Topband: Ground mounted 1/2 and 1/4 wave verticals (was GAP) - A Hoot! - A "Dream"?

ZR zr at jeremy.mv.com
Mon Dec 17 21:40:36 EST 2012


I worked in one for several years testing my designs but this was at 2.4 and 
5.6GHz.

Long before that it was as a range tech for a defense contractor 
designing/building/installing military EME arrays of yagis as well as 
troposcatter antennas used during Vietnam. Sometimes the same yagi designs 
were used, just in different configurations.

It was all about measurement, measurement, measurement as the slightest 
inconsistency had to be examined, reasoned why, and solved. Over and over 
and over.

Carl

Carl
KM1H


----- Original Message ----- 
From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
To: "'DAVID CUTHBERT'" <telegrapher9 at gmail.com>; "'ZR'" <zr at jeremy.mv.com>
Cc: "'Donald Chester'" <k4kyv at hotmail.com>; <topband at contesting.com>
Sent: Monday, December 17, 2012 6:31 PM
Subject: RE: Topband: Ground mounted 1/2 and 1/4 wave verticals (was GAP) - 
A Hoot! - A "Dream"?


> Wouldn't it be something if we had a fully instrumented spherical anechoic
> chamber large to enclose a 160 m vertical, or inverted L or TEE  and their
> radial systems - and then we could answer some of these challenginq
> questions by MEASUREMENT?  !!!  :-)
>
> Charlie, K4OTV
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of DAVID
> CUTHBERT
> Sent: Monday, December 17, 2012 5:23 PM
> To: ZR
> Cc: Donald Chester; topband at contesting.com
> Subject: Re: Topband: Ground mounted 1/2 and 1/4 wave verticals (was GAP)
>
> Carl,
>
> What we do in the near-field to control ground loss affects the far-field
> signal equally at all elevations. Therefore there is no need to measure
> far-field field strength at more than one elevation.
>
> We have control of the near-field and anything we do in that region shows 
> up
> as a change in input impedance.
>
> Dave WX7G
> On Dec 17, 2012 3:08 PM, "DAVID CUTHBERT" <telegrapher9 at gmail.com> wrote:
>
>> 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 at 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 at gmail.com>
>>> To: "Donald Chester" <k4kyv at hotmail.com>
>>> Cc: <topband at 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 at 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_dept
>>>>> h_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 at 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 at contesting.com
>>>>>>
>>>>>>
>>>>>
>>>>>  ______________________________**_________________
>>>> Topband reflector - topband at 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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