Topband: Modeling the proverbial vertical on a beach
Guy Olinger wrote: Just to mention that the prior opinion is controversial and not universally agreed upon. Nor to date has anyone surfaced with actual measurements made at the distances (25 to 50 km) and with span of altitudes (0 to 10 km) to either prove or disprove either side. Not exactly as described in the quote above, but below is a link comparing the real-world groundwave fields measured by a consulting engineer using a calibrated field intensity meter (bottom of that page) with fields calculated later by NEC for those same conditions (top of the page). Agreement is quite good. The fields calculated by NEC include the surface wave, and do not go to zero in the horizontal plane as they would for a NEC far-field analysis excluding the surface wave. Arguments on both sides remain basically intuitive. In January 2012, Jerry Burke of LLNL (co-author of NEC2/4) and I exchanged some e-mail bearing on this discussion. I sent him a NEC plot of field intensity vs distance similar to the one I linked earlier in this thread, and asked, Also, would you expect the fields at elevation angles of 1 to 10 degrees in these plots to continue on to the ionosphere, and under the right conditions be reflected back to the earth as skywaves? J. Burke response: The low angle 1/R fields should reach the ionosphere, although perhaps not accurately predicted by NEC, since it does not include the effects of earth curvature and the ionosphere. The near field in NEC (NE) and the surface wave (RP1...) include the 1/R field that is given by the Fresnel reflection coefficients and goes to zero at the interface and also higher order terms for the surface wave. The formulas that NEC uses are similar to the Norton formulas, but are derived directly from an asymptotic analysis. Norton has some terms that make them more accurate at moderately close distances at the expense of fixed errors for large distances, while NEC should get increasingly accurate as distance increases (except for neglecting earth curvature). The NEC study I attached to his e-mail and the one I linked in my post of Sat, 9 Aug 2014 18:23:58 -0500 in this thread do not consider the reflections produced at/by the ionosphere, and the path distance is so short that earth curvature is nil. (I requested and received J. Burke's permission to publicly quote his comments to me shown above.) http://s20.postimg.org/oo0j2dur1/Measured_vs_NEC2_D_Fields2.jpg _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling the proverbial vertical on a beach
Just an observation to all: When Tom, N6BT went to Jaimaca and operated 6Y2J (I think was the call) with verticals on the beach I was blown away. I heard them 2 hours before Sunset here on 160nuff said. The proof is in the pudding. 73 N7RT - Original Message - From: Guy Olinger K2AV k2av@gmail.com To: Richard Fry r...@adams.net Cc: TopBand List topband@contesting.com Sent: Saturday, August 09, 2014 8:35 PM Subject: Re: Topband: Modeling the proverbial vertical on a beach Just to mention that the prior opinion is controversial and not universally agreed upon. Nor to date has anyone surfaced with actual measurements made at the distances (25 to 50 km) and with span of altitudes (0 to 10 km) to either prove or disprove either side. It remains unproven modelling from NEC at those distances either way. This situation may, alas, persist this way, because the precise subject resolution appears to be without benefit to any commercial interest and therefore without funds to pay for some pretty expensive experimenting involving precision measurements from aircraft. Additionally, there is considerable suspicion that moving from LF to MF in this general subject involves a ground modal change of some sort that would render 50x10 km measurments at 0.5 or 1 MHz unlike those at 2 MHz, rendering commercial measurements at low and possibly high BC of no value for extrapolation to ham use. Arguments on both sides remain basically intuitive. I have reasonable arguments to BOTH concur with Richard AND to not. NEC near field calculations over sea water at 50 km follow Richard's assertions, and the same over average ground does not. The model clearly thinks that 50 km over most types of ground slowly dissipates low angles resulting in the controversial notch in low angle elevation patterns. So NEC based modelling cannot be used as a proof text to decide an argument NEC has with itself. 73, Guy K2AV. On Sat, Aug 9, 2014 at 7:23 PM, Richard Fry r...@adams.net wrote: Just to note that the low-angle radiation produced by monopoles is not accurately shown by a NEC model/study that does not include the surface wave, regardless of whether one or two ground-plane media are specified in the model. Below is a link to a NEC study of the low-angle fields of a monopole __including the surface wave__ for three values of earth conductivity ranging from extremely good to very poor. The curves there all show maximum relative field in the horizontal plane. If the surface wave had not been included in these studies then all of those fields would have a zero value in the horizontal plane, and reduced fields at low angles just above the horizontal plane. Reality is that radiation leaving the monopole at elevation angles of at least 5 degrees decays at a 1/r rate. Therefore that radiation is a space wave which propagates in a ~ straight line to reach the ionosphere, where (with suitable conditions) it can return to the earth as a skywave. NEC analyses of a vertical monopole of 5/8-lambda and less, and not including the fields of the NEC surface wave do not recognize the radiation sector capable of producing the greatest single-hop skywave service range that can be provided by that monopole. http://s20.postimg.org/9xqgzu9d9/Monopole_Low_Angle_Radiation.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: 140' Self Support Tower-How to use for 160M?
OK,I hope a few Gurus come out of the woodwork on this. Given a 140' Self support Rohn SSTV starting with a 9N base (about 6' on a leg) section, a 20' high building 8' to the south of the tower approx 100X120', what are the possibilities to use this tower/setup to produce a good signal on Top Band? There is a pulley at 120' with a rope attached.A 105' crane for antenna work is available.Operating room for Transmitter is about 30' from the tower and inside the building so coax run is very short. Would you?:(A) Use pulley to support a wire antenna of what type?(B) Shunt feed Tower with a Gamma or Omega match and use a few elevated Radials at 20' non-symmetrical? However, you must lay the radials on the roof line or perimeter. Where is all this gray matter when I need it? All suggestions welcomed.ValN4RJ The #1 Worst Carb Ever? Click to Learn #1 Carb that Kills Your Blood Sugar #40;Don#39;t Eat This!#41; http://thirdpartyoffers.juno.com/TGL3141/53e803d9553883d92638st02vuc _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling the proverbial vertical on a beach
My point is if no one else is on, we really don't how other signals would be. It's like a drag race with just one car, or a pony show with one horse. - Original Message - From: Hardy Landskov n...@cox.net To: Tom W8JI w...@w8ji.com; TopBand List topband@contesting.com Sent: Sunday, August 10, 2014 9:08 PM Subject: Re: Topband: Modeling the proverbial vertical on a beach Tom, I was totallly not expecting any station from that direction, just thought I'd work a few locals with high incident angles before Sunset here. Then I heard the 6Y2 guys and it was amazing. He was the only station--no KV4FZ, NP4A, etc and certainly no EU at our time. Made me a believer in beach verticals. 73 N7RT - Original Message - From: Tom W8JI w...@w8ji.com To: TopBand List topband@contesting.com Sent: Sunday, August 10, 2014 5:20 PM Subject: Re: Topband: Modeling the proverbial vertical on a beach How was his signal compared to someone from a similar heading and distance at the same time who was not on the beach? - Original Message - From: Hardy Landskov n...@cox.net To: Guy Olinger K2AV k2av@gmail.com; Richard Fry r...@adams.net Cc: TopBand List topband@contesting.com Sent: Sunday, August 10, 2014 7:35 PM Subject: Re: Topband: Modeling the proverbial vertical on a beach Just an observation to all: When Tom, N6BT went to Jaimaca and operated 6Y2J (I think was the call) with verticals on the beach I was blown away. I heard them 2 hours before Sunset here on 160nuff said. The proof is in the pudding. 73 N7RT - Original Message - From: Guy Olinger K2AV k2av@gmail.com To: Richard Fry r...@adams.net Cc: TopBand List topband@contesting.com Sent: Saturday, August 09, 2014 8:35 PM Subject: Re: Topband: Modeling the proverbial vertical on a beach Just to mention that the prior opinion is controversial and not universally agreed upon. Nor to date has anyone surfaced with actual measurements made at the distances (25 to 50 km) and with span of altitudes (0 to 10 km) to either prove or disprove either side. It remains unproven modelling from NEC at those distances either way. This situation may, alas, persist this way, because the precise subject resolution appears to be without benefit to any commercial interest and therefore without funds to pay for some pretty expensive experimenting involving precision measurements from aircraft. Additionally, there is considerable suspicion that moving from LF to MF in this general subject involves a ground modal change of some sort that would render 50x10 km measurments at 0.5 or 1 MHz unlike those at 2 MHz, rendering commercial measurements at low and possibly high BC of no value for extrapolation to ham use. Arguments on both sides remain basically intuitive. I have reasonable arguments to BOTH concur with Richard AND to not. NEC near field calculations over sea water at 50 km follow Richard's assertions, and the same over average ground does not. The model clearly thinks that 50 km over most types of ground slowly dissipates low angles resulting in the controversial notch in low angle elevation patterns. So NEC based modelling cannot be used as a proof text to decide an argument NEC has with itself. 73, Guy K2AV. On Sat, Aug 9, 2014 at 7:23 PM, Richard Fry r...@adams.net wrote: Just to note that the low-angle radiation produced by monopoles is not accurately shown by a NEC model/study that does not include the surface wave, regardless of whether one or two ground-plane media are specified in the model. Below is a link to a NEC study of the low-angle fields of a monopole __including the surface wave__ for three values of earth conductivity ranging from extremely good to very poor. The curves there all show maximum relative field in the horizontal plane. If the surface wave had not been included in these studies then all of those fields would have a zero value in the horizontal plane, and reduced fields at low angles just above the horizontal plane. Reality is that radiation leaving the monopole at elevation angles of at least 5 degrees decays at a 1/r rate. Therefore that radiation is a space wave which propagates in a ~ straight line to reach the ionosphere, where (with suitable conditions) it can return to the earth as a skywave. NEC analyses of a vertical monopole of 5/8-lambda and less, and not including the fields of the NEC surface wave do not recognize the radiation sector capable of producing the greatest single-hop skywave service range that can be provided by that monopole. http://s20.postimg.org/9xqgzu9d9/Monopole_Low_Angle_Radiation.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com
