Carl, why would we need a helicopter when we have simulation software? How much ground loss, or if you prefer, what difference in field strength do you calculate for a half wavelength vertical with a gnd rod vs a full radial field?
Dave WX7G On Dec 17, 2012 4:00 PM, "Carl" <k...@jeremy.mv.com> wrote: > You did absolutely nothing useful that I remember reading so far. > > Get a helicopter and get real data. Or ask Richard Fry for his plots. > > Carl > KM1H > > > ----- Original Message ----- From: "DAVID CUTHBERT" < > telegraph...@gmail.com> > To: "ZR" <z...@jeremy.mv.com> > Cc: "Donald Chester" <k4...@hotmail.com>; <topband@contesting.com> > Sent: Monday, December 17, 2012 5:08 PM > Subject: Re: Topband: Ground mounted 1/2 and 1/4 wave verticals (was GAP) > > > 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_****<http://www.antennasbyn6lf.com/**files/ground_skin_depth_and_**> >>>>> wavelength.pdf<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 >> >> >> ----- >> 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