Re: Topband: RX cables in woods
There is a formula that road builders use when burying culverts. I don't know what it is but the guy building and maintaining roads told me once. I thought it was dependent on the diameter of the tube or culvert. I used 3 inch tile drainage tubing across a drive in a couple of places that were not very deep, which were then covered by road base, mostly river rock. It worked great until the critters took refuge in them from the dogs and then the dogs managed to tear them all out of the ground before I could get around to capping them with screen etc. Mike W0MU On 2/23/2015 2:31 PM, Tom W8JI wrote: You're right, the larger dia. PVC makes it worse sometimes. When it breaks in two, it actually puts more shear on the coax inside. If it is like what happens here, the hard PVC turns the small radius that the soil and rubber can deform around into a speed bump. :) I do have flooded F-6 running on the ground, along a fence feeding my Beverages, where it's not likely that any vehicles can drive over it. And it's withstood the horses that used to be here; not even their hooves that pushed it into the earth seemed to hurt it any. I put this one run of F-6 (to the inverted-L) in PVC conduit for several reasons, one of which was to keep my neighbor's cows from biting it as they graze. I just didn't think of what would happen when the ground under it got muddy. It seemed like a good idea at the time. :-) My damage issue is mostly Racoons, but occasionally field rats. Baby cows used to be bad until they learned cable isn't cud. I have a 1000' spool of F-11 with a messenger wire. I'll likely replace the stuff on the ground with it, about 15' high. I only do that where necessary to cross roads or creeks. I have occasional cable and wire damage from lighting, and I also have too many antennas crossing the cables to make me feel good about elevating the feed cables. Best thing I ever built was a radial and cable burying plow. Even in the clay, I can run coax up to 1/2 inch into the ground several inches deep at a good clip. Nothing easier than just loading a cable reel, and driving along at a walk or jog speed. :) I can go real fast, but a big rock can bust the hitch pins if the tractor is going too fast. I occasionally weld a new front edge on the plow when it gets too thin. Otherwise, it is pretty much maintenance free. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: TI9/3Z9DX
I ran across them in the ARRL DX contest and managed to work them too! I am glad some others got in there too! Mike W0MU On 2/23/2015 6:31 PM, K1FZ-Bruce wrote: Mike. I emailed Dom asking for a 160 meter, time specific, North America standby. On 02/22/2015 they were on working mixed instead of just Europe. The opening to Northern New England was only about 15 minutes long. Found their listening frequency, called them at 0331 UTC and made the contact on the first call. It also worked out well with many other North America stations making the contact. Thanks Mike, appreciate the help, Bruce-K1FZ On Thu, 19 Feb 2015 09:40:49 -0700, W0MU Mike Fatchett wrote: Email Dom 3Z9DX. I had a log problem and he answered me immediately. I am sure they are open to suggestions if asked nicely. Mike W0MU _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: TI9/3Z9DX
Thanks for doing that Bruce. You helped me log a new one on 160. I worked them at 0348Z on Feb. 22, under extremely poor conditions. Most of the difficulty was on my end. With man-made noise to deal with and no receive antennas, hearing TI9/3Z9DX was touch and go. The op at their end did a superb job of copying my 100 watts and making the QSO. My thanks to whoever it was on the island who put me in the log. 73, JackK2RS On 2/23/2015 8:31 PM, K1FZ-Bruce wrote: Mike. I emailed Dom asking for a 160 meter, time specific, North America standby. On 02/22/2015 they were on working mixed instead of just Europe. The opening to Northern New England was only about 15 minutes long. Found their listening frequency, called them at 0331 UTC and made the contact on the first call. It also worked out well with many other North America stations making the contact. Thanks Mike, appreciate the help, Bruce-K1FZ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: TI9/3Z9DX
Mike. I emailed Dom asking for a 160 meter, time specific, North America standby. On 02/22/2015 they were on working mixed instead of just Europe. The opening to Northern New England was only about 15 minutes long. Found their listening frequency, called them at 0331 UTC and made the contact on the first call. It also worked out well with many other North America stations making the contact. Thanks Mike, appreciate the help, Bruce-K1FZ On Thu, 19 Feb 2015 09:40:49 -0700, W0MU Mike Fatchett wrote: Email Dom 3Z9DX. I had a log problem and he answered me immediately. I am sure they are open to suggestions if asked nicely. Mike W0MU _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: RX cables in woods
You're right, the larger dia. PVC makes it worse sometimes. When it breaks in two, it actually puts more shear on the coax inside. If it is like what happens here, the hard PVC turns the small radius that the soil and rubber can deform around into a speed bump. :) I do have flooded F-6 running on the ground, along a fence feeding my Beverages, where it's not likely that any vehicles can drive over it. And it's withstood the horses that used to be here; not even their hooves that pushed it into the earth seemed to hurt it any. I put this one run of F-6 (to the inverted-L) in PVC conduit for several reasons, one of which was to keep my neighbor's cows from biting it as they graze. I just didn't think of what would happen when the ground under it got muddy. It seemed like a good idea at the time. :-) My damage issue is mostly Racoons, but occasionally field rats. Baby cows used to be bad until they learned cable isn't cud. I have a 1000' spool of F-11 with a messenger wire. I'll likely replace the stuff on the ground with it, about 15' high. I only do that where necessary to cross roads or creeks. I have occasional cable and wire damage from lighting, and I also have too many antennas crossing the cables to make me feel good about elevating the feed cables. Best thing I ever built was a radial and cable burying plow. Even in the clay, I can run coax up to 1/2 inch into the ground several inches deep at a good clip. Nothing easier than just loading a cable reel, and driving along at a walk or jog speed. :) I can go real fast, but a big rock can bust the hitch pins if the tractor is going too fast. I occasionally weld a new front edge on the plow when it gets too thin. Otherwise, it is pretty much maintenance free. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling "Ground"
For most of the past century the intractability of the equations was the excuse for just laying down "textbook" overkill radial systems. If you can't solve the "real world problem", then just change the real world to match the problem you can solve!!! (Google "spherical cow"). The FCC says: "(4) At the present development of the art, it is considered that where a vertical radiator is employed with its base on the ground, the ground system should consist of buried radial wires at least one-fourth wave length long. There should be as many of these radials evenly spaced as practicable and in no event less than 90. (120 radials of 0.35 to 0.4 of a wave length in length and spaced 3° is considered an excellent ground system and in case of high base voltage, a base screen of suitable dimensions should be employed.)" The FCC exempts stations from proving efficiency through tedious (and expensive) full field-strength measurements when the station has at least *90* 1/4 wave radials. I assume this minimum of 90 radials is what they think is a safe amount over the 50-60 radials that have generally shown to be up near 100% efficiency. Most of the FS measurements I have seen wobble around a few dB, so the engineer has to use a mean value of what he measures. This gives some latitude to "fudge things" a few dB by how measurements are made or interpreted. None of this means much for Ham radio. We would be very lucky to notice six or eight dB (or more) shortfall without an A-B comparison. We tend to believe "the signal was strong so it must be 100%", when we are actually unlikely to know or notice a six dB change without A-B comparisons. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling "Ground"
For most of the past century the intractability of the equations was the excuse for just laying down "textbook" overkill radial systems. If you can't solve the "real world problem", then just change the real world to match the problem you can solve!!! (Google "spherical cow"). Today I think the variable moisture depending on weather, and poor measurement of soil RF properties is the limit to tractability of computations. It doesn't matter how good your equations or computers are if you are not using the right material properties. Garbage in, garbage out. The folks who do ground penetrating radar make very good measurements and some go as low as 10MHz. Still when comparing cost of massive copper systems to cost of making ground penetrating radar measurements in a variety of weather conditions, I suspect massive radial systems will still win. Tim N3QE On Sun, Feb 22, 2015 at 8:18 PM, Jim Brown wrote: > On Sun,2/22/2015 4:40 PM, Guy Olinger K2AV wrote: > >> Ground, as it affects numerous wire on/in/around ground situations, is >> poorly understood, and there is no Daddy Warbucks out there willing to pay >> the bill for the research it would take to fill in those blanks. >> > > I agree with W8JI and others who have observed that the earth's surface > layer (what we call "ground" in a modeling context), is quite complex, and > far from uniform. There's also the matter skin depth, the contribution of > moisture, chemical composition, and so on. As I view it, there may be > nothing at all wrong with the math -- we've had math figured out quite well > for several centuries -- but rather with KNOWING enough about that surface > layer we call "ground" to write the equations, and the complexity of the > "ground" that makes those equations impossibly complex. > > And even if we could know enough to write the equations or plug numbers > into them, how many Crays would it take to compute the model? :) > > In my professional life as a designer of sound systems for large acoustic > spaces (theaters, churches, stadiums, arenas), I often built rather > sophisticated and detailed 3D models of these spaces that included the > reflection characteristics of hundreds of different surface materials, > inserted 3D models of loudspeakers generated by measurements of the > performance characteristics in octave bands (later in one-third octave > bands), then had the software compute the response of the system (the > loudspeaker and the room) at hundreds of points over the audience area, > used the computed result to predict speech intelligibility, and convolved a > .wav sound file (usually speech, but it could be music) with a .wav file > describing the system response to produce a new .wav file that we could > listen to that predicts what the system would actually SOUND like. > > This acoustic modeling software started out life in the early 80s in what > was then East Berlin, and ran on PCs of those days. It was far simpler > then, only modeling the direct sound on the audience. Development was, and > still is, ongoing, and every five or so years, new versions allowed more > and more complex calculations, more data for surfaces and loudspeakers have > been made available, computers that can we can buy and put on our desk > become more and more powerful, and with more storage. > > I suspect that somewhere, someone (or many someones) are working on > modeling software of comparable complexity to that acoustic software -- > indeed, K6OIK has listed several professional packages of considerably > greater capability and complexity as compared to the NEC engines. Here's a > presentation he did in 2008 at Pacificon. I've heard him do a newer > version, but I can't find it on the internet. > > http://archive.k6ya.org/docs/Antenna-Modeling-for-Radio-Amateurs.pdf > > 73, Jim K9YC > > > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling "Ground"
Agree with Tom I found that the 160 foot BOG antenna that was buried was more unstable with dry/rain conditions, than when on/above ground. Also the 1/8 wave spaced 160 meter 4 square, I had some years ago, was more stable with more radials, with changing ground moisture conditions. Single in ground wires are not very stable with moisture changes. Larger ground radial fields offer much more stability. 73 Bruce-K1FZ www.qsl.net/k1fz/bogantennanotes/index.html . On Mon, 23 Feb 2015 07:58:13 -0500, Tom W8JI wrote: > In reality, NEC4 can produce quite accurate results when modeling > buried > radial wires and groundwave propagation losses along a real > earth path -- > as long as earth conductivity is known for that path > and operating > frequency. > > > > Calculating a good result for one situation, like field strength at a > distance for a vertical radiator when gradual attenuation is > involved, is worlds different than calculating pattern produced by a > long buried wire. _ > Topband Reflector Archives - http://www.contesting.com/_topband > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: RX cables in woods
But I'm not sure whether that would hold up here. Once in awhile, the power company drives their heavy bucket trucks over my land. And people that I hire to brush hog my 'pasture' have heavy tractors. That's what breaks my PVC conduit lying on the ground, and damages the coax inside it. I drive over skinnier coaxial cables all the time with my tractors and 4WD truck. Maybe the hard larger diameter PVC is making things worse, not better? The main reason I bury cables are animals, catching them with rotary cutters, and crushing the large diameter soft cables like Heliax. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling "Ground"
In reality, NEC4 can produce quite accurate results when modeling buried radial wires and groundwave propagation losses along a real earth path -- as long as earth conductivity is known for that path and operating frequency. Calculating a good result for one situation, like field strength at a distance for a vertical radiator when gradual attenuation is involved, is worlds different than calculating pattern produced by a long buried wire. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling "Ground"
In reality, NEC4 can produce quite accurate results when modeling buried radial wires and groundwave propagation losses along a real earth path -- as long as earth conductivity is known for that path and operating frequency. The link below shows the value of the groundwave E-field at a range of ~28 miles produced by a NEC4 model of an AM broadcast station. Even though NEC does not account for earth curvature, this groundwave path is short enough for that error to be negligible. The NEC field is rather a close match to the value shown for this set of conditions when using the FCC's groundwave propagation curves for this frequency, radiated power and earth conductivity (see the table at the bottom of the graphic). http://s20.postimg.org/tkg5hcfsd/WLS_NEC_vs_FCC_Field.jpg R. Fry, CPBE _ Topband Reflector Archives - http://www.contesting.com/_topband
