[TowerTalk] Ground System suggested for QRO Amps

[Jim Reid]

Hi  Pat,

What Paul suggested was an array of four ground rods,  in a "squared off"
question mark pattern.  Starting at the bottom of the ? sign.

Drive one  ground rod in.  Then measure straight up about 5 feet,  and put
in another rod.  From that rod, go towards the upper right,  at a 45 degree
angle a distance of 3 feet,  in goes another rod.  From that rod,
go left 4 feet,  and plant another one.  Now you have a pattern
something as follows:            __
                                                    /
                                                    |              

Lengths in that are not to scale,  but the shape is close to correct,  hi.
Of course the upper ends of the rods are connected together with
wide strapping or copper tubing.  This was N6VLV's recommended
ground set up.

Now,  I also recv'd another input which takes a different approach to
the RF "ground" situation in the shack,  from Chuck Constantine  KR6C,

"What you're interested in is a equi-potential ground reference.  That
means ALL equipment is at the same potential.  You do NOT need a (earth)
connection for a RF ground reference.  People seem to think the earth is
a magical RF sink where spent electrons go.  They want to get back to
their source...not necessarily earth (Kirchhoff's first law). Aircraft
do not drag ground wires and ones I work on run several kW transmitters
and things are not hot! We make sure things have low
resistance/Impedance connections and EVERYTHING is bonded together
(multi-point).  You can make a great RF ground reference by putting a
patch (4' sq) piece of copper sheet on your floor and use wide straps
from your ground bus on the back of your desk to this plate and be
guaranteed better RF performance than any rod driven into the
earth...especially on a Volcanic island. (think of it as a big RF bypass
capacitor if you like.  Major computer installations tie all the
flooring webs together for low inductance equi-potential groundplanes).

There are three basic types of RF grounds, Single point (where everything
connects to a single point best for eliminating possible ground loops)
Mulit-point (where grounds are made to a common reference like different
points on a copper plate or different points on a ground bus) and Hybrid

(combination of both).  Most Amateurs use multi-point (like whats shown
in ARRL handbook) because of simplicity and in order for a single point
to work properly you would have to separate all your equipment several
feet from each other to prevent stray capacitive coupling between
boxes...not worth the effort. The ARRL handbook or antenna book method
is acceptable and works fine if done correctly.

The two most important things to minimize are Resistance and INDUCTANCE!

I use the 1/2" 6' length of copper waterpipe attached to the back of my
desk then every piece of equipment is connected with a braided strap to
several points on this ground buss then the end of the bus connects with
a large fat tinned copper braid strap to the ground rod.  The attachment
to the ground rod only provides electrical SAFETY ground and if you
install separate ground rods you MUST make sure they are ALL connected
together.  This means connected to the main ground rod at your power
service entrance to your house so everything is at the same potential.
If not your shack ground might have a lower resistance than your house
electrical ground and fault currents could use your station and
equipment as ground for electrical shorts making things very dangerous!

Electrons want to return to their source via a LOW INDUCTANCE path. So
if things are not at the same potential (equi-potential) currents will
flow in the ground leads and this can lead to ground loops and things
being hot in the shack. The reason I use a 1/2" copper tube for my main
ground bus is because its LOW INDUCTANCE and LOW RESISTANCE at RF. Fat,
wide, or large diameter objects have lower inductance at RF. Remember
the Inductance of a piece of 12 gage wire at 60Hz is zilch but can be
several Ohms at 28mHz!  Inductance at RF will impede the flow of current
like a resistor will to DC.  NEVER use wire for RF ground connections. a
8' length of wire at 28mHz will act like a 1/4 wave inverter making a
high impedance connection at one end.  Someone once told me the copper
pipe makes a good antenna element because it can be resonated. .I say
B.S. with all the equipment connected to it and the parasitic capacitive
coupling between equipment its very hard to "resonant" the ground.  You
can use an antenna bridge connoted between your ground rod and station
multi-point ground and try to find a resonance if your really concerned
and if by chance you do...bet its because you used wire between the rod
and station bus bar and thats whats resonating.

This is what I use...

       ___________________________1/2"  Ground Bus_large strap_to ground
rod
        |           |       |         |          |          |
        |           |       |         |          |          |
<-Straps to equip.
        |           |       |         |          |          |
    Comp   Rig    vfo     tnc     tuner    Amp

I can run 1kW plus and have no problems with things being hot or
upsetting the computer/TNC or even the color TV thats right next to the
amp!  This provides a good equi-potential ground reference for RF and a
good electrical safety ground.  People dont realize not only is there

the DC resistance, the inductance of ground straps and all the
interconnecting power/data wire but also LOTS of capacitive coupling
between all the metal cases of the equipment.  Who knows which path is
actually the real RF path at a particular frequency:  I don't care what
anyone says ELECTRONS DONT FOLLOW SCHEMATICS...they take the path of
least resistance and at RF this could be just about anything.

Grounding for Lightning is a different story but it didnt sound like
thats what you were looking for.

Build your station ground system and evaluate it:

   Do the transmitter and amp load up like they should?
   Do the equipment cases or mic feel warm (tingle) when transmitting?
   Do I get feedback or strange sounding audio?

If not...dont worry about it.  How it visually looks and really works
are two different things.

Hope this helps...73
Chuck Constantine  KR6C"

Chuck put a lot of info into his note.  Useful also.  Should you have
a question for Chuck,  his e-mail is:  kr6c@juno.com

What Chuck shows he uses appears very similar to the stuff advertised
on page 111 of the May QST,  page centerd below the Ten Tec ad,
where the Omni is tuned to the Ten Tec Sunday net SSB frequency,
station grounding set up stuff sold by J. Martin Systems.  Wonder if
their bar of only 1/8 inch by  1/2 inch is low enough inductance?
Another suggested the use of a copper sheet on top of the operating
table (available at roofing supply houses for flashing use); each
shack RF box is strapped to the sheet to which the strap could be
soldered,  forms very low inductance,  low R common equipotential
common ground plane for the gear.  Lots of ideas,  all good.

73,  Jim,  KH7M
On the Garden Island of Kauai


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