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#1
January 21st 05, 05:33 PM
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Questions on Inverted L antenna
K9RZZ,
.. AHaaaaa  )We have a difference of 'opinion' and a matter of perspectives ;-) .. I would agree with you that it could be called a "Bent" Random Wire Antenna: If the Lay of the Wire Antenna Element was in the Horizontal Plane [Flat]. - Across-and-Out View - - Top-Down Perspective - - - Only Horizontal Polarized .. However, in this instance the Lay of the Wire Antenna Element is both in the Horizontal Plane and the Vertical Plane. - Bottom-Up View - - Side Perspective - - - Both Horizontal and Vertical Polarized .. Then Again - Going back to the 'original' 45 Foot Horizontal Wire Antenna with a 22 Foot Vertical Ground Wire; that is fed with a Matching Transformer. It could be 'viewed' as an Off-Center-Fed Dipole with One Side Terminated. .. NOW - If the 'original' 45 Foot Horizontal Wire Antenna with a 22 Foot Vertical Ground Wire is Modified with the addition of a Vertical Down-Leg at the End of the Horizontal Wire; and still is Fed with a Matching Transformer at the Top Near Corner. It could be 'view' as directive array of Two Vertical Elements; on the Far-End a Driven Vertical Element and on the Near-End a Vertical Reflector Element. .. for any piece of wire being used as an antenna . . . - there are no rights or wrongs - - its all a matter of perspective - - - what works - works ! |
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#3
January 22nd 05, 10:42 PM
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JP,
When All Is Said and Done {Written}. .. For the casual Shortwave Radio Listener; the Inverted "L" Antenna is easy to visualize and conceive of building. .. READ - The 'simple' Answer (in most cases) is the Low Noise Inverted "L" Antenna http://groups.yahoo.com/group/Shortw...a/message/1785 .. When properly laid-out, arranged and constructed; the Inverted "L" Antenna provides a relatively 'low noise' "Omni-Directional" Shortwave Listener's (SWL) Antenna. .. READ - The Inverted "L" Antenna - It's 'basic' Lay-Out and Structure {Why It Works} http://groups.yahoo.com/group/Shortw...a/message/1969 .. For the 'non-technical' Shortwave Listener the Inverted "L" Antenna meets the "KISAP" Test and that is good. KISAP = Keep-It-Simple And Practical [.] TIP - For those who do not wish to go through the process of building their own Inverted "L" Antenna; they can buy a pre-build Random {LongWire} Wire Antenna and configure it as an Inverted "L" Antenna - Two come to mind: READ - Par EF-SWL End-Fed Shortwave Antenna configured as an Inverted "L" Antenna http://groups.yahoo.com/group/Shortw...a/message/1562 http://groups.yahoo.com/group/Shortw...a/message/1711 http://groups.yahoo.com/group/Shortw...a/message/1717 READ - High-Z Shortwave Longwire Antenna with Matching Transformer (MLB) and SO-239 Connector http://groups.yahoo.com/group/Shortw...a/message/1659 http://groups.yahoo.com/group/Shortw...a/message/1709 .. I applaud your level of technical expertise and the mastery of the subject of Antennas. But for many casual Shortwave Listeners; it is a burden of knowledge that they do not wish to acquire; just to simply Listen and Enjoy their Radios a little better. READ - Inverted "L' Antenna Reading List http://groups.yahoo.com/group/Shortw...na/message/374 .. When All Is Said and Done {Written} .. . . What Works - WORKS ! .. .. iane ~ RHF .. All are WELCOME and "Invited to Join" the Shortwave Listener (SWL) Antenna eGroup on YAHOO ! http://groups.yahoo.com/group/Shortwave-SWL-Antenna/ .. Some Say: On A Clear Day You Can See Forever. http://groups.yahoo.com/group/Shortw...na/message/502 .. I BELIEVE: On A Clear Night . . . You Can Hear Forever and Beyond, The BEYOND ! With a Shortwave Listener SWL Antenna of your own making. "If You Build It {SWL Antenna} You Will Hear Them !" |
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#4
January 22nd 05, 11:13 PM
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In article d4yId.20312$B95.14800@lakeread02,
"Jack Painter" wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I agree with all that you wrote except for that last sentence. Every location is a different situation and so generalizations can be made about antenna type, radials or ground performance but there are no absolutes here. What is better in one place will not necessarily be better in another. Likely yes, but not necessarily. Some locations may be far better off with a counterpoise of some type rather than depending on RF ground return through the radio and mains supply, which is all that is left if that one ground rod the BALUN is connected to is not up to the job. As one example if you have good ground conductivity then that one rod might be all you need but if ground conductivity is poor then a radial or radials will make an improvement. You can always lay wires on the ground and see if they help. If they do then you can go through the trouble to make them perminent. Any type of single element antenna (unbalanced) requires a good RF ground to be effective. The RF ground is the other half of the antenna. -- Telamon Ventura, California |
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#5
January 22nd 05, 11:31 PM
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"Telamon" wrote "Jack Painter" wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I agree with all that you wrote except for that last sentence. Every location is a different situation and so generalizations can be made about antenna type, radials or ground performance but there are no absolutes here. What is better in one place will not necessarily be better in another. Likely yes, but not necessarily. Some locations may be far better off with a counterpoise of some type rather than depending on RF ground return through the radio and mains supply, which is all that is left if that one ground rod the BALUN is connected to is not up to the job. As one example if you have good ground conductivity then that one rod might be all you need but if ground conductivity is poor then a radial or radials will make an improvement. You can always lay wires on the ground and see if they help. If they do then you can go through the trouble to make them perminent. Any type of single element antenna (unbalanced) requires a good RF ground to be effective. The RF ground is the other half of the antenna. I agree with that. While only some "incomplete" (unbalanced wire) antennas can radiate without a good RF ground, all antennas can receive with no RF ground at all. But some receivers can benefit from better ground than the AC-grounded case of the radio provides. Noise limiting is one reason we do try to improve both the DC and RF ground capabilities of the coax-shield to improve this possibility, agreed. Jack Painter Virginia Beach, Virginia |
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#6
January 25th 05, 05:22 AM
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Jack Painter wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I think you've missed the point. A so called 'low noise' inverted-L is intended to reduce noise on the feed line to the receiver which comes from domestic sources like appliances in the home. This is not the same as the noise being received by the antenna wire itself. When the feed line is part of the vertical section of the antenna, like the typical inverted-L or random wire, it can pick up noise from the domestic environment. The solution is to use a coax feed line which connects to a balun near the ground. The vertical section of the antenna comes down to the balun. This allows for a short RF ground from the coax shield to earth which decouples the noise on the shield. |
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#7
January 26th 05, 06:08 AM
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"starman" wrote Jack Painter wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I think you've missed the point. A so called 'low noise' inverted-L is intended to reduce noise on the feed line to the receiver which comes from domestic sources like appliances in the home. This is not the same as the noise being received by the antenna wire itself. When the feed line is part of the vertical section of the antenna, like the typical inverted-L or random wire, it can pick up noise from the domestic environment. The solution is to use a coax feed line which connects to a balun near the ground. The vertical section of the antenna comes down to the balun. This allows for a short RF ground from the coax shield to earth which decouples the noise on the shield. Well I didn't mean to miss the point, and I'm afraid you're far off base in suggesting that an inverted-L radiates part of the feedline or that feedline (coax-shield) noise has anything to do with an antenna configuration. The use of coax minimizes feedline noise, and shield-grounding the coax further reduces noise from either being brought into the shack or carried to the antenna from the shack. In an inverted-L, either a Balun or a choke is always used to prevent inadvertent feedline radiation. The vertical portion of the end-fed inverted-L is where the feedline ends and the antenna begins. The real noise-limiting design of any beverage-style or inverted-L wire antenna is to ground one half of the Balun output. This is whether the coax shield is grounded earlier or not. That does affect signals picked up on the antenna wire itself, although experts are not agreed as to whether there is a measurable improvement in signal to noise ratio as a result of this. As Telemon mentioned, having a counterpoise or good RF ground could make a difference there. In my particular case, there is a marked improvement in signal strength and possibly some reduction in noise when the connection from ground rod to Balun is made. I also transmit through this antenna with pretty good results. The original concept of grounding one-half of a current-type wire-fed Balun for noise limiting came from an 1980's issue of Fine Tuning's PROCEEDINGS. I was borrowing the issue from a friend and cannot remember the original author of this but I don't believe it was the venerable John Doty to which it is lately accredited. Jack Painter Virginia Beach, Virginia |
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#8
January 26th 05, 09:44 AM
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Jack Painter wrote:
"starman" wrote Jack Painter wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I think you've missed the point. A so called 'low noise' inverted-L is intended to reduce noise on the feed line to the receiver which comes from domestic sources like appliances in the home. This is not the same as the noise being received by the antenna wire itself. When the feed line is part of the vertical section of the antenna, like the typical inverted-L or random wire, it can pick up noise from the domestic environment. The solution is to use a coax feed line which connects to a balun near the ground. The vertical section of the antenna comes down to the balun. This allows for a short RF ground from the coax shield to earth which decouples the noise on the shield. Well I didn't mean to miss the point, and I'm afraid you're far off base in suggesting that an inverted-L radiates part of the feedline or that feedline (coax-shield) noise has anything to do with an antenna configuration. The use of coax minimizes feedline noise, and shield-grounding the coax further reduces noise from either being brought into the shack or carried to the antenna from the shack. In an inverted-L, either a Balun or a choke is always used to prevent inadvertent feedline radiation. The vertical portion of the end-fed inverted-L is where the feedline ends and the antenna begins. The real noise-limiting design of any beverage-style or inverted-L wire antenna is to ground one half of the Balun output. This is whether the coax shield is grounded earlier or not. That does affect signals picked up on the antenna wire itself, although experts are not agreed as to whether there is a measurable improvement in signal to noise ratio as a result of this. As Telemon mentioned, having a counterpoise or good RF ground could make a difference there. In my particular case, there is a marked improvement in signal strength and possibly some reduction in noise when the connection from ground rod to Balun is made. I also transmit through this antenna with pretty good results. The original concept of grounding one-half of a current-type wire-fed Balun for noise limiting came from an 1980's issue of Fine Tuning's PROCEEDINGS. I was borrowing the issue from a friend and cannot remember the original author of this but I don't believe it was the venerable John Doty to which it is lately accredited. If the coax shield of an inverted-L does not have a good RF ground, which requires a short ground wire to earth, the domestic noise on the shield can couple to the center conductor of the coax where it connects to the antenna. The noise will then become part of the antenna signal to the radio. That's the point I think you missed. |
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#9
January 26th 05, 06:51 PM
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"starman" wrote Jack Painter wrote: "starman" wrote Jack Painter wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I think you've missed the point. A so called 'low noise' inverted-L is intended to reduce noise on the feed line to the receiver which comes from domestic sources like appliances in the home. This is not the same as the noise being received by the antenna wire itself. When the feed line is part of the vertical section of the antenna, like the typical inverted-L or random wire, it can pick up noise from the domestic environment. The solution is to use a coax feed line which connects to a balun near the ground. The vertical section of the antenna comes down to the balun. This allows for a short RF ground from the coax shield to earth which decouples the noise on the shield. Well I didn't mean to miss the point, and I'm afraid you're far off base in suggesting that an inverted-L radiates part of the feedline or that feedline (coax-shield) noise has anything to do with an antenna configuration. The use of coax minimizes feedline noise, and shield-grounding the coax further reduces noise from either being brought into the shack or carried to the antenna from the shack. In an inverted-L, either a Balun or a choke is always used to prevent inadvertent feedline radiation. The vertical portion of the end-fed inverted-L is where the feedline ends and the antenna begins. The real noise-limiting design of any beverage-style or inverted-L wire antenna is to ground one half of the Balun output. This is whether the coax shield is grounded earlier or not. That does affect signals picked up on the antenna wire itself, although experts are not agreed as to whether there is a measurable improvement in signal to noise ratio as a result of this. As Telemon mentioned, having a counterpoise or good RF ground could make a difference there. In my particular case, there is a marked improvement in signal strength and possibly some reduction in noise when the connection from ground rod to Balun is made. I also transmit through this antenna with pretty good results. The original concept of grounding one-half of a current-type wire-fed Balun for noise limiting came from an 1980's issue of Fine Tuning's PROCEEDINGS. I was borrowing the issue from a friend and cannot remember the original author of this but I don't believe it was the venerable John Doty to which it is lately accredited. If the coax shield of an inverted-L does not have a good RF ground, which requires a short ground wire to earth, the domestic noise on the shield can couple to the center conductor of the coax where it connects to the antenna. The noise will then become part of the antenna signal to the radio. That's the point I think you missed. OK I didn't restate the obvious, agreed. The best place to terminate the antenna and mount the Balun is *at* the ground rod, which means the connection is about 4 inches long. Ty-wrap the Balun to the protruding ground rod. After applying coax-seal to the wire-wrapped and then soldered connections, cut the bottom and slit one side of a plastic beverage bottle to just fit over the Balun and tape the bottle shut afterwards. Spray paint the bottle with bow-flex cammo and it becomes part of the background, and weather-proofed for years of service. Some designs advise terminating the vertical drop of the inverted-L about 6 feet above ground. That's more important for a center fed or off-center fed (dipole type) antenna than the end-fed wires. Users should have no problems terminating the inverted-L at ground level, and sink a good ground rod (with buried radials if you desire) at that same point. Jack Painter Virginia Beach, Virginia |
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#10
January 27th 05, 02:41 AM
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Jack Painter wrote:
"starman" wrote Jack Painter wrote: "starman" wrote Jack Painter wrote: "starman" wrote A low noise inverted-L will have the vertical downlead at the far end of the horizontal section with the balun located at the lower end of the single wire downlead, near the ground. Then you can run coax back to the house from the balun. The near end of the horizontal section shouldn't be too close to the house where it might pick up noise. The 'low noise inverted-L' (paragraph above) can make a big difference in lowering the noise that the antenna picks up from local sources. There is not one ounce of truth to an "Inverted-L" being ANY quieter than a 45 degree random wire, and especially a horizontal-dipole, which is generally quieter than any antenna with a vertical component. Most interference is vertically polarized, and the verticals, random-wires, slopers, or inverted-L antenna designs all pick up more vertically polarized "noise" than a horizontally polarized antenna. Adding a vertical or even a 45 degree sloped component to an antenna DOES make it less directional than a horizontal, and that is all it does. Any noise-limiting realized from these designs comes strictly from the grounded-Balun and not the design, configuration or dimensions of the antenna. Shield-grounding (for static and lightning protection) at the feedpoint will achieve 99% of the noise-limiting benefit that a grounded Balun does. The missing 1% is an equal loss of signal and noise through the Balun. All RF noise (but not all energy has RF components) is coupled right across the Balun windings, their function of electrically decoupling is true of some DC energy, but not RF energy, which is rather efficiently coupled across the Balun by design. The same application of a grounded-Balun works equally well on both the random (straight) wire antennas and inverted-L antenna btw. Both the random wire and inverted-L benefit from (require in most cases) a counterpoise ground or radials to provide effective transmitting. Neither a counterpoise nor radials affect reception from the either the random wire or inverted-L, however. I think you've missed the point. A so called 'low noise' inverted-L is intended to reduce noise on the feed line to the receiver which comes from domestic sources like appliances in the home. This is not the same as the noise being received by the antenna wire itself. When the feed line is part of the vertical section of the antenna, like the typical inverted-L or random wire, it can pick up noise from the domestic environment. The solution is to use a coax feed line which connects to a balun near the ground. The vertical section of the antenna comes down to the balun. This allows for a short RF ground from the coax shield to earth which decouples the noise on the shield. Well I didn't mean to miss the point, and I'm afraid you're far off base in suggesting that an inverted-L radiates part of the feedline or that feedline (coax-shield) noise has anything to do with an antenna configuration. The use of coax minimizes feedline noise, and shield-grounding the coax further reduces noise from either being brought into the shack or carried to the antenna from the shack. In an inverted-L, either a Balun or a choke is always used to prevent inadvertent feedline radiation. The vertical portion of the end-fed inverted-L is where the feedline ends and the antenna begins. The real noise-limiting design of any beverage-style or inverted-L wire antenna is to ground one half of the Balun output. This is whether the coax shield is grounded earlier or not. That does affect signals picked up on the antenna wire itself, although experts are not agreed as to whether there is a measurable improvement in signal to noise ratio as a result of this. As Telemon mentioned, having a counterpoise or good RF ground could make a difference there. In my particular case, there is a marked improvement in signal strength and possibly some reduction in noise when the connection from ground rod to Balun is made. I also transmit through this antenna with pretty good results. The original concept of grounding one-half of a current-type wire-fed Balun for noise limiting came from an 1980's issue of Fine Tuning's PROCEEDINGS. I was borrowing the issue from a friend and cannot remember the original author of this but I don't believe it was the venerable John Doty to which it is lately accredited. If the coax shield of an inverted-L does not have a good RF ground, which requires a short ground wire to earth, the domestic noise on the shield can couple to the center conductor of the coax where it connects to the antenna. The noise will then become part of the antenna signal to the radio. That's the point I think you missed. OK I didn't restate the obvious, agreed. The best place to terminate the antenna and mount the Balun is *at* the ground rod, which means the connection is about 4 inches long. Ty-wrap the Balun to the protruding ground rod. After applying coax-seal to the wire-wrapped and then soldered connections, cut the bottom and slit one side of a plastic beverage bottle to just fit over the Balun and tape the bottle shut afterwards. Spray paint the bottle with bow-flex cammo and it becomes part of the background, and weather-proofed for years of service. Some designs advise terminating the vertical drop of the inverted-L about 6 feet above ground. That's more important for a center fed or off-center fed (dipole type) antenna than the end-fed wires. Users should have no problems terminating the inverted-L at ground level, and sink a good ground rod (with buried radials if you desire) at that same point. I mounted my balun in a plastic electrical junction box with a cover gasket, the kind used with plastic conduit. The ground wire to the rod is about 2-feet long. |
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