Topband: DXpedition Beverage Termination Grounding Schemes??

[Frank W3LPL]

Hi Steve,

Never use a common ground rod to feed multiple Beverages. The feed
points for each Beverage should be independent and separated at least
6 to 10 feet from each other.

Two short radials may be adequate as an alternative to -- or in addition
to -- ground rods at each end of a Beverage. You don't want the radials
to behave like BOG antennas inducing signals into the ground connection,
they should be short and tight to the ground or even better they should
be buried.

Beverage antenna performance is not very sensitive to exact termination
resistance, especially when installed over lossy soil. It doesn't
make sense to drive ground resistance to a very low value only to then
install a 470 ohm termination resistor at the end of the Beverage!

Ground resistance at the Beverage feed point affects only efficiency
and suppression of voltages induced into the ground connection by
common mode current on the coaxial cable shield.  Efficiency isn't
a concern with Beverage antennas for 160, 80 or 40 meters.  Common mode
currents are easily suppressed by a common mode choke or by burying the
transmission lines rather than by very low ground resistance at the
feed point.

I use this very simple -- but adequate -- test of receiving antenna
ground resistance for non-demanding applications:
   - connect your antenna analyzer to the receiving antenna feed point
   - place you hand on the ground connection
   - if your hand changes the VSWR or impedance, your ground resistance
     may be too high

Ground resistance isn't critical for Beverage antennas unless your
soil has very poor conductivity or if you need operate your
Beverage above about 10 MHz. Low ground resistance is somewhat more
important for passive (not Hi-Z) short receiving verticals, but
that's an entirely different story not addressed in this email.

For the 64 phased Beverage array installed over solid rock,
we used roughly (only because I don't remember the exact length)
30 foot lengths of chicken wire laid lengthwise under each end
of the Beverages. 

As an aside -- totally unrelated to ham use of Beverage antennas --
for our application we also needed to achieve:
  - very low and flat VSWR,
  - very low side lobes especially from signals received by the Beverage
    feed point and termination at the upper end of the frequency
    range where the connections to the ends of the Beverage behave
    like efficient short verticals
  - very high feed point efficiency especially up to 30 MHz

To achieve this, each Beverage consisted of three wires spaced
about six feet apart. The ends of each Beverage sloped down to the
ground over the chicken wire ground mat to a common feed point
(or resistive termination) for the three wires.  

Sloping wires over highly conductive ground mats forced the wires
to no longer behave as antennas but to behave as sloping unbalanced
transmission lines with low sensitivity to received signals.

We outfitted a helicopter equipped with accurate navigation to
precisely measure the pattern and sidelobes of the Beverages.
They behaved just like to computer models all the way up to and
well above 30 MHz.

It was fun -- but very tedious -- to have a military budget and lots of
available labor to perform extensive antenna construction, testing
and documentation of this huge phased Beverage array. We even used 
road construction equipment to precisely level the entire phased
Beverage antenna field so it was precisely level it within a few inches.
Of course we deeply buried all of the feed lines from the feed points
all the way to the receivers.

73
Frank
W3LPL



----- Original Message -----
From: "Steve" <k0xp at k0xp.com>
To: "topband" <topband at contesting.com>
Sent: Saturday, March 9, 2024 12:08:36 AM
Subject: Re: Topband: DXpedition Beverage Termination Grounding Schemes??

On 3/8/2024 6:02 PM, Frank W3LPL wrote:
> We used a chicken wire mat at each end of the Beverages (similar to NC0B's use of chicken wire on his verticals).
How large were the mats, and how were they laid out: in line with the
Beverages, or perpendicular?
> Instead of using a ground rod for each vertical I use eight 65 foot wires laid on the surface of the ground.

In-line, or perpendicular to the Beverages?

I recall that on a much-earlier posting, you mentioned laying down a
pair of 120-foot radials on the ground at the far end, I presume
perpendicular to the Beverages; but I don't recall whether you said to
use the same at the feed end? And what about where you are using the
same pole as the beginning of several Beverages heading off into the
back-40?

TNX,

Steve K0XP



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