noticed the guy who wrote that article mounted his tuner on an el cheapo cutting board, probably just for that reason. S.T.W. And you can also thank Tom Rauch, W8JI who questioned my incorrect belief, causing me to re-think it. Roy Lewallen, W7EL |
Horizontal loop antenna - Dual Wire
I seem to remember an article about someone taking a full-wave
horizontal loop antenna and making two loops (or was it a half-wave loop?). The second loop caused the antenna to match 50 ohms so it could be fed with coax and (I think) it operated multiple bands. Anyone remember this article and know where it might be? Thanks Buck N4PGW -- 73 for now Buck, N4PGW www.lumpuckeroo.com "Small - broadband - efficient: pick any two." |
Horizontal loop antenna
Sum Ting Wong wrote:
Saw that and wondered about isolating the coax and DC power with the ferrite and maybe changing the rules about doing that. Since you're a whole lot sharper than I am on this stuff, what do you figure the reason is for not tuning a balanced feeder with it? I was so sharp, I called SGC. :-) They said if the transmission line accidentally opened up, the SG-230 could develop 30,000 volts at its output. If it was mounted in an attic, for instance, it could burn the house down. I think they are worried about being sued. Moral: If you decide to use transmission line on the output, put it in a location that will not matter if it catches on fire. -- 73, Cecil http://www.w5dxp.com |
Horizontal loop antenna
Dave Platt wrote:
On the other hand, page 16 of the SGC-230 manual PDF specifically shows a balanced dipole, being fed through "balanced line feeders, 300-600 ohms, up to 40 feet". My 1990 manual shows nothing like that. Maybe they changed their minds about balanced line feeders. -- 73, Cecil http://www.w5dxp.com |
Horizontal loop antenna
On the other hand, page 16 of the SGC-230 manual PDF specifically
shows a balanced dipole, being fed through "balanced line feeders, 300-600 ohms, up to 40 feet". My 1990 manual shows nothing like that. Maybe they changed their minds about balanced line feeders. Could be... I was using a PDF copy of the manual I downloaded from the SGC website. Possibly the newer versions of their couplers have more flexibility in their tuning algorithm? -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Horizontal loop antenna - Dual Wire
On Tue, 19 Feb 2008 22:55:20 -0500, Buck
wrote: I seem to remember an article about someone taking a full-wave horizontal loop antenna and making two loops (or was it a half-wave loop?). The second loop caused the antenna to match 50 ohms so it could be fed with coax and (I think) it operated multiple bands. Anyone remember this article and know where it might be? Hi Buck, It is a small tuned loop (less than a tenth wave) with a smaller loop (about a third to a fifth in size of the first loop) inside it. Not much else to say except that polarity is vertical/horizontal when the loops are in the horizontal/vertical plane. Make every effort to build low Ohmic connections and elements. The capacitor will have to stand off a high voltage (and many caps suffer from ESR). 73's Richard Clark, KB7QHC |
Horizontal loop antenna
Roy Lewallen wrote:
"I don`t see anywhere in the response which explains how "radiation is a function of loop area" and why increasing the loop circumference would be advantageous." Didn`t want to bore with details. Terman knows all and tells all. His loop antenna story begins on page 907 of his 1955 opus: "The radiation resistance of a loop antenna is less the smaller the loop area. For the radiation resistance to be large enough to give good antenna efficiency, it is necessary that the loop perimeter be of the order of a wavelength. This introduces a difficulty, since when the perimeter approaches or exceeds a half wavelength, then the loop current in Fig. 23-40 will not be constant, nor will its phase nnecessarily be the same in different parts of the loop. The prectical solution is to build up the loop in such a way that the perimeter consists of resonant antennas so arranged that the current everywhere in the loop perimeter flows in the same direction around the loop. A variety of practical physical arrangements for achieving this result have been devised, three examples of which are illustrated in Fig. 23-41." Yet another elegant phase inverter from Kraus as applied to a colinear dipole appears on Cecil`s webpages. Best regards, Richard Harrison, KB5WZI |
Horizontal loop antenna
Roy Lewallen wrote:
"Perhaps you build antennas for radiation resistance, but I think most people build them to maximize radiation in some particular direction.." You must have some radiation resistance or you have no signal, but not all antennas are highly directional. Page 8-10 of the 20th edition of the ARRL Antenna Book has (Eq 5): Efficiency = radiation resistance / radiation resistance + loss resistance Zero radiation resistance = zero efficiency. Best regards, Richard Hsarrison, KB5WZI |
Horizontal loop antenna - Dual Wire
On Tue, 19 Feb 2008 22:44:48 -0800, Richard Clark
wrote: On Tue, 19 Feb 2008 22:55:20 -0500, Buck wrote: I seem to remember an article about someone taking a full-wave horizontal loop antenna and making two loops (or was it a half-wave loop?). The second loop caused the antenna to match 50 ohms so it could be fed with coax and (I think) it operated multiple bands. Anyone remember this article and know where it might be? Hi Buck, It is a small tuned loop (less than a tenth wave) with a smaller loop (about a third to a fifth in size of the first loop) inside it. Not much else to say except that polarity is vertical/horizontal when the loops are in the horizontal/vertical plane. Make every effort to build low Ohmic connections and elements. The capacitor will have to stand off a high voltage (and many caps suffer from ESR). 73's Richard Clark, KB7QHC The antenna article I was referring to is either full size or 1/2 size horizontal loop and he used window line (twin-lead) wire for the loop crossing the connection of the coax so that the wire made a continuous loop twice going from the center conductor to the shield (he may have used a balun, but you get the idea). This was a large loop running around his yard. Thanks, tho. Buck N4PGW -- 73 for now Buck, N4PGW www.lumpuckeroo.com "Small - broadband - efficient: pick any two." |
Horizontal loop antenna
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Horizontal loop antenna
Jon, LA4RT wrote:
"---but presumably there`s a reason that you`re using a small loop in the first place." True. In Norway I specified large dishes for scatter communications with North Sea platforms but the government sponsored the geosynchronous satellite program and ignored scatter. In the many tunnels I specified 300-ohm twinlead which works about as well as Andrew`s leaky coax and costs much less. I think Norway is too rich to care about cost. Best regards, Richard Harrison, KB5WZI |
Horizontal loop antenna
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