Re: Topband: Tree losses....
Very nice study and IMO neither small nor inelegant. Thanks From: Roger Parsons ve...@yahoo.com To: Topband topband@contesting.com Sent: Friday, August 9, 2013 7:29 AM Subject: Re: Topband: Tree losses I just did a small and inelegant piece of modelling with EZNEC. I took a wire 128' vertical, and it showed a gain of about 1.7dBi over a particular ground. Keeping everything else the same, I introduced a 'tree' 3ft away from it, with no branches, exactly parallel, also 128' high and initially with zero resistance. This changed the gain to 2.0 dBi with a 0.7 dB front to back ratio. I then introduced series resistances at 20 equally spaced points in the 'tree', and looked at the effect of varying these. With 1R resistances (20R total) gain was about 0.6dBi and 0.6dB f/b. With 2R resistances (40R total) gain was about 0dBi and 0.5 dB f/b. With 3R resistances (60R total) gain was about -0.1dBi and 0.3 dB f/b (the minimum gain modelled) and so on, until with 10R resistances (200R total) gain was about 0.7dBi and 0.1 dB f/b and so on again, until with 100R resistances (2000R total) gain was back to 1.7dBi and 0dB f/b. Of course this is highly unrealistic in many respects, but I would be amazed if any 128' high tree under any conditions of sap would have a total end to end resistance of only 2000R. And bear in mind that this is a self resonant tree selected to couple very strongly indeed to the main radiator. I then repeated the process with a non-resonant tree only 64' in height. No value of series resistances produced even 0.01 dB change in gain. (Of course at this point the wire vertical was being supported by an invisible sky hook.) I do believe that trees can affect things in at least two ways - as others have said, high voltage points adjacent to foliages can definitely cause losses - and these are very hard to quantify. My own past experience with tree supported inverted L and T antennas has been that quite small changes in the position of the element can cause big changes in feed impedances - but that is not quite the same thing at all. 73 Roger VE3ZI _ Topband Reflector _ Topband Reflector
Re: Topband: Tree losses....
I just did a small and inelegant piece of modelling with EZNEC. I took a wire 128' vertical, and it showed a gain of about 1.7dBi over a particular ground. Keeping everything else the same, I introduced a 'tree' 3ft away from it, with no branches, exactly parallel, also 128' high and initially with zero resistance. This changed the gain to 2.0 dBi with a 0.7 dB front to back ratio. I then introduced series resistances at 20 equally spaced points in the 'tree', and looked at the effect of varying these. With 1R resistances (20R total) gain was about 0.6dBi and 0.6dB f/b. With 2R resistances (40R total) gain was about 0dBi and 0.5 dB f/b. With 3R resistances (60R total) gain was about -0.1dBi and 0.3 dB f/b (the minimum gain modelled) and so on, until with 10R resistances (200R total) gain was about 0.7dBi and 0.1 dB f/b and so on again, until with 100R resistances (2000R total) gain was back to 1.7dBi and 0dB f/b. Of course this is highly unrealistic in many respects, but I would be amazed if any 128' high tree under any conditions of sap would have a total end to end resistance of only 2000R. And bear in mind that this is a self resonant tree selected to couple very strongly indeed to the main radiator. I then repeated the process with a non-resonant tree only 64' in height. No value of series resistances produced even 0.01 dB change in gain. (Of course at this point the wire vertical was being supported by an invisible sky hook.) I do believe that trees can affect things in at least two ways - as others have said, high voltage points adjacent to foliages can definitely cause losses - and these are very hard to quantify. My own past experience with tree supported inverted L and T antennas has been that quite small changes in the position of the element can cause big changes in feed impedances - but that is not quite the same thing at all. 73 Roger VE3ZI _ Topband Reflector
Re: Topband: tree losses
As Tom, Rudy, and Richard have noted, this stuff is potentially important, but awfully difficult to quantify for a variety of reasons. One is that what's happening in the trees is not the only thing that is happening when the seasons change. Out here along the Pacific coast, we have a rainy season when the soil is increasingly well saturated (thankfully, for 160M operation, from Nov to April) and a dry season when it is not. So when I see seasonal variations with vertical antennas in my very dense redwood forest, the obvious question is, how much of what I'm seeing is soil, and how much of it is sap? :) Almost none of my trees are deciduous (shedding leaves in the fall), so I don't see those changes. I loved Tom's story of hoping that he would have a measurement opportunity and circumstances made it impossible. I have three verticals for topband. One is an 86 ft tall Tee, more or less in the center of a large clearing (~ 90 ft radius) and a lot of radials on the ground. The other two are sloping wires fed from a base about 40 ft from a 120 ft tower that supports the top of the wires, which are insulated from the tower. One wire slopes east, the other to the west, both have four quarter wave radials elevated about 20 ft, and there are ten quarter-wave radials on the grounded tower. The tower supports the small 3-3l SteppIR, and the clearing is barely large enough to turn it (roughly 24 ft radius) -- that is, it's in the middle of very dense, very tall (150 ft) redwoods. NEC predicts gain in the range of 4-5 dBi for these two slopers, but I am not yet convinced I am seeing that. More anecdotal stuff -- the 160M Tee is the only vertical of several I've tried for 160, 80, and 40 that I find even slightly useful. OTOH, my horizontal antennas for 80M-6M, nearly all of them at 110-120 ft, play very well. What I take from all of this is an hypothesis (and that's all it is) that trees like redwoods and tall pines have a much greater effect on vertical antennas when they are in the near field, and that up to about 6M, the radiation from horizontal antennas doesn't seem to be strongly attenuated. I do OK on 6M Es, MS, and tropo, considering the fact that the ridge above me to the north, east, and SE gives me a horizon of about 7-8 degrees. But attenuation increases with frequency, so 2M and up is almost a lost cause, and it doesn't matter much whether the polarization is horizontal or vertical. One experiment I'm thinking of, based partly on the comments I've seen here, is to string a horizontal rope strung between two trees with pulleys at each end, a pulley that can support an end-fed vertical dipole using a method that Rudy inspired -- a ferrite coax choke as the lower end insulator a quarter wave from the end of the coax, with the center conductor connected to a quarter wave wire. For the test, you simply move the vertical dipole so that it is very close to one of the trees, then vary the spacing to the trees. This sounds fairly easy and simple, but I've got a lot of large and small towers and antennas with more or less vertical feedlines that can interact with the antenna being tested, tree climbers cost something like $800/day, and it could take more than a day to rig it, so it's a non-trivial exercise, but I believe it's worth doing. Based on the heights at which I could rig things, I would probably have to do this on 40M, although I MIGHT be able to do it on 80M with non-resonant somewhat shortened dipoles. As I'm certain any well trained engineer who has attempted it (or even thought seriously about it) will tell you, MEANINGFUL antenna testing is a non-trivial exercise. Thoughts? 73, Jim K9YC _ Topband Reflector
Re: Topband: tree losses
Well Tom, you surprise me since I thought in the past you were one of those who felt tree losses were minimal and part of mythology for HF/MF. I guess you changed your mind now that others have shown different. I think they are minimal, if the tree is not right next to the antenna. I never thought they were zero, and never thought they were horrible like they would be if a tree would be useful as an antenna.. What it clearly is not is something to make a big deal out of especially when there is nothing many can do about it. Perhaps you dont understand that and think that actual attenuation numbers for every species on the planet is important. People often like to know how much. We can't have it both ways, Carl. We can't believe trees make antennas of some sort in one case, and then decide they are meaningless in another case. They either are low enough resistivity to conduct significant current compared to a normal metallic conductor, or they are not. They certainly do not change conductivity based on application. OTOH most of us dont have the room to clear cut several acres just to play ham radio and accept what they cant control. With some it is all about control I guess. Is nasty stuff like that really necessary in technical conversation? It almost sounds like you are bitter. No one I know of clear cuts trees for antennas. Even if they did, I wouldn't really care enough to be jealous about it. It's their trees. :) 73 Tom _ Topband Reflector
Re: Topband: Tree losses....
Gentlemen: I wanted to weigh-in on the discussion of the impact of tree losses on transmitting antenna performance. Of course I have no quantitative data, but experience is suggestive of potentially significant losses. I used to live in Grayson County, Virginia, on a completely wooded hilltop. By completely wooded, I mean a dense mixed forest, with a fair percentage of pitch pine in the immediate area of my lowband vertical. I built a version of the Battle Creek Special that was 40' high and had a fairly sparse radial field, with (8) 135' radials, (16) 66' radials, and (16) 35' radials -- all insulated copper. The antenna was on a small knoll, which dropped off gently in all directions. The forest were quite dense and low angle radiation had to travel through hundreds of feet of forest to finally clear the ground clutter. I used that antenna for several years and became well acquainted with its characteristics. In good conditions and with 50-watts, I could work out 6000 miles or so on 160-meters. I remember it was a struggle to work Eu and I was quite unable to work JA or VK in two seasons. Eventually, I moved to a small farm at the bottom of a valley in Pulaski County, VA, and transplanted the Battle Creek Special, radial field and all. I would have called it a worse RF site than the Grayson County site, but the results indicate not. There are very few trees anywhere near the antenna and the takeoff angle from due West and through North and to the East is unobstructed, with the hill falling away in those general directions. The southern half is less favorable and actually slopes uphill. The soil conductivity in the pasture may be a bit better, but the relative lack of trees is a big difference. At the old location, a 500' circle contained hundreds of trees, vs. the new QTH which has a dozen or so in the same radius. The difference in the performance of the antenna was noticeable in that I could now work EU routinely and also worked JA and VK on Topband for the first time--with the same 50-watts output. Of course, there were more variables than tree density in this story and no way of knowing for sure how many others were present. There had to be some some absorption of the signal due to gently heating tree sap and certainly losses due to gently heating earth and earth worms. The two locations were about 70-miles apart and quite different--one mountainous and one agricultural, so the take-off angles were likely a bit different too. It's hard to quantify all that, but operationally there is no question which installation gave the better results on Topband, by a fair margin. 73, Steve, AB4I _ Topband Reflector
Re: Topband: Tree losses....
The only way to say which location is better is to do a side by side comparison which didn't happen. You are making assumptions which may be wrong or may be right. Blaming it on trees is a guess. There are many other factors to consider. Doug -Original Message- It's hard to quantify all that, but operationally there is no question which installation gave the better results on Topband, by a fair margin. 73, Steve, AB4I _ Topband Reflector
Re: Topband: Tree losses....
Hi Doug , Like so many things related to antenna installations, side by side comparisons are usually impossible. Without the ability to do meaningful measurements, it is also unlikely that one can capture all the unknowns that can add up to a large effect. I could do only relative field strength measurements in the near field at the time, which appeared to be pretty similar. I could also get a useful inference of the ground loss component, which was also similar between the two sites, with the new site being a little better. All the equipment and feed lines were exactly the same--just transplanted. One site is clearly better than the other, by whatever mechanisms make one site better than another. Personally, I suspect that several factors were in play, and I will never know all the factors. BTW, I am RF engineer by profession and I know very well that a great many factors influence the field strength of a transmitting antenna system. I wish that I knew the full story of the two installations, but I do not. Wet wood is lossy and I know that I did a certain amount of heating of the trees. RF wood dryers work by RF heating after all. Was my wood heating enough to give the observed differences? Probably not. Did my country total on 160M jump from 56 in 2-years of trying to something past 150 the first winter after the move? Yes it certainly did. That much can be quantified. The rest is educated guessing. I have decided that the next time that I am in that area, I am going to snag a piece of pitch pine and spend some lab time and characterize it. It is a very resinous wood that may have interesting RF properties. I had a hundred or more pitch pine in the near field of my low band vertical and and many were upwards of twice its height and 20 thick. They are not transparent to RF, but to what extent they are sticky vertical RF absorbers is currently unknown. 73, Steve, AB4I On Tuesday, August 6, 2013, Doug Renwick wrote: The only way to say which location is better is to do a side by side comparison which didn't happen. You are making assumptions which may be wrong or may be right. Blaming it on trees is a guess. There are many other factors to consider. Doug -Original Message- It's hard to quantify all that, but operationally there is no question which installation gave the better results on Topband, by a fair margin. 73, Steve, AB4I _ Topband Reflector
Re: Topband: tree losses
I cant think of anyone claiming a tree is resonant on any particular frequency but that doesnt mean it cant be used as an antenna. Anyone disagreeing with that should discuss it with the military who have been loading trees for decades for emergency communications; in the 3-8MHz range if I remember and going back as far as the 50's. Read the old CQ and QST's. On another note I spent most of today outside doing tree trimming and other sweaty exercises. I noted that my best producing Bartlett pear tree was dead at the top and also a bit down on one side. Now it may be just coincidence but the 80M sloper passes about 5' from the farthest out branches and the end is exactly at the same height as the tree top. This antenna is used at the vintage gear bench and also on the one for amp repairs where Ive been hitting it rather hard this year with AM with serious carrier power; the most recent being an Alpha 77SX. I also remember wilting the top of a sugar maple about 20 years ago with 1200W on 6M to a 6/6 yagi array. After I moved the antenna to another tower the tree recovered the following year. Another coincidence? Carl KM1H - Original Message - From: Rudy Severns rseve...@gmail.com To: Topband topband@contesting.com Sent: Sunday, August 04, 2013 5:39 PM Subject: Topband: tree losses Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. 73, Rudy N6LF _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3209/6051 - Release Date: 08/04/13 _ Topband Reflector
Topband: tree losses
Rudy Severns wrote: Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Here are several data points on this subject. Recording the relative readings on the dBµ and S/N displays of a Tecsun PL-310 tuned to a 790 kHz directional station about 52 miles east of me, radiating about 1 kW in my direction: Location dBµS/N (dB) (Tecsun 4-1/2 ft AGL) Area clear for 50 ft around32 15 Pin oak tree, 3' diameter trunk, 42 24 east side against trunk Ditto, but west side of trunk 34 14 Gnd Wire of 50' utility pole48 24 (Tecsun 9 ft AGL) Gnd Wire of 50' utility pole50 24 The field improvement when the rx is held against the east side of the trunk is completely gone when the receiver is moved to the east about 15 feet. So the effects are quite localized. These locations were all within 100' of each other. _ Topband Reflector
Re: Topband: tree losses
Carl et al, Interesting, my 80M full size (66') sloper comes within about 5 ft of a dogwood tree and it is dying. The sloped is fed 8' AGL with 2 full size elevated radials and about 500w and the dogwood is dying from that height(8') to the top of the tree at about 15'. Unfortunately for me, my XYL pointed this out to me - not good. The sloper has been in that position for about 1 year, before that the tree was doing fine. Coincidence? Jim N4DU On 8/4/13 9:42 PM, ZR wrote: I cant think of anyone claiming a tree is resonant on any particular frequency but that doesnt mean it cant be used as an antenna. Anyone disagreeing with that should discuss it with the military who have been loading trees for decades for emergency communications; in the 3-8MHz range if I remember and going back as far as the 50's. Read the old CQ and QST's. On another note I spent most of today outside doing tree trimming and other sweaty exercises. I noted that my best producing Bartlett pear tree was dead at the top and also a bit down on one side. Now it may be just coincidence but the 80M sloper passes about 5' from the farthest out branches and the end is exactly at the same height as the tree top. This antenna is used at the vintage gear bench and also on the one for amp repairs where Ive been hitting it rather hard this year with AM with serious carrier power; the most recent being an Alpha 77SX. I also remember wilting the top of a sugar maple about 20 years ago with 1200W on 6M to a 6/6 yagi array. After I moved the antenna to another tower the tree recovered the following year. Another coincidence? Carl KM1H - Original Message - From: Rudy Severns rseve...@gmail.com To: Topband topband@contesting.com Sent: Sunday, August 04, 2013 5:39 PM Subject: Topband: tree losses Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. 73, Rudy N6LF _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3209/6051 - Release Date: 08/04/13 _ Topband Reflector _ Topband Reflector
Topband: tree losses
Another way of looking at it: There is loss in vegetation that goes up as the frequency goes up. At low frequencies, in a seconds time, only a small amount of wavelengths pass through a given bit of vegetation. As the frequency goes up to UHF, and into gigahertz range, for a given second, many many more wavelengths pass through. Each pass contributing heat to this (slightly re-radiating) dummy load. They give the gigahertz range, a name of ionization waves, but this post is trying for an alternate way of looking at it. Microwave oven= hot dummy load= Lunch. ( ; - )) 73 Bruce-K1FZ - Original Message - From: jim rogers jd...@bellsouth.net To: ZR z...@jeremy.mv.com Cc: Topband topband@contesting.com; Rudy Severns rseve...@gmail.com Sent: Monday, August 05, 2013 6:03 AM Subject: Re: Topband: tree losses Carl et al, Interesting, my 80M full size (66') sloper comes within about 5 ft of a dogwood tree and it is dying. The sloped is fed 8' AGL with 2 full size elevated radials and about 500w and the dogwood is dying from that height(8') to the top of the tree at about 15'. Unfortunately for me, my XYL pointed this out to me - not good. The sloper has been in that position for about 1 year, before that the tree was doing fine. Coincidence? Jim N4DU On 8/4/13 9:42 PM, ZR wrote: I cant think of anyone claiming a tree is resonant on any particular frequency but that doesnt mean it cant be used as an antenna. Anyone disagreeing with that should discuss it with the military who have been loading trees for decades for emergency communications; in the 3-8MHz range if I remember and going back as far as the 50's. Read the old CQ and QST's. On another note I spent most of today outside doing tree trimming and other sweaty exercises. I noted that my best producing Bartlett pear tree was dead at the top and also a bit down on one side. Now it may be just coincidence but the 80M sloper passes about 5' from the farthest out branches and the end is exactly at the same height as the tree top. This antenna is used at the vintage gear bench and also on the one for amp repairs where Ive been hitting it rather hard this year with AM with serious carrier power; the most recent being an Alpha 77SX. I also remember wilting the top of a sugar maple about 20 years ago with 1200W on 6M to a 6/6 yagi array. After I moved the antenna to another tower the tree recovered the following year. Another coincidence? Carl KM1H - Original Message - From: Rudy Severns rseve...@gmail.com To: Topband topband@contesting.com Sent: Sunday, August 04, 2013 5:39 PM Subject: Topband: tree losses Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. 73, Rudy N6LF _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3209/6051 - Release Date: 08/04/13 _ Topband Reflector _ Topband Reflector _ Topband Reflector
Re: Topband: tree losses
I hope all of us can keep the topic at least somewhat scientific, logical, or rational, and less subjective, blind faith, or outright off-the-wall.. Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. I've wanted to catch logging operations around here and make field strength measurements before and after trees are removed. Unfortunately I've always been busy at the wrong times to click with tree removal, or the weather has been a factor. It wouldn't do much good to measure FS if one reading is in rain, and the other is in dry weather, unless a few unchanged path readings were taken to normalize the system. My general thought was to read absolute signal levels between TX antennas here and a remote fixed antenna on the other side of tree removal, with another reference point outside the removal area as a standard. But then, even if we know that, I always wonder what good it does. Foliage hundreds of feet. let alone miles away, is out of our control. As for trees being antennas, that would be a simple experiment. One could simply try to load the tree, however that might be accomplished, and compare the signal level with the same size loading system (properly rematched) without the tree. Several reruns with different trees could give a baseline. I think the reason that has never been done is most people who understand losses and radiation also understand the few feet of wire in the matching system is probably the major radiator in the system, so there is very little interest in proving the obvious. Most of us already understand an insulated copper wire thrown over a tree is a far better antenna than the tree could ever be, and that removing the tree actually INCREASES field strength. The logical conclusion is the tree is much more a dissipative load than an antenna. After all, if a tree was even a marginally effective LF or HF radiator, we would increases in field strength from reflections rather than just absorption. At some higher frequency there are measureable echoes, but they pale compared to the incident wave. Remember the moon, as horrible a conductor as it is, still has useful reflections when the illumination is over a wide surface area. In the real world, it often isn't a case of if something is or isn't, like a toggle switch being on or off. It is often a case of how much it is or isn't. Some things that are way over in the isn't meaningful column get publicity as being is, just because they are not perfectly zero or infinite. 73 Tom _ Topband Reflector
Re: Topband: tree losses
I found this and at least it makes a good old read. http://www.rexresearch.com/squier/squier.htm regards, Raoul ZS1REC From: Tom W8JI w...@w8ji.com To: Topband topband@contesting.com Sent: Monday, August 5, 2013 4:53 PM Subject: Re: Topband: tree losses I hope all of us can keep the topic at least somewhat scientific, logical, or rational, and less subjective, blind faith, or outright off-the-wall.. _ Topband Reflector
Re: Topband: tree losses
Bingo! Just because the military does (or did) something with antennas doesn't means it's good for us all to repeat. There was a discussion some time back that a Beverage must make a good transmitting antenna, because the military does it somewhere. I can vouch for the fact that while we can indeed transmit on a Beverage and make contacts with it, a vertical with a few radials makes a *much *better TX antenna. 73, Mike www.w0btu.com On Mon, Aug 5, 2013 at 9:53 AM, Tom W8JI w...@w8ji.com wrote: ... the few feet of wire in the matching system is probably the major radiator in the system ... Most of us already understand an insulated copper wire thrown over a tree is a far better antenna than the tree could ever be, and that removing the tree actually INCREASES field strength. The logical conclusion is the tree is much more a dissipative load than an antenna. After all, if a tree was even a marginally effective LF or HF radiator, we would increases in field strength from reflections rather than just absorption. _ Topband Reflector
Re: Topband: tree losses
I found this and at least it makes a good old read. http://www.rexresearch.com/squier/squier.htm This is how things get started! once something is in print, no matter how wrong or unsubstantiated, it lives forever. Look at this statement: It will puzzle the amateur as it has puzzled the experts, how a tree, which is certainly well grounded, can also be an insulated aerial. The method of getting the disturbances in potential from treetop to instrument is so simple as to be almost laughable. One climbs a tree to two-thirds of its height, drives a nail a couple of inches into the tree, hangs a wire therefrom, and attaches the wire to the receiving apparatus as if it were a regular lead-in from a lofty copper or aluminum aerial. Apparently some of the etheric disturbances passing from treetop to ground through the tree are diverted through the wire --- and the thermionic tube most efficiently does the rest. In about 100 years, we should reasonably believe there would be logically conducted experiments with documentation showing trees make reasonable antennas. We should also expect that trees would, by now, be universally hailed as useful antennas. The article even claims it makes no difference if the tree antenna is in a thick woods, something we know cannot be true, and that simply disconnecting the wire from the tree causes the set to go dead, something else we know is untrue. It also claims a 40 ft wire cannot work on multiple frequencies, which I suppose people who like magic 43 foot verticals would disagree with. Instead we have only reports and measurements that trees cause increased loss, and all those multiband single length antennas. :) 73 Tom _ Topband Reflector
Re: Topband: tree losses
Hi Tim, Here's how I did it. http://www.w0btu.com/Beverage_antennas.html#transmitting_on_a_Beverage I left the termination resistor off, and it still had a 5 dB F/B ratio. I also connected the two wires at each end and added a few extra radials. It surprised me how well it worked on 75 meters and up. It was fun to try, but I wouldn't recommend trying to win any contests with it. :-) 73, Mike On Mon, Aug 5, 2013 at 1:06 PM, Shoppa, Tim tsho...@wmata.com wrote: Every time I accidentally transmit into my receive antennas, I burn out the matching transformers and/or termination resistors in short order! I would guess the military termination resistors are quite a bit beefier :-) Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Mike Waters Sent: Monday, August 05, 2013 2:04 PM To: Tom W8JI; topband Subject: Re: Topband: tree losses Bingo! Just because the military does (or did) something with antennas doesn't means it's good for us all to repeat. There was a discussion some time back that a Beverage must make a good transmitting antenna, because the military does it somewhere. I can vouch for the fact that while we can indeed transmit on a Beverage and make contacts with it, a vertical with a few radials makes a *much *better TX antenna. _ Topband Reflector
Re: Topband: tree losses
It depends on what the measure of much better is. .. For many years US special forces have used field expedient long wire HF antennas close to the ground (i.e., Beverage antennas) pointed at the net control station to reduce the probability of being intercepted by opposing forces and to improve jam resistance and signal to noise ratio. 73 Frank W3LPL - Original Message - From: Mike Waters mikew...@gmail.com To: Tom W8JI w...@w8ji.com, topband topband@contesting.com Sent: Monday, August 5, 2013 7:04:16 PM Subject: Re: Topband: tree losses Bingo! Just because the military does (or did) something with antennas doesn't means it's good for us all to repeat. There was a discussion some time back that a Beverage must make a good transmitting antenna, because the military does it somewhere. I can vouch for the fact that while we can indeed transmit on a Beverage and make contacts with it, a vertical with a few radials makes a *much *better TX antenna. 73, Mike www.w0btu.com On Mon, Aug 5, 2013 at 9:53 AM, Tom W8JI w...@w8ji.com wrote: ... the few feet of wire in the matching system is probably the major radiator in the system ... Most of us already understand an insulated copper wire thrown over a tree is a far better antenna than the tree could ever be, and that removing the tree actually INCREASES field strength. The logical conclusion is the tree is much more a dissipative load than an antenna. After all, if a tree was even a marginally effective LF or HF radiator, we would increases in field strength from reflections rather than just absorption. _ Topband Reflector _ Topband Reflector
Re: Topband: tree losses
That's what we need, real data. Expand the experiment and see what we can learn. While I feel that our data on the subject is pretty thin and I'm not about to make any pronouncements I'm still quite happy that at my new QTH the trees are many hundreds of feet away. I would also go out of my way to keep the HV points of an antenna as far as practical away from a tree. No data, just a sense of caution. 73, Rudy N6LF _ Topband Reflector
Re: Topband: tree losses
Jim, it seems to be a difficult subject for those who want to make a huge case out of taking measurements as if this was a scientific undertaking requiring a decade of reviews, papers, and the usual academia way of wasting time. For the rest of us ancedotal evidence is often sufficient...if the tree or parts of it died coincidental with installing an antenna or increasing ERP then that is good enough IMO. Others can hire an arborist and a passle of investigators from the County Extension who just might take you to court along with a screaming horde of tree huggers demanding your scalp (-; Foliage induced attenuation without obvious damage is another subject all together. That will vary by the tree, climate, phase of the moon and when the dog last peed on it. And like the perennial discussion on groundseveryone has an opinion and different circumstances. Carl KM1H - Original Message - From: jim rogers jd...@bellsouth.net To: ZR z...@jeremy.mv.com Cc: Topband topband@contesting.com; Rudy Severns rseve...@gmail.com Sent: Monday, August 05, 2013 9:03 AM Subject: Re: Topband: tree losses Carl et al, Interesting, my 80M full size (66') sloper comes within about 5 ft of a dogwood tree and it is dying. The sloped is fed 8' AGL with 2 full size elevated radials and about 500w and the dogwood is dying from that height(8') to the top of the tree at about 15'. Unfortunately for me, my XYL pointed this out to me - not good. The sloper has been in that position for about 1 year, before that the tree was doing fine. Coincidence? Jim N4DU On 8/4/13 9:42 PM, ZR wrote: I cant think of anyone claiming a tree is resonant on any particular frequency but that doesnt mean it cant be used as an antenna. Anyone disagreeing with that should discuss it with the military who have been loading trees for decades for emergency communications; in the 3-8MHz range if I remember and going back as far as the 50's. Read the old CQ and QST's. On another note I spent most of today outside doing tree trimming and other sweaty exercises. I noted that my best producing Bartlett pear tree was dead at the top and also a bit down on one side. Now it may be just coincidence but the 80M sloper passes about 5' from the farthest out branches and the end is exactly at the same height as the tree top. This antenna is used at the vintage gear bench and also on the one for amp repairs where Ive been hitting it rather hard this year with AM with serious carrier power; the most recent being an Alpha 77SX. I also remember wilting the top of a sugar maple about 20 years ago with 1200W on 6M to a 6/6 yagi array. After I moved the antenna to another tower the tree recovered the following year. Another coincidence? Carl KM1H - Original Message - From: Rudy Severns rseve...@gmail.com To: Topband topband@contesting.com Sent: Sunday, August 04, 2013 5:39 PM Subject: Topband: tree losses Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. 73, Rudy N6LF _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3209/6051 - Release Date: 08/04/13 _ Topband Reflector _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3209/6052 - Release Date: 08/05/13 _ Topband Reflector
Re: Topband: tree losses
Jim, it seems to be a difficult subject for those who want to make a huge case out of taking measurements as if this was a scientific undertaking requiring a decade of reviews, papers, and the usual academia way of wasting time. Carl, There isn't any reason to turn everything into something it clearly is not, so you probably just don't understand what I am saying. We ALL (or nearly nearly all) agree trees have an effect. But just having an effect, all by itself, isn't very useful information to any of us for anything. I don't think many rational adults would disagree with the idea it would be nice to have some reasonable idea how significant the effect is, or how much worry it is. Few of us like to worry about insignificant things, and anyone with any reasonable curiousity generally want to know how much. How much horsepower does a car have, how many years of smoking does it take to harm us, how high can the SWR be before it causes a problem, how many radials do we need, and how big a worry is that tree. Those all seem like logical, reasonable, questions that many people would enjoy having actual answers, rather than It has an effect. I read it somewhere. Next topic. 73, Tom _ Topband Reflector
Re: Topband: tree losses
Hi, For me the effect the trees have is purely academic. I live in the northern Michigan forests. I am surrounded and even protected by the trees. My antennas are *in* the trees. I'm sure the trees have some effect. There is nothing I can do but operate anyway. If the tree studies find that radio is impossible in the presence of trees I suppose I'll have to find a different hobby. Meanwhile I'll keep on keeping on. 73, Bill KU8H _ Topband Reflector
Re: Topband: tree losses
Bingo! Just because the military does (or did) something with antennas doesn't means it's good for us all to repeat. While Beverage antennas for transmitting are indeed one example, two more good examples are: 1.) that silly Maxcom antenna tuner sold from Florida, the thing that had the chopped up pieces of circuit board inside 2.) stainless steel terminated folded dipoles The problem with stuff like that is no one had actually quantified the loss, and even if they had, no one probably cared about signal levels. Just as long as they made contacts and the SWR looked OK, it was all working. The same type of thing is what sells those magical CB rings and the little dipole parasitic elements (about a foot long) that go on CB mobile antennas. Anecdotal evidence is that it all works, just like healing rocks and deer whistles for cars. :)It all has an effect that people feel or find useful, so it all works at some level. 73 Tom _ Topband Reflector
Re: Topband: tree losses
Tom and all, After spending 25 years in the military (Navy specifically), I can say, with a fair amount of authority, that the antennas used by them are often used for much different purposes than what people on this forum use them for. he he he. Never would a scenario arise where 1.8mhz DX would be of any interest whatsoever to a guy in the field. He/she is most likely trying to make contact with someone less than 200 miles away (and usually MUCH closer than that, like over the next hill, but not within range of a vhf/uhf signal). Antenna efficiency is often sacrificed for stealth. again, for extremely obvious reasons. Long distance HF and MF comms are rarely of any concern these days, whereas it is almost everything to us amateur radio ops. The T2FD antenna is one example of a purpose built antenna whose intention was ALWAYS short range comms (NVIS). It does what the military wanted it to do and then some. Same with almost every antenna in the military's RF arsenal. This is especially true today where high gain antennas, and dx type distances, are almost exclusively devoted to vhf, uhf, shf satellites. Satcom is (and has been for a fairly long time) ubiquitous in the military, as most of you probably already know. Now, having said that, I used some absolutely dynamite antennas on HF while underway. Simple antennas, like a horizontal end-fed that was roughly 60 feet long and stood about 70 feet out of the water. sea water. Had a practically infinite tuning range and could handle all the power that I could feed it for phone patches and amtor (when we started using it). Needless to say, in a situation where your horizontal (or vertical) is over salt water, in the clear (no houses, trees or anything else to block the RF), and about 70 to 80 feet above that water is darned near a perfect reflective surface for a horizontal ANYTHING, right? Anyway, unless you want to talk about the military's advances in NVIS, which it has done in spades, you are barking up the wrong antenna source. If you are wanting to do short range, NVIS, comms then DO take a look at military antenna designs. they work and they work well for that purpose, in particular. There ARE antenna designs used by the military for backup long range HF purposes, but they are mainly the same designs we all use for that purpose.. efficient vertical radiators (think verticals over a SHIP's deck as a groundplane, surrounded by salt water) or large log periodic beams that are mounted at the top (or nearly so) of the highest mast on the ship, etc, etc, etc. Again, those are really obvious and nothing new to us. So that is my two cents. keep in mind what the military wants its HF to do and those much maligned military antennas are all of a sudden almost perfect for their intended purpose. :) :) Seven-thirds, Mike AB7ZU Kuhi no ka lima, hele no ka maka On Aug 5, 2013, at 18:51, Tom W8JI w...@w8ji.com wrote: Bingo! Just because the military does (or did) something with antennas doesn't means it's good for us all to repeat. While Beverage antennas for transmitting are indeed one example, two more good examples are: 1.) that silly Maxcom antenna tuner sold from Florida, the thing that had the chopped up pieces of circuit board inside 2.) stainless steel terminated folded dipoles The problem with stuff like that is no one had actually quantified the loss, and even if they had, no one probably cared about signal levels. Just as long as they made contacts and the SWR looked OK, it was all working. The same type of thing is what sells those magical CB rings and the little dipole parasitic elements (about a foot long) that go on CB mobile antennas. Anecdotal evidence is that it all works, just like healing rocks and deer whistles for cars. :)It all has an effect that people feel or find useful, so it all works at some level. 73 Tom _ Topband Reflector _ Topband Reflector
Re: Topband: tree losses
On Mon, Aug 5, 2013 at 2:54 PM, ZR z...@jeremy.mv.com wrote: Youre unfairly throwing a huge spin on it Mike. Am I? Okay. Sorry. :-) If the military or a government agency does it, it could be an experiment or a purpose built project where the alternatives werent adequate or too expensive. Nothing at all wrong with an experiment. But ONE of the things I was thinking of (but didn't mention) was a publication by the military (about transmitting on a Beverage) that clearly showed it wasn't anything of the kind. I can't find it right now. Perhaps they did use multiple Beverages, and perhaps what they did was the right thing for what they needed. But is it for us 160m operators? I think not. An array of phased Beverages has a very narrow azimuth lobe and a controllable elevation lobe plus a high F/R. You phase enough of them and you have actual gain in +dB over a wide bandwidth for point to point communications. Not easy to do with a vertical. I agree. Is that what you used when you transmitted on a Beverage? But I think most of us don't have phased Beverages. I assumed that everyone would understand that I was talking about a single Beverage that the majority use on Topband (like my 580' ones). But the real point of the original post was the phenomenon of increasing foliage attenuation at 160 meters (more so that 80m, 40m, etc.) and later, using trees as radiators (which I think is ridiculous). It is similar with tree antennas. The military does it for a reason and it works for that specific purpose. Yet you will always have someone spinning that all around on here for whatever reasons. I thought that my point was that the major radiator is the WIRE going to the tree, and NOT the tree itself. Thats the problem with web sites that are not peer reviewed and misinformation is repeated forever if the author wont admit to an errorsome never will. Understand now? What I understand is that valid measurements need to be made. But as you said, nothing wrong with sharing anecdotal info (which was the basis for my original post). It's interesting about the dying foliage near an antenna, but (of course) that doesn't mean we can expect to use a tree as an antenna. Maybe I need to stop writing such short posts, and describe everything in detail, and include every possible scenario when I make a statement. :-) 73, Mike www.w0btu.com _ Topband Reflector
Topband: tree losses
Tom's correct, the issue is not resonance but rather what, if anything, happens when you have a so-so conductor/insulator (a tree) in the near-field and/or further out. Do the losses matter? Performing a definitive set of experiments would be a serious undertaking. I've fiddled around a bit but not much more than the tree conductivity work mentioned earlier. At this point I'm an agnostic: we really don't have good data. There are a number of Vietnam era papers on trees as antennas and propagation through jungle but most of that was at frequencies well above 160m. Here's a challenge for experimenters that'll keep you busy and out of the bars. 73, Rudy N6LF _ Topband Reflector
