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Length & number of radials
If you are considering a new vertical antenna, instead of guesswork
and copying somebody else's un-thought-out efforts, download program RADIAL_3 from website below. The program assists with choosing an economic length and number of shallow-buried ground radials. It takes a new look at how radials work by considering them to be lossy, single-wire transmission lines, open-circuit at the other end. RADIAL_3 is a self contained file, 55 kilibytes. Easy to use. No training needed. Download in a few seconds and run immediately. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Length & number of radials
Reg, a bit confused by these results from RADIAL_3
96 radials, 7MHz, antenna height 10.72m. Soil 500ohm*m, permittivity 13\ Radials and antenna 1.024mm (18AWG), radials 3mm deep(surface) Radial Length, %Efficiency 2m, 93.19% 3m, 93.83% 4m, 92.47% 5m, 86.01% 6m, 80.39% 7m, 85.92% 8m, 89.06% 9m, 89.59% 10m, 88.22% 11m, 85.99% 12m, 85.51% 13m, 86.67% ?? Dan |
Length & number of radials
BTW, love your programs... tried this one out because I've bought 4
kilofeet of 18 gauge wire for a vertical antenna when I get a backyard in a couple of weeks. 73, Dan |
Length & number of radials
Reg, a bit confused by these results from RADIAL_3 96 radials, 7MHz, antenna height 10.72m. Soil 500ohm*m, permittivity 13\ Radials and antenna 1.024mm (18AWG), radials 3mm deep(surface) Radial Length, %Efficiency 2m, 93.19% 3m, 93.83% 4m, 92.47% 5m, 86.01% 6m, 80.39% 7m, 85.92% 8m, 89.06% 9m, 89.59% 10m, 88.22% 11m, 85.99% 12m, 85.51% 13m, 86.67% ?? Dan ======================================== Dan, The up-and-down change in efficiency versus radial length is due to resonance effects. With a high value of soil resistivity of 500 ohm-meters resonance is not completely damped down. This is also indicated by the relatively small decibels per 1/4-wavelength figure. As radial length is varied the input resistance of the 96 radials changes. Look at the wavelength of 1 wire figure. It will be seen that length passes through 0.5 wavelength resonance at 6.0 metres. It passes through 1.0 wavelength resonance at 11.6 metres. At both these lengths the input resistance is at a maximum and so efficiency is at a minimum. At 2.9 metres and 8.8 metres the radials are in 1/4-wave and 3/4-wave resonant and the input resistance is at a minimum and efficiency is at a maximum. Vary length while watching the resistive component of input impedance to see what happens. It's highlighted in red. If you reduce soil resistivity from 500 to 50 ohm metres the resonance effects will probably disappear and the decibels per quarter wavelength will increase. All resonant effects will have disappeared when radial attenuation is about 18 or 20dB or greater. The effects of resonance are not observed so well when frequency is varied because so many other things change as frequency is varied over an octave or more. Resonant effects are much greater at 20 MHz and above with very high resistance soils such as desert sand. The radials then behave very similarly to the elevated variety. I trust your confusion has now gone away. ;o) ---- Reg, G4FGQ |
Length & number of radials
"Reg Edwards" wrote in message ... If you are considering a new vertical antenna, instead of guesswork and copying somebody else's un-thought-out efforts, download program RADIAL_3 from website below. The program assists with choosing an economic length and number of shallow-buried ground radials. It takes a new look at how radials work by considering them to be lossy, single-wire transmission lines, open-circuit at the other end. RADIAL_3 is a self contained file, 55 kilibytes. Easy to use. No training needed. Download in a few seconds and run immediately. ---- .................................................. ......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. ......... That is quite a bold statement and looks like trivilializing, ignoring the real workings of vertical antennas and radials! What would NEC4 say? 73 Yuri, K3BU |
Length & number of radials
"Reg Edwards" wrote in
: If you are considering a new vertical antenna, instead of guesswork and copying somebody else's un-thought-out efforts, download program RADIAL_3 from website below. The program assists with choosing an economic length and number of shallow-buried ground radials. It takes a new look at how radials work by considering them to be lossy, single-wire transmission lines, open-circuit at the other end. RADIAL_3 is a self contained file, 55 kilibytes. Easy to use. No training needed. Download in a few seconds and run immediately. Very nice. But one thing I have noticed is that radial effectiveness begins to fall off at a distance from the antenna very similar to its height. This seems to be due to capacitive coupling between the top of the antenna and the radials. Does your algorithm take this effect into consideration? I modelled an antenna I used to use and the results did seem consistent with the behaviour, though. Actually I used to use two of them, and actually had a gain over a single perfect-ground antenna. Not a LARGE gain, but still, useful. More useful was the fact that I could control the take-off angle and pattern to the point where the antenna actually sounded about 10db louder than a low dipole--at distances of 1000 mi or more. -- Dave Oldridge+ ICQ 1800667 |
Length & number of radials
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Length & number of radials
I don't know about boundary conditions, but when I use this program to
evaluate the following system: 3.62 Mhz, 18.3 meter height (simulating an inverted L with 25.4 ohms Rrad) Resistivity 25, Permittivity 25 2mm radials, 4mm antenna wire, radials 1 mm depth (actually #14 insulated wire, stapled to the lawn and sinking in gradually) ...it shows my predicted efficiency with (26) 50' long radials to be about 90%. My measurements indicated I am getting about 88%. Pretty good agreement. What causes me to cringe, is that the program shows that I can reduce the length of my radials from 16.1 meters to a little over 4 meters without losing ANY significant efficiency. Given everything else I've read over the years, that just seems to be way too good to be true. Now, I suppose I could rip up my 26 radials and shorten them all to about 5 meters and re-measure my efficiency, but that's a LOT of work (and it's 97 degrees out with a dew point in the mid 70's). Not going to happen. Here's the kicker... I have 1000' of remaining wire to put down (and I am going to add it). If this value of 4 or 5 meters (15 feet, let's say) is even remotely correct, I can put down 66 more radials (although they would be interlaced with the existing 26 longer ones of 50' each). Using my initial length of 50', I can put down 20 more radials, giving me a total of 46 radials 50' long. Reg, you program seems to be telling me that I would get the maximum benefit by putting in 66 more radials approximately 15' long, and that installing them at 50' would be wasting 35' of wire per radial, and reducing radial coverage as well. So...what should I do: 1. Add 66 greatly shortened radials (accepting Reg's program as correct) or 2. Add 20 radials, maintaining my 50' length that I originally used. I look forward to comments. ....hasan, N0AN |
Length & number of radials
On Wed, 19 Jul 2006 11:48:47 -0500, "hasan schiers"
wrote: So...what should I do: 2. Add 20 radials, maintaining my 50' length that I originally used. Hi Hasan, Build for the future. Anticipate working 160M. Enjoy the advantages (as slim as they may be) at 80M. 73's Richard Clark, KB7QHC |
Length & number of radials
Good thinking, Richard, as I may try to get this inverted L to do 160 in the
fall/winter by adding a trap to the 80m inverted L and extending the wire for 160m resonance. Incidentally, over the weekend I tried to add a 40m wire parallel to the 80m L...it was a complete failure. (I used a "fan" approach with 6" standoffs for the 33' vertical wire). I thought I might get 2 fer 1 at the feedpoint, but it just didn't work worth a darn. Very low noise level, signals were significantly weaker than my Carolina Windom 80 (on 40m) up 42'. I did work a few DX stations with it, but just not up to my expectations. A properly performing 40m 1/4 w vertical over very good soil and a full radial field as described in my prior message should have been outstanding. It wasn't. It was very hard to tune, showed no better than a 3:1 VSWR at resonance, and was only marginally better on a very few signals between sunset and sunrise. Very disappointing. So...your suggestion for 160m is a good one. I could do a trap pretty easily. If I wanted to try 40m with the same feedpoint, I could put a parallel tuned circuit at the feedpoint and run the 80m inverted L as a 40m half-wave. Of course, this requires switching at the feedpoint and I'm not sure I'd bother. I also have to get a 1.9 uH coil and 250 pf variable cap to do the tuned circuit (per ON4UN's Low Band DXing Handbook). I found an acceptable cap for 40 bucks and coil stock is readily available. I just have to get motivated and work out the relay switching. I wondered if I could EVALUATE the effectiveness of the 80m inverted L on 40m as a half wave, by temporarily taking an antenna tuner with wide range (T-network matches almost anything) out to the feedpoint and matching it there. If it hears well, and works ok at 300w (tuner limit), then it might be worth investing in the coil/cap/relays to switch a more standard high-Z feed in and out. What do you think? Thanks for your input. 73, ....hasan, N0AN "Richard Clark" wrote in message ... On Wed, 19 Jul 2006 11:48:47 -0500, "hasan schiers" wrote: So...what should I do: 2. Add 20 radials, maintaining my 50' length that I originally used. Hi Hasan, Build for the future. Anticipate working 160M. Enjoy the advantages (as slim as they may be) at 80M. 73's Richard Clark, KB7QHC |
Length & number of radials
hasan schiers wrote:
I wondered if I could EVALUATE the effectiveness of the 80m inverted L on 40m as a half wave, by temporarily taking an antenna tuner with wide range (T-network matches almost anything) out to the feedpoint and matching it there. If it hears well, and works ok at 300w (tuner limit), then it might be worth investing in the coil/cap/relays to switch a more standard high-Z feed in and out. What do you think? The configuration of 35ft vertical + 35ft (or so) horizontal worked well for me on 40m at the old QTH, and was quite effective on 80m DX. For 160m, I added a 100ft loading wire to bring the total length up to about 130ft, and that configuration doubled as an end-fed half-wave for 80m short-skip. Having a QRO auto-ATU made band changing easy, so it wasn't necessary to resonate the antenna on any band. However, the quarter-wave resonances on 80m and 160m could have been trimmed to length. Coming back to the difference between the 40m vertical quarter-wave and the bent half-wave, I compared the bare 35ft mast and the same mast with the added loading wire and didn't find much difference. For DX, the bent-half-wave should have been down on the quarter-wave (because some of the radiation was being wasted at high angles); but in contests, both antennas seemed to work the same regular DX stations. The bent half-wave was louder for short-skip, which meant more QRM at night, but made it easier to continue making low-point contacts during daylight hours. If you use an 80m trap, the antenna could still work on 40m but the horizontal section would be way over-long. Unless rapid band changing between 80m and 160m is a priority, I'd suggest you use a physical disconnect at the end of the 35ft horizontal section. (My setup made it very easy to loosen a rope and lower the connection into reach, so I used simple banana plugs, with snap links to add either wire or plain cord.) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Length & number of radials
On Wed, 19 Jul 2006 13:03:16 -0500, "hasan schiers"
wrote: Incidentally, over the weekend I tried to add a 40m wire parallel to the 80m L...it was a complete failure. (I used a "fan" approach with 6" standoffs for the 33' vertical wire). I thought I might get 2 fer 1 at the feedpoint, but it just didn't work worth a darn. Hi Hasan, I must think that you were only slightly off in length, and that the proximity, even at 6 inches, is still proximal. Very low noise level, signals were significantly weaker than my Carolina Windom 80 (on 40m) up 42'. Not unlike many similar reports. I did work a few DX stations with it, but just not up to my expectations. A properly performing 40m 1/4 w vertical over very good soil and a full radial field as described in my prior message should have been outstanding. It wasn't. Some of those same reporters suggest split operation where the vertical is the radiator and a high horizontal is the receiving antenna. I wondered if I could EVALUATE the effectiveness of the 80m inverted L on 40m as a half wave, by temporarily taking an antenna tuner with wide range (T-network matches almost anything) out to the feedpoint and matching it there. If it hears well, and works ok at 300w (tuner limit), then it might be worth investing in the coil/cap/relays to switch a more standard high-Z feed in and out. What do you think? I would encourage that, simply because you seem to be amenable to such a path already. Gaining experience is always a noble work. 73's Richard Clark, KB7QHC |
Length & number of radials
What would NEC4 say? Who or what is NEC4? |
Length & number of radials
"Reg Edwards" wrote in message ... What would NEC4 say? Who or what is NEC4? http://en.wikipedia.org/wiki/Numeric...magnetics_Code |
Length & number of radials
You need at least an odd number of 1/4 wavelengths to satisfy the boundary
conditions. You need at least three to define a plane (or cone, if you want a 50 ohm feedpoint) 73 H. NQ5H |
Length & number of radials
"hasan schiers" wrote in message ... I don't know about boundary conditions, but when I use this program to evaluate the following system: 3.62 Mhz, 18.3 meter height (simulating an inverted L with 25.4 ohms Rrad) Resistivity 25, Permittivity 25 2mm radials, 4mm antenna wire, radials 1 mm depth (actually #14 insulated wire, stapled to the lawn and sinking in gradually) ..it shows my predicted efficiency with (26) 50' long radials to be about 90%. My measurements indicated I am getting about 88%. Pretty good agreement. ========================================= Yes Hasan, good agreement. How did you determine efficiency to THAT degree of accuracy? ========================================= What causes me to cringe, is that the program shows that I can reduce the length of my radials from 16.1 meters to a little over 4 meters without losing ANY significant efficiency. Given everything else I've read over the years, that just seems to be way too good to be true. ========================================= You've been reading books and magazines about rules-of-thumb written by old-wives. At 3.62 MHz and a radial length of 16 metres the attenuation approaches 100 decibels. So there's no current flowing in the radials beyond 5 metres. You can remove the excess 12 metres. They are not doing anything. What small current density there is beyond 5 metres is all flowing in the soil. The cross-sectional area of the soil carries the small current just as well as the radials. ========================================= Now, I suppose I could rip up my 26 radials and shorten them all to about 5 meters and re-measure my efficiency, but that's a LOT of work (and it's 97 degrees out with a dew point in the mid 70's). Not going to happen. Here's the kicker... I have 1000' of remaining wire to put down (and I am going to add it). If this value of 4 or 5 meters (15 feet, let's say) is even remotely correct, I can put down 66 more radials (although they would be interlaced with the existing 26 longer ones of 50' each). Using my initial length of 50', I can put down 20 more radials, giving me a total of 46 radials 50' long. ========================================== Yes. Use the program to calculate efficiency with the extra 20 radials. Assume all the radials are 5 metres long. But you may not think the meagre 3% or 0.13dB in efficiency is worth all the labour and back-ache. By now you are beginning to appreciate how useful the program is. ========================================== Reg, you program seems to be telling me that I would get the maximum benefit by putting in 66 more radials approximately 15' long, and that installing them at 50' would be wasting 35' of wire per radial, and reducing radial coverage as well. So...what should I do: 1. Add 66 greatly shortened radials (accepting Reg's program as correct) or 2. Add 20 radials, maintaining my 50' length that I originally used. I look forward to comments. ========================================== Hasan, if I were you I would lay some extra short radials between the existing long radials - and get some Sloan's liniment to be massaged into my back. But the increase in efficiency would be un-measurable. You are fortunate to have very low soil resistivity. Mine is about 70 ohm-metres and for years on the 160m band I have had 7 radials about 3 metres long plus an incoming lead water pipe. ---- Reg, G4FGQ |
Length & number of radials
Reg wrote among other stuff:
You've been reading books and magazines about rules-of-thumb written by old-wives. At 3.62 MHz and a radial length of 16 metres the attenuation approaches 100 decibels. So there's no current flowing in the radials beyond 5 metres. You can remove the excess 12 metres. They are not doing anything. What small current density there is beyond 5 metres is all flowing in the soil. The cross-sectional area of the soil carries the small current just as well as the radials. ========================================== Yes. Use the program to calculate efficiency with the extra 20 radials. Assume all the radials are 5 metres long. But you may not think the meagre 3% or 0.13dB in efficiency is worth all the labour and back-ache. By now you are beginning to appreciate how useful the program is. ========================================== Reg, NEC4 engine can accommodate on the ground or buried radials in modeling and calculating vertical antenna parameters and performance. I bet Roy has his hair standing up, or perhaps still trying to recover from the "appreciation" of your program, unless he is still running calculations :-) You are trivilializing, ignoring 100 years or so of vertical antenna research, measurements and misleading innocent users of your program. You might be right in calculating the resonant frequency of piece of wire in the dirt, but that is far from its contribution to the vertical antenna performance and efficiency. You better switch to some better quality vino and read up on the subject. :-) Yuri K3BU |
Length & number of radials
NEC4 engine can accommodate on the ground or buried radials in
modeling and calculating vertical antenna parameters and performance. ======================================= How many weeks of user training does NEC4 require? Hour many hours of work and imagination are required to enter input data? What is the purchase price of the latest version? Is it legally available to non-USA citizens? ---- Reg, G4FGQ. |
Length & number of radials
Reg Edwards wrote: You've been reading books and magazines about rules-of-thumb written by old-wives. At 3.62 MHz and a radial length of 16 metres the attenuation approaches 100 decibels. So there's no current flowing in the radials beyond 5 metres. You can remove the excess 12 metres. They are not doing anything. What small current density there is beyond 5 metres is all flowing in the soil. The cross-sectional area of the soil carries the small current just as well as the radials. How did you verify your program Reg? I can go outside right now and measure current in a 40 meter vertical radial system, and 100 feet from the base there is significant radial current. Your programs results also dramatically disagree with Brown, Lewis, and Epstein's data in one of the most comprehensive radial studies ever done. 73 tom |
Length & number of radials
Your programs results also dramatically disagree with Brown, Lewis, and Epstein's data in one of the most comprehensive radial studies ever done. 73 tom ========================================= All three of B,L & E forgot to determine ground resistivity and permittivity. That's hardly comprehensive! ---- Reg. |
Length & number of radials
Reg Edwards wrote:
Your programs results also dramatically disagree with Brown, Lewis, and Epstein's data in one of the most comprehensive radial studies ever done. 73 tom ========================================= All three of B,L & E forgot to determine ground resistivity and permittivity. That's hardly comprehensive! Do your predictions fit BL&E's measurements, or those of Sevick, for *any* assumed values of ground resistivity and permittivity? Also , please tell us more about the fan of 1.0m radials, on the ground, that will give ninety-several percent feedpoint efficiency. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Length & number of radials
That is quite a bold statement and looks like trivilializing, ignoring the
real workings of vertical antennas and radials! What would NEC4 say? 73 Yuri, K3BU NEC 4 produces significantly different results. I can provide NEC code and NEC 4 output files if anybody is interested. 73, Frank (VE6CB) |
Length & number of radials
Not vouching for "degree of accuracy", but here's how I estimate efficiency:
(Known Rrad/Measured R at X=0) at the feedpoint. If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the R at resonance as 29 ohms, the 3.1 ohms is return loss. This would indicate an approximate efficiency of 89%. It seems to me to be a fair approximation. When you have added as many radials as possible and watched the input R at the feedpoint (at resonance) drop asymptotically toward the predicted or "known" Rrad, your final "R" value is used in: Rrad/R. For a perfect ground Rrad = R I use an MFJ-269 antenna analyzer for the measurements. Have I gone astray? (aside from my starting value of Rrad, which I took from two sources: your rule of thumb formula for Inverted L's, and ON4UN's Low Band DX'ing Handbook). Both your formula and ON4UN agree as to the value of Rrad for my antenna. I'll replay to other aspects of your response in another post. 73 and thanks for the new program. As you can tell, I've been playing with it. As you can also tell, the implications with respect to length of radials required for good efficiency are causing my brain to cramp. ....hasan, N0AN "Reg Edwards" wrote in message ... ========================================= Yes Hasan, good agreement. How did you determine efficiency to THAT degree of accuracy? ========================================= |
Length & number of radials
Frank,
How about posting a summary of them, for my example in an earlier post (I listed all the input values for Reg's program). I'd LOVE to have the data for my measurement verification!. If you need the my values I can send them to you for a run. I'd be very excited to see what NEC-4 says, and use them to validate my measurements. 73, ....hasan, N0AN "Frank" wrote in message news:NTLvg.147445$771.19250@edtnps89... That is quite a bold statement and looks like trivilializing, ignoring the real workings of vertical antennas and radials! What would NEC4 say? 73 Yuri, K3BU NEC 4 produces significantly different results. I can provide NEC code and NEC 4 output files if anybody is interested. 73, Frank (VE6CB) |
Length & number of radials
Reg,
I think you made a typo...if I go with the shorter 5 metre radials, I have enough wire to put in 66 more radials, not 20. If I stay with my existing 50' length per radial, then I have enough wire for 20 more. I have the wire. It won't be used for antennas. I have 200 more lawn staples, so there is no burying, they are "stapled" to the surface, soon to fall below the "thatch". My 1000' of copper wire has become too valuable to let sit on spools in the basement. (In case you haven't noticed, copper prices have gone through the roof!) So...I'll be putting down either (20) x 50 ft or (66) x 15 ft radials. Don't worry about my back. When you have a radial plate and a light hammer, stringing tons of radials is a piece of cake...paying for the copper (in the future) is going to generate pain elsewhere. 73, ....hasan, N0AN "Reg Edwards" wrote in message ... ========================================== Yes. Use the program to calculate efficiency with the extra 20 radials. Assume all the radials are 5 metres long. But you may not think the meagre 3% or 0.13dB in efficiency is worth all the labour and back-ache. By now you are beginning to appreciate how useful the program is. ========================================== .. ========================================== Hasan, if I were you I would lay some extra short radials between the existing long radials - and get some Sloan's liniment to be massaged into my back. But the increase in efficiency would be un-measurable. You are fortunate to have very low soil resistivity. Mine is about 70 ohm-metres and for years on the 160m band I have had 7 radials about 3 metres long plus an incoming lead water pipe. ---- Reg, G4FGQ |
Length & number of radials
Frank,
How about posting a summary of them, for my example in an earlier post (I listed all the input values for Reg's program). I'd LOVE to have the data for my measurement verification!. If you need the my values I can send them to you for a run. I'd be very excited to see what NEC-4 says, and use them to validate my measurements. 73, Hasan, I ran a sample model from Cebik's 2nd book, and compared it with results from Reg's program. The antenna used in the example is a 160 m vertical, with four buried radials. The height of the vertical is 40 m, and the radial lengths are 40.95526 m. The diameter of the vertical section is 25 mm, and the radials 2 mm. Ground Er = 20, and conductivity 30.3 mS/m (33 ohm-m). The radials are buried 0.163821 m (0.001 WL). The test frequency is 1.83 MHz. NEC 4 shows in input Z of 47.2 + j 14.44 ohms. Max gain 2.11 dBi at 17 degree elevation angle. At the moment I have not figured out how to obtain the total radiated power from NEC, other than the numerical integration of the normalized far field data. For a symmetrical pattern this is fairly trivial using Excel. The model does not include copper losses, so this should be added for accuracy. Reg's program computes the input impedance as 30.35 - j 53.1. I think I have all the data for your antenna from your previous post. There may be some difficulty in actually running it in NEC 4 with the parameters you have provided. The depth of the radials is so small (1mm), in relation to the wire diameter of 4 mm. Wire junctions must occur at Z = 0, and the wire diameter must be less than the segment length, which obviously cannot be met. Also segment length tapering would be required in order to keep the number of segments at a minimum, and avoid excessively long run times. In effect your radials are close enough to be considered laying directly on the surface of the ground. Cebik does imply this is acceptable in his book, but on his web site states that NEC 4 becomes unstable with wires in the region of Z = 0. I assume this also applies to wires below ground. Under certain conditions wires can approach the ground to within 10^(-6) Lambda (about 0.1 mm at 3.62 MHz). Based on these constraints I could develop a model, which will probably be close enough. 73, Frank |
Length & number of radials
"Yuri Blanarovich" wrote in message
... Reg wrote among other stuff: You've been reading books and magazines about rules-of-thumb written by old-wives. At 3.62 MHz and a radial length of 16 metres the attenuation approaches 100 decibels. So there's no current flowing in the radials beyond 5 metres. You can remove the excess 12 metres. They are not doing anything. What small current density there is beyond 5 metres is all flowing in the soil. The cross-sectional area of the soil carries the small current just as well as the radials. ========================================== Yes. Use the program to calculate efficiency with the extra 20 radials. Assume all the radials are 5 metres long. But you may not think the meagre 3% or 0.13dB in efficiency is worth all the labour and back-ache. By now you are beginning to appreciate how useful the program is. ========================================== Reg, NEC4 engine can accommodate on the ground or buried radials in modeling and calculating vertical antenna parameters and performance. I bet Roy has his hair standing up, or perhaps still trying to recover from the "appreciation" of your program, unless he is still running calculations :-) You are trivilializing, ignoring 100 years or so of vertical antenna research, measurements and misleading innocent users of your program. You might be right in calculating the resonant frequency of piece of wire in the dirt, but that is far from its contribution to the vertical antenna performance and efficiency. You better switch to some better quality vino and read up on the subject. :-) Yuri K3BU Has anybody confirmed the "on-ground" accuracy of NEC 4? Cebik has published conflicting statements regarding this capability. Frank |
Length & number of radials
hasan schiers wrote: Not vouching for "degree of accuracy", but here's how I estimate efficiency: (Known Rrad/Measured R at X=0) at the feedpoint. If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the R at resonance as 29 ohms, the 3.1 ohms is return loss. This would indicate an approximate efficiency of 89%. Hi Hasan, Roy Lewallen and I just measured some ground systems. Actual measurements using good instruments, not guesses or models. In one case we had an antenna with four elevated radials that within measurement error (using lab type gear) had equal signal strength level as the very same vertical element over 16 buried radials. As I recall the buried radials had over 60 ohms of base impedance, the six foot high elevated radials was down around 40 ohms or less. Over the years I have measured many antenna with very low base impedance and terrible efficiency, I have measured verticals where changing the ground system did not change impedance but improved field strength, and it is very easy to find cases where changes in a ground system can have MORE efficiency with higher feed impedance without changing anything but the ground system. Over simplification of a complex system will often not produce reliable results. Just look at the results of Reg's progam where it predicts highest efficiency with very short radials. We all know that doesn't happen, but the oversimplified program says it does. 73 Tom |
Length & number of radials
"Ian White wrote please tell us more about the fan of 1.0m radials, on the ground, that will give ninety-several percent feedpoint efficiency. ========================================== Ian, you must have had no experience of a few short radials. Try 16 or 32 radials, 1 or 2 metres long, in good soil, with a 1/4 or 3/8-wave vertical or inverted-L antenna. Radiating and receiving efficiency will surprise you. Also at all higher frequencies. At your new QTH you may not find much good soil. But try it anyway. Or persuade someone else to try it. I managed for many years with 7 radials 2 metres long, covering an angle of only 90 degrees. Soil resistivity was only 70 ohm-metres. Unfortunately, had to abandon it when the garden was turned into a patio. Damned concrete! ---- Reg. |
Length & number of radials
Reg Edwards wrote: Try 16 or 32 radials, 1 or 2 metres long, in good soil, with a 1/4 or 3/8-wave vertical or inverted-L antenna. Radiating and receiving efficiency will surprise you. Also at all higher frequencies. That sounds like scientific validation of a program or theory, compared to all the work Brown, Lewis, and Epstein did with field strength meters. Maybe that's where S units came from? S-urprise units? At your new QTH you may not find much good soil. But try it anyway. Or persuade someone else to try it. ....and they will be able to quantify what? Emotions? I managed for many years with 7 radials 2 metres long, covering an angle of only 90 degrees. Soil resistivity was only 70 ohm-metres. Unfortunately, had to abandon it when the garden was turned into a patio. Damned concrete! I managed with a ground rod. I managed 12 dB better with radials. Who was it that said if you can put a number on it you don't understand it? Someone in England I think. 73 Tom |
Length & number of radials
NEC4 engine can accommodate on the ground or buried radials in modeling and calculating vertical antenna parameters and performance. ======================================= How many weeks of user training does NEC4 require? Hour many hours of work and imagination are required to enter input data? What is the purchase price of the latest version? Is it legally available to non-USA citizens? ---- Reg, G4FGQ. ====================================== What! - after 2 days - no reply? The silence is deafening! ---- Reg, G4FGQ |
Length & number of radials
Hi Tom,
I understand there are measurement issues (and certainly assumption issues for Rrad). Isn't is fairly certain that increasing the number of radials (of proper length) until the feedpoint R (at resonance, at the antenna) no longer drops, is a reasonable approximation of "high efficiency"? The only issue I see, is determining the target Rrad to compare it to when trying to "estimate" efficiency. Are you saying (for example), that the feedpoint R of a 1/4 w vertical against perfect ground cannot be reliably estimated at 37 ohms? If it can, then isn't 37/R a measure of efficiency? Again, I'm thinking of the efficiency of the ground system... I have no way to look at field strength. Is it really possible to reduce ground losses to the absolute minimum and not have a corresponding increase in field strength? This is starting to turn into "black magic" for me. I can understand questioning a particular "number" for efficiency based on the simplistic Rrad/R formula. If the implications go further...indicating there is no meaning to Rrad/R, then I'm lost. Perhaps the issue is that it's known how to maximize efficiency, it's just completely unknown what that efficiency really is, and there is no simple way to measure it. If that's what your saying, then I understand. That position does seem to muddy up the "how many radials and of what length" efficiency info presented in ON4UN's book and referenced in other texts. They all seem to acccept some sort of accuracy for the Rrad/R formula with 1/4 w verticals. If I understand you correctly, the formula is rejected outright as hopelessly simplistic, and of no particular value. Do I have it now? If so, I'll refrain from using it in the future. Thanks for the comments. 73, ....hasan, N0AN wrote in message ups.com... hasan schiers wrote: Not vouching for "degree of accuracy", but here's how I estimate efficiency: (Known Rrad/Measured R at X=0) at the feedpoint. If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the R at resonance as 29 ohms, the 3.1 ohms is return loss. This would indicate an approximate efficiency of 89%. Hi Hasan, Roy Lewallen and I just measured some ground systems. Actual measurements using good instruments, not guesses or models. In one case we had an antenna with four elevated radials that within measurement error (using lab type gear) had equal signal strength level as the very same vertical element over 16 buried radials. As I recall the buried radials had over 60 ohms of base impedance, the six foot high elevated radials was down around 40 ohms or less. Over the years I have measured many antenna with very low base impedance and terrible efficiency, I have measured verticals where changing the ground system did not change impedance but improved field strength, and it is very easy to find cases where changes in a ground system can have MORE efficiency with higher feed impedance without changing anything but the ground system. Over simplification of a complex system will often not produce reliable results. Just look at the results of Reg's progam where it predicts highest efficiency with very short radials. We all know that doesn't happen, but the oversimplified program says it does. 73 Tom |
Length & number of radials
"Reg Edwards" wrote in message
... NEC4 engine can accommodate on the ground or buried radials in modeling and calculating vertical antenna parameters and performance. ======================================= How many weeks of user training does NEC4 require? Hour many hours of work and imagination are required to enter input data? What is the purchase price of the latest version? Is it legally available to non-USA citizens? ---- Reg, G4FGQ. ====================================== What! - after 2 days - no reply? The silence is deafening! ---- Reg, G4FGQ NEC 4 can be easily used in a few hours with some reading. To really understand the program would probably require the equivalent a 3rd year university semester. The program can, however model an infinite number of antenna designs. Inputting data is relatively trivial. NEC 4.1 is free, but does require the purchase of a license from the Lawrence Livermore National Laboratory. The cost of a license for non-commercial use is $500.00, and is available to those living outside the USA. For US residents the license is $300. For much easier data entry, and error checking etc., GNEC, from Nittany Scientific makes life a lot simpler -- cost $795. Frank |
Length & number of radials
I understand there are measurement issues (and certainly assumption
issues for Rrad). Isn't is fairly certain that increasing the number of radials (of proper length) until the feedpoint R (at resonance, at the antenna) no longer drops, is a reasonable approximation of "high efficiency"? The only issue I see, is determining the target Rrad to compare it to when trying to "estimate" efficiency. Are you saying (for example), that the feedpoint R of a 1/4 w vertical against perfect ground cannot be reliably estimated at 37 ohms? If it can, then isn't 37/R a measure of efficiency? Again, I'm thinking of the efficiency of the ground system... I have no way to look at field strength. Is it really possible to reduce ground losses to the absolute minimum and not have a corresponding increase in field strength? This is starting to turn into "black magic" for me. I can understand questioning a particular "number" for efficiency based on the simplistic Rrad/R formula. If the implications go further...indicating there is no meaning to Rrad/R, then I'm lost. Perhaps the issue is that it's known how to maximize efficiency, it's just completely unknown what that efficiency really is, and there is no simple way to measure it. If that's what your saying, then I understand. That position does seem to muddy up the "how many radials and of what length" efficiency info presented in ON4UN's book and referenced in other texts. They all seem to acccept some sort of accuracy for the Rrad/R formula with 1/4 w verticals. If I understand you correctly, the formula is rejected outright as hopelessly simplistic, and of no particular value. Do I have it now? If so, I'll refrain from using it in the future. I had always assumed that a NEC model of a perfectly conducting monopole above a perfect ground would provide the radiation resistance. For example, considering your antenna of 18.3 m at 3.62 MHz, the input impedance is 27.5 - j 64.7. The radiation resistance would therefore be 27.5 ohms. This appears to be fairly close to your estimate of 25.4 ohms. Frank |
Length & number of radials
Frank's wrote:
I had always assumed that a NEC model of a perfectly conducting monopole above a perfect ground would provide the radiation resistance. For example, considering your antenna of 18.3 m at 3.62 MHz, the input impedance is 27.5 - j 64.7. The radiation resistance would therefore be 27.5 ohms. This appears to be fairly close to your estimate of 25.4 ohms. If the field strength coordinates were the same for a perfect antenna model and a real-world antenna model, would the ratio of the areas under the curves yield the simulated efficiency of the real-world model? -- 73, Cecil, http://www.qsl.net/w5dxp |
Length & number of radials
"hasan schiers" wrote in message ... Not vouching for "degree of accuracy", but here's how I estimate efficiency: (Known Rrad/Measured R at X=0) at the feedpoint. If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the R at resonance as 29 ohms, the 3.1 ohms is return loss. This would indicate an approximate efficiency of 89%. It seems to me to be a fair approximation. When you have added as many radials as possible and watched the input R at the feedpoint (at resonance) drop asymptotically toward the predicted or "known" Rrad, your final "R" value is used in: Rrad/R. For a perfect ground Rrad = R I use an MFJ-269 antenna analyzer for the measurements. Have I gone astray? (aside from my starting value of Rrad, which I took from two sources: your rule of thumb formula for Inverted L's, and ON4UN's Low Band DX'ing Handbook). Both your formula and ON4UN agree as to the value of Rrad for my antenna. I'll replay to other aspects of your response in another post. 73 and thanks for the new program. As you can tell, I've been playing with it. As you can also tell, the implications with respect to length of radials required for good efficiency are causing my brain to cramp. ...hasan, N0AN "Reg Edwards" wrote in message ... ========================================= Yes Hasan, good agreement. How did you determine efficiency to THAT degree of accuracy? ========================================= To Hassan et al, In all my programs, where antennas are involved, accuracy of results is usually better than than that needed for the purpose of the program. In the case of RADIAL_3 the obvious purpose of the program is to assist with choosing an economic length and number of radials to be used with a given test antenna height. It is also educational in that after reading the introductory notes and using it, the user will have a better understanding of how radials work. To summarise, the program tells the user the maximum economic radial length occurs when the attenuation along it is about 18 to 20dB at the lowest frequency of use. But where his back yard is not big enough, even shorter lengths can be quite satisfactory. At HF, where small standing waves may occur with normal soils, radial lengths can sometimes be judiciously adjusted to minimise loss. To increase efficiency when the 20dB limit has been reached it is necessary to increase the number of radials. And that is subject to rapidly diminishing returns. As is easily and adequately demonstrated by the program. Prediction accuracy can be no better than that of the input data. And nobody knows what the soil resistivity is in the near field, ie., under the antenna, to better than + or - 40 or 50 percent. That's why NEC4 and the like (or B,L&E) can be no better at predicting results than RADIAL_3. NEC4 may be highly accurate at predicting radiation patterns in a hoped-for ideal environment but that is NOT the purpose of RADIAL_3 which is essentially practical. If I published the source code hardly anybody would be capable of making any sense out of it. Some of you old-wives, who imagine you know more about modelling and programming than I do, would attempt to ridicule it, thus degrading its usefulness to the ordinary amateur user. Mud-throwing always sticks. In the meantime, WW3 is escalating with even greater rapidity! ---- Reg, G4FGQ |
Length & number of radials
Hi Frank,
I think the general question became "can one use this Rrad value in calculating efficiency". I'm waiting for Tom's response to my last posting. On the other issue, radial length vs. usefulness, (I tried a diect mail to you and it didn't make it cuz I forgot to take out the nospam part), here is what I want to know from NEC-4: Radial wire is #14 THHN inslulated wire. I approximated it at 2mm. The antenna wire is 4 mm. For these purposes, you can probably forget that the wire is insulated. Now...looking at radial length (assuming 26 radials), and given the constants I previously provided, how long does a radial in this configuration have to be, before it is no longer valuable to increase its length. Tom says he measured significant current in a radial well beyond where Reg's program says the current had diminished to insignifcant levels. I would be MOST interested if you can confirm Tom's measurements. If NEC-4 says there is substantial radial current where Reg's program says there isn't, then that is an important contradiction, putting Reg's model into question. I'm giving more credibility to NEC-4 (properly used) than I am to Reg's own design. If, however, we have two sources (one measurement based: Tom, one model based: NEC-4), that say Reg's theory that radials quickly approach maximum effectiveness over a MUCH shorter run than has been previously understood (in moderate to very good soils), that contradict Reg's algorithim. Having only looked at conclusions from BL&E, I can't say what their measurements indicated in terms of radial current vs. length. Ian has suggested that they did measure the radial current vs length and they concur with Tom. So, if BL&E and Tom (both empirical), as well as NEC-4 (model based), all say that important levels of current are present in radials well beyond where Reg's program predicts, then there's only one conclusion left. (Unless I'm missing something). This, to me, is much more interesting stuff than a month long peeing contest over precipitation static.(which may be rearing its ugly head yet again in the "double bazooka" thread. God help us! 73, and thanks for your comments and efforts to help me understand what is going on. ....hasan, N0AN "Frank's" wrote in message news:ZO5wg.115459$A8.61548@clgrps12... I understand there are measurement issues (and certainly assumption issues for Rrad). Isn't is fairly certain that increasing the number of radials (of proper length) until the feedpoint R (at resonance, at the antenna) no longer drops, is a reasonable approximation of "high efficiency"? The only issue I see, is determining the target Rrad to compare it to when trying to "estimate" efficiency. Are you saying (for example), that the feedpoint R of a 1/4 w vertical against perfect ground cannot be reliably estimated at 37 ohms? If it can, then isn't 37/R a measure of efficiency? Again, I'm thinking of the efficiency of the ground system... I have no way to look at field strength. Is it really possible to reduce ground losses to the absolute minimum and not have a corresponding increase in field strength? This is starting to turn into "black magic" for me. I can understand questioning a particular "number" for efficiency based on the simplistic Rrad/R formula. If the implications go further...indicating there is no meaning to Rrad/R, then I'm lost. Perhaps the issue is that it's known how to maximize efficiency, it's just completely unknown what that efficiency really is, and there is no simple way to measure it. If that's what your saying, then I understand. That position does seem to muddy up the "how many radials and of what length" efficiency info presented in ON4UN's book and referenced in other texts. They all seem to acccept some sort of accuracy for the Rrad/R formula with 1/4 w verticals. If I understand you correctly, the formula is rejected outright as hopelessly simplistic, and of no particular value. Do I have it now? If so, I'll refrain from using it in the future. I had always assumed that a NEC model of a perfectly conducting monopole above a perfect ground would provide the radiation resistance. For example, considering your antenna of 18.3 m at 3.62 MHz, the input impedance is 27.5 - j 64.7. The radiation resistance would therefore be 27.5 ohms. This appears to be fairly close to your estimate of 25.4 ohms. Frank |
Length & number of radials
NEC 4 can be easily used in a few hours with some reading. To
really understand the program would probably require the equivalent a 3rd year university semester. The program can, however model an infinite number of antenna designs. Inputting data is relatively trivial. NEC 4.1 is free, but does require the purchase of a license from the Lawrence Livermore National Laboratory. The cost of a license for non-commercial use is $500.00, and is available to those living outside the USA. For US residents the license is $300. For much easier data entry, and error checking etc., GNEC, from Nittany Scientific makes life a lot simpler -- cost $795. Frank ====================================== Thank you very much Frank. ---- Reg, G4FGQ |
Length & number of radials
"Reg Edwards" wrote in message ... In the case of RADIAL_3 the obvious purpose of the program is to assist with choosing an economic length and number of radials to be used with a given test antenna height. It is also educational in that after reading the introductory notes and using it, the user will have a better understanding of how radials work. I understand that Reg, but somewhere in all this an important consideration is being lost. The issue isn't +/- some questionable percentage of accuracy, it is the underlying assumption in the model you are using to arrive at the "much shorter than everyone else's radial length". You have to admit, predicting 90% efficiency with 5 metre long radials (26 in my example) is stunning...given BL&E, Tom's measurements, and the yet to be run NEC-4 analysis. We aren't talking small differences here, we are talking NIGHT and DAY in terms of length. It really is this simple: Your program predicts neglible current at distances greater than 5 metres in the example being discussed. Your program says that any further lengthing is borderline useless. Tom's measurements completely disagree. BL&E, I am told (I haven't read that section) also completely disagree. I'm waiting to see what NEC-4 says. They key is this: are their ANY soil conditions wherein your model of 5 metre long radials (26 of them) will agree with the existing experimental data, or NEC-4 modeled data? If not, then the "radial as transmission line" model fails, and should not be used. If one doesn't get the 20 to 25 dB of attenuation within the radial length limits your program predicts, then the program is in error and will lead to false conclusions...not just "inaccuracies", outright major errors. I would love to put in 66 radials 5 metres long and know that they work every bit as well as 66 radials 18 metres long. It would save a lot of money in copper and extra lawn staples. If, on the other hand, your model is wrong, then a lot of work has been done for next to nothing. If the purpose of the program is to help in this process, the program must be trustworthy in its MAJOR assertions. ================================================== ===== We need to know: does the predicted attenuation of current along a radial wire happen as quickly as you predict? This can be measured. This can be modeled. That's what makes this fun. Let's find out. Let's see what agrees with what and what doesn't. Then we can conjecture as to why, and which approach is to be "believed". ================================================== ====== I'm not denigrating your work. I have all your programs and play with many. I have found several to be wonderfully useful. However, when something is called into question, I'm just not religious in scientific matters. Even the Qur'an says, "Bring your proof, if ye are truthful." (sorry, I couldn't resist) 73, ....hasan, N0AN |
Length & number of radials
On Fri, 21 Jul 2006 16:24:49 +0100, "Reg Edwards"
wrote: If I published the source code hardly anybody would be capable of making any sense out of it. Hi Reggie, This posted foolishness was too hard to pass up. It is a superlative example of the scope of your trolling skills when you troll yourself. Imagine, writing code so poorly to blame the readers' comprehension when you yourself are the source of that shoddy effort? This is classic playing both sides against the middle. I have to ask, is it written in sonnet form in middle English? This blighted artwork of yours must come from the bottom of a bottle in comparison to other code you've written. Of course, lacking that source, we must accept your own dismal appraisal. Some of you old-wives, who imagine you know more about modelling and programming than I do, And this from someone who claims wholesale ignorance with modeling and has just admitted to the worst of programming skills. ;-) would attempt to ridicule it, thus degrading its usefulness to the ordinary amateur user. Reggie, your ridicule has already surpassed all imagined critics. Mud-throwing always sticks. Wash your hands before opening that next bottle. 73's Richard Clark, KB7QHC |
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