[TowerTalk] Re: One more ground radial question

[Jan Erik Holm]

Yes excactly, that´s the question.
One example: I remember once when I was attending a
antenna seminar at the Swedish Telecom one antenna
guru professor was talking about how vertical antennas
worked, in this case example was a VHF vertical. Usually
VHF verticals was constructed with 4 ground planes (or rods).
Now this professor said that 2 groundplanes was enough and
the other two was just waist of material, i e the antenna
would still produce a uniform pattern, we are now talking
about a vertical antenna many many wl above ground so near
field is not an issue.
If this is true it looks like decreasing near field loss
in the desired direction of radiation would be a good idea,
i e adding more radials in that direction, however I have
never seen any measurements to confirm this.

73 Jim SM2EKM
----------------------------------------

Jim Lux wrote:

> 
> Interesting point you raise...
> 
> In the near field, the radials are mostly there to provide a "return 
> path" or image for the current in the vertical.  The question would be 
> whether that "image" gets bent or warped if the radials are not evenly 
> spaced.  Since they are, by geometry, very much closer than 1/4 
> wavelength apart, there's a lot of mutual interaction, and one would 
> intuitively expect the current to adjust itself to be even (spread over 
> all the available radials)..
> 
> Example.. if you had 20 radials over 180 deg, and 40 radials over the 
> other 180 deg, the current in each radial on the 20 side would be twice 
> that on the 40 side, but, the virtual image formed below the radials 
> will probably be exactly the same.  There's probably some limit (for 
> instance, if the radials are exactly tuned, and there's not many of 
> them, so they aren't strongly coupled to each other)
> 
> 
> 
> At 06:16 PM 12/18/2003 +0100, Jan Erik Holm wrote:
> 
>> Yes but 4 wl long you will start to "modify" the
>> far field and brewster angle would get smaller.
>> What you then did would not be relevant for anything
>> but your QTH, i e your type of far field...conductivity
>> etc etc.
>> If we consentrate only on the near field I still
>> wounder if you really can benefit much from haveing
>> more radials in one direction (i e 5 or 10 degree sector
>> forexample), I´m not convinced.
>> If so you could stretch the example further. Lets say
>> someone just likes to work one direction, he then
>> puts lets say 90% of the radials in that direction,
>> well well....no I´m not convinced.
>>
>> 73 Jim SM2EKM
>> -------------------------
>>
>> Richard Karlquist wrote:
>>
>>> I put up a 20 meter vertical with closely
>>> spaced radials 4 wavelengths long spread over about
>>> 60 degrees centered on Europe.  I A/B'ed it
>>> with an ordinary vertical.  The vertical with the
>>> long radials had an advantage of perhaps 3 dB
>>> vs the ordinary vertical toward Europe (a
>>> just discernable difference).  In other directions,
>>> it had no advantage.  Not what I would call
>>> gangbusters.
>>> Rick N6RK
>>> (A report on this and other vertical experiments
>>> is on my web site www.n6rk.com)
> 
> 
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