Re: Topband: Inverted L SWR Jumps ???
The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. Remove the balun. It's not doing anything for your and is a potential source of loss and problems. Coaxial cable is unbalanced, as is a ground-fed inverted L. No need for a balun. Check all your connections - make sure they're tight and well soldered or clamped. You're pushing a lot of RF current through them and a marginal connection will generate much heat and expand. -Jeff W0ODS ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
The sloper loads fine all the way up to 1500 watts. The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. I've tried various feed line lengths, I've replaced every component in the system except for the antenna wire. The antenna does climb along the branches of a tall pine before L-ing outward at about 55 feet. I think the problem is worse at night time when things are cold (and perhaps more humid). There could be many things at work. One problem common with amplifiers are defective or misplaced lightning arrestors, or bad coax connectors. I high-pot all of my connectors. Ohmmeters will not test for the stray strands or bad insulation that cause problems like yours. A good PL259/SO239 combination will hold off 5,000 volts peak, as will any reasonable size cable (RG58 or larger). You also (as Timmy pointed out) have two antennas, and on 160 it is pretty tough to get enough spacing to really be safe. An UNUSED antenna can sometimes arc at the open feedpoint. Lightning arrestors have historically been problematic for damaging amplifiers, including blowing bandswitches or causing SWR trips. A lightning arrestor has a rating of power/SWR. An arrestor that triggers at 3000 watts peak into 50 ohms will trigger as low as 1500 watts into a 2:1 SWR at the arrestor insertion point, or as low as 1000 watts peak into a 3:1 SWR. Most manufacturers of protection devices fail to tell consumers this important information. They also can go bad. It is unlikely anything except the area out toward the open end of the Inverted L can arc, so I would primarily suspect antenna coupling, a defective component or connector, or a lightning protection device. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
The sloper loads fine all the way up to 1500 watts. The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. I've tried various feed line lengths, I've replaced every component in the system except for the antenna wire. The antenna does climb along the branches of a tall pine before L-ing outward at about 55 feet. I think the problem is worse at night time when things are cold (and perhaps more humid). I'll be trying everything I can think of tomorrow afternoon, starting by trying to minimize contact with the tree branches. All suggestions welcome. 73 KQ0C Ash Ash, Are you using any variable capacitors in your matching network? If so the plates could be warping at high power. I had this happen and went to vacuum variable capacitors. This cured the problem. 73...Price W0RI ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Hi Ashton, I had some arcing into a coral tree at the 20 ft level. The vertical part of the inverted L was supported by a 40 ft bamboo pole that was nested close to the coral tree. The wire was #14 with varnish that probably had long departed. As the wind blew, the wire would come in contact with a branch and burn into it. I was running an old TL-922 which doesn't have any fancy protection so it kept on doing it's job. This was at about 1 kW. I didn't notice any observations in the shack until my wife came screaming into the house that the tree was on fire. I burnt halfway through a 3 inch diameter branch. So there is a possibility this might be the problem depending on how your wire is routed. 73 Jack --- On Tue, 11/27/12, Ashton Lee ashton.r@hotmail.com wrote: From: Ashton Lee ashton.r@hotmail.com Subject: Topband: Inverted L SWR Jumps ??? To: topband@contesting.com Date: Tuesday, November 27, 2012, 9:49 PM So I am trying to get set up better on 160 meters. I now have two antennas up (pretty well separated). One is an Alpha Delta DX A sloper hung in a tree with a grounding wire led to a ground rod and small radial field. The other is an inverted L on a good radial system of about 2000 feet in various lengths of about 50 feet each as fit the yard. Both are resonant at about 1.830 . The sloper loads fine all the way up to 1500 watts. The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. I've tried various feed line lengths, I've replaced every component in the system except for the antenna wire. The antenna does climb along the branches of a tall pine before L-ing outward at about 55 feet. I think the problem is worse at night time when things are cold (and perhaps more humid). What I see on the amp is output power suddenly seem to surge to 2500 watts, and reflected power jump from a few watts to over what the amp can read… then in a flash the amp faults out. This all happens with only about 20 watts of drive, so the amp can't actually be putting out 2500 watts unless something very strange has happened. As I noted, using the other antenna all is good. I need to get the inverted L working since it seems to have substantial receive gain vs the sloper, so I assume it will be equally better on transmit. All advice is welcome. Am I likely to be arc-ing to the tree branches? Could the wire be the problem? Do inverted L's have trouble with full power? The same wire worked fine for the last few years, but fed against a much lesser radial field and run through a less dense, lower tree. I'll be trying everything I can think of tomorrow afternoon, starting by trying to minimize contact with the tree branches. All suggestions welcome. 73 KQ0C Ash ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Ash, You said, I've replaced every component in the system except for the antenna wire. Also, if the antenna wire is (or is partly) an insulated variety, it is possible to have an open fault inside a good exterior insulation. Charles - N5UL Hobbs, NM ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Remove the balun. It's not doing anything for your and is a potential source of loss and problems. Coaxial cable is unbalanced, as is a ground-fed inverted L. No need for a balun. Unfortunately, that is not a universally true statement. MOST antennas are in a neither world of being neither perfectly balanced nor perfectly unbalanced. Perfectly balanced would be equal and opposite currents entering and leaving each conductor at each end of a balanced line, with equal voltages to the world around the line from each conductor. Perfectly unbalanced would be the same equal and opposite currents entering and leaving each conductor (shield and center) at each line end, and zero voltage from the shield to the outside world around the line. Very few antenna systems meet that criteria, although Marconi systems with many radials are close enough to be nearly perfectly unbalanced. Significant departure from UNbalanced occurs when radial systems are sparse, or truncated, or the feedline exits above the plane of the radials. There isn't any clear boundary, but a slow system dependent transition from the perfect case (feedline exits below the radial plane and an infinite full size radial system) to the worse case (a single radial of any design). Even four 1/4 wave radials have significant voltage to ground at the common point. Choking impedance required varies with the number, configuration, and length of radials and how the feeder is routed and grounded, and in nearly all cases a few hundred ohms is enough. An exception might be if the ground system common point has abnormally high voltages to earth (for example, a single truncated radial) or if the coax is elevated and coupled to the antenna. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Ok, everyone thanks for all the help. I rebuilt the antenna from new wire, built a two insulator termination at the end of the horizontal section where the high voltage is, I rehung the new antenna so that it doesn't touch anything… and the problem persisted. I then looked into Tom W8JI's suggestion about a bad lightning arrestor, and indeed that was the problem. I had blown the little cartridge in my Alpha Delta lightning stopper. I don't know why the issue only showed up on a single antenna of the many I have fed through that device. But it did. So Tom, thanks in particular. I did leave the choke balun in place. Who knows if that makes a difference? Everyone, please listen for the weak signal from Western Colorado this weekend. KQ0C Ash On Nov 28, 2012, at 10:30 AM, Tom W8JI w...@w8ji.com wrote: Remove the balun. It's not doing anything for your and is a potential source of loss and problems. Coaxial cable is unbalanced, as is a ground-fed inverted L. No need for a balun. Unfortunately, that is not a universally true statement. MOST antennas are in a neither world of being neither perfectly balanced nor perfectly unbalanced. Perfectly balanced would be equal and opposite currents entering and leaving each conductor at each end of a balanced line, with equal voltages to the world around the line from each conductor. Perfectly unbalanced would be the same equal and opposite currents entering and leaving each conductor (shield and center) at each line end, and zero voltage from the shield to the outside world around the line. Very few antenna systems meet that criteria, although Marconi systems with many radials are close enough to be nearly perfectly unbalanced. Significant departure from UNbalanced occurs when radial systems are sparse, or truncated, or the feedline exits above the plane of the radials. There isn't any clear boundary, but a slow system dependent transition from the perfect case (feedline exits below the radial plane and an infinite full size radial system) to the worse case (a single radial of any design). Even four 1/4 wave radials have significant voltage to ground at the common point. Choking impedance required varies with the number, configuration, and length of radials and how the feeder is routed and grounded, and in nearly all cases a few hundred ohms is enough. An exception might be if the ground system common point has abnormally high voltages to earth (for example, a single truncated radial) or if the coax is elevated and coupled to the antenna. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Tom: MOST antennas are in a neither world of being neither perfectly balanced nor perfectly unbalanced. How about an inverted L longer than 1/4 wave but optimized with series capacitor? Any closer to perfect unbalanced? Bob VE7BS ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
On 11/27/2012 10:45 PM, Tim Duffy K3LR wrote: There is significant coupling between 160 meter antennas that are separated by as much as 500 feet YES! and this coupling could be problem for your set up. But it can also be a good thing if you know what you have and how to take advantage of it. I have three resonant verticals for 160M, as well as a tower that is resonant on 160M. Studying them in NEC early this summer, I've learned how I can drive each of them, one at a time, and use the others as passive reflectors to get 4-5 dB of gain in several directions. The patterns that NEC predicts are clearly observable on the air. It doesn't take much to couple and change an antenna's pattern. I first saw this when I had hung a new dipole near an 80M vertical, and that feedline coupled to the vertical. I choked the feedline and the coupling went away. N6LF published something quite useful on this topic several years ago showing that even a fairly short tower that is well below resonance, even loaded with aluminum on top, can significantly affect a pattern. I have one such tower that NEC predicts will resonate around 2.3 MHz, and a bump of a few dB. Taming that (probably by detuning it) is something else I need to work on. N6LF's piece is on his website. 73, Jim K9YC ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
On 11/28/2012 10:14 AM, Ashton Lee wrote: I rebuilt the antenna from new wire, built a two insulator termination at the end of the horizontal section where the high voltage is, One thing I observed here several years ago with a dipole with an end touching tree branches is arcing to the branch, accompanied by scorching of the wire insulation (white THHN). Also, a common mode choke whose choking impedance is too low can overheat if the common mode voltage is high enough. That voltage depends on the degree of imbalance, which, as Tom observes, is highly dependent on the antenna system, INCLUDING the feedline and the radial system (and/or counterpoise). Tom's analysis of Guy's folded counterpoise design showed it to have significant imbalance, which fried common mode chokes, but was at least partially corrected by the stray Z of an isolation transformer. Overheating in a common mode choke wound on a lossy ferrite core shows up in the wire itself (the coax shield) and can melt the dielectric, allowing it to either short, arc, or change spacing. I've done some experiments purposely intended to observe what happens when the choking Z is inadequate. 73, Jim K9YC ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
W8JI solved another problem and saved someone much time and frustration. I'd like to thank Tom for the great help and knowledge he has imparted in me and many, many others over the years. In my expert opinion as an engineer he is one of just a very small number of super engineers I know. Dave WX7G On Nov 28, 2012 11:57 AM, Jim Brown j...@audiosystemsgroup.com wrote: On 11/28/2012 10:14 AM, Ashton Lee wrote: I rebuilt the antenna from new wire, built a two insulator termination at the end of the horizontal section where the high voltage is, One thing I observed here several years ago with a dipole with an end touching tree branches is arcing to the branch, accompanied by scorching of the wire insulation (white THHN). Also, a common mode choke whose choking impedance is too low can overheat if the common mode voltage is high enough. That voltage depends on the degree of imbalance, which, as Tom observes, is highly dependent on the antenna system, INCLUDING the feedline and the radial system (and/or counterpoise). Tom's analysis of Guy's folded counterpoise design showed it to have significant imbalance, which fried common mode chokes, but was at least partially corrected by the stray Z of an isolation transformer. Overheating in a common mode choke wound on a lossy ferrite core shows up in the wire itself (the coax shield) and can melt the dielectric, allowing it to either short, arc, or change spacing. I've done some experiments purposely intended to observe what happens when the choking Z is inadequate. 73, Jim K9YC __**_ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
I second that! Being acquainted with Tom over the years and reading his informative posts has wonderfully enriched my enjoyment of radio. :-) 73, Mike www.w0btu.com On Wed, Nov 28, 2012 at 1:56 PM, DAVID CUTHBERT telegraph...@gmail.comwrote: W8JI solved another problem and saved someone much time and frustration. I'd like to thank Tom for the great help and knowledge he has imparted in me and many, many others over the years. In my expert opinion as an engineer he is one of just a very small number of super engineers I know. ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
The change in an overheating core has a swing to it and you can watch the SWR change, in a continuous fashion, while you are transmitting, while arcs exhibit sudden change. What you call imbalance was on purpose, but true. The more the radiating length of an antenna is shortened, the more severe the voltage is at the end(s). Enough so that a motorcycle at a W3LPL open house, with a KW in a motorcycle trailer, even the rounded end of the 8 foot whip on SSB peaks would crackle and sizzle with corona, visible in broad daylight. Quite the show. Even with full size devices, toward the ends of dipoles, vees, etc, the RF voltages are well in excess of insulation on the THHN insulation on wires from home improvement stores. But I'll vote with Tom's likely assessment, arcs in connectors, etc. You may have some surprisingly high voltages in the UNselected antenna plus feedline. 73, Guy. On Wed, Nov 28, 2012 at 1:56 PM, Jim Brown j...@audiosystemsgroup.comwrote: Also, a common mode choke whose choking impedance is too low can overheat if the common mode voltage is high enough. That voltage depends on the degree of imbalance, which, as Tom observes, is highly dependent on the antenna system, INCLUDING the feedline and the radial system (and/or counterpoise). Tom's analysis of Guy's folded counterpoise design showed it to have significant imbalance, which fried common mode chokes, but was at least partially corrected by the stray Z of an isolation transformer. Overheating in a common mode choke wound on a lossy ferrite core shows up in the wire itself (the coax shield) and can melt the dielectric, allowing it to either short, arc, or change spacing. I've done some experiments purposely intended to observe what happens when the choking Z is inadequate. ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
On 11/28/2012 1:14 PM, Ashton Lee wrote: I don't know why the issue only showed up on a single antenna of the many I have fed through that device. But it did. Simply because the ratio of voltage varies along the feedline if the SWR is anything other than a perfect 1:1. The feedline length and SWR for your inverted L was probably just right to put a high voltage point right at the switch/arc plug on that antenna but not on any others. 73, ... Joe, W4TV ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
That's true; I did assume a reasonably good ground plane, to the extent that the unbalanced assumption would be accurate. Still - it's a component that can be removed - at least temporarily - to see if it is contributing to the problem. Here's another thought: connect a dummy load out at the antenna end of the feedline and run up to full power. This will effectively determine whether it's something in the feel line/balun/lightning arrestor. If all is well to that point then the problem is in the antenna itself, perhaps the arc-over to the tree that others have reported. 73 -Jeff From: Tom W8JI w...@w8ji.com To: Jeff Woods jmwoo...@yahoo.com; Ashton Lee ashton.r@hotmail.com; topband@contesting.com Sent: Wednesday, November 28, 2012 11:30 AM Subject: Re: Topband: Inverted L SWR Jumps ??? Remove the balun. It's not doing anything for your and is a potential source of loss and problems. Coaxial cable is unbalanced, as is a ground-fed inverted L. No need for a balun. Unfortunately, that is not a universally true statement. MOST antennas are in a neither world of being neither perfectly balanced nor perfectly unbalanced. Perfectly balanced would be equal and opposite currents entering and leaving each conductor at each end of a balanced line, with equal voltages to the world around the line from each conductor. Perfectly unbalanced would be the same equal and opposite currents entering and leaving each conductor (shield and center) at each line end, and zero voltage from the shield to the outside world around the line. Very few antenna systems meet that criteria, although Marconi systems with many radials are close enough to be nearly perfectly unbalanced. Significant departure from UNbalanced occurs when radial systems are sparse, or truncated, or the feedline exits above the plane of the radials. There isn't any clear boundary, but a slow system dependent transition from the perfect case (feedline exits below the radial plane and an infinite full size radial system) to the worse case (a single radial of any design). Even four 1/4 wave radials have significant voltage to ground at the common point. Choking impedance required varies with the number, configuration, and length of radials and how the feeder is routed and grounded, and in nearly all cases a few hundred ohms is enough. An exception might be if the ground system common point has abnormally high voltages to earth (for example, a single truncated radial) or if the coax is elevated and coupled to the antenna. 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Tom: MOST antennas are in a neither world of being neither perfectly balanced nor perfectly unbalanced. How about an inverted L longer than 1/4 wave but optimized with series capacitor? Any closer to perfect unbalanced? Bob VE7BS Hi Bob, Take the case of a 1/4 wave groundplane with four perfectly resonant radials. There is enough common point voltage to excite the supporting mast and coax with so much current the pattern is changed and SWR changes a quite noticeable amount with mast or cable length. When designing and testing a commercial low-band VHF groundplane I found SWR could be made to go out of acceptable range from common mode. I never would have thought so, but it did. The point I want to make is **perfect** unbalance is as rare as perfect balance. This does not mean we need perfection, but we should be aware that a not balanced feedpoint does not mean the antenna is perfectly unbalanced. Most systems are in a world of being neither perfectly balanced nor perfectly unbalanced, and live someplace between the ideal condition of perfect balance or unbalance in a shade of gray. Certainly the less current driving the ground, the lower ground system common point voltage will be for a given ground system. I don't mean to alarm people into thinking they need extreme measures (they almost never do with more than a several resonant radials), but in a case of high common mode noise or higher radial voltages (from sparse or truncated grounds) some additional isolation or feedline planning can be good. Isolation may not be necessary, and certainly we have gone overboard in some cases, but isolation is almost never harmful. I would not worry on ground mounted verticals with 15-20 or more reasonable length radials, unless the installation had high levels of common mode noise. I would worry with smaller systems, and the smaller the ground system the more I would worry. 73 Tom ___ Topband reflector - topband@contesting.com
Topband: Inverted L SWR Jumps ???
So I am trying to get set up better on 160 meters. I now have two antennas up (pretty well separated). One is an Alpha Delta DX A sloper hung in a tree with a grounding wire led to a ground rod and small radial field. The other is an inverted L on a good radial system of about 2000 feet in various lengths of about 50 feet each as fit the yard. Both are resonant at about 1.830 . The sloper loads fine all the way up to 1500 watts. The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. I've tried various feed line lengths, I've replaced every component in the system except for the antenna wire. The antenna does climb along the branches of a tall pine before L-ing outward at about 55 feet. I think the problem is worse at night time when things are cold (and perhaps more humid). What I see on the amp is output power suddenly seem to surge to 2500 watts, and reflected power jump from a few watts to over what the amp can read… then in a flash the amp faults out. This all happens with only about 20 watts of drive, so the amp can't actually be putting out 2500 watts unless something very strange has happened. As I noted, using the other antenna all is good. I need to get the inverted L working since it seems to have substantial receive gain vs the sloper, so I assume it will be equally better on transmit. All advice is welcome. Am I likely to be arc-ing to the tree branches? Could the wire be the problem? Do inverted L's have trouble with full power? The same wire worked fine for the last few years, but fed against a much lesser radial field and run through a less dense, lower tree. I'll be trying everything I can think of tomorrow afternoon, starting by trying to minimize contact with the tree branches. All suggestions welcome. 73 KQ0C Ash ___ Topband reflector - topband@contesting.com
Re: Topband: Inverted L SWR Jumps ???
Hello Ashton, I am curious what pretty well separated is at your QTH? Two 160 meter antennas separated by 240 feet is the same as having two 2 meter antennas 38 inches apart. There is significant coupling between 160 meter antennas that are separated by as much as 500 feet and this coupling could be problem for your set up. 73, Tim K3LR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Ashton Lee Sent: Tuesday, November 27, 2012 11:49 PM To: topband@contesting.com Subject: Topband: Inverted L SWR Jumps ??? So I am trying to get set up better on 160 meters. I now have two antennas up (pretty well separated). One is an Alpha Delta DX A sloper hung in a tree with a grounding wire led to a ground rod and small radial field. The other is an inverted L on a good radial system of about 2000 feet in various lengths of about 50 feet each as fit the yard. Both are resonant at about 1.830 . The sloper loads fine all the way up to 1500 watts. The inverted L loads just fine to about 700 watts and then causes the Alpha amp to fault out. I think I am getting a sudden change in antenna impedance. The antenna is fed through a 5 KW rated choke balun. The feed line exits the base between radials. I've tried various feed line lengths, I've replaced every component in the system except for the antenna wire. The antenna does climb along the branches of a tall pine before L-ing outward at about 55 feet. I think the problem is worse at night time when things are cold (and perhaps more humid). What I see on the amp is output power suddenly seem to surge to 2500 watts, and reflected power jump from a few watts to over what the amp can read. then in a flash the amp faults out. This all happens with only about 20 watts of drive, so the amp can't actually be putting out 2500 watts unless something very strange has happened. As I noted, using the other antenna all is good. I need to get the inverted L working since it seems to have substantial receive gain vs the sloper, so I assume it will be equally better on transmit. All advice is welcome. Am I likely to be arc-ing to the tree branches? Could the wire be the problem? Do inverted L's have trouble with full power? The same wire worked fine for the last few years, but fed against a much lesser radial field and run through a less dense, lower tree. I'll be trying everything I can think of tomorrow afternoon, starting by trying to minimize contact with the tree branches. All suggestions welcome. 73 KQ0C Ash ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
