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Program GRNDWAV4
It may be recalled I recently reported an error in program GRNDWAV3
which deals with groundwave propagation from a short vertical antenna versus frequency and type of terrain. Although the field strength at the receiving site was correctly computed, the available receiver input power was exactly 6 dB greater than it should be. The error was due to a misunderstanding of vertical antenna gain relative to an isotrope when mounted above a groundplane. It appears some of the learned text books are unclear on this point. My immediate problem was eventually sorted out by Roy and proved by EZNEC-type programs which are not interested in man-made notions about antenna gain and isotropes. The faulty program has now been replaced by program GRNDWAV4 which makes no use of antenna gains at either end of the path. Download it and delete the older version. I am grateful to Icelandic radio amateur, Villi, TF3DX for informing me of the error. He went back to fundamental principles to prove me wrong. I have no idea what aroused his suspicions and we are not in contact with each other at present. He said he intended to write a paper on the subject. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Program GRNDWAV4
"Reg Edwards" wrote in message
... It may be recalled I recently reported an error in program GRNDWAV3 which deals with groundwave propagation from a short vertical antenna versus frequency and type of terrain. Although the field strength at the receiving site was correctly computed, the available receiver input power was exactly 6 dB greater than it should be. The error was due to a misunderstanding of vertical antenna gain relative to an isotrope when mounted above a groundplane. It appears some of the learned text books are unclear on this point. My immediate problem was eventually sorted out by Roy and proved by EZNEC-type programs which are not interested in man-made notions about antenna gain and isotropes. The faulty program has now been replaced by program GRNDWAV4 which makes no use of antenna gains at either end of the path. Download it and delete the older version. I am grateful to Icelandic radio amateur, Villi, TF3DX for informing me of the error. He went back to fundamental principles to prove me wrong. I have no idea what aroused his suspicions and we are not in contact with each other at present. He said he intended to write a paper on the subject. ---- .................................................. ......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp Thanks Reg. My NEC2 agreed with your previous program, so do not know where I went wrong. Will try and figure it out. Regards, Frank |
Program GRNDWAV4
Thanks Reg. My NEC2 agreed with your previous program, so do not know where I went wrong. Will try and figure it out. Regards, Frank ========================================== Frank, The situation changes by the hour so I suggest you don't spend a great deal of time trying to sort things out. Either the program is in error or you have entered incorrect data. Or (see below) both you and I have the correct answer in the first place. From the situation at present we have :- It seems the numerous Bibles written by learned professors don't agree on the subject. Computer programs, whose results are falsely taken as being gospel truths, don't agree on the subject. The 'experts' who contribute to this newsgroup can't agree on the subject. But, from the frequency of arguments which result. this is perfectly normal. I remain as an innocent, neutral bystander, in danger of being unjustly accused of being a troll, whereas - All I need is an answer to my simple but essentially fundamental and practical question - "What is the voltage measured between the bottom end of a 1 metre high vertical antenna and ground, when the field strength is 1 volt per metre?" It goes without saying, a perfect ground is assumed, the antenna height is less than 1/4-wavelength and the radio wave is vertically polarised. Is the measured voltage 1 volt or is it 0.5 volts? There's a simple factor of 2 involved somewhere. Should I take a statistical average of the replies if there are any? What happens on an isolated dipole is irrevalant. It is just a time-wasting diversion. I don't have access to the 'learned Bibles' or to computer programs (except my own). So there is no point in referring to them. But I don't consider this to be any handicap. Short, logical, convincing explanations in plain English and perhaps a little arithmetic would be welcome of course. ---- Reg, G4FGQ. |
Program GRNDWAV4
As I said, I do not have access to the many ancient, learned volumes
about radio transmission and antennas. Or to the many computer programs. But I do recall mention of "Effective Height" of vertical antennas which has NOT been mentioned in the numerous prolonged threads on this newsgroup about the relationship between receiver input power and field strength. What "Effective Height" means may be vague. But some sort of a definition may be a clue to solving my problem. Don't mention Marconi, Terman, Kraus, Balani, et al., ---- Reg, G4FGQ |
Program GRNDWAV4
On Fri, 16 Dec 2005 17:57:08 +0000 (UTC), "Reg Edwards"
wrote: I remain as an innocent, neutral bystander, in danger of being unjustly accused of being a troll, whereas - .... There's a simple factor of 2 involved somewhere. Hmm, I asked a simple question involving your arbitrary use of a factor of two (2) and you dismissed it as my "anger," or somesuch clumsy diversion. Most of your correspondence has been tainted with trolling, what is different in this case? Sorry, that is now two (2) simple questions which, no doubt, you will find undecipherable. Don't worry, we are all capable of observing that given Richard H. directly responded to your question with a straight answer - your lack of returning to him puts this troll squarely at your doorstep. As for your observation (if it quacks like a troll...): Computer programs, whose results are falsely taken as being gospel truths, don't agree on the subject. it seems you are now the author of two (2) such programs that covers both sides of the argument. I suppose the chance of being 50% right outweighs the risk of being 100% wrong. ;-) That, of course, presumes an insecure perspective (which is validated by having two answers for any question - rather returns us to your typical trolls, doesn't it?). Lord Kelvinator is winding up another pitch to wing a chunk of railroad chalk off your noggin'. Watching you duck throughout these threads has become an amusing prospect. Thanx for the entertainment, Richard Clark, KB7QHC |
Program GRNDWAV4
Punchinello has no time to waste on drivel and says "phooey".
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Program GRNDWAV4
As I said, I do not have access to the many ancient, learned volumes
about radio transmission and antennas. Or to the many computer programs. But I do recall mention of "Effective Height" of vertical antennas which has NOT been mentioned in the numerous prolonged threads on this newsgroup about the relationship between receiver input power and field strength. What "Effective Height" means may be vague. But some sort of a definition may be a clue to solving my problem. Don't mention Marconi, Terman, Kraus, Balani, et al., ---- Reg, G4FGQ Repeating what was previously posted. The following model treats a 1 meter (perfect conductor) monopole, of 0.814 mm diameter, connected to a perfectly conducting ground. I have applied a vertically polarized incident E-field of 1 V/m (peak). The base of the antenna is loaded with the antennas complex conjugate of 1.747 + j823.796. NEC2 computes the current through the load ast 0.2863 Amps (peak), which is 0.5001 V peak. This appears to agree with Reg's program. Possibly someone can point out if there are any errors in the following code: CM 1 Meter Vertical CE GW 1 50 0 0 1 0 0 0 0.000814 GS 0 0 1 GE 1 GN 1 EX 1 1 1 0 90 0 0 1 1 1 LD 4 1 50 50 1.747 823.796 FR 0 3 0 0 19.9 0.1 RP 0 181 1 1000 -90 90 1.00000 1.00000 EN Regards, Frank |
Program GRNDWAV4
Hopefully my recent posting on the "Antenna reception theory" thread
will clarify things a bit. Roy Lewallen, W7EL Reg Edwards wrote: Frank, The situation changes by the hour so I suggest you don't spend a great deal of time trying to sort things out. Either the program is in error or you have entered incorrect data. Or (see below) both you and I have the correct answer in the first place. From the situation at present we have :- It seems the numerous Bibles written by learned professors don't agree on the subject. Computer programs, whose results are falsely taken as being gospel truths, don't agree on the subject. The 'experts' who contribute to this newsgroup can't agree on the subject. But, from the frequency of arguments which result. this is perfectly normal. I remain as an innocent, neutral bystander, in danger of being unjustly accused of being a troll, whereas - All I need is an answer to my simple but essentially fundamental and practical question - "What is the voltage measured between the bottom end of a 1 metre high vertical antenna and ground, when the field strength is 1 volt per metre?" It goes without saying, a perfect ground is assumed, the antenna height is less than 1/4-wavelength and the radio wave is vertically polarised. Is the measured voltage 1 volt or is it 0.5 volts? There's a simple factor of 2 involved somewhere. Should I take a statistical average of the replies if there are any? What happens on an isolated dipole is irrevalant. It is just a time-wasting diversion. I don't have access to the 'learned Bibles' or to computer programs (except my own). So there is no point in referring to them. But I don't consider this to be any handicap. Short, logical, convincing explanations in plain English and perhaps a little arithmetic would be welcome of course. ---- Reg, G4FGQ. |
Program GRNDWAV4
Frank wrote:
Repeating what was previously posted. The following model treats a 1 meter (perfect conductor) monopole, of 0.814 mm diameter, connected to a perfectly conducting ground. I have applied a vertically polarized incident E-field of 1 V/m (peak). The base of the antenna is loaded with the antennas complex conjugate of 1.747 + j823.796. NEC2 computes the current through the load ast 0.2863 Amps (peak), which is 0.5001 V peak. This appears to agree with Reg's program. . . . Possibly someone can point out if there are any errors in the following code: CM 1 Meter Vertical CE GW 1 50 0 0 1 0 0 0 0.000814 GS 0 0 1 GE 1 GN 1 EX 1 1 1 0 90 0 0 1 1 1 LD 4 1 50 50 1.747 823.796 FR 0 3 0 0 19.9 0.1 RP 0 181 1 1000 -90 90 1.00000 1.00000 EN You've specified a plane wave of 1 V/m peak arriving in a horizontal direction over a ground plane. This results in a field strength of 2 V/m peak at the antenna. For more information about this, look at my postings over the last couple of weeks on the thread "Antenna reception theory". Roy Lewallen, W7EL |
Program GRNDWAV4
On Sat, 17 Dec 2005 23:38:13 -0500, "J. Mc Laughlin"
wrote: I have dealt with approximations of the subject device. In each case, an extremely high input impedance amplifying device is placed at the base of the antenna that has a known voltage amplification and a 50 ohm output impedance. Knowing that a close approximation of the open circuit voltage is amplified by a known amount, a calibrated, tuned voltmeter (at 50 ohms) is able to measure the size of vertically polarized E (with the usual uncertainties). (and a bit of arithmetic) Hi Mac, I too, will jump in with alternatives to this short, thin rod feeding an infinite Z. It makes for a simple specification, but when the frequency begins to climb such is not very practical. Input Z's tend to be dominated with strays and that "short" rod begins to become enormous. Such artifacts of the MF era are quickly discarded. The NIST methods (NIST technical note numbers 1309 and 1098) employ resonant sized dipoles feeding a DC Hi R (and hence AC Hi Z load) at the gap of the elements. By DC Hi R, the detector filter employs 50KOhm components in a balanced cascading filter that in turn feeds a Hi R voltmeter through 250KOhm leads (carbon impregnated plastic conductors to decouple both loading and induction). Uncertainty, worst case, is 1dB. Schelkunoff's algorithm is used to find the length of the dipole (no real surprise here for halfwave length). The effective length is not half, but rather closer to 62 - 63%. 73's Richard Clark, KB7QHC |
Program GRNDWAV4
"Roy Lewallen" wrote in message ... Frank wrote: Repeating what was previously posted. The following model treats a 1 meter (perfect conductor) monopole, of 0.814 mm diameter, connected to a perfectly conducting ground. I have applied a vertically polarized incident E-field of 1 V/m (peak). The base of the antenna is loaded with the antennas complex conjugate of 1.747 + j823.796. NEC2 computes the current through the load as 0.2863 Amps (peak), which is 0.5001 V peak. This appears to agree with Reg's program. . . . Possibly someone can point out if there are any errors in the following code: CM 1 Meter Vertical CE GW 1 50 0 0 1 0 0 0 0.000814 GS 0 0 1 GE 1 GN 1 EX 1 1 1 0 90 0 0 1 1 1 LD 4 1 50 50 1.747 823.796 FR 0 3 0 0 19.9 0.1 RP 0 181 1 1000 -90 90 1.00000 1.00000 EN You've specified a plane wave of 1 V/m peak arriving in a horizontal direction over a ground plane. This results in a field strength of 2 V/m peak at the antenna. For more information about this, look at my postings over the last couple of weeks on the thread "Antenna reception theory". Roy Lewallen, W7EL Not sure I really understand what is going on, but have been aware of your previous postings, also on the NEC-list. What I should have said is that the above program agrees with Reg's previous assumption -- but not with his new program "grndwav4.exe". In any case, just to satisfy my curiosity, I ran the following code, which is, in essence, almost identical to your NEC-list post with 5.555.... kW input producing 1V/m peak at 1000m. The following agrees exactly with Reg's new program. CM Short Monopoles CE GW 1 50 0 0 1 0 0 0 0.000814 GW 2 50 1000 0 1 1000 0 0 0.000814 GS 0 0 1 GE 1 GN 1 EX 0 1 50 00 65698.12106 0.00000 LD 4 2 50 50 1.747 823.796 FR 0 3 0 0 19.9 0.1 RP 1 1 360 0000 0 0 1.00000 1.00000 1000 RP 0 181 1 1000 -90 45 1 1 EN Noting the comments by others, obviously familiar with ATR measurement techniques, this exercise with NEC is purely academic. There is no way you could experimentally prove these results. Since I have never made measurements on an "Open-air" test site it will be interesting to verify Mac's assumptions, which I am sure are correct. The confusions I have are now related to the fact that NEC results depend on how the incident E-field is generated. I will check all previous posting by Roy to see if I can figure out this anomaly. For some reason I have not received any update concerning the NEC list postings. Frank |
Program GRNDWAV4
Dear Richard:
I am obliged to you for your useful comments. In the large TEM cells that I use to about 200 MHz (with care above about 150 MHz) a very small probe is inserted through the roof of the cell. That probe is used, with the sort of processing you mentioned, to provide one verification of the E inside of the cell. (The other verification comes from measuring the power going in and coming out of the cell, and the internal dimensions.) The probe-scheme's success is helped by the fact that E can go up to 200 v/m (or more) so a lot of signal is available. Interesting things happen to some electronic equipment well before 200 v/m. A TEM cell with a spectrum analyzer can inform about what a device is radiating. Still, outdoors, a one meter rod over a large ground screen placed well clear of other structures provides the means to measure (with reasonable uncertainties) the low TOA vertical E field up to 20 or so MHz. A scheme that I saw at NBS circa 1975 (now NIST) to measure an estimate of total field uses orthogonal, very small doublets with diodes at their center. They received a patent on the idea. To bring the DC to a measuring device, lossy transmission lines were used so as to make the transmission lines "invisible" to the field. In other words, the step up from rod-and-screen is a big step. In my youth, I measured VHF signals propagated by FM broadcast stations in the "hills" of West Va. to enhance the VHF propagation models that then existed. The purpose was to be able to predict interference to a radio astronomy site. We used tuned dipoles elevated some standard distance that I do not remember. As many here have said: It is not easy to measure fields. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Richard Clark" wrote in message ... On Sat, 17 Dec 2005 23:38:13 -0500, "J. Mc Laughlin" wrote: I have dealt with approximations of the subject device. In each case, an extremely high input impedance amplifying device is placed at the base of the antenna that has a known voltage amplification and a 50 ohm output impedance. Knowing that a close approximation of the open circuit voltage is amplified by a known amount, a calibrated, tuned voltmeter (at 50 ohms) is able to measure the size of vertically polarized E (with the usual uncertainties). (and a bit of arithmetic) Hi Mac, I too, will jump in with alternatives to this short, thin rod feeding an infinite Z. It makes for a simple specification, but when the frequency begins to climb such is not very practical. Input Z's tend to be dominated with strays and that "short" rod begins to become enormous. Such artifacts of the MF era are quickly discarded. The NIST methods (NIST technical note numbers 1309 and 1098) employ resonant sized dipoles feeding a DC Hi R (and hence AC Hi Z load) at the gap of the elements. By DC Hi R, the detector filter employs 50KOhm components in a balanced cascading filter that in turn feeds a Hi R voltmeter through 250KOhm leads (carbon impregnated plastic conductors to decouple both loading and induction). Uncertainty, worst case, is 1dB. Schelkunoff's algorithm is used to find the length of the dipole (no real surprise here for halfwave length). The effective length is not half, but rather closer to 62 - 63%. 73's Richard Clark, KB7QHC |
Program GRNDWAV4
Frank wrote: Not sure I really understand what is going on, but have been aware of your previous postings, also on the NEC-list. What I should have said is that the above program agrees with Reg's previous assumption -- but not with his new program "grndwav4.exe". In any case, just to satisfy my curiosity, I ran the following code, which is, in essence, almost identical to your NEC-list post with 5.555.... kW input producing 1V/m peak at 1000m. The following agrees exactly with Reg's new program. CM Short Monopoles CE GW 1 50 0 0 1 0 0 0 0.000814 GW 2 50 1000 0 1 1000 0 0 0.000814 GS 0 0 1 GE 1 GN 1 EX 0 1 50 00 65698.12106 0.00000 LD 4 2 50 50 1.747 823.796 FR 0 3 0 0 19.9 0.1 RP 1 1 360 0000 0 0 1.00000 1.00000 1000 RP 0 181 1 1000 -90 45 1 1 EN Noting the comments by others, obviously familiar with ATR measurement techniques, this exercise with NEC is purely academic. There is no way you could experimentally prove these results. Since I have never made measurements on an "Open-air" test site it will be interesting to verify Mac's assumptions, which I am sure are correct. The confusions I have are now related to the fact that NEC results depend on how the incident E-field is generated. I will check all previous posting by Roy to see if I can figure out this anomaly. For some reason I have not received any update concerning the NEC list postings. I've just now finally gotten around to posting a response to the NEC-list. It might help clarify things for you. The essential point is that when you specify a plane wave source, it acts like a plane wave of the specified amplitude coming from the specified direction. That wave interacts with the ground plane just as any other field would. When a ground plane is specified, the result is a field strength -- and polarization -- which isn't generally the same as that of the original wave. You can illustrate this by specifying a plane wave which originates at an angle of 45 degrees above the horizon, and looking at the current induced in a short circuited vertical wire or the base voltage of an open circuited wire (the latter simulated by putting a high impedance load at the base). Begin with the wire vertical, then tilt the wire so the direction of the plane wave source is broadside to the wire, and again so the direction of the source is in line with the wire. You'll get the same result from the last two tests, and the induced current or voltage in those two is less (by about 1/sqrt(2)) than when the wire is vertical. This shows that the field is purely vertically polarized (normal to the ground plane) at the location of the wire. (I think there's actually a small horizontal component except exactly at the ground plane surface.) It does show conclusively that the orientation of the field isn't the same as it was when it left the source -- otherwise the induced current or voltage would be greatest when the wire was tilted broadside to the plane wave source and zero when tilted in the source direction. So the interaction of the plane wave source's field with the ground plane alters both the amplitude and the polarization of the field. When the source is in the horizontal direction and the ground plane is perfect, the field strength just above the ground plane is exactly twice the amplitude of the plane wave source. So a 1 V/m plane wave source at zero elevation angle (90 degree zenith angle) produces 2 V/m just above the ground plane, which induces 1 V at the base of an open circuited electrically short 1 m vertical wire. Roy Lewallen, W7EL |
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