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80 meter loaded vertical versus 80 meter loaded dipole ?
All,
I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil |
Put a capacity hat on the top of the antenna. This will give you the most
performance increase with the least effort. "dansawyeror" wrote in message ... All, I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet |
Burying the radials will make zero difference in performance.
"dansawyeror" wrote in message ... All, I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. [stuff] Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil |
I have been using an 80 meter loaded vertical for a couple of years with
moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil How high is the antenna, where is the loading coil placed, what is its value, and Q? Frank |
I have limited space and the most common solutions are not available to
me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. .............. Probably so for short/med haul. Will be a toss for long haul. Even a semi lossy vertical can outdo a low dipole to dx if the path is long enough. But for talking 200 miles away, the dipole will blow the vertical away. 12 radials is not many for a ground mount. If you were to add more radials or screen, I'd do it at the base of the antenna. IE: add 50 10 ft radials for 500 ft of wire... Should be better than a few full size radials. Some say screen can cause problems after a while do to corrosion. I'd probably just stick with wire radials myself... How far you want to talk on that band should determine what antenna is best. For most general use within 1000 miles, I'd rather be on a dipole than a vertical. But dx, I'd go vertical, and improve it. Loaded does not have to mean crippled. But loading/short verticals do make the ground system more critical. My mobile is better than my home dipole late at night on 40m if I'm talking over 1000 miles away... And if it ain't loaded, I dunno what is...What power it radiates is at the perfect fairly low angle for that path/time of night. BTW, I'd install the dipole outside if at all possible. Less noise from the house, and will generally work better. Won't hurt it to be close to the roof, unless metal is underneath to detune. I've layed dipoles directly on composition shingles with no problems at all. Or at least when dry anyway... But elevated a bit would be better. MK |
Hello Dan,
Some thoughts: The 10 dB loss is, of course, referenced to a "perfect ground." Even with a full length (quarter-wave) vertical and your ground system, performance would improve by about 3 dB. Not a blockbuster. Improving the radial system, as noted by others, is a more realistic course. You ought to be able to get the ground resistance closer to 20 ohms with more radials close in. Then you will be only 6 dB worse than if your ground were perfect. Putting up an indoor dipole is cheap and quick. Put it up and compare it with the vertical. But don't hold your breath. You will probably find that with some paths, the dipole is better. you may want to keep both. I assume you've ruled out a capacity hat, center loading, and a coil with lower losses, as suggested by others. But with these changes and an improved ground system, you might get a full (6 dB) S-unit improvement. Good luck. 73, Chuck dansawyeror wrote: All, I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil |
dansawyeror wrote:
I will defiantly try adding radials. Who are you defying? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Sat, 20 Aug 2005 13:34:36 -0500, Cecil Moore wrote:
dansawyeror wrote: I will defiantly try adding radials. Who are you defying? Lawn gnomes, probably. |
Frank,
The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Frank wrote: I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil How high is the antenna, where is the loading coil placed, what is its value, and Q? Frank |
Frank,
The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Frank wrote: I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil How high is the antenna, where is the loading coil placed, what is its value, and Q? Frank |
Frank,
The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Frank wrote: I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Thanks, Dan kb0qil How high is the antenna, where is the loading coil placed, what is its value, and Q? Frank |
The local gardener who takes great pride and ownership in the lawn. The garage
can go mostly to seed, however the lawn must be pristine. Each antenna change meets with great resistance. Although defiantly was definitely a spell checker choice, it is also the correct one for getting radials. Dan Cecil Moore wrote: dansawyeror wrote: I will defiantly try adding radials. Who are you defying? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
"dansawyeror" wrote in message ... Frank, The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Maybe I missed something, but how high is the TOP of the antenna. I.E. How long is the whip? Is the loading coil at the base, or partway up the antenna? Tam/WB2TT |
Tam,
The description was for the coil. The total antenna is about 15 feet base to tip. The coil is about 1/3 of the way up. The base is about 3 feet off the ground so the tip would be about 18 feet up. Dan Tam/WB2TT wrote: "dansawyeror" wrote in message ... Frank, The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Maybe I missed something, but how high is the TOP of the antenna. I.E. How long is the whip? Is the loading coil at the base, or partway up the antenna? Tam/WB2TT |
"dansawyeror" wrote in message ... Tam, The description was for the coil. The total antenna is about 15 feet base to tip. The coil is about 1/3 of the way up. The base is about 3 feet off the ground so the tip would be about 18 feet up. Dan Tam/WB2TT wrote: "dansawyeror" wrote in message ... Frank, The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Maybe I missed something, but how high is the TOP of the antenna. I.E. How long is the whip? Is the loading coil at the base, or partway up the antenna? Tam/WB2TT Dan, Over perfect ground, I get an impedance of about 2.4 Ohms, with resonance very close to 3.8 MHz. What is the tallest tree in your yard? Tam |
Tam
That would relate very close to what the models predict. Where or how do you have such good ground? Dan Tam/WB2TT wrote: "dansawyeror" wrote in message ... Tam, The description was for the coil. The total antenna is about 15 feet base to tip. The coil is about 1/3 of the way up. The base is about 3 feet off the ground so the tip would be about 18 feet up. Dan Tam/WB2TT wrote: "dansawyeror" wrote in message ... Frank, The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Maybe I missed something, but how high is the TOP of the antenna. I.E. How long is the whip? Is the loading coil at the base, or partway up the antenna? Tam/WB2TT Dan, Over perfect ground, I get an impedance of about 2.4 Ohms, with resonance very close to 3.8 MHz. What is the tallest tree in your yard? Tam |
dansawyeror wrote:
All, I have been using an 80 meter loaded vertical for a couple of years with moderate success. The ground system is a dozen 'untuned' radials 40 or so feet laying on the ground. The feed line is about 100 feet of RG-8 coax. The SWR in the shack is about 1.1 to 1. I have done some research on the antenna and based on it parameters it should have a radiation resistance of about 4 Ohms. This says that the coil and ground are absorbing on the order of 45 Ohms. This is 10db performance loss. I have limited space and the most common solutions are not available to me. From a practical perspective it would seem to me that building a 40 foot center feed loaded dipole and putting it in the attic or on the roof would probably perform somewhat better. Is this a reasonable assumption? I'm not sure you can count on that. You'd still lose some in a matching/loading network, there'd be a lot of ground loss because of the low height, and absorption of some of the power from conductors in the house might occur. It wouldn't hurt to try, but leave your vertical up. Would burying the radials and connecting them to several 4 square foot buried screens substantially help the ground system? Just about anything you can do to increase the conductivity of the ground system, particularly close to the antenna, will help. Using screen is one thing. Burying the radials won't help. Adding more radials and making them longer will help. Unfortunately, making a few radials longer doesn't do much, and adding a bunch of short radials doesn't do much either -- you really have to do both to have a big effect. If possible, connect to any other nearby buried conductors such as metallic water pipes. The other thing you can do to improve the efficiency is to increase the radiation resistance of the antenna. You can do this of course by increasing the height of the antenna. Moving the loading coil upward will help, too, although you'll need more inductance. (The coil still won't be a major part of the overall loss, though.) A top hat is better yet. You can also increase the radiation resistance by making your antenna fatter. Use multiple wires in parallel, spaced about as far as you can, either along side each other, or fanned out, converging at the bottom. Finally, if you've got room, you can improve your overall efficiency by about 3 dB by putting in another identical antenna/ground system somewhere nearby and connecting the two in parallel. Roy Lewallen, W7EL |
"dansawyeror" wrote in message ... Tam That would relate very close to what the models predict. Where or how do you have such good ground? Dan You don't. That is just the best case. If you can add another 20 feet of wire to the top, and redo the inductor, the Z comes up to 16 Ohms. That's why I asked about the trees. Tam Tam/WB2TT wrote: "dansawyeror" wrote in message ... Tam, The description was for the coil. The total antenna is about 15 feet base to tip. The coil is about 1/3 of the way up. The base is about 3 feet off the ground so the tip would be about 18 feet up. Dan Tam/WB2TT wrote: "dansawyeror" wrote in message ... Frank, The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Maybe I missed something, but how high is the TOP of the antenna. I.E. How long is the whip? Is the loading coil at the base, or partway up the antenna? Tam/WB2TT Dan, Over perfect ground, I get an impedance of about 2.4 Ohms, with resonance very close to 3.8 MHz. What is the tallest tree in your yard? Tam |
Frank,
The coil measures about 60 uH. The antenna is elevated about 3 feet on a short tripod. The radials angle down the tripod legs and then out. The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It is centerloaded. I am looking at it accross the yard, it is about 6 inches long. It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a Q of about 450. Thanks, Dan Thanks for the info Dan. From your comments the radials appear to be parallel with the tripod legs to ground level, and then continue at ground level for the rest of their length. What is the angle of the tripod legs? I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. 73, Frank |
Frank wrote:
. . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL |
Dan, KB0QIL wrote:
"From a practical perspective it would seem to me that building a 40 foot crnter loaded dipole and putting it in the sttic or on the roof would probably perform somewhat better." The roof or attic may be noisy receiving locations. The ionospheric spot which effectively reflects a high frequency signal to a point beyond the horizon is variable so that the received signal direction varies from the true bearing of the transmitter, The received signal elevation angle also varies from that predicted by the assumed layer height for any given path length, and may change from instant to instant. The differences between predicted and actual azimuth and elevation angles may at any momement be several degrees. These differences make high frequency direction finding complicated, but results may be good enough for some pracical purposes. Optimum vertical and horizontal angles are sought in directional antenna design but enough beamwidth is needed to accommodate the angular variations which occur. Over sea water, ground wave propagation is good and loss is low as compared with propagation over earth. Frequencies up to about 5 MHz are used for communications beyond the line of sight between ships and between ships and shore. These frequencies are also used for tropical broadcasting among islands. For ionospheric reflection to near spots beyond the line of sight, near vertical incidence reflections are used. The frequency must be below the maximum usable frequency for vertical incidence at the transmitting site. For ground wave propagation a vertical transmitting antenna is used. Horizontally polarized antennas are often used for sky wave signals because reflection from the ionosphere makes equal strength components, horizontally polarized and vertically polarized, from the incident wave, regardless of its initial polarization. Most disturbing noise is that generated within ground wave range of the receiving antenna. It is vertically polarized.There is no ground wave propagation of horizontally polarized waves. Thus, a horizontally polarized receiving antenna ignores much of the available noise. However, it receives as much signal from the sky wave as a vertically polarized antenna would. If a single antenna is to be used for both transmitting and receiving a shy wave, a forizontally polarized antenna may be the better choice due to its noise rejection. See "Radio Antenna Engineering" by Edmund A. Laport for details. Best regards, Richard Harrison, KB5WZI |
"Richard Harrison" wrote in message ... Dan, KB0QIL wrote: "From a practical perspective it would seem to me that building a 40 foot crnter loaded dipole and putting it in the sttic or on the roof would probably perform somewhat better." The roof or attic may be noisy receiving locations. The ionospheric spot which effectively reflects a high frequency signal to a point beyond the horizon is variable so that the received signal direction varies from the true bearing of the transmitter, The received signal elevation angle also varies from that predicted by the assumed layer height for any given path length, and may change from instant to instant. The differences between predicted and actual azimuth and elevation angles may at any momement be several degrees. These differences make high frequency direction finding complicated, but results may be good enough for some pracical purposes. Optimum vertical and horizontal angles are sought in directional antenna design but enough beamwidth is needed to accommodate the angular variations which occur. Over sea water, ground wave propagation is good and loss is low as compared with propagation over earth. Frequencies up to about 5 MHz are used for communications beyond the line of sight between ships and between ships and shore. These frequencies are also used for tropical broadcasting among islands. For ionospheric reflection to near spots beyond the line of sight, near vertical incidence reflections are used. The frequency must be below the maximum usable frequency for vertical incidence at the transmitting site. For ground wave propagation a vertical transmitting antenna is used. Horizontally polarized antennas are often used for sky wave signals because reflection from the ionosphere makes equal strength components, horizontally polarized and vertically polarized, from the incident wave, regardless of its initial polarization. Most disturbing noise is that generated within ground wave range of the receiving antenna. It is vertically polarized.There is no ground wave propagation of horizontally polarized waves. Thus, a horizontally polarized receiving antenna ignores much of the available noise. However, it receives as much signal from the sky wave as a vertically polarized antenna would. If a single antenna is to be used for both transmitting and receiving a shy wave, a forizontally polarized antenna may be the better choice due to its noise rejection. See "Radio Antenna Engineering" by Edmund A. Laport for details. Best regards, Richard Harrison, KB5WZI ================================ Richard, I am impressed by your logical descriptions and explanations of skywave and groundwave propagation. You are more than convincing. No doubt reinforced from practical experience. It all makes sense. Something much needed on these newsgroups. I notice you do not treat the works of so-called 'experts' as bibles but as a means of further study. ---- Reg, G4FGQ |
Roy,
Thanks. This might be feasible. The site would support 50 foot wire from the tip. At 500 watts what would the current in the horizontal leg be? In other words what is the minimum effective gage? What is the purpose of this leg? Is it capacitive or does it begin to look like something else. What are it directional characteristics? Dipoles nodes are perpendicular while long wire nodes are parallel. Dan Roy Lewallen wrote: Frank wrote: . . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL |
To determine the horizontal wire current, download the free EZNEC demo
from http://eznec.com. That's exactly the kind of thing it's good for. If you put a single horizontal wire out to make an L shape, the wire radiates a considerable amount. Being as low as it is, a lot of the power will be dissipated in the ground, and only a small fraction will be radiated at a low elevation angle. But if you connect to the center of a horizontal wire to make a T shape, the fields from the two halves of the horizontal wire will nearly cancel, so it'll radiate very little. Its main effect, like a capacitive top hat, will be to even out the current in your vertical wire, which will raise the radiation resistance and therefore the efficiency. EZNEC or a similar program will quickly show you the differences in field strength in various directions for the antenna as it is, and with either of the top loading configurations. Roy Lewallen, W7EL dansawyeror wrote: Roy, Thanks. This might be feasible. The site would support 50 foot wire from the tip. At 500 watts what would the current in the horizontal leg be? In other words what is the minimum effective gage? What is the purpose of this leg? Is it capacitive or does it begin to look like something else. What are it directional characteristics? Dipoles nodes are perpendicular while long wire nodes are parallel. Dan Roy Lewallen wrote: Frank wrote: . . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL |
There is no ground wave
propagation of horizontally polarized waves. Thus, a horizontally polarized receiving antenna ignores much of the available noise. There can be exceptions to this though. There is a horizontal "space wave" and it can cause all kinds of noise problems. In fact, I have had just as much noise problems with horizontal dipoles, as I have with verticals. Much of the local noise here is power line noise. The lines are horizontal in general, and do emit a horizontaly polarized space wave which can travel a fair piece. I've found at this qth, polarization and noise don't always follow the expected norms. I've had horizontal antennas that picked up horrible amounts of noise. But....On the bright side...it does verify that they are working... :/ Here in the cement jungle, I think noise can be about any polarization depending on the source. Some is vertical, but just as much is also horizontal. Of course, being vertical can follow a true ground wave type of propogation, I would expect vertical noise to travel farther than horizontal if you exceeded the direct line of sight. MK |
I think Roy is referring to a T configuration rather than an upside-down L.
The currents will balance in the T so wire size is limited by physical considerations rather than electrical. This is just another form of a capacity hat. The net result is to raise the radiation resistance. "dansawyeror" wrote in message ... Roy, Thanks. This might be feasible. The site would support 50 foot wire from the tip. At 500 watts what would the current in the horizontal leg be? In other words what is the minimum effective gage? What is the purpose of this leg? Is it capacitive or does it begin to look like something else. What are it directional characteristics? Dipoles nodes are perpendicular while long wire nodes are parallel. Dan Roy Lewallen wrote: Frank wrote: . . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL |
Fred W4JLE wrote:
I think Roy is referring to a T configuration rather than an upside-down L. The currents will balance in the T so wire size is limited by physical considerations rather than electrical. This is just another form of a capacity hat. The net result is to raise the radiation resistance. In a tee type antenna, there will be considerable current at the junction of the horizontal and vertical wires. While it's unlikely that any wire strong enough to be used won't be able to handle the current from a heating standpoint, it is possible that using a wire on the small end of the range might result in noticeable loss. A quick run with a modeling program would show whether or not that might happen with a given set of dimensions. One thing I should mention. If the horizontal portion is higher than about 0.2 wavelength, MININEC-type ground can be used for modeling either a T or L. The vertical wire is connected directly to ground, and ground loss can be inserted at the base as a resistive load. If the horizontal wire is much less than 0.2 wavelength high, the MININEC-type ground can still be used with reasonable accuracy only for the T type antenna. For an L type antenna where the horizontal wire is less than 0.2 wavelength high, a model has to use the High Accuracy ground model, with the ground system modeled as radial wires just above the ground. Roy Lewallen, W7EL |
Mark Keith, NM5K wrote:
"I`ve had horizontal antennas that picked up horrible amounts of noise." Yes, the protectection comes from noise beyond the line of sight range but not so far away as to require aky wave propagation. Propagation is a function of frequency. Below 100 KHz, gtound waves are little affected by the earth`s attenuation and the sky wave is reflected with little loss by the ionosphere. Waves travel up to 600 miles with little perturbation from the time of day, season, or year, but at greater distances, low frequency reception is better at night and in the winter due to ionospheric changes affecting the reflected signal.. On a yearly basis, signal strength over long distances correspond with the 11-year sunspot cycle. Low frequency signal strength changes only slowly without rapid fades which characterize high frequency operation. At frequencies above 100 KHz but below 535 KHz, ground wave attenuation is greater than at frequencies below 100 KHz. Daytime ionospheric losses are very high. Daytime ground wave propagation is better at the lower end of this frequency range and over soil of higher conductivity. Signals may extend to several hundred miles, where noise levels in the receiving location are low. Nighttime transmission to distant points is possible due to ionospheric reflection. Dependable daytime reception in the 100 to 535 KHz range is bad due to lack of ionospheric propagation and high attenuation of the ground wave especially at the higher frequency end of this band over poorly conductive earth and during the summer months when there may be thunder storms producing static eithin ground wave range.. At frequencies between 535 KHz and 1600 KHz, only the ground wave is useful in the daytime beyond the line of sight, as the sky wave is completely absorbed. The higher the frequency in this range, and the poorer the earrth`s conductivity,, the greater the attenuation of the ground wave. High powered transmitters at the lower frequencies in this range reach 50 to 100 miles over high conductivity soil. This may be pessimistic. I listen 24 hours to 50 KW KKYX in San Antonio which is 200 miles to my west satisfactorily. It broadcasts on 680 KHz. My receivers are quite ordinary and use internal loop antennas. The earth is highly conductive but there is no sea water in the path. At night, other stations produce low frequency carrier beats with KKYX causing undesirable automatic volume control action. but KKYX`s sky wave is stronger than its groundwave and its reception is still acceptable.. Radio Havana is one of its competitors. I hear all about "El Comandante" at times. Sky wave goes far in the 535 to 1600 KHz band. During Hurricane Carla in the 1960`s I listened to Dan Rather describe the storm blow by blow on KTRH, Houston`s 50 KW outlet, from Tierra del Fuego where I was working, and listening on a Hitachi pocket transistor portable radio with its built in loop antenna. The path is about 6000 miles long but mostly over the ocean. KTRH transmits on 740 KHz from the banks of Cedar Bayou. They have a 4-tower directionnal array with a North-South bias. Reception was good in Tierra fel Fuego as it is nearly at the Antarctic Circle and there are no thunder storms there. It is too cold. Groundwave extends hundreds of miles from KTRH, but not 6000 miles. My reception was shy wave using several hops.. Broadcast transmitters concentrate energy along the horizon so low elevation angles are favored.. This works well for sky wave DX, especially over the ocean. Sky wave attenuation in the 535 to 1600 KHz band is about the same throughout the band, so nighttime coverage of broadcast stations in this range is almost independent of frequency, while daytime ground waves favor the lower frequencies. When I was a kid, I had a crystal set fixed tuned to KTRH which directly drove a loudspeaker, if I could find a sensitive spot on the galena. I lived almost in sight of the station. At frequencies between 1600 KHz and 30 MHz, the ground wave attenuates so rapidly as to be usseless except over very short distances. Propagation is either line of sight or via ionospheric reflection or via tropospheric scattering. Frequencies above 30 MHz are often used for scattering ao that extremely high gain antennas are practical. Scatterihg often uses brute force to extend the range of signals beyond the line of sight. Most long-distance short-wave communications result from ionnospheric reflection. In the frequency range of 1600 KHz to 30 MH, a band of frequencies can almost always be found that provides communications by sky wave over a path between two points on earth. The maximum usable frequency depends on the distance between the points and ionospheric conditions. The minimum usable frequency depends on ionospheric conditions, effective radiated power, and the noise level at the receiver. Losses in the ionosphere increase with wavelength, so the frequency which gives the best signal is usually the maximum usable frequency. For communocations reliability, the maximum usable frequency is often discounted by 15% to provide an "Optimum Working Frequency". Daytime DX requires a high frequency. Shorter paths require lower frequencies. Typically 10 to 29 MHz during the day and 5 to 10 MHz, at night, are best for transmission over transoceanic distances (thousands of miles). Rember the Zenith portable? The best frequencies are usually higher during the day for long paths than they are at night Optimum frequency increases with the length of the path up to the maximum distance for one-hop transmission, about 1200 to 2400 miles. Low elevation-angle radiation such as 5 to 15 degrees is usually most desirable. Radiation below an angle of about 3.5 degrees may be absorbed by the earth near the transmitting antenna and wasted. Frequencies above 30 MHz are usually not reflected by the ionosphere and provide only sporadic sky wave communications. Best regards, Richard Harrison, KB5WZI |
Now that is interesting, Roy. I was going to put up a 160 m inverted L this
summer. I am limited to only being able to go up about 45 feet, so I would need about another 90 feet horizontal. Are you suggesting that it might be a better arrangement to go up the 45' and then put up the top "T"? If so, roughly how long should the top part of the T be (each side of center) to get me to 160? I'm guessing it may not be accomplished without some base loading...and that is what took me to the Inverted L in the first place...direct coax feed, albeit not a particularly good low angle radiator. I am prepared to put down a radial field...but I want to stick with a simple vertical wire, either extended horizontally as an Inverted L or as you suggest, a T, if it can be done. I have about 100' either side of center available to construct the top part of the T. In either case, the top loading wires will need to be somewhat of the inverted v construction, as I don't have 45' high supports for each end. Thanks for any thoughts you might have. I need to get something done before winter! 73, ....hasan, N0AN "Roy Lewallen" wrote in message ... To determine the horizontal wire current, download the free EZNEC demo from http://eznec.com. That's exactly the kind of thing it's good for. If you put a single horizontal wire out to make an L shape, the wire radiates a considerable amount. Being as low as it is, a lot of the power will be dissipated in the ground, and only a small fraction will be radiated at a low elevation angle. But if you connect to the center of a horizontal wire to make a T shape, the fields from the two halves of the horizontal wire will nearly cancel, so it'll radiate very little. Its main effect, like a capacitive top hat, will be to even out the current in your vertical wire, which will raise the radiation resistance and therefore the efficiency. EZNEC or a similar program will quickly show you the differences in field strength in various directions for the antenna as it is, and with either of the top loading configurations. Roy Lewallen, W7EL dansawyeror wrote: Roy, Thanks. This might be feasible. The site would support 50 foot wire from the tip. At 500 watts what would the current in the horizontal leg be? In other words what is the minimum effective gage? What is the purpose of this leg? Is it capacitive or does it begin to look like something else. What are it directional characteristics? Dipoles nodes are perpendicular while long wire nodes are parallel. Dan Roy Lewallen wrote: Frank wrote: . . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL |
"Roy Lewallen" wrote in message ... Frank wrote: . . . I agree with comments about adding a horizontal wire to the top of the vertical; it will probably be easier than a capacity hat. I am overloaded with work at the moment, but would like to attempt a model in a week or so when I have less work. Take a look also at a tee type arrangement. That is, a horizontal wire with the tip of the vertical connected at or near its center. It might have some advantages over connecting the wire's end to the vertical. But of course it might be more involved to construct. Roy Lewallen, W7EL Roy, I built basically a loaded mobile antenna that went onto an airport building in Raleigh, NC (about 60 feet) I was reluctant to build it because I was afraid the people that I made it for (CAP) might not know how to do the elevated radials. I was afraid they might come back on me. I reckon I am one of those "trial and error" hams that has tried about everything in the last 40 years and I am still learning. Anyhoo, BOY was I WRONG! They put the thing on the air and it really puts out a good signal! None of us have done any measurements or NEC modeling, etc. Frankly, I was surprised as I had done very few vertical installations (well, I've got an AV8 vertical all-bander). All I know is, at the 60-70 foot level with tuned radials, it really sings! 73 Jerry K4KWH |
hasan schiers wrote:
Now that is interesting, Roy. I was going to put up a 160 m inverted L this summer. I am limited to only being able to go up about 45 feet, so I would need about another 90 feet horizontal. Are you suggesting that it might be a better arrangement to go up the 45' and then put up the top "T"? It might be. You might benefit from the radiation from the horizontal portion of an L, and you might not. But if it's quite low, the radiation will be mostly straight up, and a fair amount will be expended warming up the ground. Neither will occur with a T. If so, roughly how long should the top part of the T be (each side of center) to get me to 160? That's just what antenna modeling programs are for! Dust off your EZNEC and you'll have the answer in minutes. . . . Roy Lewallen, W7EL |
Jerry wrote:
Roy, I built basically a loaded mobile antenna that went onto an airport building in Raleigh, NC (about 60 feet) I was reluctant to build it because I was afraid the people that I made it for (CAP) might not know how to do the elevated radials. I was afraid they might come back on me. I reckon I am one of those "trial and error" hams that has tried about everything in the last 40 years and I am still learning. Anyhoo, BOY was I WRONG! They put the thing on the air and it really puts out a good signal! None of us have done any measurements or NEC modeling, etc. Frankly, I was surprised as I had done very few vertical installations (well, I've got an AV8 vertical all-bander). All I know is, at the 60-70 foot level with tuned radials, it really sings! 73 Jerry K4KWH I spend a lot of time learning about how antennas work, and try to pass the information along as best I can. But I find over and over again that most people don't have the ability to evaluate things in anything but a binary fashion -- everything has to be "good" or "bad" (or "good" and "evil"), "theory" or "experiment", "perfect" or "no good"; antennas either "work" or "don't work". So what I say is often interpreted as a statement that an antenna has to be perfect in order to work well, or to "work" at all -- whatever that means. But that's not at all what I'm saying. Let me try once again to clarify what I mean. Just about anything will radiate, from a dummy load on up. But some antennas radiate a greater fraction of the applied power than others, and some radiate more in desired directions than others. What I try to do is to understand how they work so I can, if I want, optimize an antenna for a particular purpose. (And I don't necessarily always want to -- sometimes it's not worth the trouble.) But an antenna doesn't have to be optimum in order to talk to people. It doesn't even have to be optimum to get sixty-over-nine reports and break pileups. And it doesn't even have to be anywhere near optimum in order to provide you with many pleasant QSOs. You don't have to understand anything at all about how antennas work to put one up that will give you many hours of fine QSOs -- I must have put up hundreds without having a clue about how they really worked, and I worked plenty of stations. And I, like anyone else who's been around a few years, have a handful of great stories about some really crappy antenna that worked the rare DX. (I've even done it with a crappy antenna and QRP.) What you have to understand is that you can work *more* stations, more reliably, if you do take the time and trouble (and if your yard and pocketbook will allow) to make your antenna more efficient and make it concentrate its radiation in the directions you want. But to a lot of people, it's not worth the time and trouble -- and that's fine. Some people simply aren't interested in the technical aspects of the hobby, and would rather spend their time doing something other than learning about or even modeling antennas. There's nothing at all wrong with that. Those folks won't find many of my postings to be interesting, and won't read them, which is fine. And, like I did for a long time, they'll put up plenty of antennas that work well enough -- and even from time to time one that works exceptionally well. But I hope my postings will be useful to those people who are interested in learning more about antennas and/or who enjoy squeezing more performance out of them. And I learn from this, too! Learning about antennas doesn't diminish your ability to experiment and successfully create working antennas. What it does is to give you more tools, so you can -- if you choose, but only if you choose -- make an antenna do what you want, rather than putting it up and settling for whatever it does. Roy Lewallen, W7EL |
Roy,
Is there an EZNEC howto. I have tried to use the demo a few times and can't seem to get started. I tried to model a simple dipole and a center loaded vertical and got very lost. Thanks, Dan Roy Lewallen wrote: hasan schiers wrote: Now that is interesting, Roy. I was going to put up a 160 m inverted L this summer. I am limited to only being able to go up about 45 feet, so I would need about another 90 feet horizontal. Are you suggesting that it might be a better arrangement to go up the 45' and then put up the top "T"? It might be. You might benefit from the radiation from the horizontal portion of an L, and you might not. But if it's quite low, the radiation will be mostly straight up, and a fair amount will be expended warming up the ground. Neither will occur with a T. If so, roughly how long should the top part of the T be (each side of center) to get me to 160? That's just what antenna modeling programs are for! Dust off your EZNEC and you'll have the answer in minutes. . . . Roy Lewallen, W7EL |
On Thu, 25 Aug 2005 19:15:13 -0700, dansawyeror
wrote: Is there an EZNEC howto. I have tried to use the demo a few times and can't seem to get started. I tried to model a simple dipole and a center loaded vertical and got very lost. Hi Dan, It would be far simpler to hit the "Open" button and select an already existing example of an antenna and see where that goes. 73's Richard Clark, KB7QHC |
On Thu, 25 Aug 2005 19:15:13 -0700, dansawyeror
wrote: Is there an EZNEC howto. I have tried to use the demo a few times and can't seem to get started. I tried to model a simple dipole and a center loaded vertical and got very lost. Perchance have you happen to read the help file? Hint; that information is there. Danny, K6MHE |
dansawyeror wrote:
Roy, Is there an EZNEC howto. I have tried to use the demo a few times and can't seem to get started. I tried to model a simple dipole and a center loaded vertical and got very lost. In the main window, click Help, then Contents. This is the EZNEC manual. Read the Getting Started section, and go through the "Test Drive" tutorial it directs you to. That should get you started. Roy Lewallen, W7EL |
All I know is, at the 60-70 foot level with tuned radials, it
really sings! They do. I've always preferred an elevated vs ground mount vertical. At that height on 80m, you appx equal to a ground mount system with 60+ radials, if they are using 3 or 4. Also, more clear of surroundings, etc.. Your local ground/space wave will usually be better. I bet it's good to dx at 2-3 AM... I've also used the usual L's and T's on 160m. Like Roy mentioned, which is better will depend on the angle needed. The T is better for strict DX, but often the L can be better to regional stuff. I'd have to double check, but I don't think adding the other half of the "T" top really changes the resonant freq a whole lot vs the L. IE: when using a "T", you will still need nearly a full 1/4 wave from the base to either end of the top horizontal section if not loaded. What can be handy for low banders, is nearly any dipole can be loaded up as a T vertical, if you short the conductors. Doesn't matter what type of feedline. Loading a 80m dipole as a T on 160m, is usually far better than trying to load the dipole as a dipole... If you don't short the feed together, but only feed one conductor, you then have a quicky L...Thats one quick way to compare them on different signals to see which is best at a given time. 160 is kinda weird...Often an L will outdo a T early in the evening, but usually later, the T will be better, even on the same short paths. Would seem to indicate the higher angles are less used later at night.. Sometimes I run a 80 meter turnstyle, and feed that as a vertical with an "X" capacity hat... That made a pretty good vertical which usually beat the L late at night. BTW, the vertical part of both antennas are appx 40-45 ft or so.. So fairly equal in that regard. MK |
I bought EZNEC +,v4 and enrolled in the ARRL antenna course. With my
many years of experience (bad & good!) I knew it was unlikely I would really get much out of either.... It has turned into one of the best educational bargains I have ever encountered. I am less than halfway through the course and find my biggest problem is that I keep running off in all directions to check out my past antenna failures. My wounded ego is healing nicely and I am satisfied that I am no antenna expert. I am a perpetual antenna student! On Thu, 25 Aug 2005 19:15:13 -0700, dansawyeror wrote: Roy, Is there an EZNEC howto. I have tried to use the demo a few times and can't seem to get started. I tried to model a simple dipole and a center loaded vertical and got very lost. Thanks, Dan |
John Ferrell wrote:
. . . I am a perpetual antenna student! And so are we all. Roy Lewallen, W7EL |
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