|
How to estimate groundwave distance?
Can anyone tell me the best way to estimate the groundwave coverage I'm likely to get on 75 meters? I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions about type of terrain, frequency, power output, and antenna efficiency, and got an answer of around 50 miles for an S-5 signal at the other end. (With the noise level around here, S-5 is about the minimum to shoot for around here...) And yet, in the real world, I am lucky to be able to establish reliable contact with another station that's a bit less than 10 miles away. We are both using horizontal NVIS antennas, which I guess aren't as good for groundwave as vertical antennas. In any case I have no idea what to put in to G4FGQ's program for "antenna efficiency". I tried 25 percent and got the 50 miles for S-5, then reduced antenna efficiency to 10 percent and got 40 miles for S-5... still well below what I am seeing in the real world. I switched to a terrain type of "City blocks, roads, streets, industrial areas, rivers" and got 32 miles for S-5, then switched to "Mountainous regions, bare rock, vegetation in valleys" (we do have a few molehills around here that people call mountains) and got 28 miles... still beyond what I'm really seeing. So, how can I estimate the longest reliable groundwave distance on 75? Thanks... |
How to estimate groundwave distance?
Eric wrote:
Can anyone tell me the best way to estimate the groundwave coverage I'm likely to get on 75 meters? I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions about type of terrain, frequency, power output, and antenna efficiency, and got an answer of around 50 miles for an S-5 signal at the other end. (With the noise level around here, S-5 is about the minimum to shoot for around here...) And yet, in the real world, I am lucky to be able to establish reliable contact with another station that's a bit less than 10 miles away. We are both using horizontal NVIS antennas, which I guess aren't as good for groundwave as vertical antennas. In any case I have no idea what to put in to G4FGQ's program for "antenna efficiency". I tried 25 percent and got the 50 miles for S-5, then reduced antenna efficiency to 10 percent and got 40 miles for S-5... still well below what I am seeing in the real world. I switched to a terrain type of "City blocks, roads, streets, industrial areas, rivers" and got 32 miles for S-5, then switched to "Mountainous regions, bare rock, vegetation in valleys" (we do have a few molehills around here that people call mountains) and got 28 miles... still beyond what I'm really seeing. So, how can I estimate the longest reliable groundwave distance on 75? Thanks... I don't think that a NVIS antenna is a "ground wave" antenna. It works by sending the signal straight up and bouncing it off the ionosphere back down covering the area around the antenna. But you should do better than what your doing if you are using on both ends a NVIS antenna. It strikes me that maybe the antennas are not at the right hight to function correctly. Also if only one station is using a NVIS antenna and the other is using a vertical or dipole that is high off the ground that could be the problem. Those antennas have a reduced response to signals coming in from high angles. It is a well known effect. 73 John Passaneau W3JXP |
How to estimate groundwave distance?
"Eric" wrote in message ... Can anyone tell me the best way to estimate the groundwave coverage I'm likely to get on 75 meters? I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions about type of terrain, frequency, power output, and antenna efficiency, and got an answer of around 50 miles for an S-5 signal at the other end. (With the noise level around here, S-5 is about the minimum to shoot for around here...) And yet, in the real world, I am lucky to be able to establish reliable contact with another station that's a bit less than 10 miles away. We are both using horizontal NVIS antennas, which I guess aren't as good for groundwave as vertical antennas. In any case I have no idea what to put in to G4FGQ's program for "antenna efficiency". I tried 25 percent and got the 50 miles for S-5, then reduced antenna efficiency to 10 percent and got 40 miles for S-5... still well below what I am seeing in the real world. I switched to a terrain type of "City blocks, roads, streets, industrial areas, rivers" and got 32 miles for S-5, then switched to "Mountainous regions, bare rock, vegetation in valleys" (we do have a few molehills around here that people call mountains) and got 28 miles... still beyond what I'm really seeing. So, how can I estimate the longest reliable groundwave distance on 75? Thanks... Consider using vertically polarised antennas because a ground wave is predominantly vertically polarised. NVIS antennas are usually horizontally polarised with respect to zero degrees elevation. Chris |
How to estimate groundwave distance?
On Dec 30, 8:50*am, Eric wrote:
So, how can I estimate the longest reliable ground wave distance on 75? Thanks... You need to use verticals if you want to use the ground wave on the lower bands. There basically is no ground wave when horizontal. Only a space wave, which is not likely to go as far. So in order to use the ground wave on the low bands, you need to be using a vertical antenna to transmit. How well that will do depends on the antenna, amount of noise, etc. 50 miles should be a good average, with some times better, maybe others worse. IE: you will almost always do a lot better in the winter, than summer just due to lower noise. Try it in the daytime. The noise is usually lower, and the ground wave doesn't care what time it is.. :/ It should always be about the same no matter what time of day. You lose a lot of ionospheric clutter in the day, and can get a better idea what the ground wave is doing. But there is still some skip in the day.. So if you end up working someone 200 miles away, it's probably *not* via the ground wave. More likely the D layer or whatever. But on the other hand, if you can work someone 50 miles away, and the signal is the same appx level every day, day in, day out, it's probably the ground wave. There could be minor season and moisture changes, but overall it should stay fairly stable strength. I know when I ran a 40m dipole at 36 ft, and also had a full size ground plane with the base at the same height, the difference in local coverage was drastic. Some times the band conditions "NVIS" would stretch out, and I would lose the locals that were across town if I were on the dipole. But I could switch to the ground plane, and no problem. In the daytime on 40m, I could often work people way out west of town in mobiles, that the locals on dipoles wouldn't hear due to the often long skip and lower signals due to being mobile and vertical. Some of these were 70-90+ miles away. I don't know how much of the total was ground wave vs space wave, vs the ionosphere , but when I would switch to the dipole, they would drop way down. The ground plane did put out a pretty decent space wave being it was elevated. Way better than the same antenna ground mounted. And it was fairly efficient, which helps no matter which path it takes. The lower the frequency, the better the ground wave. IE: tune AM radio in the daytime. Any station you pick up that is out of town is coming to you via the ground wave. With a good radio and antenna, you can receive quite a distance. IE: from Houston, I can hear Dallas, San Antonio, even farther, no problem at all. Almost pure ground wave, and being such, it's easy to null out if needed vs sky wave which usually comes from multiple paths. But say take a 10m vertical at 50 ft in the air. The space wave is the primary path in case of working local. Not the ground wave like the low frequencies. |
How to estimate groundwave distance?
On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau
wrote: I don't think that a NVIS antenna is a "ground wave" antenna. It works by sending the signal straight up and bouncing it off the ionosphere back down covering the area around the antenna. But you should do better than what your doing if you are using on both ends a NVIS antenna. It strikes me that maybe the antennas are not at the right hight to function correctly. Also if only one station is using a NVIS antenna and the other is using a vertical or dipole that is high off the ground that could be the problem. Those antennas have a reduced response to signals coming in from high angles. It is a well known effect. We're both using horizontal antennas... his is a dipole up about 25 feet, and mine is an inverted vee that's up about 40 feet in the center and 10 feet at the ends. I know that a vertically polarized antenna would work groundwave better, but we need to be able to maintain reasonably reliable communications pretty much everywhere within about a 200-mile circle. We can use 160, 80, and 40 meters to do it, and theoretically we can use any amount of power up to the legal limit but in reality, as a practical matter we are limited to 100-200 watts. There are some in our group who really, REALLY think that the vertical is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. Does seem to be a wasted effort but WDIK? While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? |
How to estimate groundwave distance?
There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. Does seem to be a wasted effort but WDIK? While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? Note that radiation from the end of a low dipole is vertically polarized. Antenna efficiency, and surface wave field strength, can be computed with NEC. Frank, VE6CB |
How to estimate groundwave distance?
"Eric" wrote in message ... On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau wrote: I don't think that a NVIS antenna is a "ground wave" antenna. It works by sending the signal straight up and bouncing it off the ionosphere back down covering the area around the antenna. But you should do better than what your doing if you are using on both ends a NVIS antenna. It strikes me that maybe the antennas are not at the right hight to function correctly. Also if only one station is using a NVIS antenna and the other is using a vertical or dipole that is high off the ground that could be the problem. Those antennas have a reduced response to signals coming in from high angles. It is a well known effect. We're both using horizontal antennas... his is a dipole up about 25 feet, and mine is an inverted vee that's up about 40 feet in the center and 10 feet at the ends. I know that a vertically polarized antenna would work groundwave better, but we need to be able to maintain reasonably reliable communications pretty much everywhere within about a 200-mile circle. We can use 160, 80, and 40 meters to do it, and theoretically we can use any amount of power up to the legal limit but in reality, as a practical matter we are limited to 100-200 watts. There are some in our group who really, REALLY think that the vertical is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. Does seem to be a wasted effort but WDIK? While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? Why don't you connect together the two terminals of your 'NVIS' thing, drive it with respect to a good earth, and use it as a monopole with a capacity hat? There's a lot of chat going on about those here at the moment, and some of it is correct, like no appreciable HP radiation from a symmetrical horizontal hat. All it really does is to move the radiating part into a higher-current portion of the quarter sine wave. Chris |
How to estimate groundwave distance?
"Frank" wrote in message news:1Iw6l.480$PH1.385@edtnps82... There are some in our group who really, REALLY think that the vertical is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. Does seem to be a wasted effort but WDIK? While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? Note that radiation from the end of a low dipole is vertically polarized. Antenna efficiency, and surface wave field strength, can be computed with NEC. Frank, VE6CB Given the type of antennas you mentioned with 100 W. If they are facing end to end, and, over an average ground, you should expect: 21uV (S7 - 8) at 20 mi, and 14 uV ( S6 - 7) at 30 mi. If the antennas are parallel then the signals will be 10 db weaker. I used NEC for the analysis. Frank |
How to estimate groundwave distance?
Eric wrote:
I know that a vertically polarized antenna would work groundwave better, but we need to be able to maintain reasonably reliable communications pretty much everywhere within about a 200-mile circle. We can use 160, 80, and 40 meters to do it, and theoretically we can use any amount of power up to the legal limit but in reality, as a practical matter we are limited to 100-200 watts. There are some in our group who really, REALLY think that the vertical is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? You really need both. I'd not put in a vertical unless I had a horizontal one also. If I had to choose one, it would be the dipole. But if you can do both, the vertical has it's uses. Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. That is the ticket. I'd done some experiments between the two antennas, using an attenuator and antenna switch. Aside from generalities, which have become "truth" under different circumstances, the antenna that performed best at any given time changed, and not always in the way you thought. Sometimes in mid-QSO. Too many people think of take off angle as some sort of blob of RF that comes out of the antenna at one place, and not much elsewhere. All antennas radiate at all angles. Some just more at some angles than others. The point of this is that that vertical better be pretty efficient, because what use is a lower angle of radiation if it is putting out less RF than another antenna that even though the other antenna might have a higher take off angle, but have still more power output at the lower angle. While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? Best way is to use an antenna design program. This would probably be a very good idea if you need to convince your cohorts The big thing is, don't just look at the SWR plots, and don't just look at the antenna patterns. Looking at the bigger picture, it becomes more than just a Ford versus Chevy argument. - 73 de Mike N3LI - |
How to estimate groundwave distance?
Eric wrote in
: On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau wrote: I don't think that a NVIS antenna is a "ground wave" antenna. It works by sending the signal straight up and bouncing it off the ionosphere back down covering the area around the antenna. But you should do better than what your doing if you are using on both ends a NVIS antenna. It strikes me that maybe the antennas are not at the right hight to function correctly. Also if only one station is using a NVIS antenna and the other is using a vertical or dipole that is high off the ground that could be the problem. Those antennas have a reduced response to signals coming in from high angles. It is a well known effect. We're both using horizontal antennas... his is a dipole up about 25 feet, and mine is an inverted vee that's up about 40 feet in the center and 10 feet at the ends. I know that a vertically polarized antenna would work groundwave better, but we need to be able to maintain reasonably reliable communications pretty much everywhere within about a 200-mile circle. We can use 160, 80, and 40 meters to do it, and theoretically we can use any amount of power up to the legal limit but in reality, as a practical matter we are limited to 100-200 watts. There are some in our group who really, REALLY think that the vertical is the way to go, and I need some debating points. So, if I had a decent ground-mounted vertical, should I expect to get the ground wave distances that G4FGQ indicates in his calculation program? Is there any area / radius that would be covered by a ground-mounted vertical that wouldn't be covered by an NVIS horizontal (assuming that we're operating below the critical frequency)? I have always assumed that by the theory behind NVIS, the answer would be no... NVIS should cover everything out to a radius well beyond groundwave distance. But, I suppose we could install NVIS antennas AND verticals and switch between them to see which one works best at any given time. Does seem to be a wasted effort but WDIK? While I'm at it, how do I estimate antenna efficiency? What is the average range of efficiencies normally seen with a quarter-wave ground-mounted vertical, with an adequate ground radial system, in average soil? Are your NVIS antennas oriented the same way, geographically? And are you seeing a nice spike in the signals during the early part of the evening, only to lose them later? If so, consider dropping to 160 after signals fade in the evening. Consider 40m to be only a daytime band at best under present conditions. You might try 60m during the day. Ground wave on 75 and 160 can work with good quality vertical antennas, but my experience has been that it works best with a salt water ground or with at least a couple of KW over a good radial ground system (I used 2mhz commercially with 2 and 5kw transmitters for a long while and typical daytime range over ocean was about 250 miles. We had a VERY quiet location over a mile from our own tranmitters). -- Dave Oldridge+ ICQ 454777283 VA7CZ |
How to estimate groundwave distance?
Predicting ground wave distances isn't exactly an 'exact' science by
any means. An 'aproximate' answer is about as good as it gets. Try 'FGQ's program with a very low and a very high efficiency number. Average it. that'll give you a 'ball-park' figure to play with. - 'Doc |
How to estimate groundwave distance?
Since your operation seems to be NVIS rather than ground wave, I highly
recommend _Near Vertical Incidence Skywave Communication: Theory, Techniques, and Validation_, by Fiedler and Farmer, published by Worldradio Books. Don't know if it's still in print, but it shouldn't be hard to find a copy on the web. Roy Lewallen, W7EL |
How to estimate groundwave distance?
On Dec 30 2008, 8:50*am, Eric wrote:
Can anyone tell me the best way to estimate the groundwave coverage I'm likely to get on 75 meters? ___________ NEC shows this for a theoretically perfect 1/4-wave vertical monopole system: Frequency = 3.9 MHz Conductivity = 5 mS/m Applied Power = 100 watts Groundwave Field at 10 miles = 31.7 µV/m Groundwave Field at 20 miles = 14 µV/m RF |
How to estimate groundwave distance?
Richard Fry wrote:
On Dec 30 2008, 8:50 am, Eric wrote: Can anyone tell me the best way to estimate the groundwave coverage I'm likely to get on 75 meters? ___________ NEC shows this for a theoretically perfect 1/4-wave vertical monopole system: Frequency = 3.9 MHz Conductivity = 5 mS/m Applied Power = 100 watts Groundwave Field at 10 miles = 31.7 µV/m Groundwave Field at 20 miles = 14 µV/m RF Wouldn't a 200 degree vertical work better? |
How to estimate groundwave distance?
On Jan 10, 9:06*am, Dave wrote:
Richard Fry wrote: On Dec 30 2008, 8:50 am, Eric wrote: NEC shows this for a theoretically perfect 1/4-wave vertical monopole system: etc I need to correct the values I posted earlier. I mis-read the larger table I had constructed, which was apparent when calculating the values for a ~200 degree vertical. Frequency = 3.9 MHz Conductivity = 5 mS/m Applied Power = 100 watts Groundwave Field at 10 miles = 131 µV/m (Correction) Groundwave Field at 20 miles = 31.7 µV/m (Correction) Wouldn't a 200 degree vertical work better? Yes, by a little over 2 dB (other things equal). Groundwave Field at 10 miles = 167 µV/m Groundwave Field at 20 miles = 41 µV/m RF |
How to estimate groundwave distance?
"Richard Fry" wrote in message ... On Jan 10, 9:06 am, Dave wrote: Richard Fry wrote: On Dec 30 2008, 8:50 am, Eric wrote: NEC shows this for a theoretically perfect 1/4-wave vertical monopole system: etc I need to correct the values I posted earlier. I mis-read the larger table I had constructed, which was apparent when calculating the values for a ~200 degree vertical. I don't work the low bands enough , but I would have thought someone would have just gave some prctical experiance instead of all the NEC stuff. Not many hams are going to put up a 60 some foot vertical and the required ground system for 80 meters. Could not someone say that with horizontal dipoles about 30 feet up (or whatever is being used) you may get so many miles ground wave and during the day so many miles skywave and so many more at night ? NEC and other programs are fine for predicting the coverage, but it does not take into account all the variatables that can be answered by the experiance of actual operations. |
How to estimate groundwave distance?
On Sat, 10 Jan 2009 11:49:11 -0500, "Ralph Mowery"
wrote: I don't work the low bands enough , but I would have thought someone would have just gave some prctical experiance instead of all the NEC stuff. Not many hams are going to put up a 60 some foot vertical and the required ground system for 80 meters. That's OK, not many hams read these threads either. They fully expect they are doing their best, and certainly their experience proves it. Could not someone say that with horizontal dipoles about 30 feet up (or whatever is being used) you may get so many miles ground wave and during the day so many miles skywave and so many more at night ? Those same Hams that don't read these threads, and don't build 60+ foot radiators with elaborate ground systems don't realize that horizontal antennas don't have ground waves anyway. So what coverage they do get is perfect and they probably got an ARRL award for horizontal antenna ground wave WAC already when they sent in the box-top of their favorite breakfast. NEC and other programs are fine for predicting the coverage, but it does not take into account all the variatables that can be answered by the experiance of actual operations. NEC doesn't predict coverage, it is an antenna modeler, not a propagation modeler (which would fit into your "other programs"). That aside, these programs account for more variables than imagined by those Hams that don't read these threads and don't build 60+ foot radiators with elaborate ground systems. They have already had the experience of actual operations and nothing is better than that. So, why are we writing about those experienced, award winning Hams who don't read these threads, expect ground wave from their horizontal antenna, couldn't list more than one variatable and are satisfied with sub-par to mediocre performance? 73's Richard Clark, KB7QHC |
How to estimate groundwave distance?
Save wrote:
"Wouldn`t a 200 degree vertical wotk better?" Field strength versus tower height rises with height up to about 225 degrees. See Fig. 2.1 on page 80 of E.A. laport`s "Radio Antenna Engineering". Best regards, Richard Harrison, KB5WZI |
How to estimate groundwave distance?
Ralph Mowery wrote:
I don't work the low bands enough , but I would have thought someone would have just gave some prctical experiance instead of all the NEC stuff. Not many hams are going to put up a 60 some foot vertical and the required ground system for 80 meters. Could not someone say that with horizontal dipoles about 30 feet up (or whatever is being used) you may get so many miles ground wave and during the day so many miles skywave and so many more at night ? The basic problem is that there isn't a simple answer to your question. Any simple answer you'd get would be wrong much or most of the time. It's safe to say that you won't get any ground wave communication at all with a horizontal antenna, unless a vertical feedline is radiating. The range with a vertical antenna depends on the noise level, which changes day to day, season to season, and day to night, as well as ground conductivity and power level. The ARRL Antenna Book gives a "typical" ground wave range of around 60 miles at 3.5 MHz, but of course this depends on the factors I've mentioned, among others -- it's one of those "simple" answers. Sky wave communication range depends on the condition of the ionosphere. Sometimes you'll be able to communicate hundreds of miles, sometimes zero. There is no range you can depend on. If you're interested in the performance of a low dipole on 80 meters, I highly recommend _Near Vertical Incidence Skywave Communication_ by Fiedler and Farmer. NEC and other programs are fine for predicting the coverage, but it does not take into account all the variatables that can be answered by the experiance of actual operations. Unfortunately, experience doesn't take into account all the variables either. No one or group of people have experience with all possible antennas, ground conditions, ionospheric conditions, and noise levels, so one person's experience is likely to be different from another's. The value of modeling is that it allows you to see which factors are important and in what way, so you can get a better idea of what performance you might get under your particular set of circumstances -- rather than someone else's. Roy Lewallen, W7EL |
| All times are GMT +1. The time now is 04:51 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com