On Sat, 21 Mar 1998 17:07:47 -0600 philk5pc@connect.net (Phil Clements)
writes:
>At 01:21 PM 3/21/98 -0700, Eric wrote:
>
>
. IMO, it is also a given
>that the number of elevated radials will be more than 12 and less
>than 120 to do the same job as `120 buried radials.
Well more than 6 maybe and less than 60. At least if you are satisfied
for all but that last .5dB or so.
Interesting tho about the zero signal beneath the radials....how high
were they?
When you can
>walk around under the radial system and detect no presence of a 1kw
>signal being transmitted from the G.P., you have arrived at "radial
>nirvana!"
>
>
>>>I can understand with HF and VHF horizontal Yagis but not for a
>>>160M vertical. If rocky hilltops were superior then that is where
>>>the BCB towers would be.
>
>When I moved to Honolulu years ago, I asked why all the B.C. stations
>antennas were on the beach instead of atop those beautiful 4,000 foot
>hills. They said it was because a radial system would be impossible to
>construct on such steep terrain, and even if it weren't, a good
>portion of the listening audience would be 4,000 feet below the radial
>system and hear little or nothing.
Doesnt make sense to me...but the 4000' difference IS a bit much. If
those of us with simple 1/4 wave groundplanes at high elevations can work
into all the local low spots on 10M, 2M, etc , why not 160M? I suspect
it is NOT height but soil conductivity that is the deciding issue. Poor
soil (typical at hilltops) equals a high TOA and not ground wave. On the
higher bands the antenna base is up high enough to not be ground
dependent.
If I lived on a super conducting hill then the waves would combine at
some xxx distance away for a fine low TOA. Since that combining takes
place DOWN the hill it would then seem that the ground wave would also
somewhat follow the terrain....at least out from the point that the
waves reinforced.
I'm talking about simple hills...200-500' above the low points...not
monster mountains.
>>>I have a very simple question: With my soil AND terrain, what is
>>>the lowest TOA I can expect......with any # of radials? I
>>>suspect it is around 15 degrees or higher...per ON4UN and the
>>>ARRL ANtenna Manual.
>
>It has been well established on this thread and elsewhere that
>near-field changes have little to do with TOA. Only the height
>of the vertical radiator and the far-field affect TOA.
Near field (practical) changes ...NO; near field soil conditions YES.
That was established ages ago...or so it seems.
In my case I was asking about the far field terrain which drops off in
the usually accepted distances for field combining, cancellation, etc.
What CAN I expect there at several hundred feet below the antenna? So far
no one has answered the question of sloping terrain....just textbook flat
terrain models.
I already accept that my TOA is around 15 degrees....with 1mS/M soil
that is all I can expect.
>
>The soil conductivity here in the Dallas area is >30 ms/m...very
>good. I started out years ago with 2 buried radials on my shunt
>fed tower. Over the years I have added more radials each spring;
>now totaling over 35, and the base impedance has never changed!
Have you made FS measurements to see if the EFFICIENCY changed? Several
have suggested that base impedence is misleading. I hope to find out this
spring with elevated radials....not on/in ground.
Your experimenting in that great soil would be a big help.
>>>Would you think that my extremely poor soil is the reason the
>>>elevated radials appear to work well? With true ground somewhere
>>>around 50' + below the surface the coupling effect is
>>>minimized. This might tend to explain why BCB sites over
>>>excellent ground do not benefit from elevated radials.
>
>The ground conductivity in Spokane is 8ms/m. This might explain
>why 120 elevated radials work so good over poor ground.
That is usually considered above average ( 5 is "average" by accepted
definitions) and well into good. I wonder if they tried 60 radials or
less? The height of the radials is also important...what BCB frequency?
IMO, this discussion may find a final agreement on technical merits but
not be in agreement with individual applications. Different locations,
soils, latitudes, etc all play a part. Yuri, Steve "down under", and
others have been quite vocal about their own local experiences. Listen to
them and then get your hands dirty...then go fishing.
73 Carl KM1H
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