Topband: GAP Vertical Question

[Grant Saviers]

I second this motion.  Nearly every day brings some new insights.

Thanks,

Grant KZ1W


On 12/17/2012 11:30 AM, Lew Sayre wrote:
> Yo,
>      Tom, et. al.  please do keep taking this seriously!  Most of us on this
> reflector do not have
> engineering degrees involving the physics of RF. However we do greatly
> enjoy developing systems
> to receive and fling RF energy into the ether and try desperately to follow
> the discussion here in order
> to improve both our hardware and the understanding of how it works.
>       Exercising the little grey cells in disciplines where I am minimally
> competent is enjoyable and adds to the
> operating experience in radio. Minimizing the magic in radio by showing how
> the tricks are done makes me a better magician..
>      Thanks to all those who contribute! I hope you all continue to do so in
> a professional manner.
>      73 and I remain,
>      Lew      W7EW
>
> On Mon, Dec 17, 2012 at 10:21 AM, Lennart M
> <lennart.michaelsson at telia.com>wrote:
>
>> Tom et al,'this a hobby, pse dont take it that seriously
>> 73
>> Len
>> SM7BIC
>>
>> -----Ursprungligt meddelande-----
>> Från: Topband [mailto:topband-bounces at contesting.com] För Tom W8JI
>> Skickat: den 17 december 2012 18:55
>> Till: topband at contesting.com
>> Ämne: Re: Topband: GAP Vertical Question
>>
>>> To work at its maximum efficiency a vertical needs a real ground
>>> system and the image is its fictitious counterpart to isotropic. Im
>>> oversimplyfing here so no need to pick nits.
>> Besides being untrue, that is confusing or misleading.
>>
>> 1.) Some verticals need no ground. What would also be true is that end-fed
>> antennas always require a counterpoise of some sort, because there always
>> has to be a second terminal of some type for the feedline to "push
>> against".
>>
>> 2.) The image is a shortcut tool used to allow longhand pattern
>> calculations. It is not used for efficiency, antenna descripition, or
>> actual
>> operation.
>>
>> 3.) dBi, on the other hand, is a reference condition for a field strength
>> ratio.
>>
>>> According to Kraus that image, mirror, or whatever you care to call it
>>> occurs at a distance from the base and at a mathematical relationship
>>> to where the current peak is on the vertical radiator.
>>>
>>> In the case of this half wave discussion the reflection occurs around
>>> .35 wave out unless you, or others, want to try and discredit Kraus.
>>> Thus radials do work with a 1/2 wave and "system" efficiency is
>>> dependent upon the actual ground and how well the radials perform.
>>> Since this forum is predominantly DX oriented I prefer to qualify the
>>> "system" efficiency by how well the main lobe extends between its peak
>>> and the ground. IOW those low angles needed for DX.
>> There is not wrong with what Kraus teaches. The problem comes when we
>> misunderstand or misapply what he teaches.
>>
>>> Using modeling it is easy to realize that significant degradation of
>>> the radiated field at the lower angles is very real.
>> I'm not sure models we use are all that meaningful at low angles on low
>> bands. They are OK on extended groundwave, and probably OK on upper HF.
>> They are, however, all we have.
>>
>>> Various verticals (mostly VHF/UHF) on tall buildings or towers are not
>>> subjected to those ground losses and place a strong signal at the
>> horizon.
>>
>> I'm not going to touch that one, other than to say ground losses for a
>> given
>> soil and condition are dependent of intensity of the electric, magnetic,
>> and
>> electromagnetic fields in a given volume of lossy media.
>>
>> This is why we can have moonbounce, even though losses in the moon's
>> surface
>> are horrible, and why moving an antenna up away from earth or distributing
>> the fields over a wider area by using more radials reduces loss.
>>
>> Where we create a misunderstanding or problem is when we ignore how it
>> works, and pretend all field intensities in a given volume of lossy media
>> are equal at all distances with all antennas.  When we do that, we get
>> false
>> ideas................such as half wave verticals have high loss without
>> large radial fields. If that was true, our horizontal half-wave dipoles 1/4
>> wave or more high would have poor efficiency without large counterpoise
>> fields below the dipole.
>>
>> 73 Tom
>>
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