> >Larry:
> >
> >One concern that surfaced from the description of your station and
grounding
> >technique. You indicated that you have a common ground connected to an
> >outside driven ground. Is this ground rod connected or bonded to the AC
> >mains ground? It should be in order to prevent a difference in voltage
> >between the station ground and the AC mains ground. Typically your radio
is
> >connected between these two and thus any current differences are flowing
> >through the radio equipment. Not good.
> >
> >
> There is no simple answer to this, I will describe: I have a total of 5
> ground rods spaced around the outside of the house that directly attach
> to the house wiring... I have a #6 copper "backbone" running the length
> of the house along the basement ceiling (shack is in the basement.) This
> is what the (electrical system) ground rods are connected to.
>
> However, I also have the HyTower out on the front lawn. There are 4 more
> rods spaced around the HyTower, all connected to the radial system (77
> approx. 80' long radials) with copper strap (plus cadwelded #6.) There
> is a spark gap at the base of the HyTower. Then, a #6 wire runs from
> there, parallel with the feedline (both buried) all the way back to the
> house, where there is another rod, and the box with my Polyphaser
> protectors in it, connected to the rod with strap. Finally, this ground
> system continues inside where it meets the electrical backbone near the
> center.
>
As you describe these various ground systems, it is clear that there are
some very long wires connecting the various ground system components
together. These long wires likely have significant RF impedance. They do
not constitute bonding the ground systems together, in the RF sense. They
may well do just fine at DC and at low frequency AC (like 60 Hz). So you
may have significant step voltage differentials at RF.
Also, a wire out the window, to a single ground rod, is likely to to a poor
RF ground. How long is the path total ? I bet it approaches or exceeds
1/4 wave at some (many ?) frequencies. Might be an "open circuit" at RF.
You might have no ground at all, effectively.
Hearing HUM on audio devices, turning on appliances, and the like, as you
have described, certainly makes me wonder.
I try to make each of my grounds (in the shack, at the tower, etc) as
totally effective as possible. Then there is no RF remaining on the ground
system. Then, the bonding wires are just there for DC and low frequency AC.
And, of course, to meet the national code for wiring in the US. All grounds
are to be bonded. But I know these bonding wires are totally ineffective as
RF bonds).
73 de Gary, AA2IZ
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