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In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
I agree on the choke, but it seems to me the right angle coax would be
an antenna, but not aimed with the rest of the loop. For instance, a horizontal loop connected to vertical coax would fit your description, but I would still say the coax unbalanced the loop. FWIW, I get better results with vertical loops than horizontal. Telamon wrote: In article . com, "RHF" wrote: M... - " The loop will be unbalanced if you don't use a balun. " Please Educate me as to Why the Loop Antenna would be Un-Balance without using a Balun ? i want to know - cause -iane ~ RHF Any time you connect a transmission line directly to a antenna the coax shield can affect the antenna unless you decouple it. You can: 1. Run the coax at a right angle from the antenna elements. 2. Use a choke of some type on the coax. Otherwise the coax shield become part of the antenna. -- Telamon Ventura, California |
In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
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In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
In article .com,
"RHF" wrote: Telamon, Yes - A 'smaller' Vertical Coax Cable Loop Antenna is another opinion to consider for an In-Door Antenna. The "TRICK" to TV 'type' Coax Cable [Shielded] SWL Loop Antennas {RHF} http://groups.yahoo.com/group/Shortw...a/message/1626 http://groups.google.com/group/rec.r...a0aadd03af7bc7 Yes the 75 ohm TV stuff will work OK if that is what you have around. The only problem there is the cable size does not match up with the 50 ohm connectors. Usually you can hack that well enough to connect things together. If you are going to buy the coax you might as well but the 50 ohm cable. -- Telamon Ventura, California |
In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
Telamon,
Thank You for remind me of this simple fact about a properly Terminated Coax Cable and the need to have it Matched on both ends. [ Making It an Effective Signal Conduit. ] to live is to learn - cause - iane ~ RHF |
In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
Telamon,
FWIW - Most of my better performing "GreerTech" Coax Cable Veritcal Loop Antennas are made using full size RG8 Coax Cable. Yes - Sometimes Bigger (Thicker) is Better. The basic design of the "GreerTech" Coax Cable [Shielded] Loop Antenna is good and very practical. GREERTECH = http://www.greertech.com/hfloop/mymagloop.html LOOP= http://www.greertech.com/hfloop/mymagloop.html http://groups.yahoo.com/group/Shortw...a/message/1625 http://groups.yahoo.com/group/Shortw...a/message/1730 http://groups.yahoo.com/group/Shortw...a/message/1539 http://groups.yahoo.com/group/Shortw...a/message/1008 http://groups.google.com/group/rec.r...8005ce8c7f5c9c ~ RHF |
In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
"bpnjensen" wrote the impedance for this type of antenna is about 100 ohms. At what frequency? A large horizontal loop of about 40 feet or larger circumference will exhibit different impedance across the bands as will any single wire antenna or dipole. Except that a large horizontal loop will exhibit a significantly less impedence variation. would suggest that, if this type of antenna is used, for best match it be mated to the low-Z input of the radio (50 ohms rather than 500), although an appropriate transformer could easily resolve this (probably minor) problem regardless of the input. I wouldn't be too concerned about the impedance for receiving purposes. The broadband nature of a large horizontal loop will offset any loss from impedance mismatch compared to any other type of single wire antenna or dipole at the same height. As a once famous person said, "It's all relative." Or better, "If you build it 'RF' will come." Just do it and experiment. |
To RHF Again: Quest: Connect End Of Loop To Beginning ?: In-Door Horizontal [Flat] Loop Antenna - - - No Grounding Required
"Robert11" wrote a. Would coax work (meaningfully) better than the 300 ohm TV wire for the feed line ? Would I need a Balun also ? Using 300 ohm line gently twisted (don't kink it) in a spiral (any direction - L or R) once about every 12-18 inches or so is generally a better "match" than coax for the broadband large horizontal loop. b. What are the major performance differences, therefore, between the apparently 3 different ways of doing it: - your suggestion of a balanced twin line to receiver Don't be concerned about impedence mismatch using a large horizontal loop for reception purposes. It is superior to any other single wire antenna or dipole. The large horizontal loop will perform equally to your random wire on your random wires resonant frequency or multiple but will out perform it over all other bands. Assuming they are compared at the same height. My horizontal loop is about 80 meters in circumference in the shape of a fat "L" using a 450ohm ladderline feed. It is about 15 meters in height - not ideal, but so what. I can transmit on any HF amateur frequency without using any balun or matching device. Reception exhibits the same characteristics, as it should. - what I now have, a single wire forming a sort of loop, with the end open This is a random wire regardless of the configuration. It is NOT a loop. Creating a loop would make it far more "broadbanded" than a random wire or dipole. Just try it and experiment. |
The In-the-Attic Horizontal [Flat] Loop Antenna - Just may be the better choice to fill the available space.
Conclusion - Having stated the three above sets of parameters
for the above three types / shapes of Antennas that are often used as In-the-Attic Antenna : It now becomes apparent to me that the Loop Antenna is the better choice with a potential for : * Higher Signal Levels due to the fact for the available space there is simply more Wire in the Air....................................... This can vary though. Would depend on the bands used, etc.. Just having more wire in the air doesn't mean much in itself. It's quite possible and common for a smaller footprint antenna to trounce the larger one. IE: my coax fed dipoles have a total of 440 ft of wire in the air. Yes, it works well on any HF band, but my yagi would eat it for lunch on the bands the yagi is designed for. And the yagi uses a total of appx 90 ft of element/s to do it. * Equally as low Noise due to the natural properties of a Loop. And what would these properties be? The only "noise" property a loop has that differs from any other wire antenna is the reduction of corona, or static buildup, etc. And only in locations where that could help, would it be any advantage. Here in Houston, it would mean nada. At HCJB, with the large amounts of element eating corona up in those high mountains, it can help. Other than that, the loops behave no different than any other antenna. * Greater Antenna Aperture {Signal Capture Area} due to the natural shape and size of a Loop in any given space; with less apparent signal fading. This means little in general.. I can run a full wave loop on 80m for NVIS, and compare it to a dipole, and they are almost exactly the same in the real world. If you model a 80 dipole at 40 ft and compare it with a 80 horizontal loop at 40 ft, the loop has the small advantage of 1 db. In the real world, this is basically unnoticable on HF. It's not the aperture you would want to worry about. It would be the pattern of the antenna on the various bands, vs whatever you would compare it to. This can easily be modeled. Going One Step Farther : A Vertical [Tall] Loop Antenna In-the-Attic could offer almost as many advantages over the Random Wire Antenna and Dipole Antenna; as does the Horizontal [Flat] Loop Antenna. You say? What would these advantages be? Have you tried modeling it? You might be surprised... A full wave loop has no advantage over a dipole, except in differences in pattern. They are both about equally efficient. What would that mean? On some bands, the dipole could be better. On others, the loop... Basically, it's a crap shoot. Here, I have enough room to run either full wave loops, or dipoles. I run the dipoles. Why? Same appx performance, with less work involved. On the higher bands, I'd generally prefer the dipoles, vs a horizontal loop due to current distribution concerns. Vertical loop vs dipole? About 2 db or so, and barely worth the trouble. I'd rather run an extended double zepp, vs the vertical fed loop. Has about 1 db more gain on it's design freq. Intuitively I would think that for a Vertical Loop Antenna to perform up to its potential the maximum Length-to-Height (Aspect) Ratio would be about 4:1 or 5:1 . Nope. The maximum performing loop is a perfect circle. A square would be better than a tall narrow loop. Whatever covers the largest area is best as far as gain. If you want horizontal, you feed at the top or bottom. Vertical, from either side.. A loop is a loop no matter the orientation. Same properties will apply to both. Anyway, there is no real advantage to a loop vs dipole, unless the pattern of the loop is more favorable for a certain band and direction, etc, in use at the time. This will vary. As far as s/n ratio, you could run either one with little or no difference on most the bands, assuming both are properly decoupled from the feedline.. MK |
The In-the-Attic Horizontal [Flat] Loop Antenna - Just may be the better choice to fill the available space.
MK - By Definition "In-the-Attic"
In-the-Attic = Limited Space and Antenna Size In-the-Attic = Usually means that the Wire Antenna Element is 12 Feet to 18 Feet High above AGL for a single story house. Maybe twice that for a two story house or split-level condo. NOTE - For a Shortwave Listener's (SWL) "Receive Only" Antenna that is designed to "Fill" the Available Space : Whether these Antennas are : a Random Wire; a Dipole, or a Loop they are not "Cut' for any specific Wave Length and Frequency; they are simply Random Wire Antennas IN-THE-ATTIC AND ATTIC SIZE : In a 30 Foot by 40 Foot size Attic a basic straight Random Wire Antenna can be 30 Feet along the short side; 40 Feet along a the long side; or 50 Feet across a the diagonal. In a 30 Foot by 40 Foot size Attic a simple straight Wire Dipole Antenna can be 30 Feet along the short side; 40 Feet along a the long side; or 50 Feet across a the diagonal. In a 30 Foot by 40 Foot size Attic a common Wire Loop Antenna would be : 30 Feet along one short side; 40 Feet along one the long side; 30 Feet along the other short side; 40 Feet along the other long side; for a total of 140 Feet around the Attic [.] MK - It should be self-evident that " there is simply more Wire in the Air. " and that is all I said and meant to say. RELATIVE ANTENNA NOISE : " Equally as low Noise due to the natural properties of a Loop. " The usual ascertion is that a Dipole Antenna has a Lower Noise Factor (Property) then the same Length Random Wire at the same Height; all other things being equal : Balun / No Balun; Coax Cable / Twin Lead / Ladder Line; ETC. The Horizontal [Flat] Loop Antenna has the same Lower Noise Factor (Property) then the Dipole Antenna has in the same relative Available "In-the-Attic" Space : All other things being equal : Balun / No Balun; Coax Cable / Twin Lead / Ladder Line; ETC. There is Nothing to be gained or lost by using the Dipole or Loop Antenna in the Attic Noise Wise : But with the Loop Antenna more Wire is in the Air which can result in more Signal from the Antenna. ANTENNA APERTURE : RHF Said - " Greater Antenna Aperture {Signal Capture Area} due to the natural shape and size of a Loop in any given space; with less apparent signal fading. " MK - You model two 80 Meter Band Antennas; a Half-Wave Dipole Antenna and a Full-Wave Horizontal Loop Antenna and say that they are the same with little measurable difference between the two. "OK" Again here my beginning point is "In-the-Attic" were both the Dipole Antenna and the Horizontal [Flat] Loop Antenna are using the same Available Space and are in fact simply two 'random wire' antennas that happen to be laid-out in the confines of the Attic. Here the 50 Foot long Dipole Antenna with lets say 50 Square Foot of Signal Capture Area has less potential as an Antenna : Then the 140 Foot long Horizontal [Flat] Loop Antenna with lets say 120 Square Foot of Signal Capture Area that has more potential as an Antenna. To my simple way of thinking relative size and area does matter. ? Now is this Theoretically or Machine Measurable - Most Likely. ? Now is this Discernable by the Shortwave Listener (SWL) - Maybe. THE CRAP SHOOT : MK you say : "Basically, it's a crap shoot." "I run the dipoles." RHF says : For an In-the-Attic Antenna "Crap Shoot" I prefer the Horizontal [Flat] Loop Antenna - It's a matter of choice. MY INTUITIVE STATEMENT ABOUT VERTICAL LOOP ANTENNAS : RHF Said - " Intuitively I would think that for a Vertical Loop Antenna to perform up to its potential the maximum Length-to-Height (Aspect) Ratio would be about 4:1 or 5:1 ." Again here my beginning point is "In-the-Attic" most every Attics that I have been in is Longer and Wider then they are High {Tall}. So 'if' we are trying to Maximizing the Size of the Vertical Loop Antenna then a simple Circle or Square would not produce as much Wire Length and Combined Area as a Rectangle or Triangle using up the Available Space inside the Attic. The added comment about the Length-to-Height (Aspect) Ratio being about 4:1 or 5:1 was to not have the Vertical Loop become to flat compressed and effectively become a fat Folded Dipole Antenna of sorts. RESTATING MY CONCLUSIONS {NON-TECHNICAL OPINIONS} : For a "Receiver Only" Antenna being used by a Shortwave Listener (SWL) The Horizontal [Flat] Loop Antenna used In-the-Attic may/could/should perform better then the simple Dipole Antenna with potentially Higher Signal Levels; the same relative Noise Level; and less apparent Fading. STAYING ON MESSAGE - THIS CONVERSATION : MK - You appear to be a "Technical Person" and that is well and good. However, I am for the most part a non-technical person who simply tries to Keep It Simple And Practical [KISAP]. For me these Conversations can be an interesting exercise in restating my simple minded opinions : But for you these Conversations may turn out to be an exercise in futility - a Fools Errant so to speak. MK - Part of my 'iane' signature { I Ain't No Elmer } Means : I Don't Get Techincal - Because - I simply am not smart enough to try and WOW anyone with the all that math or science. MK - I Am Glad We Had This Talk :o) kisap - keeping it simple and practical ~ iane ~ RHF |
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