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1-10 of 10 messages
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grounding
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by KE4IOK on February 25, 2007
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Every time (it seems) I ask a question about grounding I get more "don't do's" and not many real answers. I'm second floor. Can I use the electrical system ground for anything? Should I ground my power supply (it has a 2-prong plug)? Where (how) do I ground it? Can I use an "artificial ground?" A few simple answers will be appreciated.
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RE: grounding
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by N3OX on February 25, 2007
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"Can I use the electrical system ground for anything?"
Not for RF.
"Should I ground my power supply (it has a 2-prong plug)?"
If that's how it shipped from the factory, no. If someone hacked a two prong plug to it, you might want to ground the case.
"Where (how) do I ground it?"
Replace the two conductor cord with a three conductor one from Radio Shack and run the ground wire to the metal case of the power supply. Bolt it down to clean metal.
" Can I use an "artificial ground?" "
An artificial ground might be useful if all you can use is an end fed wire. Otherwise, use a dipole or ladder-line fed doublet with equal length legs and don't worry about an RF ground at all.
73,
Dan
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RE: grounding
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by WB4QNG on February 25, 2007
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Just my thoughts but people worry about grounding too much. If you have dipoles or verticles with ground planes you don't need to worry about RF ground. The manufactor of your PS should have taken care of the electrical ground.
Terry
WB4QNG
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RE: grounding
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by K8AG on February 25, 2007
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There are different types of ground. The can be separated into two categories (technically there are more but essentially these are the divisions):
1) DC and low frequency AC grounds.
2) RF grounds.
The first is the kind of grounding that is used for safety in electrical systems. It is why we went to 3-prong outlets. The ground on the equipment case will take the current and probably blow a fuse if a hot AC conductor should contact the case. Its a safety thing.
The second is many times not needed, except for antennas that use the ground as part of the antenna. And that ground is at the antenna not the rig. Then a ground plane or radials are needed. These act as another half of the antenna. The more and better grounds, at the antenna, the better your antenna will perform.
Some try to obtain an RF ground by driving a copper stake as near as possible to their operating position. Unless they are really a small fraction of a quarter wave from the ground point, it serves little purpose.
A dipole is a balanced antenna that requires no ground at all. Sometimes, with balanced antennas, RF will find itself back into the shack via coax shield. 10 or 12 6" turns of coax will serve as a choke and keep RF out of the shack from a balanced antenna.
One final observation; with a non-grounded rig on the second floor of a house. The antenna was a random wire and every time the transmitter was keyed RF was on the equipment case. The electrical ground did nothing to help with the RF. I changed antennas to a dipole and the problem went away. Some say attaching a half wave wire to the case can eliminate the rf burns, but I didn't try that.
Hope this helps.
73, JP, K8AG
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RE: grounding
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by N3OX on February 25, 2007
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"Some say attaching a half wave wire to the case can eliminate the rf burns, but I didn't try that. "
You want a quarter wave wire for that, but it's been my experience that if you have high RF voltage on the case, a quarter wave wire will tame it so you don't get RF burns, but that quarter wave wire ends up with a lot of current flowing it it, radiates effectively, and actually makes the RFI to electronic equipment WORSE.
- - - - - -
Using a random wire antenna terminating at your second floor shack is really one of the worst things you can do for a lot of reasons. I did it from an apartment where I fed a random wire against the balcony railing. It worked, but the electrical noise from everything in the building was on my ground system... which is half of the antenna.
I saw a drop of a 2 to 3 S-units noise level when I switched over to using a balanced doublet fed in the center instead of the wire fed against the balcony railing. Also, I stopped interfering with the TV, and with my laptop computer (which would shut down when I transmitted on 80m, and lost the modem connection on all other bands)
Furthermore, grounding the ground lug on the tuner case to the balcony railing made the noise come back, even though I was using the "balanced" output terminals and a balanced antenna.
RF grounding of the rig case to eliminate RF burns is a band-aid. If you're going to use a single ended antenna that needs an RF ground, you should use radials on the earth or at least one tuned elevated radial for every band right at the feedpoint of the antenna.
Dan
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RE: grounding
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by K9KJM on February 25, 2007
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As mentioned, There are a number of different "Grounds" Including, Safety, RF, Lightning.
It sounds like you are interested in Safety and RF only.
Each one has its own requirements. For RF ground, Counterpoise wires usually will work. Safety ground could be as simple as the 3rd prong on properly wired 120 volt AC outlets. Or lacking that a simple copper wire going out to a ground rod.
Lightning protection grounding is a huge subject. For good info see: http://members.cox.net/pc-usa/station/ground0.htm
It is important that all "grounds" be bonded together.
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RE: grounding
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by AA8LL on February 26, 2007
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I feel your pain. Here's the thing. I got my first short wave receiver, a Hallicrafters S-38E, in 1960. There was a screw on the back for A1, A2, and G. There was a jumper from A2 to G that could be removed. (Also, this radio was an AC/DC model that could have a hot chassis if the AC plug was the wrong way around. After a few nasty shocks, I marked that with red paint. But that's another story.) I connected my antenna wire to A1, but what to do about that G? My Dad said he had a crystal set as a boy and I could hear lots more with a "good ground." I ordered a ground rod from Allied Radio in Chicago and had it shipped to me in Dayton. Now you probably know that I could have gotten one at the hardware store but all of my electronic knowledge came mail order and the Allied Radio catalog had everything. The rod came and I got up on a stepladder and beat it into the ground outside my bedroom window. The radio didn't hear any more at all.
The subject of grounds is not so simple. You will read nothing about ground and grounding here in one amateur's post that will not be contradicted by another post. From the description of your station in a post last September, I would suggest you not worry much about grounds. We spend too much time on the ground as it is.
73,
Wade
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RE: grounding
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by AA4PB on February 26, 2007
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Take a look at some of the info on the ARRL web site and on the Polyphaser web site.
There are a lot of issues to consider. Its not something that can be adaquately covered in a forum post. There is also a whole lot of mis-information floating around.
The bigest thing to remember is that there are three types of ground systems: RF, electrical safety, and lightning. Each has its own purpose and unique requirements, although it is sometimes possible to design one grounding system that will provide for more than one.
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RE: grounding
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by WB6BYU on February 26, 2007
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> Every time (it seems) I ask a question about grounding I get more "don't do's" and not many real answers.
Yes, grounding is one of the most confusing issues because there are
multiple functions that we tend to lump together as "ground" which
really have different requirements. And often folks don't really
understand why attaching a ground to their equipment caused the
differences they observed.
So, to start, a few simple answers. First, you don't need a ground on
your equipment. There may be some reasons why you would want one,
but it is perfectly possible to operate - even from the second floor -
without anything directly connected to the dirt outside.
> I'm second floor. Can I use the electrical system ground for anything? Should I ground my power supply (it has a 2-prong plug)? Where (how) do I ground it?
This is your safety ground - in case there is a short circuit inside your
equipment it should cause the circuit breaker or fuse to blow at the
panel rather than leaving the case of the rig hot to ground. I was
fortunate that I survived my lesson on this - I had a short in my power
supply and had the plug in the wrong way and was using the metal
window frame as a ground for my antenna. The result was that the
metal door frame downstairs was live with 120VAC, and when I tried to
ground it to a nearby water faucet to reduce those "static" tingles that
I got from it the wire evaporated. If your power supply has a two conductor
plug you can replace the cord and plug with a three-conductor version
and wire the green wire (ground plug) to the chassis of your power
supply. Or you can connect an external wire to your power supply or
rig and connect it under the screw that holds the plastic plate over the
outlet (which should be connected to the ground lug of the outlet.)
Of course, your power supply is probably much better that the one that
I had built that caused the fault, so the chance is low that this will be
a problem. But it is cheap insurance.
Note, however, that this has nothing to do with RF grounding or
lightning protection.
> Can I use an "artificial ground?" A few simple answers will be appreciated.
That depends WHY you want a ground. Unfortunatly, too many books
make it appear that you HAVE to have one - this is not true.
First, let me make it clear that I am NOT addressing the question of
lightning protection. You have to make a personal decision about the
level of risk you are willing to live with vs. the chance of a lightning
strike in your area. Some folks on these forums get their antennas hit
several times a year. Other parts of the country haven't seen any lightning
in 7 years or more. If you are going to so something for lightning
protection, read up on the commercial web sites and do it right. Simple
solutions like using a spark plug for a lightning arrestor rarely work.
Now, back to the question of "grounds", and why you would want one.
If you are feeding a dipole antenna with coax and the dipole has a balun
at the feedpoint, you shouldn't need a "ground" for RF because this is
a complete antenna (with wires connected to both sides of the coax.)
If you are feeding a dipole without a balun, there may be RF flowing back
down the outside of the coax shield giving "RF in the shack". Whether
this is a problem or not depends on a lot of factors, especially the
length of the coax and what all is connected to the station. It tends to
be worse when the combination of factors causes a low impedance at
the antenna connection (so more current flows on the coax) and a high
impedance at the rig (so you feel it when it arcs from your microphone
to your lips.) In this case, adding a balun to the antenna can help.
Connecting a quarter wavelength "radial" wire to grounding bolt on the
back of the tuner or rig can also reduce it because it forces the rig to
be at a low impedance, which then likely changes the current distribution
along the coax so it looks like a high impedance at the feedpoint and
less current flows in the coax in the first place. You can use an "artificial
ground" for this if you want to (though wire is much cheaper) as long
as the wire connected to the "artificial ground" is less than a quarter
wavelength at the HIGHEST freqency you are using - otherwise it may
not give a low impedance on some bands. But the setting that gives
the higher current reading on the meter may NOT be the best one.
If you are using an end-fed wire on the second floor, then you need to
provide somewhere for the return currents to flow. This is like the two
wires on a power cord - you have to connect both for the circuit to
work. In the case of antennas, you have current flowing on both sides
of the transmission line to the antenna (even if it is only an inch long)
and for every amp of current that flows into the antenna circuit, the
same current has to flow in the other half of the antenna. And there
is the problem - what other half???
In this case, a quarter wave wire "radial" attached to the tuner will often
suffice, or more than one wire if there is room. The full antenna current
will flow on this wire and it will radiate as part of the antenna system.
(Note that this is different than the case where the antenna was fed
with coax - in that case adding the wire could result in reducing the
current in the coax so very little current actually flowed in the wire.)
You would generally need one quarter wave wire for each band you are
operating on, though in some cases one wire will work for two bands
(like 15 and 40m). You can also use an "artificial ground" here, but
the settings will interact with those of the antenna tuner and it may
not be easy to find the right setting. (Note that the "artificial ground"
is simply a series-resonant circuit to tune out the reactance of a short
wire. You can build one yourself with a coil that you can tap at each
turn, or a deluxe version with an additional capacitor and switch.)
What about running a wire down to a ground rod? There are two reasons
this may not work as well as one might think. First, dirt is not a good
conductor or dielectric for RF. The more the electromagnetic fields
flow from wire to ground return through dirt, the higher the losses
will be. In some cases these losses may be tolerable, such as a long
wire with a high impedance. If the wire is less than a quarter wavelength
long the losses can be considerable, and adding wire radials along the
surface of the ground will allow a more efficient RF return.
Second - the wire from the tuner to the ground has a length that may
be resonant on some HF bands - especially from the second floor.
For example, a 12' wire to a ground rod will be about a quarter wave
on 15m and will act as an impedance transformer: a low impedance
at the bottom (as we hope our ground rod would be) will look like a
high impedance at the other end, which happens to be where we want
it to look like a low impedance so current will flow down the wire
rather than back down the coax. So, while such a ground rod may be
useful for low frequency AC or draining static charges, it may not work
well as an RF ground for the "other side" of a long wire antenna.
Does that mean that you can't use an end-fed wire from upstairs? Not
at all. I've done it several times, and I currently have a 130' wire end-fed
from an upstairs shack. With no direct ground connection, since my
rig is powered by a battery and the charger has a 2-wire plug. Yes, I
get RF in the shack on some bands, because I haven't strung my 40m
radial wire yet. Actually it worked fine when the tuner was right at the
rig with the wire connected directly to it, but now I have about 20 feet
of coax between them and enough other patch cables so that the
coax+rig is close to resonant on 40m. (My station and antennas are
always in a state of flux.)
In place of the radial wire(s) you can connect the ground of the tuner
to some large piece of metal. Except for the unfortunate incident with
the short in the power supply, I had great results using the metal
window frames in that apartment (which were all connected together.)
A copper pipe water system or hot air ducts might work, or possibly a
mat of chicken wire on the floor. You'll have to try it and see.
But this brings up one of the other reasons why straight answers are so
difficult to find - so much depends on the specifics of each individual
installation. Some folks may find that connecting their rig to a ground
rod solves their RF problem, while for others it may have no effect or
even make it worse. Some people operate without a ground on their
tuner with no apparent ill effect, and for others their rig shuts down and
their smoke alarm rings. There are just too many variables to make any
sort of generalization for all stations, and, unfortunately, too many
people have done just that based on their own experiences. (And of
course there will be those who group me in that last category!) But in
my experience most of the problems are caused by RF on the ground
side going places where it shouldn't. You can't always predict this in
advance. Which is another reason why you get contradictory information:
some take every possible step to keep the RF where it belongs, and
others of us take a more lax approach and only fix it when we have a
problem. And you'll often see arguments about this - they are simply
different approaches to operating.
So when someone tells you that your station needs a ground, the first
step is to ask "why?" and "what type of ground?" Because there are
several types - an 8' ground rod, wire radials laid on the grass, an
elevated ground plane, a quarter wave wire connected to your tuner or
rig, the third wire of your AC power system, or an "artificial ground".
They all serve different purposes. And it is because we lump them all
together under the term "ground" without distinguishing their different
functions that the topic gets so confusing.
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RE: grounding
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by K0FF on March 1, 2007
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Ground the power supply case if it is metal. Ground the radio to the center screw on the AC coverplate. Do not rely on a ground through the coax shield or through the power supply negative lead. Ground the radio separately. This is for AC safety, it does not provide RF or meaningful lightning protection.
Tell us more about your radio and antennas as this makes a difference what to do next. If HF, and the antenna is near the shack, you can cut resonant wires and place them below the carpet to act as an RF ground. Lightning grounding is another matter and is difficult to provide unless you can run heavy gauge wire or copper strapping to the ground from the shack.
Consider a disconnet system to remove the radio from any connection to power, antenna etc. during bad weather. Antennas should be grounded as best as can be during non use. A well grounded antenna will drain the air of charge and actually protect about a 150 foot radius against lightning ( according to Polyphaser)
Geo>K0FF
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