Re: Topband: Ground conductivity discussions … oops
> Hi Jim … thanks for the info. Rudy’s latest method is the one I was > planning to employ. Brian, K6STI also mentioned Rudy’s method. Good > consensus on which method to use! > > Yes, all other elements were either de tuned or on the ground. I have > checked each vertical one at a time (with others decoupled) and read 25 > ohms on all 4 elements. Such a head scratcher! I’m beginning to the my > aluminum elements are doped with Nichrome! :-) > > Dennis, K7FL > > > On Mon, Dec 5, 2022 at 9:33 AM James V Redding PE > wrote: > >> Here is a link to a method of actually measuring the soil complex >> conductivity characteristics and it is focused on 80M: >> >> https://rudys.typepad.com/files/soil-characteristics-qex.pdf >> >> Since the depth of the measurement is a function of frequency, the >> numbers for 80M may be quite different than for other HF bands. >> >> Was also curious whether the elements were detuned for their individual >> impedance measurements like would be done with a BCB array or if the 25 >> ohms is a common point measurement. >> >> Jim/VEZ >> >> >> >> On Sun, Dec 4, 2022 at 9:21 AM Dennis Ashworth >> wrote: >> >>> I meant to post this to the TowerTalk group. It still may be relevant to >>> Topband ops. >>> >>> Dennis, K7FL >>> >>> -- Forwarded message - >>> From: Dennis Ashworth >>> Date: Sat, Dec 3, 2022 at 8:54 AM >>> Subject: Ground conductivity discussions >>> To: >>> >>> >>> Very interesting and timely discussions on radials and ground >>> conductivity. >>> I’m currently rebuilding an 80M broadside array (with shortened, top >>> loaded >>> elements) in SW Utah that I’ve modeled at 12 ohms impedance. The current >>> antenna was tested and the impedance measured was 25 ohms. Each element >>> in >>> the array (4 total) also measured 25 ohms. What accounts for additional >>> system loss? >>> >>> Upon consulting the original builders, I learned they had also predicted >>> an >>> impedance of approximately 12 ohms. I’m not clear what methods or models >>> they used for their prediction. There are 4:1 baluns at the base of each >>> vertical which begs the question whether the array impedances were ever >>> checked post-install. I suspect not … and I doubt anything has changed >>> over >>> the years that would equally affect the impedance *on all 4 verticals.* >>> >>> Where I don’t blindly trust models (antennas or otherwise), I do believe >>> the 12 ohm figure is reasonable given the short, top loaded elements. I >>> reviewed the FCC conductivity tables for the locale and they indicate >>> 15-30 >>> millimos/meter. That’s pretty good! I would think the loss from a ground >>> system of 32, 1/4 wave plus radials would NOT account for the 12 ohms of >>> loss ground losses. But what if my ground conductivity is less than the >>> FCC >>> tables report? >>> >>> I’m going to the site again next week to install 26 additional 1/4 wave >>> radials on one of the verticals and see if (and how much) the measured >>> impedance drops. I’ll share my results here. >>> >>> This loss has to be a ground system issue. If so, adding radials and >>> seeing >>> a corresponding drop in impedance should confirm my suspicions. >>> >>> At some point, I’ll measure the ground conductivity, but it needs to wait >>> for warmer temps (current temp at site is 19F!). >>> >>> Insight from the masses always appreciated. >>> >>> >>> Dennis, K7FL >>> Las Vegas, NV >>> _ >>> Searchable Archives: http://www.contesting.com/_topband - Topband >>> Reflector >>> >> _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground conductivity discussions
Grant, that higher Rr is the path I took as well. My 160m antenna is a bit longer than 1/4wl - trimmed in length so that the resistivity component of Z was 50 ohms. It's got Xl of course, so I use a series C bread slicer at the tower base to to cancel the Xl. My thought back then was that whatever the ground loss was, it would be about 1/3 less if the native feedpoint R was 50 ohms instead of something more close to a true 1/4 WL of around 35 ohms. 73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com On 12/4/2022 11:19 AM, Grant Saviers wrote: Sounds like a great project. Isn't the reality that conductors (radials) in or near lossy mediums (earth, even salt water) have loss? And that the near field extends beyond the 1/4wl of the radials? The coupling among elements might be the reason 4:1 matching was used. So while more & longer radials reduce the loss, there is a limit. Note that my prior post for my antenna shows the feedpoint Z equals the Rr value of about 14 ohms only when the radials are elevated 100ft. Often called a ground plane antenna. I played a bit in Eznec with my antenna and a lot (128) more radials a few inches above your ground and saw essentially no change in Rg. Your higher conductivity ground will improve the pattern - more gain at lower angles. So I suspect adding 26 more radials to the existing 32 1/4wl will not make much improvement in Rg. I think Severns and Christman show this in their papers. Other solutions to lower ground loss is higher Rr of the antenna to improve the ratio Rr/Rg. eg 1/4wl tall verticals. The center fed 720ft BCB antennas eg KDKA are another solution. ie vertical dipoles. Grant KZ1W On 12/3/2022 08:54, Dennis Ashworth wrote: Very interesting and timely discussions on radials and ground conductivity. I’m currently rebuilding an 80M broadside array (with shortened, top loaded elements) in SW Utah that I’ve modeled at 12 ohms impedance. The current antenna was tested and the impedance measured was 25 ohms. Each element in the array (4 total) also measured 25 ohms. What accounts for additional system loss? Upon consulting the original builders, I learned they had also predicted an impedance of approximately 12 ohms. I’m not clear what methods or models they used for their prediction. There are 4:1 baluns at the base of each vertical which begs the question whether the array impedances were ever checked post-install. I suspect not … and I doubt anything has changed over the years that would equally affect the impedance *on all 4 verticals.* Where I don’t blindly trust models (antennas or otherwise), I do believe the 12 ohm figure is reasonable given the short, top loaded elements. I reviewed the FCC conductivity tables for the locale and they indicate 15-30 millimos/meter. That’s pretty good! I would think the loss from a ground system of 32, 1/4 wave plus radials would NOT account for the 12 ohms of loss ground losses. But what if my ground conductivity is less than the FCC tables report? I’m going to the site again next week to install 26 additional 1/4 wave radials on one of the verticals and see if (and how much) the measured impedance drops. I’ll share my results here. This loss has to be a ground system issue. If so, adding radials and seeing a corresponding drop in impedance should confirm my suspicions. At some point, I’ll measure the ground conductivity, but it needs to wait for warmer temps (current temp at site is 19F!). Insight from the masses always appreciated. Dennis, K7FL Las Vegas, NV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground conductivity discussions
Sounds like a great project. Isn't the reality that conductors (radials) in or near lossy mediums (earth, even salt water) have loss? And that the near field extends beyond the 1/4wl of the radials? The coupling among elements might be the reason 4:1 matching was used. So while more & longer radials reduce the loss, there is a limit. Note that my prior post for my antenna shows the feedpoint Z equals the Rr value of about 14 ohms only when the radials are elevated 100ft. Often called a ground plane antenna. I played a bit in Eznec with my antenna and a lot (128) more radials a few inches above your ground and saw essentially no change in Rg. Your higher conductivity ground will improve the pattern - more gain at lower angles. So I suspect adding 26 more radials to the existing 32 1/4wl will not make much improvement in Rg. I think Severns and Christman show this in their papers. Other solutions to lower ground loss is higher Rr of the antenna to improve the ratio Rr/Rg. eg 1/4wl tall verticals. The center fed 720ft BCB antennas eg KDKA are another solution. ie vertical dipoles. Grant KZ1W On 12/3/2022 08:54, Dennis Ashworth wrote: Very interesting and timely discussions on radials and ground conductivity. I’m currently rebuilding an 80M broadside array (with shortened, top loaded elements) in SW Utah that I’ve modeled at 12 ohms impedance. The current antenna was tested and the impedance measured was 25 ohms. Each element in the array (4 total) also measured 25 ohms. What accounts for additional system loss? Upon consulting the original builders, I learned they had also predicted an impedance of approximately 12 ohms. I’m not clear what methods or models they used for their prediction. There are 4:1 baluns at the base of each vertical which begs the question whether the array impedances were ever checked post-install. I suspect not … and I doubt anything has changed over the years that would equally affect the impedance *on all 4 verticals.* Where I don’t blindly trust models (antennas or otherwise), I do believe the 12 ohm figure is reasonable given the short, top loaded elements. I reviewed the FCC conductivity tables for the locale and they indicate 15-30 millimos/meter. That’s pretty good! I would think the loss from a ground system of 32, 1/4 wave plus radials would NOT account for the 12 ohms of loss ground losses. But what if my ground conductivity is less than the FCC tables report? I’m going to the site again next week to install 26 additional 1/4 wave radials on one of the verticals and see if (and how much) the measured impedance drops. I’ll share my results here. This loss has to be a ground system issue. If so, adding radials and seeing a corresponding drop in impedance should confirm my suspicions. At some point, I’ll measure the ground conductivity, but it needs to wait for warmer temps (current temp at site is 19F!). Insight from the masses always appreciated. Dennis, K7FL Las Vegas, NV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Ground conductivity discussions
Very interesting and timely discussions on radials and ground conductivity. I’m currently rebuilding an 80M broadside array (with shortened, top loaded elements) in SW Utah that I’ve modeled at 12 ohms impedance. The current antenna was tested and the impedance measured was 25 ohms. Each element in the array (4 total) also measured 25 ohms. What accounts for additional system loss? Upon consulting the original builders, I learned they had also predicted an impedance of approximately 12 ohms. I’m not clear what methods or models they used for their prediction. There are 4:1 baluns at the base of each vertical which begs the question whether the array impedances were ever checked post-install. I suspect not … and I doubt anything has changed over the years that would equally affect the impedance *on all 4 verticals.* Where I don’t blindly trust models (antennas or otherwise), I do believe the 12 ohm figure is reasonable given the short, top loaded elements. I reviewed the FCC conductivity tables for the locale and they indicate 15-30 millimos/meter. That’s pretty good! I would think the loss from a ground system of 32, 1/4 wave plus radials would NOT account for the 12 ohms of loss ground losses. But what if my ground conductivity is less than the FCC tables report? I’m going to the site again next week to install 26 additional 1/4 wave radials on one of the verticals and see if (and how much) the measured impedance drops. I’ll share my results here. This loss has to be a ground system issue. If so, adding radials and seeing a corresponding drop in impedance should confirm my suspicions. At some point, I’ll measure the ground conductivity, but it needs to wait for warmer temps (current temp at site is 19F!). Insight from the masses always appreciated. Dennis, K7FL Las Vegas, NV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
It is indeed true that variations in liquid soil moisture will dramatically affect ground system performance and base fed vertical impedance when an on, or below grade ground system is used. Frozen ground moisture is on a par with dry ground. This is one of the reasons for going beyond the point-of-diminishing-returns number of radials--the more radials used, the more stable the feedpoint Z is, over varying soil moisture in the radial field. Antenna efficiency is related to radiation resistance relative to the ground system. If you have a short vertical (inverted L) with a low resistance that you cannot increase, you can improve it by lowering the ground resistance by employing more radials. 73 Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
I think there will be much more not discussed yet concerning ground conductivity. What do you have to offer? Peter, DJ7WW -Original Message- From: Topband [mailto:topband-bounces+dj7ww=t-online...@contesting.com] On Behalf Of Ham Hicks Sent: Mittwoch, 25. März 2020 21:37 To: topband@contesting.com Subject: Re: Topband: Ground Conductivity I think it's about time for this discussion about ground conductivity to come to a stop. Its approaching the number of "expert " opinions about C-19 avoidance. Ham KB4BR -Original Message- From: Topband [mailto:topband-bounces+ham306=bellsouth@contesting.com] On Behalf Of K4SAV Sent: Wednesday, March 25, 2020 2:49 PM To: topband@contesting.com Subject: Re: Topband: Ground Conductivity KZ1W said: "If NEC2 is wrong, so is NEC4." - I don't think so since a different ground modeling approach is available in NEC4.2. Running EZNEC Pro4 antennas both in 2 and 4.2 sometimes shows significant differences. I didn't mean to imply there was no difference between NEC2 and NEC4 for all situations. I only examined a couple of particular BOG situations where I was able to get the same answer in NEC2 as someone else got in NEC4. In those cases either both answers are correct or they are both wrong. Jerry, K4SAV On 3/25/2020 11:17 AM, Grant Saviers wrote: > "If NEC2 is wrong, so is NEC4." - I don't think so since a different > ground modeling approach is available in NEC4.2. Running EZNEC Pro4 > antennas both in 2 and 4.2 sometimes shows significant differences. > > My .02. Exactly where is ground? It sure isn't the flat smooth plane > in NEC. And where does "real" ground start considering the huge > variety of stuff going on in the first few inches from 100% air to > solid dirt? > > I used 4.2 to model the inductive loaded BOG idea and found very small > (0.2") differences in BOG height (0.2 to 2") made large differences in > pattern and gain, even reversing the pattern. Conclusion - not > practical, even though the "best" model was neat. > > Given the posts re NEC doesn't work at small above ground distances: > the N6LF data in his "lost" BOG performance article and some modeling > I did at small distances above and below ground convinced me that 4.2 > is very good at the small distances. Of course the conductor can't be > in the ground plane. The mathematics may blow up then but mother > nature is continuous. > > Then I was surprised by the difference a mild freeze made in my DC > ground field resistance (the freeze was just a few inches). The > change had to be in the earth resistance of the rod interconnections > (bare #2 & #6), not the 8 & 10ft long rods. Ice has much lower > conductivity than water so even a frost, freezing the grass, might > have a noticeable effect on a BOG. > > As the N6LF work shows and perhaps this is another example of "you get > what you pay for" - ie BOGs are small, easy, and useful, but much more > sensitive to the environment than elevated Beverages. > > Bing found this cool essentially "Engineer's Handbook for AM > Antennas". > http://crawfordbroadcasting.com/Eng_Files/AM%20Antenna%20Systems.pdf > > Included is this: > "14.2 Antenna Resistance > Periodic checks should be made of the resistance at the common point > or non-directional antenna base. The frequency of this resistance > check will vary from station to station, and will probably be > determined by the nature of the environment around the antenna. Areas > with poor ground conductivity or sites with poor or deteriorated > ground systems may see a considerable shift in base or common point > resistance with changes in the amount of water in the soil. Similar > (and sometimes more dramatic) changes can occur when the ground freezes." > > Grant KZ1W > > On 3/24/2020 19:46, Michael Tope wrote: >> Dan, >> >> Reading that QRZ.com thread you linked to and reflecting on K4SAV's >> measurements and how much they appeared to vary over a fairly short >> period of time, got me wondering about what could be responsible. I >> am fairly certain that at least part of the radial system for my 160 >> meter vertical is over the drain field of the septic system for my >> cabin. Who knows, maybe a properly timed toilet flush could make the >> difference between working a new one and coming up empty :-) >> >> Okay, the toilet aided pileup busting is a stretch, but seriously, I >> am not sure if I can think of any better explanations than septic >> discharge for why ground characteristics could change that quickly. I >> do know in some cases there can be water table very close to the >> surf
Re: Topband: Ground Conductivity
Ham, I, for one, was thoroughly enjoying this discussion I just learned some valuable information concerning one particular limitation of even the most advanced modeling software. You may not know these men, but they are among the top technical experts in the field. They dispel a lot of myths that well-meaning but ignorant hams repeat until they have a large flock of sheep that bleat the same utter nonsense to other hams. We should all thank them for that, friend. 73, Mike W0BTU On Wed, Mar 25, 2020, 4:02 PM Ham Hicks wrote: > I think it's about time for this discussion about ground conductivity to > come to a stop. Its approaching the number of "expert " opinions about C-19 > avoidance. > > Ham > KB4BR > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
I think it's about time for this discussion about ground conductivity to come to a stop. Its approaching the number of "expert " opinions about C-19 avoidance. Ham KB4BR -Original Message- From: Topband [mailto:topband-bounces+ham306=bellsouth@contesting.com] On Behalf Of K4SAV Sent: Wednesday, March 25, 2020 2:49 PM To: topband@contesting.com Subject: Re: Topband: Ground Conductivity KZ1W said: "If NEC2 is wrong, so is NEC4." - I don't think so since a different ground modeling approach is available in NEC4.2. Running EZNEC Pro4 antennas both in 2 and 4.2 sometimes shows significant differences. I didn't mean to imply there was no difference between NEC2 and NEC4 for all situations. I only examined a couple of particular BOG situations where I was able to get the same answer in NEC2 as someone else got in NEC4. In those cases either both answers are correct or they are both wrong. Jerry, K4SAV On 3/25/2020 11:17 AM, Grant Saviers wrote: > "If NEC2 is wrong, so is NEC4." - I don't think so since a different > ground modeling approach is available in NEC4.2. Running EZNEC Pro4 > antennas both in 2 and 4.2 sometimes shows significant differences. > > My .02. Exactly where is ground? It sure isn't the flat smooth plane > in NEC. And where does "real" ground start considering the huge > variety of stuff going on in the first few inches from 100% air to > solid dirt? > > I used 4.2 to model the inductive loaded BOG idea and found very small > (0.2") differences in BOG height (0.2 to 2") made large differences in > pattern and gain, even reversing the pattern. Conclusion - not > practical, even though the "best" model was neat. > > Given the posts re NEC doesn't work at small above ground distances: > the N6LF data in his "lost" BOG performance article and some modeling > I did at small distances above and below ground convinced me that 4.2 > is very good at the small distances. Of course the conductor can't be > in the ground plane. The mathematics may blow up then but mother > nature is continuous. > > Then I was surprised by the difference a mild freeze made in my DC > ground field resistance (the freeze was just a few inches). The > change had to be in the earth resistance of the rod interconnections > (bare #2 & #6), not the 8 & 10ft long rods. Ice has much lower > conductivity than water so even a frost, freezing the grass, might > have a noticeable effect on a BOG. > > As the N6LF work shows and perhaps this is another example of "you get > what you pay for" - ie BOGs are small, easy, and useful, but much more > sensitive to the environment than elevated Beverages. > > Bing found this cool essentially "Engineer's Handbook for AM > Antennas". > http://crawfordbroadcasting.com/Eng_Files/AM%20Antenna%20Systems.pdf > > Included is this: > "14.2 Antenna Resistance > Periodic checks should be made of the resistance at the common point > or non-directional antenna base. The frequency of this resistance > check will vary from station to station, and will probably be > determined by the nature of the environment around the antenna. Areas > with poor ground conductivity or sites with poor or deteriorated > ground systems may see a considerable shift in base or common point > resistance with changes in the amount of water in the soil. Similar > (and sometimes more dramatic) changes can occur when the ground freezes." > > Grant KZ1W > > On 3/24/2020 19:46, Michael Tope wrote: >> Dan, >> >> Reading that QRZ.com thread you linked to and reflecting on K4SAV's >> measurements and how much they appeared to vary over a fairly short >> period of time, got me wondering about what could be responsible. I >> am fairly certain that at least part of the radial system for my 160 >> meter vertical is over the drain field of the septic system for my >> cabin. Who knows, maybe a properly timed toilet flush could make the >> difference between working a new one and coming up empty :-) >> >> Okay, the toilet aided pileup busting is a stretch, but seriously, I >> am not sure if I can think of any better explanations than septic >> discharge for why ground characteristics could change that quickly. I >> do know in some cases there can be water table very close to the >> surface, but I don't know how much that typically varies over the >> short term. My only other thought is that maybe in K4SAV's case the >> lay of the grass under the wire is changing slightly over time and >> the impedance is super-sensitive to the gap between the antenna and >> the ground (although I think K4SAV sai
Re: Topband: Ground Conductivity
On 3/25/2020 11:57 AM, Jim Brown wrote: ... I don't know if it's still required today, but when I worked in broadcasting, each station using a directional antenna was required to make periodic field strength measurements in their nulls to proof their pattern. Back in the 1960s when I was chief engineer at an AM station along the Rhode Island coast (Westerly) we had to pass periodic checks, not for nulls - it was a single stick - but for verifying the required signal strength over the licensed coverage area. The issue was the radial system that was in swampy land on the bank of a river where it dumped into the Atlantic Ocean. The salinity varied widely with river flow, tides, and seasons. Gus Hansen KB0YH _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Rudy is not the only one taking measurements. I've been doing EZNEC since 1996 (v2) and NEC4/EZNEC Pro since 2002. The latter cost me well over a thousand bucks, but has been well worth it in the long run and then some. NEC4 does on the ground and under the ground in a reliable way, but still does not match some aspects of reality. Rudy got it to track in very confined circumstances, which by the way is a huge clue. Rudy's confines are not available to most folks. Back before we published on the FCP, we were trying to make sense of how BOGs behaved, and decided on a plan to measure VF to either confirm or blast a theory that the electrical length of a BOG varied enormously and simply had to be taken into account if modeled dimensions were to be of any use at all. A lot of us roughly in the Raleigh area were putting a 151 foot (46m) dipole on the ground (DOG) and taking measurements, frequency and R where X=0 and ditto for X = +/- 25 ohms. About ten of us were taking measurements in a roughly 100 mile radius around Raleigh. The 151 feet was to give an even metric equivalent, and to get X=0 roughly in the 160 meter region. The **measured**, not modeled, velocity factor (VF) of a DOG was anywhere between 45 and 85 percent. The R at X=0 was anywhere from 80 to 200 ohms. Very frequently various placements of the DOG on the same property made maximal changes in the results. Rotating a DOG 90 degrees around its center would sometimes make huge differences. A permanently set, frequently measured DOG would have large variations with dampness of the general weather pattern and under snow, etc, and exhibited the gradual change "settling in" measured by Rudy. This resulted in a realization that a BOG would have to be modeled for it's electrical length, and adjusted somehow at the exact placement. E.g. if a DOG is trimmed to get it's X=0 at 1142 kHz, and then soldered back together and insulated at the center and grounds, terminations and cable only placed when the end points that matched the model's electrical length were known. The composition and behavior of ground varies wildly from place to place. A very dense, uniform around the compass, and decently large ground radial system will tame that. Elevated counterpoises will tame that to a lesser degree, depending on as much independence from inducing ground as can be managed. Or you can go horizontal and get into a different and more friendly paradigm. Not so easy for that on 160. I myself, and perhaps ten other NEC4 users I know of have tried to get NEC4 ground characteristics to match, with little or only isolated successes. This is known well enough by the commercial AM BC antenna folk. In filings the FCC will accept the NEC4 ground constant which generates the field strength which matches the actual measured field strength after antenna construction. Only the hams seem to think that the program has mastered the phenomena. It has not. It probably could be reprogrammed to deal with data from about a hundred ground measurements in the antenna near field. But then the square and cubic law aspects of the program run time would get in the way again, as was critically still the case when those programs were developed. Further there is an aspect to the skin effect which NONE of the programs takes into effect. At N4AF, where we were doing the NY4A multi contests, there was an interesting SWR anomaly that would sometimes creep in. Howie had a monster 5 element 40m quad fixed on Europe, and hung across a 200 foot catenary between two towers. The quad element centers were at 84 feet, so ground was in play. Some early mornings, the SWR would rise to 1.5:1 from it's normal 1:1. It coincided with a still night and dew on the grass. That was when the layer of air above the ground was at 100 percent humidity, which meant that moisture from the ground was not percolating upward and being evaporated into the air. With any wind, the ground close to surface would have less moisture the closer to surface, and if it had been dry, a good deal less. Less moisture, less conductivity. Effectively, the height above actual RF ground had changed, or its resistance had changed or some ghastly mathematical formula relating the two had changed. All the formulas about skin effect ASSUME uniform conductivity to a surface which is bounded by an insulator. NOT a layer of a more resistive conductor, and certainly not a conductor that gradually gets more resistive as it gets drier as it approaches the surface, and also varying in a daily or even hourly sense with the weather. The problem for ground radials is that frustrating most-varying medium is what the wire is on/in, and on/in at the point of most variance. I'm to the place where I view those problems as something needing avoidance altogether, IF I don't have the land and the copper to put down the commercial standard. Sparse, too-small, irregular radials will NOT avoid the near certain losses from that medium. Either go commercial
Re: Topband: Ground Conductivity
KZ1W said: "If NEC2 is wrong, so is NEC4." - I don't think so since a different ground modeling approach is available in NEC4.2. Running EZNEC Pro4 antennas both in 2 and 4.2 sometimes shows significant differences. I didn't mean to imply there was no difference between NEC2 and NEC4 for all situations. I only examined a couple of particular BOG situations where I was able to get the same answer in NEC2 as someone else got in NEC4. In those cases either both answers are correct or they are both wrong. Jerry, K4SAV On 3/25/2020 11:17 AM, Grant Saviers wrote: "If NEC2 is wrong, so is NEC4." - I don't think so since a different ground modeling approach is available in NEC4.2. Running EZNEC Pro4 antennas both in 2 and 4.2 sometimes shows significant differences. My .02. Exactly where is ground? It sure isn't the flat smooth plane in NEC. And where does "real" ground start considering the huge variety of stuff going on in the first few inches from 100% air to solid dirt? I used 4.2 to model the inductive loaded BOG idea and found very small (0.2") differences in BOG height (0.2 to 2") made large differences in pattern and gain, even reversing the pattern. Conclusion - not practical, even though the "best" model was neat. Given the posts re NEC doesn't work at small above ground distances: the N6LF data in his "lost" BOG performance article and some modeling I did at small distances above and below ground convinced me that 4.2 is very good at the small distances. Of course the conductor can't be in the ground plane. The mathematics may blow up then but mother nature is continuous. Then I was surprised by the difference a mild freeze made in my DC ground field resistance (the freeze was just a few inches). The change had to be in the earth resistance of the rod interconnections (bare #2 & #6), not the 8 & 10ft long rods. Ice has much lower conductivity than water so even a frost, freezing the grass, might have a noticeable effect on a BOG. As the N6LF work shows and perhaps this is another example of "you get what you pay for" - ie BOGs are small, easy, and useful, but much more sensitive to the environment than elevated Beverages. Bing found this cool essentially "Engineer's Handbook for AM Antennas". http://crawfordbroadcasting.com/Eng_Files/AM%20Antenna%20Systems.pdf Included is this: "14.2 Antenna Resistance Periodic checks should be made of the resistance at the common point or non-directional antenna base. The frequency of this resistance check will vary from station to station, and will probably be determined by the nature of the environment around the antenna. Areas with poor ground conductivity or sites with poor or deteriorated ground systems may see a considerable shift in base or common point resistance with changes in the amount of water in the soil. Similar (and sometimes more dramatic) changes can occur when the ground freezes." Grant KZ1W On 3/24/2020 19:46, Michael Tope wrote: Dan, Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. I am fairly certain that at least part of the radial system for my 160 meter vertical is over the drain field of the septic system for my cabin. Who knows, maybe a properly timed toilet flush could make the difference between working a new one and coming up empty :-) Okay, the toilet aided pileup busting is a stretch, but seriously, I am not sure if I can think of any better explanations than septic discharge for why ground characteristics could change that quickly. I do know in some cases there can be water table very close to the surface, but I don't know how much that typically varies over the short term. My only other thought is that maybe in K4SAV's case the lay of the grass under the wire is changing slightly over time and the impedance is super-sensitive to the gap between the antenna and the ground (although I think K4SAV said that his grass was all dead). 73, Mike W4EF.. On 3/23/2020 10:18 PM, Dan Maguire via Topband wrote: Grant wrote: If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 3/25/2020 9:17 AM, Grant Saviers wrote: Areas with poor ground conductivity or sites with poor or deteriorated ground systems may see a considerable shift in base or common point resistance with changes in the amount of water in the soil. Similar (and sometimes more dramatic) changes can occur when the ground freezes." Hi Grant, The references to "common point resistance" implies a multi-tower array, commonly used on the AM band to protect distant stations from interference on the same or adjacent frequencies. This protection is accomplished by nulls in the direction of the protected station, and achieving nulls requires a considerable degree of precision in the cancellation of radiation from the various towers. Anything around the array, including conductive objects and variations in the ground system can screw up the pattern. There are well known examples of things like a big water tank mounted on a tower in the far field of the array doing this. I don't know if it's still required today, but when I worked in broadcasting, each station using a directional antenna was required to make periodic field strength measurements in their nulls to proof their pattern. These BC arrays are generally far more complex than the 4-squares we use, and variations in our radial/counterpoise systems and the soil underneath them largely affects nulls, as opposed to forward gain. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
"If NEC2 is wrong, so is NEC4." - I don't think so since a different ground modeling approach is available in NEC4.2. Running EZNEC Pro4 antennas both in 2 and 4.2 sometimes shows significant differences. My .02. Exactly where is ground? It sure isn't the flat smooth plane in NEC. And where does "real" ground start considering the huge variety of stuff going on in the first few inches from 100% air to solid dirt? I used 4.2 to model the inductive loaded BOG idea and found very small (0.2") differences in BOG height (0.2 to 2") made large differences in pattern and gain, even reversing the pattern. Conclusion - not practical, even though the "best" model was neat. Given the posts re NEC doesn't work at small above ground distances: the N6LF data in his "lost" BOG performance article and some modeling I did at small distances above and below ground convinced me that 4.2 is very good at the small distances. Of course the conductor can't be in the ground plane. The mathematics may blow up then but mother nature is continuous. Then I was surprised by the difference a mild freeze made in my DC ground field resistance (the freeze was just a few inches). The change had to be in the earth resistance of the rod interconnections (bare #2 & #6), not the 8 & 10ft long rods. Ice has much lower conductivity than water so even a frost, freezing the grass, might have a noticeable effect on a BOG. As the N6LF work shows and perhaps this is another example of "you get what you pay for" - ie BOGs are small, easy, and useful, but much more sensitive to the environment than elevated Beverages. Bing found this cool essentially "Engineer's Handbook for AM Antennas". http://crawfordbroadcasting.com/Eng_Files/AM%20Antenna%20Systems.pdf Included is this: "14.2 Antenna Resistance Periodic checks should be made of the resistance at the common point or non-directional antenna base. The frequency of this resistance check will vary from station to station, and will probably be determined by the nature of the environment around the antenna. Areas with poor ground conductivity or sites with poor or deteriorated ground systems may see a considerable shift in base or common point resistance with changes in the amount of water in the soil. Similar (and sometimes more dramatic) changes can occur when the ground freezes." Grant KZ1W On 3/24/2020 19:46, Michael Tope wrote: Dan, Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. I am fairly certain that at least part of the radial system for my 160 meter vertical is over the drain field of the septic system for my cabin. Who knows, maybe a properly timed toilet flush could make the difference between working a new one and coming up empty :-) Okay, the toilet aided pileup busting is a stretch, but seriously, I am not sure if I can think of any better explanations than septic discharge for why ground characteristics could change that quickly. I do know in some cases there can be water table very close to the surface, but I don't know how much that typically varies over the short term. My only other thought is that maybe in K4SAV's case the lay of the grass under the wire is changing slightly over time and the impedance is super-sensitive to the gap between the antenna and the ground (although I think K4SAV said that his grass was all dead). 73, Mike W4EF.. On 3/23/2020 10:18 PM, Dan Maguire via Topband wrote: Grant wrote: If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
W4EF said: Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. You are not the only one wondering about that Mike. Those are some pretty weird measurements. I have no explanation. That's the reason I continued to take measurements over a one month period and continued to get those big variations from one measurement to the next. It's also the reason I am repeating the measurements again now, although I moved the dipole about 50 feet away from where it was before. The readings now seem to be much more reasonable and not so much variation between each measurement. I see the resonant point moving around with ground moisture content and the whole curve shifting as well but no big changes like the first time I did this. I may try to move the dipole back where it was before to see if any of the weirdness returns. I still can't fit any of the measured curves to a NEC2 analysis by varying ground parameters and height above ground in NEC2. Note that attempting to do this also violates the NEC2 guidelines for wire heights above ground. So why should I expect to be able to do this? I have duplicated NEC4 patterns for a BOG in NEC2 to an insignificant difference. If NEC2 is wrong, so is NEC4. That doesn't leave any tools for simulating BOGs. I have previously done other simulations for a BOG in NEC2 and the results never agree with measurements. I keep looking for model patches that may allow some useful information to be obtained from simulations. Jerry, K4SAV On 3/24/2020 9:46 PM, Michael Tope wrote: Dan, Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. I am fairly certain that at least part of the radial system for my 160 meter vertical is over the drain field of the septic system for my cabin. Who knows, maybe a properly timed toilet flush could make the difference between working a new one and coming up empty :-) Okay, the toilet aided pileup busting is a stretch, but seriously, I am not sure if I can think of any better explanations than septic discharge for why ground characteristics could change that quickly. I do know in some cases there can be water table very close to the surface, but I don't know how much that typically varies over the short term. My only other thought is that maybe in K4SAV's case the lay of the grass under the wire is changing slightly over time and the impedance is super-sensitive to the gap between the antenna and the ground (although I think K4SAV said that his grass was all dead). 73, Mike W4EF.. On 3/23/2020 10:18 PM, Dan Maguire via Topband wrote: Grant wrote: If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Dan, Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. I am fairly certain that at least part of the radial system for my 160 meter vertical is over the drain field of the septic system for my cabin. Who knows, maybe a properly timed toilet flush could make the difference between working a new one and coming up empty :-) Okay, the toilet aided pileup busting is a stretch, but seriously, I am not sure if I can think of any better explanations than septic discharge for why ground characteristics could change that quickly. I do know in some cases there can be water table very close to the surface, but I don't know how much that typically varies over the short term. My only other thought is that maybe in K4SAV's case the lay of the grass under the wire is changing slightly over time and the impedance is super-sensitive to the gap between the antenna and the ground (although I think K4SAV said that his grass was all dead). 73, Mike W4EF.. On 3/23/2020 10:18 PM, Dan Maguire via Topband wrote: Grant wrote: If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 3/24/2020 9:42 AM, Roy Morgan wrote: ... Your comment about over simplifying reminds me of a very early explanation of radio communication - or was it telegraph? I can remember only a little: "It's like wiggling the tail of a cat. It makes a sound at the other end. Only there's no cat." Does anyone have that quote? “The wireless telegraph is not difficult to understand. The ordinary telegraph is like a very long cat. You pull the tail in New York, and it meows in Los Angeles. The wireless is exactly the same, only without the cat.” Albert Einstein 73, Gus Hansen KB0YH _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
"You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Albert Einstein Marsh, KA5M -Original Message- From: Topband On Behalf Of Roy Morgan Sent: Tuesday, March 24, 2020 10:42 AM To: GEORGE WALLNER Cc: Topband@contesting.com Subject: Re: Topband: Ground Conductivity George, Your comment about over simplifying reminds me of a very early explanation of radio communication - or was it telegraph? I can remember only a little: "It's like wiggling the tail of a cat. It makes a sound at the other end. Only there's no cat." Does anyone have that quote? Roy Morgan K1LKY Western Mass > On Mar 24, 2020, at 9:21 AM, GEORGE WALLNER wrote: > > ...but I am over simplifying... _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
How do they measure that kind of conductivity in mS?, is it the same method as when you measure soils for safety (mains), or lightning discharge ground?. Regards Guillermo - LU5WE. El 23/3/20 a las 20:21, Dave Cuthbert escribió: AA6VB, QTH San Jose, California looks like *8 mS/m* FCC ground conductivity map https://www.fcc.gov/media/radio/m3-ground-conductivity-map A more detailed map https://www.americanradiohistory.com/FCC_Ground_Conductivity_Maps.htm 1 skin depth t 1.8 MHz in 8 mS/m soil is ~4 meters Dave KH6AQ On Mon, Mar 23, 2020 at 12:02 PM Chortek, Robert L. < robert.chor...@berliner.com> wrote: A quick question for the collective wisdom on this esteemed reflector: How would one categorize the quality of ground consisting of grass. For example, if you live next to a large (many acres) open space made entirely of well watered grass, would that qualify as “average ground“, “above average ground” or something else? Haven’t been able to find the answer anywhere. Thanks for your input, as always! 73 es DX, Bob/AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Albert Einstein: “You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.” Dave KH6AQ On Tue, Mar 24, 2020 at 5:42 AM Roy Morgan wrote: > George, > > Your comment about over simplifying reminds me of a very early explanation > of radio communication - or was it telegraph? I can remember only a little: > > "It's like wiggling the tail of a cat. It makes a sound at the other end. > Only there's no cat." > > Does anyone have that quote? > > Roy Morgan > K1LKY Western Mass > > > On Mar 24, 2020, at 9:21 AM, GEORGE WALLNER wrote: > > > > ...but I am over simplifying... > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
George, Your comment about over simplifying reminds me of a very early explanation of radio communication - or was it telegraph? I can remember only a little: "It's like wiggling the tail of a cat. It makes a sound at the other end. Only there's no cat." Does anyone have that quote? Roy Morgan K1LKY Western Mass > On Mar 24, 2020, at 9:21 AM, GEORGE WALLNER wrote: > > ...but I am over simplifying... _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
To some extent the term "ground conductivity" is misleading. It gives us false hope. If we thought of it as ground "resistance" we would gain a better appreciation of what it does to RF currents. In other words, the "average ground" is not your friend. It is a very messy resistor (and capacitor). Current through a resistor generates heat. Heat is loss. One job of radials is to keep RF currents out of the ground. In other words: you want the RF currents to flow through the copper not the resistor. (I am hugely simplifying, but...). Of course, if you do not have any radials, the ground will help, but the losses will likely to be very high (70 - 90%), unless you live over a salt-marsh, but even there, copper will be better. Over salt-water, the situation is different: the water makes a good "ground plane" (low resistance), but few of us have this advantage. 73 and Take Care! George, AA7JV/C6AGU _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Ahhh ...but what about vertical antennas with elevated radials ? On 3/24/2020 1:04 AM, Jim Brown wrote: On 3/23/2020 9:05 PM, donov...@starpower.net wrote: Excellent skin depth reference here: www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf Rudy is a great reference for anything he's chosen to study. An excellent engineer and scientist. Ground characteristics are much more significant for vertical polarization than for horizontal polarization. I'll take that one step farther -- VERY significant for vertical polarized antennas, but hardly matters for horizontal antennas. With horizontal antennas, what matters most is electrical rigging height (and, of course, terrain). 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector -- Dave manu...@artekmanuals.com www.ArtekManuals.com -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
A heuristic way to judge ground conductivity: If 160 meter Beverages work well, especially over 1 wavelength long, you don't have high ground conductivity. If Beverages are not particularly sensitive to end termination, you do have high ground conductivity. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Grant wrote: >>> If you really want to know the parameters, see antennasbyn6lf.com as Rudy >>> describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 3/23/2020 6:23 PM, Richard (Rick) Karlquist wrote: Where I live, the soil is 100% clay and the RF conductivity is high. Ten miles to the south, the soil is regular dirt. Vastly better for growing anything, even weeds. But the RF conductivity is considerable lower. A casual observer sightseeing would have no idea of this change in soil. Here's a link to the ground conductivity contour map from FCC Regs for the AM broadcast band. http://k9yc.com/FCC-GroundMap.zip 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 3/23/2020 9:05 PM, donov...@starpower.net wrote: Excellent skin depth reference here: www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf Rudy is a great reference for anything he's chosen to study. An excellent engineer and scientist. Ground characteristics are much more significant for vertical polarization than for horizontal polarization. I'll take that one step farther -- VERY significant for vertical polarized antennas, but hardly matters for horizontal antennas. With horizontal antennas, what matters most is electrical rigging height (and, of course, terrain). 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Excellent skin depth reference here: www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf Ground characteristics are much more significant for vertical polarization than for horizontal polarization. 73 Frank W3LPL - Original Message - From: "Richard (Rick) Karlquist" To: "Robert L. Chortek" , "topband" Sent: Tuesday, March 24, 2020 1:23:52 AM Subject: Re: Topband: Ground Conductivity On 3/23/2020 3:01 PM, Chortek, Robert L. wrote: > A quick question for the collective wisdom on this esteemed reflector: > > How would one categorize the quality of ground consisting of grass. For > example, if you live next to a large (many acres) open space made entirely of > well watered grass, would that qualify as “average ground“, “above average > ground” or something else? > RF conductivity depends on the soil per se, not what is growing on it. Grass (especially if watered) will grow on any kind of soil, so it indicates nothing. The lack of grass also doesn't necessarily indicate anything. Where I live, the soil is 100% clay and the RF conductivity is high. Ten miles to the south, the soil is regular dirt. Vastly better for growing anything, even weeds. But the RF conductivity is considerable lower. A casual observer sightseeing would have no idea of this change in soil. N6LF has developed techniques for measuring your ground parameters by characterizing very low dipoles. If you really want to know about your ground, this is what you need to do. Way too much work for me or nearly anyone else. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
I have saved all (I think) of Rudy's papers on antennas and ground. What a resource. He seems to have boundless energy, patience and perseverance. Wes N7WS On 3/23/2020 6:23 PM, Richard (Rick) Karlquist wrote: N6LF has developed techniques for measuring your ground parameters by characterizing very low dipoles. If you really want to know about your ground, this is what you need to do. Way too much work for me or nearly anyone else. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Ground Conductivity
Thank you all for your very helpful and informative responses. Thanks to everyone for taking the time to respond. Much appreciated! 73, Bob/AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 3/23/2020 3:01 PM, Chortek, Robert L. wrote: A quick question for the collective wisdom on this esteemed reflector: How would one categorize the quality of ground consisting of grass. For example, if you live next to a large (many acres) open space made entirely of well watered grass, would that qualify as “average ground“, “above average ground” or something else? RF conductivity depends on the soil per se, not what is growing on it. Grass (especially if watered) will grow on any kind of soil, so it indicates nothing. The lack of grass also doesn't necessarily indicate anything. Where I live, the soil is 100% clay and the RF conductivity is high. Ten miles to the south, the soil is regular dirt. Vastly better for growing anything, even weeds. But the RF conductivity is considerable lower. A casual observer sightseeing would have no idea of this change in soil. N6LF has developed techniques for measuring your ground parameters by characterizing very low dipoles. If you really want to know about your ground, this is what you need to do. Way too much work for me or nearly anyone else. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
FYI some data which I found interesting My dry earth at end of summer to very wet winter (WWA) causes my lightning ground system DC (actually about 300Hz AC) resistance to vary about 40% lower, ie 7+ ohms to 5 ohms. There was also significant differences from rod to rod re resistance measurements. How this affects RF properties is of course debatable but I do see a swr minimum shift of 10KHz or so on my T with 8 elevated radials. One nearby expert (PhD ULF propagation) told me "acid rain washed out all the minerals here long ago. We have poor ground." If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring. It is interesting to know the ground parameters, but what if you don't like them? Gain and peak angle are affected, but for 1/4wl antennas - T, L, or full ht aren't significantly differentially affected. For 160m, put up the tallest you can with the most number of ground radials or 6+ elevated radials. Much more on this on the N6LF web site. For your flat open terrain place your yagis at heights for the arrival angles from geographies of interest to your QTH as shown in HFTA. Ground doesn't matter much. Grant KZ1W On 3/23/2020 15:57, Chortek, Robert L. wrote: Hi Dave, I’m (just) starting to play with EZNEC and want to know what type of ground I’m dealing with when I’m running various models. I live on the second fairway of a.golf course and the way it’s configured I have literally 1/2 to 1 1/2 miles of grass in certain directions. It’s watered several times a week during the dry season and during the winter there is a fair bit of rain. Don’t know what’s underneath. It’s fertilized twice each year. Thoughts on quality of the ground for 10-20 meters? 30-40 meters? 80/160? Thanks! Bob/AA6VB Robert L. Chortek On Mar 23, 2020, at 3:45 PM, Artek Manuals wrote: [External Email] On 160M the " skin depth" of ground goes beyond the grass ...so it depends on more than just your yard but also the type of soil underneath, how often it is watered , fertilized etc etc. What are you trying to do that you need to know? Dave NR1DX On 3/23/2020 6:01 PM, Chortek, Robert L. wrote: A quick question for the collective wisdom on this esteemed reflector: How would one categorize the quality of ground consisting of grass. For example, if you live next to a large (many acres) open space made entirely of well watered grass, would that qualify as �average ground�, �above average ground� or something else? Haven�t been able to find the answer anywhere. Thanks for your input, as always! 73 es DX, Bob/AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector -- Dave manu...@artekmanuals.com www.ArtekManuals.com -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Robert, an EZNEC model of your vertical as described in your QRZ bio shows your measured 29.7 ohm input resistance when ground conductivity is set to *0.008 S/m*. EZNEC calls this (0.0075S/12) ground *flat, marshy, densely wooded*. Using 0.005/13 ground EZNEC reports 35 ohms. Dave KH6AQ On Mon, Mar 23, 2020 at 1:21 PM Dave Cuthbert wrote: > AA6VB, QTH San Jose, California looks like *8 mS/m* > > FCC ground conductivity map > https://www.fcc.gov/media/radio/m3-ground-conductivity-map > > A more detailed map > https://www.americanradiohistory.com/FCC_Ground_Conductivity_Maps.htm > > 1 skin depth t 1.8 MHz in 8 mS/m soil is ~4 meters > > Dave KH6AQ > > On Mon, Mar 23, 2020 at 12:02 PM Chortek, Robert L. < > robert.chor...@berliner.com> wrote: > >> A quick question for the collective wisdom on this esteemed reflector: >> >> How would one categorize the quality of ground consisting of grass. For >> example, if you live next to a large (many acres) open space made entirely >> of well watered grass, would that qualify as “average ground“, “above >> average ground” or something else? >> >> Haven’t been able to find the answer anywhere. >> >> Thanks for your input, as always! >> >> 73 es DX, >> >> Bob/AA6VB >> Robert L. Chortek >> _ >> Searchable Archives: http://www.contesting.com/_topband - Topband >> Reflector >> > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
AA6VB, QTH San Jose, California looks like *8 mS/m* FCC ground conductivity map https://www.fcc.gov/media/radio/m3-ground-conductivity-map A more detailed map https://www.americanradiohistory.com/FCC_Ground_Conductivity_Maps.htm 1 skin depth t 1.8 MHz in 8 mS/m soil is ~4 meters Dave KH6AQ On Mon, Mar 23, 2020 at 12:02 PM Chortek, Robert L. < robert.chor...@berliner.com> wrote: > A quick question for the collective wisdom on this esteemed reflector: > > How would one categorize the quality of ground consisting of grass. For > example, if you live next to a large (many acres) open space made entirely > of well watered grass, would that qualify as “average ground“, “above > average ground” or something else? > > Haven’t been able to find the answer anywhere. > > Thanks for your input, as always! > > 73 es DX, > > Bob/AA6VB > Robert L. Chortek > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Hi Dave, I’m (just) starting to play with EZNEC and want to know what type of ground I’m dealing with when I’m running various models. I live on the second fairway of a.golf course and the way it’s configured I have literally 1/2 to 1 1/2 miles of grass in certain directions. It’s watered several times a week during the dry season and during the winter there is a fair bit of rain. Don’t know what’s underneath. It’s fertilized twice each year. Thoughts on quality of the ground for 10-20 meters? 30-40 meters? 80/160? Thanks! Bob/AA6VB Robert L. Chortek > On Mar 23, 2020, at 3:45 PM, Artek Manuals wrote: > > [External Email] > > On 160M the " skin depth" of ground goes beyond the grass ...so it > depends on more than just your yard but also the type of soil > underneath, how often it is watered , fertilized etc etc. > > What are you trying to do that you need to know? > > Dave > NR1DX > >> On 3/23/2020 6:01 PM, Chortek, Robert L. wrote: >> A quick question for the collective wisdom on this esteemed reflector: >> >> How would one categorize the quality of ground consisting of grass. >> For example, if you live next to a large (many acres) open space made >> entirely of well watered grass, would that qualify as �average >> ground�, �above average ground� or something else? >> >> Haven�t been able to find the answer anywhere. >> >> Thanks for your input, as always! >> >> 73 es DX, >> >> Bob/AA6VB >> Robert L. Chortek >> _ >> Searchable Archives: http://www.contesting.com/_topband - Topband >> Reflector > > -- > Dave > manu...@artekmanuals.com > www.ArtekManuals.com > > > -- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
You may find this interesting. https://ham.stackexchange.com/a/14799/8717 How useful it is, is another matter! ;-) 73, Mike W0BTU On Mon, Mar 23, 2020, 5:02 PM Chortek, Robert L. < robert.chor...@berliner.com> wrote: > > How would one categorize the quality of ground consisting of grass. For > example, if you live next to a large (many acres) open space made entirely > of well watered grass, would that qualify as “average ground“, “above > average ground” or something else? > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
On 160M the " skin depth" of ground goes beyond the grass ...so it depends on more than just your yard but also the type of soil underneath, how often it is watered , fertilized etc etc. What are you trying to do that you need to know? Dave NR1DX On 3/23/2020 6:01 PM, Chortek, Robert L. wrote: A quick question for the collective wisdom on this esteemed reflector: How would one categorize the quality of ground consisting of grass. For example, if you live next to a large (many acres) open space made entirely of well watered grass, would that qualify as �average ground�, �above average ground� or something else? Haven�t been able to find the answer anywhere. Thanks for your input, as always! 73 es DX, Bob/AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector -- Dave manu...@artekmanuals.com www.ArtekManuals.com -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Ground Conductivity
A quick question for the collective wisdom on this esteemed reflector: How would one categorize the quality of ground consisting of grass. For example, if you live next to a large (many acres) open space made entirely of well watered grass, would that qualify as “average ground“, “above average ground” or something else? Haven’t been able to find the answer anywhere. Thanks for your input, as always! 73 es DX, Bob/AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground conductivity
Bruce, I believe that is extremely possible. I have witnessed the same exact thing here in northern lower MI where we live in giant sandbox. I have especially noticed changes in feed point impedance on RX antennas during the winter months when the soils are generally frozen versus the mid summer with lower moisture content. I have even had this issue with some transmit verticals.drove me nuts for a while at my last QTH with my 160 inv L where I didn't have a huge radial field.the feed point impedance would drift between seasons One of my next projects is actually going to be setting up a data logger to monitor the soil resistivity throughout the yearInquiring minds NEED to know! DaveKB8NNU From: K1FZ-Bruce <k...@myfairpoint.net> To: Topband <topband@contesting.com> Sent: Tuesday, March 29, 2016 10:16 PM Subject: Topband: Ground conductivity Done my yearly spring maintenance of my SE single wire Beverage antenna. With poor soil, It typically is best with a 350 ohm matching transformer and a 330 to 350 ohm termination resistor. But this year it is best with a 450 ohm matching transformer and 450 ohm termination resistor. A higher value typically means more conductive soil. I do not have the time, or equipment to make accurate RF ground conductivity measurements now. But got wondering where Maine gets the WX after it passes over most of the lower 48 states, With climate change and the highest carbon content in the air. Could rain be causing my soil to be more conductive ?. Has anyone else noticed anything like this ? 73 Bruce-K1FZ PS: Delta,Pennant, Flag antenna notes has a new address www.qsl.net/k1fz/flag_antennas.html _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Ground conductivity
Done my yearly spring maintenance of my SE single wire Beverage antenna. With poor soil, It typically is best with a 350 ohm matching transformer and a 330 to 350 ohm termination resistor. But this year it is best with a 450 ohm matching transformer and 450 ohm termination resistor. A higher value typically means more conductive soil. I do not have the time, or equipment to make accurate RF ground conductivity measurements now. But got wondering where Maine gets the WX after it passes over most of the lower 48 states, With climate change and the highest carbon content in the air. Could rain be causing my soil to be more conductive ?. Has anyone else noticed anything like this ? 73 Bruce-K1FZ PS: Delta,Pennant, Flag antenna notes has a new address www.qsl.net/k1fz/flag_antennas.html _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Ground conductivity, permittivity measurement
Cristi YO3FFF wrote: From Terman (as Richard Fry mentioned): http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg First hop distance on E layer reflection for given angles is: 20 degrees = 300miles, 30 degrees = 200miles __ But note that Terman shows much longer 1st-hop skywave paths at elevation angles below three degrees -- where a NEC far-field pattern of a vertical monopole over real earth shows very low relative field from a vertical monopole. A NEC far-field pattern of a vertical monopole over real earth also shows zero field in the horizontal plane, but clearly that is incorrect. If it WAS correct, then AM broadcast stations would have zero daytime coverage by their surface (ground) wave. Yet a 50 kW station on a low frequency can provide useful groundwave service beyond 200 miles from their antenna site, in many cases. The surface wave MUST be considered when evaluating skywave performance of a monopole, because that surface wave contains significant radiation at low elevation angles capable of producing skywave coverage. This was shown clearly in the NEC4.2 plot posted by Paul Christensen earlier in this thread, at http://72.52.250.47/images/160m.jpg , and also in my link http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg R. Fry ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
Cristi, Thank you for the thoughtful answer. If I was of a mind to verify the use of probes, I would look at the attenuation slope of sample signal from a distance source across the area being measured and carefully record that slope. THIS DOES NOT require a calibrated instrument to a certain field intensity reference or a certain radiated power, because we are only determining the slope along a distance. We don't care if it is mV/m or Cris per meter, or Tom per meter. We only care that we measure the slope. Then I would sample the earth with my proposed method, in this case the probes, and record that data. If the two correlate over seasonal, temperature, or moisture changes, then it appears logical the probes have value over that particular frequency and soil type. The problem with probes or buried lines is they at best only sample a very small cross section of earth near the surface. It is very easy to understand this might not correlate at all with fields that extend many meters deep. It is like looking at the thin skin to detect what happens deep inside. Obviously if the field is mostly gone past the thin skin, we only need look at the skin. Likewise if the field extends far beyond the skin, we are not measuring anything meaningful for the wave. I think a scholarly person wanting to verify a method like this would make a test like this over a variety of soils, but I cannot find such verification. Without such a test it is a matter of blind faith that what happens in the first meter or less is what happens several meters down. I would agree with your idea about multiple points making it meaningful if you also moved the probes deep below ground, to a depth where the field diminished to unimportant values. I think this is a case of not being able to do things right, so we dismiss what probably is a problem. 73 Tom ___ Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more info.
Re: Topband: Ground conductivity, permittivity measurement
On 10/3/2012 7:20 AM, Tom W8JI wrote: I would agree with your idea about multiple points making it meaningful if you also moved the probes deep below ground, to a depth where the field diminished to unimportant values. I think this is a case of not being able to do things right, so we dismiss what probably is a problem. I am in complete agreement with Tom on the importance of measuring to skin depth at the frequency of interest, and for mere mortals, measuring radials from a nearby broadcast station is the only way I can think of to do that. While the transmission line method is fine, and the DG8SAQ VNA is a winner (I have one), it is still limited to the depth of the length of its probes. But it is also important that we remember that there are at least three primary effects of ground. They are 1) loss in the near field; 2) reflections in the far field; 3) ground wave propagation. We can minimize #1 by heroic effects with our ground system, and this shows up in the impedance measurements of our antenna system. The only thing we can do about #2 and #3 is to move. 73, Jim K9YC ___ Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more info.
Topband: Ground conductivity, permittivity measurement
Hello all, I like to share my experiments and hear from your similar experiments regarding ground conductivity and permittivity measurements. As we all know (should know), those two parameters are esential to evaluate the ground under our antennas, especially for verticals. The ideea to measure the ground concuctivity and permittivity rise after I read Rudy's (N6LF) article, Measurement of soil electrical parameter at HF. I use the two electrodes method described on that article which is fine. The impedance were mesured with a miniVNA. Not very precise gear but enough for this proposal. The results amaze me... I start measurements at the end of May. Since then, the weather was very dry with very few rain shower. Very rough drought this year so, very poor soil humidity. In May, conductivity was about 27mS/m and now...only 5mS/m. This is a linear function because there were no important precipitations. I have an INV-L (for 160m band) antenna with about 22 optimized radial system (combined on ground and suspended) with 16m vertical section and about 27m horizontaly. The question is: What is the impact of the conductivity vatiation on the antenna caracteristics? To answer to this question, I use MMANA-GAL for simulation constructing the antenna model and using a real ground with conductivity as a variable. First, I use 27mS/m and second, 5mS/m ground conductivity. Below are the findings. Conductivity (mS/m)R(ohm)jX(ohm)SWR(50ohm)Ga(dBi)F/B(dB)Elev.(degree) 27 11.12-3.3544.523.68 1.19 22.4 511.12-3.3544.523.84 2.26 30.7 I should mention that changing permittivity does not have much impact on this simulation. On my view, the important thing to observe on the above data is the Elevation radiation angle. It rised with 37% for 81% less conductivity. Conclusion: The less ground conductivity the higher is the antenna elevation radiation angle. This is a negative impact for DX! There are some observed situations when a higher radiation angle will be better than a lower one but this is not a rule of thumb. Finally, I'd like to hear your comments on this report and also your experiments. In the mean time, the measurements of ground conductivity and permittivity are an ongoing task on my side. 73 de YO3FFF Cristi ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
As we all know (should know), those two parameters are esential to evaluate the ground under our antennas, especially for verticals. The ideea to measure the ground concuctivity and permittivity rise after I read Rudy's (N6LF) article, Measurement of soil electrical parameter at HF. I use the two electrodes method described on that article which is fine. The impedance were mesured with a miniVNA. Not very precise gear but enough for this proposal. The results amaze me... I start measurements at the end of May. Since then, the weather was very dry with very few rain shower. Very rough drought this year so, very poor soil humidity. In May, conductivity was about 27mS/m and now...only 5mS/m. This is a linear function because there were no important precipitations. I know we all want to know conductivity. This first because popular when Sevik pounded a few rods in the ground and measured on 60 Hz, which became a commonly shared but totally useless measurement. Of course it is much better when we use the actual operating frequency. It seems to me using two rods in the ground and measuring impedance, in an attempt to estimate ground conductivity, might not be very reliable. We are not doing anything more than measuring a small area around the rods and (especially) rod contact. Rod contact on a freshly pounded rod from soil wetting varies greatly, especially with a smaller diameter rod, because the soil is not fully settled against the rod. Have these methods ever been verified with impedance changes in a low dipole, or field strength readings, or are they just a proposal? Richard Fry, you know anything about this? A 5:1 change in soil seems way out of line with what I recall from fields at WSPD on 1370 kHz and WOHO on 1470 kHz. Were those stations exceptions? 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
On 10/2/2012 3:31 AM, cris blak wrote: The less ground conductivity the higher is the antenna elevation radiation angle. Excellent work, Cristi. A suggestion for this last part of the analysis. Rather than look at the vertical angle where the radiation peaks, look at the field strength at some chosen low angle, like 10 degrees for various soil conditions. Now, we can see a dB value. Another thing I've been doing with EZNEC is saving computed pattern traces for various conditions and then recalling them all on a single plot. In this way, it's easier to see the effects of a change. And it is also possible to move the cursor from one curve to another and see dB values. 73, Jim K9YC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
Excellent work, Cristi. A suggestion for this last part of the analysis. Rather than look at the vertical angle where the radiation peaks, look at the field strength at some chosen low angle, like 10 degrees for various soil conditions. Now, we can see a dB value. But, we're not done there. Next, take that data and compare it against a surface wave component analysis in 4NEC2 and see where the RF is going at low elevation angles. The results may be surprising. Paul, W9AC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
Richard Fry, you know anything about this? A 5:1 change in soil seems way out of line with what I recall from fields at WSPD on 1370 kHz and WOHO on 1470 kHz. Were those stations exceptions? I don't know about further out where you'd have to proof an AM station but I just ran some models and there's kind of a weird relationship between vertical electric field strength at 1 wavelength out and far field efficiency as ground conductivity is varied for fixed permittivity. http://n3ox.net/files/1500kHz_monopole_cond.png This was a #12 copper wire monopole fed over 64 0.5wl radials 1 foot high. Power is held fixed at 1000W. The reference 0dB case for both the vertical field measurement and the far field efficiency was their equivalent values over perfect ground, but with copper wire loss turned on, so the reference far-field case was about 82% efficient. I want to try different distances and a higher frequency like 40m because I think the results will be quite different. Would also be good to, instead of looking at the total radiated power, compare the far field gain at some elevation angle vs. total field at that elevation angle nearer the antenna.But at any rate, seems this plot is relevant to what you can deduce comparing FS measurements over different soils. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
I don't know about further out where you'd have to proof an AM station but I just ran some models and there's kind of a weird relationship between vertical electric field strength at 1 wavelength out and far field efficiency as ground conductivity is varied for fixed permittivity. One wavelength is too close to show ground loss changes. You are really just looking at radiator efficiency. The signal has to propagate for some distance on groundwave to show earth conductivity effects on signal level. What I was suggesting is if soil varies from rain as much as a ground rod test shows, we should see this change at a distance on groundwave. BC stations determine soil conductivity by the measured slope of attenuation with distance compared to an ideal attenuation slope. I was wondering if ground rods were ever correlated to a known way of determining soil conductivity. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
Conclusion: The less ground conductivity the higher is the antenna elevation radiation angle. This is a negative impact for DX! Cris, Tom, Paul et al This belief is common when looking at the far-field elevation pattern of a vertical monopole in MoM results, or in antenna textbooks. That pattern is what remains of the radiated field at an infinite distance from the monopole, over an infinite, flat ground plane. -- But in reality all vertical monopoles of 5/8-wavelength and less radiate their maximum relative field (E/Emax) in the horizontal plane.-- A NEC near-field evaluation can show the field produced in and near the horizontal plane closer to the radiator, for earth of defined conductivity/permittivity, and it will not be zero as is shown in a NEC far-field plot. The NEC study at the link below illustrates this. The groundwave field (0-deg elevation) is plotted out to 8 km. Note the good correlation between the NEC GW field and the GW field measured by a broadcast consulting engineer using an accurately-calibrated field intensity meter. On that same chart is plotted the field existing from that radiator at an elevation of 100 meters above the earth. Note that it is lower near the radiator than the GW field, because the relative field radiated by a 1/4-wave monopole at higher elevation angles is less than in the horizontal plane. In fact at the zenith it will be zero. At ~8km downrange it has reached the value of the GW field, and further downrange it will exceed the GW field. From the NEC chart it can be seen that the field at low vertical angles (less than 3 degrees) is at least as great as it is at zero degrees. There is no physical reason for that low-angle radiation NOT to continue on to the ionosphere to produce a skywave signal, given the right conditions. http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg Supporting this below is a clip from the Radio Engineers' Handbook (Terman, 1943) showing this same reality, in that the angle at which radiation leaves that antenna for greatest 1-hop skywave range is less than 3 degrees. http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg Probably the description takeoff angle commonly applied to vertical monopoles is a rather misleading specification. R. Fry ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
Hi Richard, On your referenced fields graph you caption Measured vs. Calculated intensity, but the traces are not differentiated. Which traces on the graph are measured and which are calculated? 73, Guy. On Tue, Oct 2, 2012 at 2:58 PM, Richard Fry r...@adams.net wrote: Conclusion: The less ground conductivity the higher is the antenna elevation radiation angle. This is a negative impact for DX! Cris, Tom, Paul et al This belief is common when looking at the far-field elevation pattern of a vertical monopole in MoM results, or in antenna textbooks. That pattern is what remains of the radiated field at an infinite distance from the monopole, over an infinite, flat ground plane. -- But in reality all vertical monopoles of 5/8-wavelength and less radiate their maximum relative field (E/Emax) in the horizontal plane.-- A NEC near-field evaluation can show the field produced in and near the horizontal plane closer to the radiator, for earth of defined conductivity/permittivity, and it will not be zero as is shown in a NEC far-field plot. The NEC study at the link below illustrates this. The groundwave field (0-deg elevation) is plotted out to 8 km. Note the good correlation between the NEC GW field and the GW field measured by a broadcast consulting engineer using an accurately-calibrated field intensity meter. On that same chart is plotted the field existing from that radiator at an elevation of 100 meters above the earth. Note that it is lower near the radiator than the GW field, because the relative field radiated by a 1/4-wave monopole at higher elevation angles is less than in the horizontal plane. In fact at the zenith it will be zero. At ~8km downrange it has reached the value of the GW field, and further downrange it will exceed the GW field. From the NEC chart it can be seen that the field at low vertical angles (less than 3 degrees) is at least as great as it is at zero degrees. There is no physical reason for that low-angle radiation NOT to continue on to the ionosphere to produce a skywave signal, given the right conditions. http://i62.photobucket.com/**albums/h85/rfry-100/Measured_** vs_NEC2D_Fields2.jpghttp://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg Supporting this below is a clip from the Radio Engineers' Handbook (Terman, 1943) showing this same reality, in that the angle at which radiation leaves that antenna for greatest 1-hop skywave range is less than 3 degrees. http://i62.photobucket.com/**albums/h85/rfry-100/**TermanFig55.jpghttp://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg Probably the description takeoff angle commonly applied to vertical monopoles is a rather misleading specification. R. Fry __**_ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
On your referenced fields graph you caption Measured vs. Calculated intensity, but the traces are not differentiated. Which traces on the graph are measured and which are calculated? The chart at the top of the page contains only data calculated by NEC. The chart titled Measured Data (Oct 2002) at the bottom of that page shows the measured data. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
To Rich's point, I created a buried field in 4NEC2 using the radial geometry wizard and a vertical wire radiator 40m tall, all wires being of #12. The radial field consists of 64, 0.5 wavelength radials, buried 0.1m deep in moderate soil conductivity of 3 mS/m. As a bit of a sanity check, the base impedance computes to 40.2-j18.9. Rich can keep me straight on my assumptions, but I believe they're valid. http://72.52.250.47/images/160m.jpg Using NEC version 4.2, surface wave field strength is calculated at 1km as a function of varying Z value from 0-500m with 1500W from the source at 1.8 MHz. Notice how the field strength at zero elevation does not produce a null as we typically see in far-field calculations over average soil. So, without knowing the surface wave component, it would appear the traditional far-field plots only tell half the story about low-angle radiation from base-fed monopoles. My NEC input file is available to anyone who wants to see it. Before asking, please ensure your modeling program runs under NEC 4 and not NEC 2. Paul, W9AC - Original Message - From: Richard Fry r...@adams.net To: topband@contesting.com Sent: Tuesday, October 02, 2012 2:58 PM Subject: Re: Topband: Ground conductivity, permittivity measurement Conclusion: The less ground conductivity the higher is the antenna elevation radiation angle. This is a negative impact for DX! Cris, Tom, Paul et al This belief is common when looking at the far-field elevation pattern of a vertical monopole in MoM results, or in antenna textbooks. That pattern is what remains of the radiated field at an infinite distance from the monopole, over an infinite, flat ground plane. -- But in reality all vertical monopoles of 5/8-wavelength and less radiate their maximum relative field (E/Emax) in the horizontal plane.-- A NEC near-field evaluation can show the field produced in and near the horizontal plane closer to the radiator, for earth of defined conductivity/permittivity, and it will not be zero as is shown in a NEC far-field plot. The NEC study at the link below illustrates this. The groundwave field (0-deg elevation) is plotted out to 8 km. Note the good correlation between the NEC GW field and the GW field measured by a broadcast consulting engineer using an accurately-calibrated field intensity meter. On that same chart is plotted the field existing from that radiator at an elevation of 100 meters above the earth. Note that it is lower near the radiator than the GW field, because the relative field radiated by a 1/4-wave monopole at higher elevation angles is less than in the horizontal plane. In fact at the zenith it will be zero. At ~8km downrange it has reached the value of the GW field, and further downrange it will exceed the GW field. From the NEC chart it can be seen that the field at low vertical angles (less than 3 degrees) is at least as great as it is at zero degrees. There is no physical reason for that low-angle radiation NOT to continue on to the ionosphere to produce a skywave signal, given the right conditions. http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg Supporting this below is a clip from the Radio Engineers' Handbook (Terman, 1943) showing this same reality, in that the angle at which radiation leaves that antenna for greatest 1-hop skywave range is less than 3 degrees. http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg Probably the description takeoff angle commonly applied to vertical monopoles is a rather misleading specification. R. Fry ___ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Ground conductivity, permittivity measurement
On 10/2/2012 11:30 AM, Tom W8JI wrote: I was wondering if ground rods were ever correlated to a known way of determining soil conductivity. See Rudy's work, on his website. 73, Jim K9YC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
