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" <km1h@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" <
> telegrapher9@gmail.com>
> To: "ZR" <zr@jeremy.mv.com>
> Cc: "Donald Chester" <k4kyv@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" <zr@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" <
>>> telegrapher9@gmail.com>
>>> To: "Donald Chester" <k4kyv@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" <telegrapher9@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 <k4kyv@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
>>>>
>>>>
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>>>>
>>>>
>>>>
>>> ______________________________**_________________
>> It is undesirable to believe a proposition when there is no ground
>> whatsoever for supposing it is true. — Bertrand Russell
>>
>>
>> -----
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>> Checked by AVG - www.avg.com
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>>
>>
>
_______________________________________________
It is undesirable to believe a proposition when there is no ground whatsoever
for supposing it is true. — Bertrand Russell
|