Re: Topband: Broadband Inverted L
Thu Nov 20 W8JI wrote: >A 40 ft long wire laid on earth to the radials, even if Joe had 50 x 100 ft >radials, would almost certainly make the ground path impedance hundreds of >ohms. My 160m vertical tee has an extensive buried radial system that's probably at least 2× overkill. The ATU is located in a small wooden 'dog house' about 7 feet away from the base of the series-fed tower. The grounded side of the ATU connects to the radial system via a 2" wide copper strap buried just below the surface of the ground, and the insulated tower base via apiece of #4 AWG solid copper wire elevated about 2 1/2 ft above ground. Sag and bends add about another foot to the total lengths of the ground strap and feed wire. I was amazed at how much that 8' run changes the measured impedance of the antenna. At 1800 kHz, right at the tower base, the impedance reads 117 ohms + j233. At the point where the feed wire is connected to the ATU, the reading is 140 ohms + j269. With an earlier configuration, using the same tower and radial system but with a different top hat, the readings were: At the base of the tower, 28.8 − j10.5 At the ATU feed point, 36.5 − j16.1 Even the few inches of wire running between the antenna disconnect switch inside the dog-house and the connection to the ATU coil made a measurable difference in the readings. It's not hard to imagine what a drastic effect the 40 ft run to the offset radial system would have on tuning and performance. I suspect the physical offset between the antenna base and the common point connection to the radials, and ground losses from the 40 ft run of wire lying on earth, affect the antenna performance more than the mere impedance of the ground path. If the extra impedance added in series with the inverted L were the only factor, that could easily be compensated for in the matching network, with negligible loss. I have long wondered how much loss my buried ground strap introduces into the system, and have considered replacing it with a second piece of wire closely parallel to the existing feed wire, but have never gone to the trouble to try this and take any measurements, plus the strap probably offers better lightning protection. Don k4kyv _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Joe as Charlie said your input impedance is probably in the vicinity of 20-35 ohms. So if you want a better match put an 2 to 1 Un-Un at the feedpoint giving you a 25 to 50 ohm transformer. John k9uwa/w4 >The driving point impedance of the inverted L at > resonance will be of the order of 20-35 ohms or so, with a good ground/radial > system, which would put the VSWR at resonance up in the range of 1.5 -2.0 or > so. > 73, > Charlie, K4OTV > > -Original Message- John Goller, K9UWA & Jean Goller, N9PXF Antique Radio Restorations k9...@arrl.net Visit our Web Site at: http://www.JohnJeanAntiqueRadio.com 4836 Ranch Road Leo, IN 46765 USA 1-260-637-6426 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Hi, Joe Sounds like things are3 progressing nicely! I also live on a small lot and I worked DX all over the world with and inverted L that only had two elevated resonant radials at 90 degrees to each other. Couple comments regarding you VSWR observations; 1.0 A perfectly tuned resonant inverted L over a substantial radial field will have a VSWR up in the range of 1.5-2.0:1 or a bit higher without other matching arrangements. The driving point impedance of the inverted L at resonance will be of the order of 20-35 ohms or so, with a good ground/radial system, which would put the VSWR at resonance up in the range of 1.5 -2.0 or so. 2.0 It can be shown that minimum VSWR will occur at resonance. 3.0 Therefore, your observation of a VSWR variation of 2.1-1.7 as you tune from 1.8-2.0 MHz indicates that your radiator is a little short with its resonance at or above the top end of the band at 2.0 MHz and needs to be lengthened a little to move the resonance lower in the band. May need another 1-2 feet or so of wire. Just remember that minimum VSWR WILL occur at resonance. Sounds like your relocated Inverted L is working fairly well! Have fun!! And BTW, I've had great success hanging 160m inverted Ls and 80m ground-planes from trees! Even built a KILLER 80m 5-element steerable array for a friend that was supported by oak trees! We didn't have to wait for anyone -anywhere in the world on 80 or 75 meters!! Trees work OK! Have fun! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Joe Galicic Sent: Monday, November 24, 2014 3:22 PM To: Guy Olinger K2AV Cc: Richard Fry; List, TopBand Subject: Re: Topband: Broadband Inverted L Update -- I've added 13 radials to my new L over last weekend. Ranging from 30 to 65 feet. Also connected radials to old radial field. New radials run over top of old the ones. Due to antenna placement and neighbors I can only run radials 90 degrees from the antenna base. Cant run radials 360 degrees. No matter how much I try to tune the radiator wire the SWR remains the same at 2.1-1.7 (1.8-2.0MHZ). I think the tree is causing that. The wire runs directly up the center of the tree and out over the top branches. It's #14 stranded wire with jacket. The antenna is probably still very inefficient? I now notice much better receive and transmit performance than before. Before I added the radials the old L was louder in certain directions. That's not the case any more. The new L is louder now regardless of direction. So I'm heading in the right direction. I was able to work 3 new DX entities on 160 including Italy with only 100 watts CW. The DX was about 1-2 S units louder on the new L. Thanks for all of the helpful suggestions !! It's not easy trying to put up an efficient antenna for 160 on a small lot ! Joe - Original Message - From: "Guy Olinger K2AV" To: "Richard Fry" Cc: "List, TopBand" Sent: Monday, November 24, 2014 12:27:01 PM Subject: Re: Topband: Broadband Inverted L The somewhat devastating report from NEC 4.2 offered by Mr Fry is all the more gloomy if one factors in the now-common acknowledgement that NEC 4.x underestimates ground losses with less than ideal radial configurations. Or stated another way, the gloomy NEC 4.2 report is the very best the bad situation could be, and likely is significantly worse. The "shape" of radiation patterns of this genre of antenna rarely depend on radials. The "magnitude" of the pattern depends on the radials. Mr. Fry's link shows a very typical shape to the pattern, also seen in an L with a "gold standard" radial system, the latter being much louder at the distant end. 73, Guy. On Mon, Nov 24, 2014 at 9:05 AM, Richard Fry wrote: > Joe N3HEE wrote: > >> I moved my 160 inverted L to a tall tree in my backyard to get more >> vertical height. The vertical leg is now about 65 feet and the rest >> (65feet) is horizontal. Any feedback would be great. Thanks -Joe >> N3HEE >> > __ > > A NEC4.2 model roughly approximating this system was made using a set > of > 40 symmetrically-buried radials each 50 feet long, and connected at > their common point by a 40-ft straight wire lying on the earth to an > 8-ft buried ground rod 40 feet away. The L consisted of a vertical and > a horizontal conductor of 65 feet each. The vertical axes of the > vertical conductor of the L and of the offset 8-ft ground rod were > aligned. A second 8-ft ground rod was located at the common-point of the radial field. > > The radiation resistance of the L on 1.9 MHz is 21 ohms. System > results for 1.9 MHz and earth conductivity of 5 mS/m, d.c. 13 ... > > Using the offset radial system: Feedpoint Z = 128 -j 3 ohms, peak gain > = - > 5.8 dBi at 64 degrees
Re: Topband: Broadband Inverted L
Tom, I stopped using models years ago ! Even though my 160 antenna is probably less that 30% efficient it's amazing what I've worked with it so far. Granted the receive end is doing all of the heavy lifting. For me the fun of 160 is all about overcoming the challenges presented to me on a very small lot. I know plenty of others in the same leaky boat. Thanks again for all of you help and understanding. I appreciate it. See you the ARRL 160 ! -Joe - Original Message - From: "Tom W8JI" To: "Joe Galicic" Cc: "List, TopBand" Sent: Monday, November 24, 2014 6:38:01 PM Subject: Re: Topband: Broadband Inverted L Hi Joe, Unfortunately all of that stuff renders any model or bandwidth prediction pretty much meaningless. Two antennas 40 feet apart on 160 are about like having two antennas 4 feet apart on 15 meters. We just have to do the best we can with the space we have, although the 40 ft long ground wire would always be a bad idea. You could just open circuit the unused L at the base of the antenna, or short circuit the feeder an electrical 1/4 wave away from the unused L's. if they are 1/4 wave long antennas. At least that would get rid of most of the interaction. I have to detune all of my stuff around here, even my 80M dipoles 200 feet from the 160 antennas cause interaction. 73 Tom - Original Message - From: "Joe Galicic" To: "Tom W8JI" Cc: "List, TopBand" Sent: Monday, November 24, 2014 3:56 PM Subject: Re: Topband: Broadband Inverted L Tom there are many other things in the mix here. Five houses within 30-40 feet, Hi-Z receive antenna within 10 feet of transmit antennas, three other wire antennas sharing the same trees and air space. And yes the old L is still there at about 60 feet away. I don’t think I'm the only person in this situation however. I will either detune or take down the old L. Thanks for your patience! -Joe - Original Message - From: "Tom W8JI" To: "Joe Galicic" Cc: "List, TopBand" Sent: Monday, November 24, 2014 3:45:13 PM Subject: Re: Topband: Broadband Inverted L > > I now notice much better receive and transmit performance than before. > Before I added the radials the old L was louder in certain directions. > That's not the case any more. The new L is louder now regardless of > direction. So I'm heading in the right direction. I was able to work 3 new > DX entities on 160 including Italy with only 100 watts CW. The DX was > about 1-2 S units louder on the new L. > > Thanks for all of the helpful suggestions !! It's not easy trying to put > up an efficient antenna for 160 on a small lot ! > Hi Joe, Do I understand this correctly? You have both inverted L's up only 40 feet apart, with one of them running directly over a tree?? Unless you are detuning unused antenna, anything you observe is an unknown mix of things. Are you detuning the unused antenna? How many other things are in the mix? If it is just one Inverted L, then how are you comparing levels between them? You can't compare levels with only one antenna up at a time. I don't think it is possible to reach conclusions or offer advice about systems before understanding the entire layout. 73 Tom - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4765 / Virus Database: 4189/8622 - Release Date: 11/24/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Hi Joe, Unfortunately all of that stuff renders any model or bandwidth prediction pretty much meaningless. Two antennas 40 feet apart on 160 are about like having two antennas 4 feet apart on 15 meters. We just have to do the best we can with the space we have, although the 40 ft long ground wire would always be a bad idea. You could just open circuit the unused L at the base of the antenna, or short circuit the feeder an electrical 1/4 wave away from the unused L's. if they are 1/4 wave long antennas. At least that would get rid of most of the interaction. I have to detune all of my stuff around here, even my 80M dipoles 200 feet from the 160 antennas cause interaction. 73 Tom - Original Message - From: "Joe Galicic" To: "Tom W8JI" Cc: "List, TopBand" Sent: Monday, November 24, 2014 3:56 PM Subject: Re: Topband: Broadband Inverted L Tom there are many other things in the mix here. Five houses within 30-40 feet, Hi-Z receive antenna within 10 feet of transmit antennas, three other wire antennas sharing the same trees and air space. And yes the old L is still there at about 60 feet away. I don’t think I'm the only person in this situation however. I will either detune or take down the old L. Thanks for your patience! -Joe - Original Message - From: "Tom W8JI" To: "Joe Galicic" Cc: "List, TopBand" Sent: Monday, November 24, 2014 3:45:13 PM Subject: Re: Topband: Broadband Inverted L I now notice much better receive and transmit performance than before. Before I added the radials the old L was louder in certain directions. That's not the case any more. The new L is louder now regardless of direction. So I'm heading in the right direction. I was able to work 3 new DX entities on 160 including Italy with only 100 watts CW. The DX was about 1-2 S units louder on the new L. Thanks for all of the helpful suggestions !! It's not easy trying to put up an efficient antenna for 160 on a small lot ! Hi Joe, Do I understand this correctly? You have both inverted L's up only 40 feet apart, with one of them running directly over a tree?? Unless you are detuning unused antenna, anything you observe is an unknown mix of things. Are you detuning the unused antenna? How many other things are in the mix? If it is just one Inverted L, then how are you comparing levels between them? You can't compare levels with only one antenna up at a time. I don't think it is possible to reach conclusions or offer advice about systems before understanding the entire layout. 73 Tom - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4765 / Virus Database: 4189/8622 - Release Date: 11/24/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Tom there are many other things in the mix here. Five houses within 30-40 feet, Hi-Z receive antenna within 10 feet of transmit antennas, three other wire antennas sharing the same trees and air space. And yes the old L is still there at about 60 feet away. I don’t think I'm the only person in this situation however. I will either detune or take down the old L. Thanks for your patience! -Joe - Original Message - From: "Tom W8JI" To: "Joe Galicic" Cc: "List, TopBand" Sent: Monday, November 24, 2014 3:45:13 PM Subject: Re: Topband: Broadband Inverted L > > I now notice much better receive and transmit performance than before. > Before I added the radials the old L was louder in certain directions. > That's not the case any more. The new L is louder now regardless of > direction. So I'm heading in the right direction. I was able to work 3 new > DX entities on 160 including Italy with only 100 watts CW. The DX was > about 1-2 S units louder on the new L. > > Thanks for all of the helpful suggestions !! It's not easy trying to put > up an efficient antenna for 160 on a small lot ! > Hi Joe, Do I understand this correctly? You have both inverted L's up only 40 feet apart, with one of them running directly over a tree?? Unless you are detuning unused antenna, anything you observe is an unknown mix of things. Are you detuning the unused antenna? How many other things are in the mix? If it is just one Inverted L, then how are you comparing levels between them? You can't compare levels with only one antenna up at a time. I don't think it is possible to reach conclusions or offer advice about systems before understanding the entire layout. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
I now notice much better receive and transmit performance than before. Before I added the radials the old L was louder in certain directions. That's not the case any more. The new L is louder now regardless of direction. So I'm heading in the right direction. I was able to work 3 new DX entities on 160 including Italy with only 100 watts CW. The DX was about 1-2 S units louder on the new L. Thanks for all of the helpful suggestions !! It's not easy trying to put up an efficient antenna for 160 on a small lot ! Hi Joe, Do I understand this correctly? You have both inverted L's up only 40 feet apart, with one of them running directly over a tree?? Unless you are detuning unused antenna, anything you observe is an unknown mix of things. Are you detuning the unused antenna? How many other things are in the mix? If it is just one Inverted L, then how are you comparing levels between them? You can't compare levels with only one antenna up at a time. I don't think it is possible to reach conclusions or offer advice about systems before understanding the entire layout. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Update -- I've added 13 radials to my new L over last weekend. Ranging from 30 to 65 feet. Also connected radials to old radial field. New radials run over top of old the ones. Due to antenna placement and neighbors I can only run radials 90 degrees from the antenna base. Cant run radials 360 degrees. No matter how much I try to tune the radiator wire the SWR remains the same at 2.1-1.7 (1.8-2.0MHZ). I think the tree is causing that. The wire runs directly up the center of the tree and out over the top branches. It's #14 stranded wire with jacket. The antenna is probably still very inefficient? I now notice much better receive and transmit performance than before. Before I added the radials the old L was louder in certain directions. That's not the case any more. The new L is louder now regardless of direction. So I'm heading in the right direction. I was able to work 3 new DX entities on 160 including Italy with only 100 watts CW. The DX was about 1-2 S units louder on the new L. Thanks for all of the helpful suggestions !! It's not easy trying to put up an efficient antenna for 160 on a small lot ! Joe - Original Message - From: "Guy Olinger K2AV" To: "Richard Fry" Cc: "List, TopBand" Sent: Monday, November 24, 2014 12:27:01 PM Subject: Re: Topband: Broadband Inverted L The somewhat devastating report from NEC 4.2 offered by Mr Fry is all the more gloomy if one factors in the now-common acknowledgement that NEC 4.x underestimates ground losses with less than ideal radial configurations. Or stated another way, the gloomy NEC 4.2 report is the very best the bad situation could be, and likely is significantly worse. The "shape" of radiation patterns of this genre of antenna rarely depend on radials. The "magnitude" of the pattern depends on the radials. Mr. Fry's link shows a very typical shape to the pattern, also seen in an L with a "gold standard" radial system, the latter being much louder at the distant end. 73, Guy. On Mon, Nov 24, 2014 at 9:05 AM, Richard Fry wrote: > Joe N3HEE wrote: > >> I moved my 160 inverted L to a tall tree in my backyard to get more >> vertical >> height. The vertical leg is now about 65 feet and the rest (65feet) is >> horizontal. Any feedback would be great. Thanks -Joe N3HEE >> > __ > > A NEC4.2 model roughly approximating this system was made using a set of > 40 symmetrically-buried radials each 50 feet long, and connected at their > common point by a 40-ft straight wire lying on the earth to an 8-ft buried > ground rod 40 feet away. The L consisted of a vertical and a horizontal > conductor of 65 feet each. The vertical axes of the vertical conductor of > the L and of the offset 8-ft ground rod were aligned. A second 8-ft ground > rod was located at the common-point of the radial field. > > The radiation resistance of the L on 1.9 MHz is 21 ohms. System results > for 1.9 MHz and earth conductivity of 5 mS/m, d.c. 13 ... > > Using the offset radial system: Feedpoint Z = 128 -j 3 ohms, peak gain = - > 5.8 dBi at 64 degrees elevation, 2:1 SWR BW = 270 kHz, system radiation > efficiency = 16.4% > > With the vertical conductor of the L centered over the common point of the > radials: Feedpoint Z = 29 +j 4 ohms, peak gain = 0.5 dBi at 64 degrees > elevation, 2:1 SWR BW = 90 kHz, system radiation efficiency = 72.4% > > The efficiency numbers above are based on a lossless match to the > transmission line connected at the feedpoint. The NEC gain analyses were > based on the far field. > > For this comparison study, NEC4.2 shows a system loss of more than 6 dB > when the L uses the offset radial field, however the offset system has the > better SWR bandwidth. > > R. Fry > > > > > > > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
The somewhat devastating report from NEC 4.2 offered by Mr Fry is all the more gloomy if one factors in the now-common acknowledgement that NEC 4.x underestimates ground losses with less than ideal radial configurations. Or stated another way, the gloomy NEC 4.2 report is the very best the bad situation could be, and likely is significantly worse. The "shape" of radiation patterns of this genre of antenna rarely depend on radials. The "magnitude" of the pattern depends on the radials. Mr. Fry's link shows a very typical shape to the pattern, also seen in an L with a "gold standard" radial system, the latter being much louder at the distant end. 73, Guy. On Mon, Nov 24, 2014 at 9:05 AM, Richard Fry wrote: > Joe N3HEE wrote: > >> I moved my 160 inverted L to a tall tree in my backyard to get more >> vertical >> height. The vertical leg is now about 65 feet and the rest (65feet) is >> horizontal. Any feedback would be great. Thanks -Joe N3HEE >> > __ > > A NEC4.2 model roughly approximating this system was made using a set of > 40 symmetrically-buried radials each 50 feet long, and connected at their > common point by a 40-ft straight wire lying on the earth to an 8-ft buried > ground rod 40 feet away. The L consisted of a vertical and a horizontal > conductor of 65 feet each. The vertical axes of the vertical conductor of > the L and of the offset 8-ft ground rod were aligned. A second 8-ft ground > rod was located at the common-point of the radial field. > > The radiation resistance of the L on 1.9 MHz is 21 ohms. System results > for 1.9 MHz and earth conductivity of 5 mS/m, d.c. 13 ... > > Using the offset radial system: Feedpoint Z = 128 -j 3 ohms, peak gain = - > 5.8 dBi at 64 degrees elevation, 2:1 SWR BW = 270 kHz, system radiation > efficiency = 16.4% > > With the vertical conductor of the L centered over the common point of the > radials: Feedpoint Z = 29 +j 4 ohms, peak gain = 0.5 dBi at 64 degrees > elevation, 2:1 SWR BW = 90 kHz, system radiation efficiency = 72.4% > > The efficiency numbers above are based on a lossless match to the > transmission line connected at the feedpoint. The NEC gain analyses were > based on the far field. > > For this comparison study, NEC4.2 shows a system loss of more than 6 dB > when the L uses the offset radial field, however the offset system has the > better SWR bandwidth. > > R. Fry > > > > > > > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Hi Richard, How does the radiation diagram, pattern look with offset radials? I would suspect some enhancement in the direction of the old radial field. (RF mirror) Do the numbers apply to overall average over 360 deg or is there variation in different directions. Yuri, K3BU.us On Mon, Nov 24, 2014 at 09:05 AM, Richard Fry wrote: > Joe N3HEE wrote: I moved my 160 inverted L to a tall tree in my backyard to get more vertical height. The vertical leg is now about 65 feet and the rest (65feet) is horizontal. Any feedback would be great. Thanks -Joe N3HEE __ A NEC4.2 model roughly approximating this system was made using a set of 40 symmetrically-buried radials each 50 feet long, and connected at their common point by a 40-ft straight wire lying on the earth to an 8-ft buried ground rod 40 feet away. The L consisted of a vertical and a horizontal conductor of 65 feet each. The vertical axes of the vertical conductor of the L and of the offset 8-ft ground rod were aligned. A second 8-ft ground rod was located at the common-point of the radial field. The radiation resistance of the L on 1.9 MHz is 21 ohms. System results for 1.9 MHz and earth conductivity of 5 mS/m, d.c. 13 ... Using the offset radial system: Feedpoint Z = 128 -j 3 ohms, peak gain = - 5.8 dBi at 64 degrees elevation, 2:1 SWR BW = 270 kHz, system radiation efficiency = 16.4% With the vertical conductor of the L centered over the common point of the radials: Feedpoint Z = 29 +j 4 ohms, peak gain = 0.5 dBi at 64 degrees elevation, 2:1 SWR BW = 90 kHz, system radiation efficiency = 72.4% The efficiency numbers above are based on a lossless match to the transmission line connected at the feedpoint. The NEC gain analyses were based on the far field. For this comparison study, NEC4.2 shows a system loss of more than 6 dB when the L uses the offset radial field, however the offset system has the better SWR bandwidth. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
To elaborate a bit on Tom's point -14 ga wire would have approximately 0.4 uH/ft of inductance, so 40 feet of 14 ga wire would be around 16 uH with an inductive reactance at 1.8 MHz of around j180 ohms. Compare this with the radiation resistance of the 1/4 wave inverted L, of perhaps 10-30 ohms resistive, and it becomes pretty clear that the 40' "ground" wire is not really an effective RF ground for the antenna. Furthermore, the displaced radial field is no longer beneath the antenna where it needs to be to provide an image for the antenna fields. A 4' ground rod, unless it's in salt water is not much of an RF ground either, so the losses in the system as built are horrendous! Putting even a couple of elevated resonant radials under the relocated inverted L should make a huge difference! 73, Charlie, K4OTV - -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, November 20, 2014 2:18 PM To: topband@contesting.com Subject: Re: Topband: Broadband Inverted L Ground systems cannot be evaluated or estimated by number of feet of wire, just like they cannot be evaluated by SWR or bandwidth, but I'm sure we all agree on this.. The single most important thing Joe said was: <<<< The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. >>>> Joes has virtually no ground at all on 160 meters, because his system's ground connection to the radials is via a single #14 wire 40 feet long. A 40 ft long wire laid on earth to the radials, even if Joe had 50 x 100 ft radials, would almost certainly make the ground path impedance hundreds of ohms. Joe's antenna virtually doesn't have a ground connection to radials at all, and this has almost nothing to do with the number of radials or type of radials. It has to do with the 40ft long connection. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
And in some cases where the bandwidth is clearly excessive from normal the closer you are may be closer to a dummy load at the end of the feedline...if you care to look at it that way. Herb Schoenbohm, KV4FZ On 11/20/2014 6:52 PM, Tom W8JI wrote: A few years ago I put up a temporary 60 foot vertical over my 230 foot diameter ground screen. It was top loaded with 2 "umbrella" wires sloping down. The bandwidth was MUCH narrower than your 65 foot vertical. IIRC, the 3:1 VSWR bandwidth was less than 50 kHz. The feedpoint impedance was about as predicted by EZNEC over a perfect ground. IE, very low. It got out really well in contests (anecdotal "data"). If you are seeing a bandwidth broad as a barn door, it can probably only be explained by substantial ground losses. I understand you can't get a ground like I have, do the best you can and get on the air. We have to be very careful. Bandwidth of an antenna system is not just related to loss resistance. bandwidth is also related to the ratio of applied energy to energy stored in and around the antenna, or reactance in the loading system. Bandwidth can go all over the place even without losses going opposite of what we think. For example, a 60ft vertical of #14 AWG wire over perfect ground and virtually no loss can have a 3:1 bandwidth of 100 kHz when hat loaded. The same antenna coil loaded with a coil, with significant loss, could be less than 20 kHz wide. There are countless cases where an antenna with wider BW has better efficiency, and countless cases where they have less efficiency. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
A few years ago I put up a temporary 60 foot vertical over my 230 foot diameter ground screen. It was top loaded with 2 "umbrella" wires sloping down. The bandwidth was MUCH narrower than your 65 foot vertical. IIRC, the 3:1 VSWR bandwidth was less than 50 kHz. The feedpoint impedance was about as predicted by EZNEC over a perfect ground. IE, very low. It got out really well in contests (anecdotal "data"). If you are seeing a bandwidth broad as a barn door, it can probably only be explained by substantial ground losses. I understand you can't get a ground like I have, do the best you can and get on the air. We have to be very careful. Bandwidth of an antenna system is not just related to loss resistance. bandwidth is also related to the ratio of applied energy to energy stored in and around the antenna, or reactance in the loading system. Bandwidth can go all over the place even without losses going opposite of what we think. For example, a 60ft vertical of #14 AWG wire over perfect ground and virtually no loss can have a 3:1 bandwidth of 100 kHz when hat loaded. The same antenna coil loaded with a coil, with significant loss, could be less than 20 kHz wide. There are countless cases where an antenna with wider BW has better efficiency, and countless cases where they have less efficiency. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Hi, Joe I didn't have time to write you earlier. It was obvious that you had a lot of ground loss in series with the radiation resistance of the inverted-L that was swamping the reactance variation of the inverted L. You are likely to be very pleasantly surprised at how effective two elevated resonant radials at 5-6' can be! I did that for years - worked JA, VKs, VK6, JT1, S79,many deep European and Russians, lots of, LOTs of Pacific and DXpeditons etc.. Of course you can also lay out some more radials from your feed-point! Good luck! Have fun! The taller vertical section will help a lot! Mine was about 75 feet! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Joe Galicic Sent: Thursday, November 20, 2014 2:12 PM To: Mike Waters Cc: List, TopBand Subject: Re: Topband: Broadband Inverted L Thanks everyone ! Interesting. I knew something was not quite right. I thought I could "tap" into the existing ground system but obviously that is not going to be the case. I could manage two elevated radials pretty easily but not at 10 ten feet. More like 6 feet off the ground mounted on my 6 foot high wooden privacy fence. Can I lay down radials more over top of the old ones? - Original Message - From: "Mike Waters" To: "List, TopBand" Sent: Thursday, November 20, 2014 1:23:32 PM Subject: Re: Topband: Broadband Inverted L Have you considered elevated radials? Four of them 10' high (or even two!) would be MUCH better than what you have right now. My 160m Inverted-L: http://www.w0btu.com/160_meters.html#inv-l_antenna 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
A few years ago I put up a temporary 60 foot vertical over my 230 foot diameter ground screen. It was top loaded with 2 "umbrella" wires sloping down. The bandwidth was MUCH narrower than your 65 foot vertical. IIRC, the 3:1 VSWR bandwidth was less than 50 kHz. The feedpoint impedance was about as predicted by EZNEC over a perfect ground. IE, very low. It got out really well in contests (anecdotal "data"). If you are seeing a bandwidth broad as a barn door, it can probably only be explained by substantial ground losses. I understand you can't get a ground like I have, do the best you can and get on the air. Rick N6RK On 11/20/2014 8:11 AM, Joe Galicic wrote: I moved my 160 inverted L to a tall tree in my backyard to get more vertical height. The vertical leg is now about 65 feet and the rest (65feet) is horizontal. I fed this one with about 125 feet of 75 ohm coax just because I had lots of it laying around. No tuners, baluns, ununs or chokes in the feed line. The ground is connected to the existing ground system for the old L. I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and slightly higher to 2.0. The antenna seems to be working OK (relative to the old L). This seems awfully broad banded? Any feedback would be great. Thanks -Joe N3HEE _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
On Thu,11/20/2014 11:17 AM, Tom W8JI wrote: Joe's antenna virtually doesn't have a ground connection to radials at all, and this has almost nothing to do with the number of radials or type of radials. Yes, but there's another important concept that is being missed here. The function of a radial system is NOT to couple the antenna to the earth, it is to SHIELD the antenna from the earth. Rather, the function of a radial system is to serve as a return for both the antenna current AND THE FIELD produced by the antenna. That is, a good radial system acts as a SHIELD between that field and the lossy earth. Joe's system has a counterpoise (a return for the current), albeit not a good one, but it doesn't perform the shielding function because it's not just below the base of the antenna. K2AV's folded counterpoise is another example of a system that provides an effective return for antenna current, but provides much less of a shielding function. > Time to go out and connect more radials directly to the feed point ground. NOT to the earth, to the coax shield. I can also elevate two of them. I suggest that you study the link I posted. N6LF has done a lot of excellent work on radial systems, much of which is summarized in that link. On 160M, radials must be at least 16 ft off the ground to work as "elevated radials," and they should be of equal lengths and heights. Radials on the ground can be of any length --the only more or less universal rules of thumb is that more copper on the ground is better, and more short radials is better than a few long ones. Think of it this way -- the current in any radial must be minimum at the end, and if it's less than a quarter wave, will be maximum at the feedpoint. The antenna return current divides between the radials, and the loss is I squared R, where this R is coupled from the lossy earth. The more radials there are to divide that current, the less will be the lost power! That's because the current is divided by N (the number of radials) while the loss is divided by N squared. The reason a fewer number of elevated radials can work as well as many more on the ground is that the fields from the elevated radials don't couple as closely to the earth, so there's less coupled R, and thus less lost power. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Exactly what I thought ... any way to slope the leg of the L to get it at the junction of the redials? de ns9i On 11/20/2014 1:17 PM, Tom W8JI wrote: Ground systems cannot be evaluated or estimated by number of feet of wire, just like they cannot be evaluated by SWR or bandwidth, but I'm sure we all agree on this.. The single most important thing Joe said was: The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. Joes has virtually no ground at all on 160 meters, because his system's ground connection to the radials is via a single #14 wire 40 feet long. A 40 ft long wire laid on earth to the radials, even if Joe had 50 x 100 ft radials, would almost certainly make the ground path impedance hundreds of ohms. Joe's antenna virtually doesn't have a ground connection to radials at all, and this has almost nothing to do with the number of radials or type of radials. It has to do with the 40ft long connection. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Thanks Tom. I get the picture now. Time to go out and connect more radials directly to the feed point ground. I can also elevate two of them. -Joe - Original Message - From: "Tom W8JI" To: "List, TopBand" Sent: Thursday, November 20, 2014 2:17:55 PM Subject: Re: Topband: Broadband Inverted L Ground systems cannot be evaluated or estimated by number of feet of wire, just like they cannot be evaluated by SWR or bandwidth, but I'm sure we all agree on this.. The single most important thing Joe said was: <<<< The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. >>>> Joes has virtually no ground at all on 160 meters, because his system's ground connection to the radials is via a single #14 wire 40 feet long. A 40 ft long wire laid on earth to the radials, even if Joe had 50 x 100 ft radials, would almost certainly make the ground path impedance hundreds of ohms. Joe's antenna virtually doesn't have a ground connection to radials at all, and this has almost nothing to do with the number of radials or type of radials. It has to do with the 40ft long connection. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Ground systems cannot be evaluated or estimated by number of feet of wire, just like they cannot be evaluated by SWR or bandwidth, but I'm sure we all agree on this.. The single most important thing Joe said was: The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. Joes has virtually no ground at all on 160 meters, because his system's ground connection to the radials is via a single #14 wire 40 feet long. A 40 ft long wire laid on earth to the radials, even if Joe had 50 x 100 ft radials, would almost certainly make the ground path impedance hundreds of ohms. Joe's antenna virtually doesn't have a ground connection to radials at all, and this has almost nothing to do with the number of radials or type of radials. It has to do with the 40ft long connection. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
I suppose another question is this all worth it? Meaning, is the L with 65 foot vertical leg with proper ground going to greatly outperform the L with 35 foot vertical leg ? - Original Message - From: "Joe Galicic" To: "Mike Waters" Cc: "List, TopBand" Sent: Thursday, November 20, 2014 2:12:28 PM Subject: Re: Topband: Broadband Inverted L Thanks everyone ! Interesting. I knew something was not quite right. I thought I could "tap" into the existing ground system but obviously that is not going to be the case. I could manage two elevated radials pretty easily but not at 10 ten feet. More like 6 feet off the ground mounted on my 6 foot high wooden privacy fence. Can I lay down radials more over top of the old ones? - Original Message - From: "Mike Waters" To: "List, TopBand" Sent: Thursday, November 20, 2014 1:23:32 PM Subject: Re: Topband: Broadband Inverted L Have you considered elevated radials? Four of them 10' high (or even two!) would be MUCH better than what you have right now. My 160m Inverted-L: http://www.w0btu.com/160_meters.html#inv-l_antenna 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Thanks everyone ! Interesting. I knew something was not quite right. I thought I could "tap" into the existing ground system but obviously that is not going to be the case. I could manage two elevated radials pretty easily but not at 10 ten feet. More like 6 feet off the ground mounted on my 6 foot high wooden privacy fence. Can I lay down radials more over top of the old ones? - Original Message - From: "Mike Waters" To: "List, TopBand" Sent: Thursday, November 20, 2014 1:23:32 PM Subject: Re: Topband: Broadband Inverted L Have you considered elevated radials? Four of them 10' high (or even two!) would be MUCH better than what you have right now. My 160m Inverted-L: http://www.w0btu.com/160_meters.html#inv-l_antenna 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Have you considered elevated radials? Four of them 10' high (or even two!) would be MUCH better than what you have right now. My 160m Inverted-L: http://www.w0btu.com/160_meters.html#inv-l_antenna 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Joe posted, I moved my 160 inverted L to a tall tree in my backyard to get more vertical height. The vertical leg is now about 65 feet and the rest (65feet) is horizontal. I fed this one with about 125 feet of 75 ohm coax just because I had lots of it laying around. No tuners, baluns, ununs or chokes in the feed line. The ground is connected to the existing ground system for the old L. I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and slightly higher to 2.0. The antenna seems to be working OK (relative to the old L). This seems awfully broad banded? Any feedback would be great. Thanks -Joe N3HEE and Joe added: The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. The radial field consists of 3 8 foot ground rods and nearly 2000 feet of wire spread out over my entire front and back yard. I didn't want to run "new" radials over top of the existing so that's why I did what I did. I am measuring SWR from the shack end of the feed line>>> Unfortunately there is almost no radial system ground connection at all on the new inverted L, because there is almost 1/8th wave of a single thin wire between the real ground and the feedpoint. That wire length, 40 ft, could add hundreds of ohms impedance to the ground path. While bandwidth is a terrible way to guess efficiency, it is also obvious the ground radial connection really isn't a worthwhile connection at all. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
On Thu,11/20/2014 9:25 AM, Gene Smar wrote: Don't ask questions and just enjoy the antenna's performance. A low SWR is NOT an indicator of an antenna's performance. It only indicates a match to the transmission line. In this case, the low SWR suggests that the antenna is highly resistive. The radiation resistance of an antenna of that height is less than ten Ohms. The rest of the 70 ohms or so of resistance it takes to produce that nice match is LOSS -- a bit in the wire resistance, the rest of it in the radial system. A connection to earth is NOT an efficient part of an antenna -- the earth is lossy (a big resistor). The only reason for having a driven rod is for lightning protection. It's those radials that are providing a return for antenna current, and 2,000 ft of wire is not a lot on 160M. Over average soil, 2000 ft of wire typically provides a ground loss resistance on the order of 10 ohms; over poor soil, the loss resistance will be higher, over good soil, it will be less. The high value of loss suggests that perhaps your radials might not be making a good connection to the coax shield, so all the antenna sees is those driven rods. To understand this, and for some practical ideas for radial systems, study http://k9yc.com/160MPacificon.pdf 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
In my case, I started out with four radials, great wideband match ~100KHz When I had some more time and wire, I went to 8 radials, that cut the bandwidth in half, still a good match. Each chance I had to add more radials, I did. Each time the bandwidth decreased substantially, but the antenna kept working better with more radials as measured by my success working weaker and more distant stations. I'm up to 60 radials now, antenna is no longer wideband, but works better than ever. I figured out that I was "cooking dirt" back in the days that I had only a few radials. Now it requires a tuner to QSY more that 10 KHz, but again it works so much better. Examples, 160m worked and confirmed this year, W1AW in all 50 states, Amsterdam Is, Lord Howe Is, S. Cook Is. I suggest adding ground radials or a ground screen around the new feed point - as close to the surface as possible, and attach to the previous ground system too. 73 Lloyd - N9LB -Original Message- From: Topband [mailto:topband-boun...@contesting.com]On Behalf Of Joe Galicic Sent: Thursday, November 20, 2014 11:11 AM To: Mike Waters Cc: List, TopBand Subject: Re: Topband: Broadband Inverted L Mike, The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. The radial field consists of 3 8 foot ground rods and nearly 2000 feet of wire spread out over my entire front and back yard. I didn’t want to run "new" radials over top of the existing so that's why I did what I did. I am measuring SWR from the shack end of the feed line. My old L was only 35 foot vertical. I thought 65 foot vertical would be much better but sometimes the old L hears and transmits better by a couple S units depending on where the station is of course. So I think something is off? Hopefully I didn’t build myself an accidental dummy load? -Joe - Original Message - From: "Mike Waters" To: "Joe Galicic" Cc: "List, TopBand" Sent: Thursday, November 20, 2014 11:17:16 AM Subject: Re: Topband: Broadband Inverted L It sure IS broadbanded. Couple of questions: On Thu, Nov 20, 2014 at 10:11 AM, Joe Galicic < gali...@comcast.net > wrote: The ground is connected to the existing ground system for the old L. Can you describe this? I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and slightly higher to 2.0. The antenna seems to be working OK (relative to the old L). This seems awfully broad banded? Where are you measuring the SWR? At the feedpoint or at the end of the 125' coax? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Joe: Don't ask questions and just enjoy the antenna's performance. 73 de Gene Smar AD3F On 11/20/14, Joe Galicic wrote: I moved my 160 inverted L to a tall tree in my backyard to get more vertical height. The vertical leg is now about 65 feet and the rest (65feet) is horizontal. I fed this one with about 125 feet of 75 ohm coax just because I had lots of it laying around. No tuners, baluns, ununs or chokes in the feed line. The ground is connected to the existing ground system for the old L. I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and slightly higher to 2.0. The antenna seems to be working OK (relative to the old L). This seems awfully broad banded? Any feedback would be great. Thanks -Joe N3HEE _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
Mike, The antenna feed point terminates at a four foot ground rod and then I am running a number 14 wire from that ground rod to my existing radial field. That run is about 40 feet. The radial field consists of 3 8 foot ground rods and nearly 2000 feet of wire spread out over my entire front and back yard. I didn’t want to run "new" radials over top of the existing so that's why I did what I did. I am measuring SWR from the shack end of the feed line. My old L was only 35 foot vertical. I thought 65 foot vertical would be much better but sometimes the old L hears and transmits better by a couple S units depending on where the station is of course. So I think something is off? Hopefully I didn’t build myself an accidental dummy load? -Joe - Original Message - From: "Mike Waters" To: "Joe Galicic" Cc: "List, TopBand" Sent: Thursday, November 20, 2014 11:17:16 AM Subject: Re: Topband: Broadband Inverted L It sure IS broadbanded. Couple of questions: On Thu, Nov 20, 2014 at 10:11 AM, Joe Galicic < gali...@comcast.net > wrote: The ground is connected to the existing ground system for the old L. Can you describe this? I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and slightly higher to 2.0. The antenna seems to be working OK (relative to the old L). This seems awfully broad banded? Where are you measuring the SWR? At the feedpoint or at the end of the 125' coax? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Broadband Inverted L
It sure IS broadbanded. Couple of questions: On Thu, Nov 20, 2014 at 10:11 AM, Joe Galicic wrote: > The ground is connected to the existing ground system for the old L. Can you describe this? I get a 1.1 SWR reading from 1.8 to 1.9 before it moves up to 1.3 and > slightly higher to 2.0. The antenna seems to be working OK (relative to the > old L). This seems awfully broad banded? > Where are you measuring the SWR? At the feedpoint or at the end of the 125' coax? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
