Carl. I quantified ground loss in the near field. Now it's your turn. Numbers please, not adjectives or hand waving.
Dave WX7G On Dec 17, 2012 2:59 PM, "ZR" <z...@jeremy.mv.com> wrote: > Because youre still stuck in neutral and are measuring/calculating nothing > of interest. > > The loss is determined at various elevation angles at a sufficient > distance by field strength. > > Get a helicopter. > > Carl > KM1H > > > ----- Original Message ----- From: "DAVID CUTHBERT" < > telegraph...@gmail.com> > To: "Donald Chester" <k4...@hotmail.com> > Cc: <topband@contesting.com> > Sent: Monday, December 17, 2012 1:53 PM > Subject: Re: Topband: GAP Vertical Question > > > Where is the 40-60% claimed ground loss? >> >> I get 4%. >> On Dec 17, 2012 6:12 AM, "DAVID CUTHBERT" <telegraph...@gmail.com> wrote: >> >> *Half wavelength vertical ground loss* >>> >>> Let's see if we can quantify the conduction losses of a 1.8 MHz half >>> wavelength vertical connected to average earth via a ground rod. This >>> paper >>> by N6LF shows one skin depth at 1.8 MHz to be 6 meters. >>> >>> http://www.antennasbyn6lf.com/**files/ground_skin_depth_and_** >>> wavelength.pdf<http://www.antennasbyn6lf.com/files/ground_skin_depth_and_wavelength.pdf> >>> >>> Let's assume the current magnitude in the ground mirrors that of the >>> antenna. Driving the antenna at the base such that the current at the >>> antenna center is 1 amp, the ground current 40 meters away from the >>> antenna >>> is 1 amp. The 1 amp of ground current passes through a section of earth >>> having an effective depth of of 6 meters. For a 1 meter radial length and >>> 40 meters from the antenna the section has dimensions of 1 meter X 6 >>> meters >>> X 250 meters (250 meters is the circumference). Given a resistivity of >>> 200 >>> ohms/meter the resistance of this section is 200/(6 X 250) = 0.13 ohms. >>> The >>> loss in this section is 0.13 watts. Using NEC we see with the base >>> current >>> set to give 1 amp at the antenna center the power into the antenna is 100 >>> watts. >>> >>> Closer to the base of the antenna the effective ground resistance >>> increases due to the smaller circumference. Closer to the antenna the >>> current decreases. Roughly Integrating the ground loss from the base to >>> the >>> 80 meters away gives a total ground loss of 4 watts. The no-radial ground >>> loss is 5 watts and the antenna gain is reduced by 10LOG(100/96) = 0.2 dB >>> from the full radial case. >>> >>> How about ground loss due to the induced E-field in the ground? I believe >>> this is accounted for in the previous calculation. I ran a NEC simulation >>> to explore this. The two cases were a 266' vertical fed against thirty 3' >>> radials and thirty 133' radials. The radials are 0.05' above medium >>> ground. >>> The NEC Average Gain was compared for the two cases and showed a >>> difference >>> of 0.06 dB. >>> >>> Dave WX7G >>> >>> On Sun, Dec 16, 2012 at 6:42 PM, Donald Chester <k4...@hotmail.com> >>> wrote: >>> >>> >>>> Then, why do broadcast stations that use vertical towers at >>>> approximately >>>> a half wavelength, purchase valuable real estate and spend thousands of >>>> dollars for the copper to install from 120 to 240 or more radials, each >>>> usually a half wave or more in length? >>>> >>>> See G. H. Brown: "Ground Systems as a Factor in Antenna Efficiency", IRE >>>> Proceedings, June 1937 p. 753. Brown demonstrated that the >>>> distribution of >>>> earth currents and ground losses is such that the region of maximum >>>> current >>>> and loss occurs at a distance of about 0.35 wavelengths from the base >>>> of a >>>> ground mounted half wave vertical antenna, which was verified >>>> experimentally. >>>> >>>> There is zero loss at the base of the antenna itself, since there is no >>>> base current because the antenna a fed at a current node. An rf ammeter >>>> inserted in the ground lead, as well as one inserted in in the antenna >>>> lead >>>> attached to the insulated base of the radiator will read zero. The >>>> ground >>>> losses occur farther out from the base of the antenna. Low effective >>>> earth >>>> resistance provided by a good ground system is ABSOLUTELY NECESSARY for >>>> vertical antennas of ANY height if one expects good radiation >>>> efficiency. >>>> The claim that no ground system is needed for a half wave vertical is >>>> nothing more than a long-standing popular misconception. >>>> >>>> This topic prompted me to dig out and review an anecdote I recall >>>> reading >>>> in my decades-old copy of CQ magazine's Vertical Antenna Handbook, by >>>> USNR >>>> Capt. Paul H. Lee, K6TS (1974). He reported receiving mail from a ham >>>> who >>>> had made the "discovery" that he could tune and operate a half wave >>>> vertical without a ground system, feeding it by a parallel tuned tank >>>> circuit whose lower end is grounded. Since an rf ammeter in the ground >>>> lead showed no current, he could dispense with the ground system and its >>>> loss. He suggested to the Capt. that he should "discover the new world >>>> of >>>> half verticals with no ground system". >>>> >>>> Quoting from the text (p. 84): >>>> >>>> "The correspondent's claim... is true ONLY IF HE IS CONTENT TO THROW >>>> AWAY >>>> FROM 40 TO 80 PER CENT OF HIS RADIATED POWER IN THE FORM OF EARTH >>>> LOSSES. >>>> (the correspondent) stated, 'The ZL's call ME, when I use my half wave >>>> vertical!' This is not surprising, in view of the fact that the half >>>> wave's >>>> vertical pattern has a lower main lobe angle than a quarter wave would >>>> have... However, he would hit the ZL's even harder if he would put in a >>>> ground system. Of course, the half wave vertical is not dependent on a >>>> ground plane, however lossy or efficient, for the condition of >>>> RESONANCE, >>>> since it is resonant in itself because of its half wave length. However, >>>> IT IS DEPENDENT ON A GROUND PLANE FOR ITS EFFICIENCY OF RADIATION, as is >>>> any vertical antenna...' >>>> >>>> >>>> Don k4kyv >>>> >>>> >>>> >>>> >Given that a half wave vertical has a base impedance of over 1000 ohms >>>> and a single ground rod in dirt is 100 ohms at most not a single radial >>>> is >>>> needed to obtain close to 100% radiation >efficiency. >>>> >>>> > Dave WX7G >>>> >>>> >>>> >>>> > And this statement is based on what? Publications, measurements, >>>> > modeling? >>>> > >>>> > I have built a number of 1/2 wave verticals without radials and > >>>> compared >>>> > them to 1/4 wave verticals with radials. They are >>>> > indistinguishable in performance and certainly do not exhibit >>>> > substantial ground losses AFAIK... >>>> > >>>> > Rick N6RK >>>> >>>> >>>> >I can think of NO earthly reason,that makes ANY electromagnetic sense >>>> to me, as antenna engineer fo placing a radial system under the end >>>> of a >>>> vertical 1/2 wave antenna - "earth-worms" not >withstanding! >>>> >>>> >It's CURRENT that "warms the earthworms"! NOT electric field >>>> >intensity! >>>> >>>> >...the ground system does NOT act as a "shield" from the "lossy earth" >>>> nor protect the "earth-worms"! There is absolutely NO reason to require >>>> a >>>> radial system under a 1/2 wave vertical antenna. >>>> >Such an antenna will operate just fine on its own in free-space. >>>> >>>> >Consider this - to deliver 1000 watts to a 1/4 wave vertical with a >>>> REALLY GOOD ground system and a driving point impedance of say 40 ohms >>>> would require 5 amps of RF current delivered to the >antenna system and >>>> ground. Todeliver that same 1000 watts to an end-fed vertical of >>>> 2000-4000 >>>> ohms real would require an antenna current, at the fed endof 0.5 -0.7 >>>> amps! It's the CURRENT >that produces the losses in the "lossy earth" >>>> and >>>> "warms the earth worms". At worst, for the 1/2 wave end fed vertical - a >>>> simple ground rodshould be just fine, and the earth worms should be >>>> >quite >>>> comfortable, and the antenna will work VERY well!! Of course it will be >>>> 250-260 feet tall! >>>> >>>> >Charlie,K4OTV >>>> >>>> >>>> ______________________________**_________________ >>>> Topband reflector - topband@contesting.com >>>> >>>> >>> >>> ______________________________**_________________ >> Topband reflector - topband@contesting.com >> >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 10.0.1430 / Virus Database: 2637/5466 - Release Date: 12/17/12 >> >> > _______________________________________________ It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true. — Bertrand Russell