[Lf] [Fwd: [Lowfer] Is a well a good Tx ground?]

[Andre' Kesteloot]

Cantrell Bill-QA0057 wrote:

> Hi Stewart,
> Nearby trees are definitely a negative.  I would move away from them, even
> if it means being farther away from the well casing.  I think you want
> surface radials on top of the ground for the best performance (lowest ground
> losses).  I would definitely try to measure anything and everything I could,
> so try the ground measurements at 180 kHz too!
>
> Loading coil Q becomes more important as ground losses are reduced because
> loading coil losses start to make up a larger percentage of the overall
> loss.  In my case (TEXAS), the ground loss resistance is 5 ohms total, and
> the loading coil loss resistance is 4 ohms.  (The coil is an extremely
> high-Q 2.625 mH air-wound coil using Litz wire.  It has a Q of ~ 780)  Even
> with this high of a Q, the losses in the coil are 44% (444mW).  Ground
> losses are 55% (551mW) using chicken wire ground plane.  Radiated power EIRP
> is ~0.5% (5mW) which is good, relatively speaking...
>
> Regards,
> Bill
> "TEXAS" & WD5CVG
>
> -----Original Message-----
> From: Stewart Nelson [mailto:sn at scgroup.com]
> Sent: Friday, January 28, 2000 3:25 PM
> To: lowfer at qth.net
> Subject: [Lowfer] Is a well a good Tx ground?
>
> Hi all,
>
> I am planning a new lowfer Tx, and thought that my well might be
> an excellent ground.  It's eight inches, and goes down 100 feet.
> The water level is now only about one foot below ground, and
> rarely drops below ten feet.  Sometimes there is even a small
> artesian flow.
>
> I made a rough measurement of DC resistance.  There is a pond,
> the edge of which is about 50 feet from the well.  I connected a
> 12 VDC supply from the well casing to a pie tin submerged in the
> pond.  About 50 mA flows.  About 100 feet from the well, in the
> opposite direction from the pond, I drove a shovel into the
> ground.  With the supply off, the voltage between shovel and
> well is about 200 mV (battery formed by difference in metals).
> When the supply is turned on, the voltage increases by 25 mV,
> so the well resistance appears to be about 0.5 ohms.
>
> Do you think that this is a reasonably valid measurement?
> If not, how can it be improved?  If so, how might it relate
> to impedance at 180 kHz?  Is it worth repeating the experiment
> using an audio oscillator and scope?
>
> Unfortunately, there are a couple of trees (deciduous, currently
> bare) about 12 feet from the well.  Will this wipe out any
> advantage of a low impedance ground?  Does it make sense to
> locate the antenna some distance away, and connect a ground
> radial to the well casing?
>
> With a low ground impedance, it seems that loading coil Q
> becomes more important.  I would think that a suitable
> ferrite core would help, but most lowfers use air core coils.
> Why?  How low an effective resistance can be achieved?
>
> Any advice greatly appreciated,
>
> Stewart Nelson  KK7KA
>
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