[Lowfer] SIW (WM) in CT

[JD]

On Sat, January 14, 2017 12:40 am, N8OOU wrote:
> My ground is basically sand down to the water table, so I think it would
> be fairly easy to connect the garden hose to 1/2 inch ridged copper pipe
> and use the water flow to drill the pipe in. I have never done that, but
> seen others drill water wells using that method on u-tube.
>
> Brute force sledge hammering is always an option.
>
> I am working on loading coil changes first though, with this idea on the
> back burner.

A worthwhile priority, I believe, Mike.

There's certainly more that can be done for your ground later, but when
you do, you might want to tackle the problem horizontally rather than
vertically.  A soil conductivity of 8 mS/m is not exactly terrible, but if
your ground is sandy, it may actually be an isolated spot of lower
conductivity within the nominal 8 mS/m region.  The substantial skin depth
of poorly conducting soil may make long ground rods desirable for AC
grounding, but experience shows they are of little benefit for lightning
protection for several reasons, including the RF-like nature of the
transients.  (Despite bad advice published numerous places, there is NO
magic, imaginary "ideal earth" to which we can somehow sink all that
current.  It's already got a specific destination in mind before it
strikes, some region on the surface of the earth which is charged
oppositely to the cloud base; and all we can hope to do is provide it a
variety of more favorable paths between the point of strike and all the
probable but unknowable regions of charge accumulation that _don't_
include our structures or equipment.) Ground rods are better than nothing,
but they're not necessarily ideal.

At RF --which is what counts here-- you don't want current to have to go
THROUGH that any more of that resistive soil to reach your ground return
than is absolutely necessary, either horizontally OR vertically.  That's
resistive loss.  Catch as much of it near the surface as possible! At a
minimum, I suggest you consider doubling the number of ground radials. 
They don't even necessarily need to be buried...some ops have found it
worthwhile to basically staple them to the earth and let grass grow up
over them...and they don't need to be longer than roughly the height of
the antenna plus the diameter of the top hat, if any. That's the region in
which most of the antenna current returns, so providing it as much of a
metallic path as possible in that region is essential for efficiency.

Since those wires will be spaced quite a distance apart near their outer
ends, though, that means RF current intercepted by the earth that far out
will still have some distance to travel.  That current is lower in value
than near the base of the antenna, so the loss factors will be
proportionally less, but sometimes they still matter.  Some have used a Y
and/or star pattern of extra wires attached near the outer end of ground
radials to overcome this, while others use short ground rods to good
effect at the end of radials.  There is a point of diminishing returns,
though, so it's best to concentrate first on providing as many conductive
paths as practical where the current (and therefore, the potential for
loss) is greatest, then experiment with enhancements later.

As for lower priority options:

Chicken wire as a ground screen near the tower base is an old standby
among LowFER old timers, and can be very effective. It's not as cheap as
it used to be, though, and can be physically awkward to keep flat against
the ground. You also don't want to attach it directly to copper, but
instead use stainless steel hardware to prevent electrolytic destruction
of the galvanizing. And, it may not last terribly long in contact with
some corrosive soils.

Does tying to other nearby grounds help? In some cases, yes, but very
often it can hinder effective radiation(and can be a source of noise if
the antenna is used for reception). Connecting to a household ground, for
instance, may increase the antenna current but not the radiated signal,
because it might merely provide a path for current through a vertical run
of house wiring that's flowing in the opposite direction of the antenna
current, thereby cancelling some of the signal. That's always an area
where one can experiment; but don't assume that because it works in one
specific case, it will in another. Always check the results to be sure.

As for chemical enhancement of grounds, the effectiveness will also vary
by installation. Coke breeze or other conductivity enhancers for burial
with ground rods will often help, but again, if RF has to go through much
lossy soil to get to the rods in the first place, the cost and effort may
not be worth it. In my own case, I included a little bentonite is some of
my radial trenches near the tower (thank you, Tidy Cat) and an abundance
of magnesium sulfate (Epsom salt) along the entire run of each radial. I
also broadcast Epsom salt over the whole ground field every few years to
keep the antenna characteristics stable...but while that works well in my
clay-rich soil, it probably wouldn't be very satisfactory in sand.  It'd
greatly improve conductivity for a while, but might need to be replenished
after every significant rainfall.

Just a few thoughts. I'd surely like to see WM again at signal levels at
least comparable to last year's vertical antenna, and ideally stronger.

John