jawod wrote:

I know this has been addressed on the group before but I remain confused.

I will string a dipole in the trees. The coax shield will be earth
grounded, as well as the balun and lightening arrestor.

Now, in the 2nd floor shack, I've read that running a ground line from
equipment 15 feet or more (in this case) to an earth ground will bring
RF into the shack and be a potent source for TVI, etc.

My choice, then, is to use the ground on the mains.

Given that the shield is earth grounded on the antenna and the equipment
is grounded to the mains, isn't this a good scenario for ground loop?

Seems like a catch-22.

My own gut says safety first, lower risk of RF issues after-the-fact by
? what ?

I remember suggestions of coiling the ground wire in an RF choke,
multiple ground lines of various lenghts to mess with harmonics.
Ferrite beads? Chicken blood and a black cat?

John


John,

So you are taking a balanced aerial, a dipole, chuck it onto a balun and the
feed it with a coax. Nothing wrong with that...

There should not be any "involvement" by the coax in the functionality of
that dipole. The grounding of the coax are for shielding purpose only and
as such, you ground the coax at one of the terminations, in your case, the
transceiver.

Building regs normally demand that the house's mains ground should be
connected to a ground rod somewhere, normally at a central point.

Assuming that every level adds 2.5m, you are sitting 5 meter up. Even if you
ground your rig with a separate connection to a ground rod, you'll still be
electrically 5 meter away from ground ( at least ).

You will always have RF in your shack PERIOD, It's just a question where
it is and how you discover it. It's either RF current or RF Voltage. As the
RF voltage is what you normally discovers by having a "hot" key or
transceiver, you need to phase shift the ground connection of the coax in
time so you have a max current at your rig instead of high voltage.

This is solved by using an artificial ground. Buy or build one, they are
dirt simple. MFJ sells one.

The artificial ground is basically a capacitor and an inductor in series
with the coax SHIELD(!). Both cap and coil is variable/tunable.
By changing the cap and coil, you can move the RF Voltage and RF current +/-
90 degrees. You just adjust for max RF current at your operating frequency.

This worked fine at the 32nd floor for me...


Cheers


Dan / M0DFI

One way to beat this is to tune with low power and touch the
rig. Every few days increase the power until you have built up
a tolerance to the RF tingle.

You could also try this with the household power, starting at
2 or three volts, and increasing it gradually over time until
you build up your immunity to electric shock as well.

Irv VE6BP :-)

There is absolutely no reason to have an RF ground unless:

1.) You are end feeding a single wire antenna that is brought into the
shack

2.) The two conductor feedline you have brought in, be it coax or open
wire, is connected to an antenna that is not properly designed or
installed

The safety ground is required. The RF ground is a band-aid for
something else being wrong.

73 Tom

wrote:
There is absolutely no reason to have an RF ground unless:

1.) You are end feeding a single wire antenna that is brought into the
shack

2.) The two conductor feedline you have brought in, be it coax or open
wire, is connected to an antenna that is not properly designed or
installed

The safety ground is required. The RF ground is a band-aid for
something else being wrong.

73 Tom

Tom,

If we assume that there is a well matched antenna: twin line to balun,
coax to transceiver. My RF concern was that a long line to ground would
serve as an antenna to bring RF into shack. If this is not the case, or
if this is easily dealt with, great.

The mains box is on the opposite side of the house...that ground is not
conveniently located.

My coax will go thru a lightening arrestor (Polyphase) which will be
earth grounded. If I run a low gauge wire from that earth ground to the
main box ground, then this is prevents ground loop? What if the
distance to the mains box is 60 feet?

John

On Sun, 12 Mar 2006 22:39:51 -0500, jawod wrote:

If I run a low gauge wire from that earth ground to the
main box ground, then this is prevents ground loop? What if the
distance to the mains box is 60 feet?

Hi John,

This is required by code. Violate code and insurance can dump your
policy faster than a lightning strike.

The whole point of that wire is to prevent ground loops - this one
being the mother of all loops. If and when lighting gets snubbed by
your arrestor, it will bury that charge into this inferior ground (the
non-code unconnected ground that is), lift that ground's potential,
and that potential will follow its way into the shack (along the
shield) to find your safety ground (which is far better suited for
that path) and you might happen to be sitting on the shoulder of that
current superhighway.

The resistive earth path between your arrestor ground and service
ground is not nearly as attractive as the path from safety ground,
through power supply, through chassis, through transmission line
shield to the arrestor. It is a rare power supply that breaks that
path's DC continuity, and a rarer one that RF isolates it both. Unless
you are running solely on battery, no charger, and no accessories
connected to the rig - there is a path to ground that lightning will
find as an alternative.

60 feet is trivial for safety (the RF in lighting is more LF or MF
than HF).

73's
Richard Clark, KB7QHC

jawod wrote:

If we assume that there is a well matched antenna: twin line to balun,

SWR does not cause ground currents or RFI.

coax to transceiver. My RF concern was that a long line to ground would
serve as an antenna to bring RF into shack. If this is not the case, or
if this is easily dealt with, great.

A long line to the ground definitely WILL act like an antenna, but the
effect is absolutely unavoidable.

If you look up national electrical codes you'll see external wires or
cable grounds entering a dwelling are supposed to be bonded or grounded
to the same ground as the power mains and other utilities. This is
primarily to ensure if there is any type of ground fault or surge (i.e.
lightning) everything in the house rises at the same rate. You don't
want ANY surge current flowing through the house wiring, and bonding
grounds outside the house greatly reduces currents through the house.
This is called a "common point ground", and it REDUCES ground loops.

Second, amateur gear is not normally UL/CSA approved. It sometimes
contains high voltage. High voltage inside a metal box can be a
problem. If you get a short from a transformer primary to secondary the
case can actually rise to the full amount of high voltage. That voltage
can appear on antenna cables (as it can if other components inside the
box fail), or between that device and other devices. While not all
amateur stations have HV devices, most have line operated equipment. It
is possible to have 120VAC appear on cabinets and cables in those
devices. Because of this, we should always have an independent safety
electrical ground. That ground is required by code to be bonded to the
service ground.

That leaves us RF. There are only two things required for RF in the
shack prevention.

The first is you use an antenna with a two conductor feedline. It can
be coax or twinlead. The antenna system can have ANY SWR, but it must
ensure the currents on each conductor of the coax or twinlead are
perfectly balanced and 180 degrees out of phase.

http://www.w8ji.com/verticals_and_baluns.htm

If the currents are not balanced, some current will flow back to the
power lines, telephone lines, and other connections to the station
equipment. The cure for this is really fixing the antenna system.
Although a "RF ground" in the station can cover up the problem, the
feedline will still radiate and receive signals.

The second is your station must have a common "ground buss" and all
equipment in your station should be bonded to that ground buss. The
importance of an external low impedance RF ground on that ground buss
is actually very minor. The real importance is that ALL equipment in
the shack operate at the same RF potential. In second floor locations I
actually laid aluminum foil under carpet for my shack RF ground, the
large "plate" acting like a groundplane for RF, but I ALWAYS had an
external safety ground. That's because I always ran amplifiers and
other equipment that was not UL/CSA listed. Sometimes you just do what
you have to do to get on the air.

It's best if you work out any RF problems IF they occur. If it was me,
I would not worry about RF problems until they showed. Safety is
another issue. If you are dead or the house burns down, it is too late
to work on problems.

The mains box is on the opposite side of the house...that ground is not
conveniently located.

What you do is up to you. I'm only telling you what the NEC tells us we
should do and why. It does NOT mean your insurance will be invalid if
you don't follow NEC, it only means they can cancel you. State laws
require insurance companies honor policies, but if they find out
something isn't safe they can cancel you. Otherwise they can only
refuse to pay for fraud or an intentional violation of the agreement
you signed.

You station is less safe for lightning and for electrical safety if you
don't bond the grounds, but I have had many stations over my lifetime
that did not follow that guideline. That's what you should do, and you
should do it for electrical and lightning safety.

My coax will go thru a lightening arrestor (Polyphase) which will be
earth grounded. If I run a low gauge wire from that earth ground to the
main box ground, then this is prevents ground loop? What if the
distance to the mains box is 60 feet?

Yes. It reduces chances of harmful ground loops. I believe you should
find that on polyphasers site in technical papers.

Try:

http://www.polyphaser.com/ppc_TD1016.aspx

and other technical papers.


73 Tom

Irv Finkleman wrote:
One way to beat this is to tune with low power and touch the
rig. Every few days increase the power until you have built up
a tolerance to the RF tingle.

You could also try this with the household power, starting at
2 or three volts, and increasing it gradually over time until
you build up your immunity to electric shock as well.

Irv VE6BP :-)

I tried this approach several years ago...got up to about half a kilovolt...

but my wife complained that my glow was keeping her up at night.