[TZ] Elevated radials vs buried ones

[Milton Holladay jr.]

I still say  this is overthink.

Imagine, if you will, a standard AM site raised ~20 feet or so off the 
ground and floating in thin air, _a la_ Rene Magritte's painting "Castle 
in the Pyrenees". ( Well, OK, with insulators and supports that 
approximate this.)

Set up your FIM and start measuring as you remove one radial at a time 
until the field strength starts to noticeably fall; this will happen 
when only  2 or 3 radials are left.  Four radials will leave the FS 
virtually undiminished.

What is so hard to understand ?   It's a frequency scaled version of the 
UHF/VHF ground plane antennas.

M

BT, measured it

On 5/19/2016 4:47 PM, Cowboy wrote:
> On Wednesday 18 May 2016 11:00:45 pm Harold Hallikainen wrote:
>> Interesting subject! The elevated "ground radials" seem like we're driving
>> the center of a dipole turned vertical with one side "flared out."
>   That's not a bad way to think of any vertical whether using an
>   elevated radial counterpoise, building roof, or a conventional
>   ground mounted broadcast vertical.
>
>> The
>> relationship to "ground" is interesting. I always think of a horizontal
>> dipole or inverted V or similar as having a drivepoint that is balanced
>> with respect to ground.
>   Technically, with respect to the universe.
>   The "ground plane" is unbalanced by definition, which lends itself
>   well to an unbalanced feed.
>   
>> suspect the voltage on the radials at the base are perhaps 1/4 the voltage
>> at the base of the tower with respect to ground. The radials probably
>> reach ground potential part way down the radial, then start going up
>> again. Just guessing here.
>   The voltage and current distribution is theoretically the same as the
>   other half. Minimal voltage and maximum current at the feed point,
>   with minimal current and maximum voltage at the far end.
>   Actually, maximum voltage and minimum current always occurs
>   at the far end, though the converse depends on the electrical length.
>
>> On losses, it seems that having fewer radials would not necessarily
>> increase loss but would perhaps just change the driving point impedance.
>> We might think of a tower with one radial as an inverted V turned on its
>> side. If one side is particularly close to ground, we may get losses due
>> to that (current through a resistive material).
>   That's the extreme case, yes.
>   The current is distributed about the vertical, so in the case you present,
>   the majority of the return currents are through lossy earth.
>
>> Anyway, interesting stuff to think about.
>   There is far less understanding of these things than one might expect
>   among supposedly educated and experienced engineers.
>   Some, it's understandable. That's why we have consultants.
>   Others, not so much.
>   I'd expect a Ron Rackley to understand these things, but not so much
>   about audio processing.
>   I would not expect Frank Foti, or Bob Orban to understand much about
>   antenna theory, ( though they might ) but I would expect them to know
>   considerable about audio paths and processing.
>   None the less, the brain exercise is good for us all. ( IMHO )
>   Beware dragons, for thou art crunchy, and good with catsup !
>

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