session May 21, 2015 echolink 8 pm Yl NFarl-r
Grounding (RODS and Ribbons)
May 21, 2015 YLRL echolink net
An effective ground system is necessary for every amateur station.
The mission of the ground system is twofold. FIRST, it reduces the possibility of electrical shocks if something in a piece of equipment should fail and the chassis or cabinet become “HOT.” If connected properly, three-wire electrical systems ground the chassis. A ground system to prevent shock hazard is generally referred to as “DC GROUND.”
The second job the ground system must perform is to provide a low-impedance path to ground for any stray RF current inside the station. Stray RF can cause equipment to malfunction and contributes to RFI problems. This low-impedance path is usually called “RF GROUND.”
The first step in building a ground system is to bound together the chassis of all equipment in your station. Ordinary hookup wire will do for a dc ground, but for a good RF ground you need a low-impedance conductor, COPPER STRAP sold as 'flashing copper,” is excellent for this application, it maybe hard to find. Braid for coaxial cable is popular choice; it is readily available, makes a low-impedance conductor, and is flexible. You see this on roofs in south and west.
Grounding straps can be run from equipment chassis to equipment chassis.1/2 copper water pipe runs entire length of operating bench. A thick braid from RG-8 cable runs from each piece of equipment to a clamp on the pipe.
After equipment is bonded to common ground bus the ground bus must be wired to a good earth ground. This run should be with heavy conductor (braid – I CALL RIBBON) should be short and direct as possible.
Drive one or more grounds rods into earth where conductor leaves the house. Ground rods-8 to 10 feet can be acquired from electrical supply house (home depot or lowes or the like) steel with heavy copper plating.
Once rod is in ground clamp the conductor from the station ground bus to it with a clamp that can be tightened securely and will NOT RUST. Copper-plated clamps made specifically for this purpose can be found and electrical supply stores. If possible solder the connection.
ANOTHER popular station ground is the COLD (not hot) water pipe system in the building.
Length of of ground wire should be multiple of ¼ wave.
Noise in ground systems can affect sensitive radio equipment. It is usually related to one of three problems:
1. Insufficient ground conductor wire
2. Loose ground connections ot
3. Ground loops
liberal use lock washer and star washers is highly recommended
Ground noise can affect receive and transmitted signals
The antennas that we mount are affected by the presence of ground. At times, the ground is a reflector and at other times, it is an absorber.
The ground around the base of a quarter wave vertical antenna needs considerable help in the form of radials, if this type of antenna is to perform well.
When an antenna that is a near ground radiates, some of the energy will strike the ground and some of the energy will be reflected. The reflected energy will bounce back to the antenna and effect the pattern of current distribution in the radiator, and thus effect the pattern and the feedpoint impedance of the antenna.
After antennas, station grounding is probably the most discussed subject in amateur radio and it is also the one replete with the most misconceptions. The first thing to know is that there are three functions served by grounding in ham shacks: 1. Electrical Safety 2. Stray RF Suppression (or simply RF Grounding) 3. Lightning Protection. Each has it's own set of requirements, but not all station setups need every kind of ground. In fact, some setups don't use a ground at all! The articles on this page will help clear up some of the myths and mystery surrounding this popular topic.
Grounds fulfill three distinct functions. The best ground for one function isn't necessarily the best for another. The three are:
a. Safety ground. This protects you from a shock hazard if one of the mains or high voltage power supply wires contacts the chassis due to some kind of fault. The requirements for this ground are spelled out in your state's electrical code. I believe that most states adopt the National Electrical Code (NEC). The safety ground conductor in your wall sockets should be connected to ground according to this code, and your rig's chassis should be connected to the safety ground.
b. Lightning ground. The requirements for a ground for lightning protection are much more stringent than for a safety ground. The topic has been discussed in this group many times, and there are numerous resources available for learning how to make a ground system for lightning protection. (See the TIS Page on Lightning Protection)
c. RF ground. This is required only for certain types of antennas-- ones which require current flow to ground to complete the antenna circuit. An example is a quarter-wave vertical. One wire of the feedline connects to the base of the antenna, and the other connects to ground. The connection to ground has to have a low RF resistance, or you'll expend too much of your power heating the ground. A few radial wires will provide a moderately low loss connection. A ground rod will help a little, but the RF resistance will be high, resulting in quite a bit of loss. Chapter 8 of the ARRL Antenna Book shows the approximate trade between resistance and number of radials. If your antenna is much shorter than ¼ wavelength, you'll need many, many radials to get reasonable efficiency. If it's longer, you can get by with fewer. A ½ wavelength base-fed vertical needs only a very modest ground, and a ground rod is adequate. The requirements for various other end-fed antennas depend on their length. If you use a "complete" antenna like a dipole or a ground plane (that is, one that doesn't require your feedline to connect to ground), you don't need a RF ground, as long as you keep common-mode currents off your feedline. A "current" or "choke" balun is most commonly used for this.
Besides one lead from inside the shack, the others go to several other well spaced ground rods, a lead to the tower base (which has it's own ground system), and finally, the power company ground, which is only about a foot away.
picture is taken from k9wn
Youtube video showing how to drive a 10 foot ground rod into the ground with water.
You may believe your radio equipment, antenna and tower are well-grounded. After all, you drove the ground rods into the earth yourself and connected the ground wire to the rods with heavy-duty clamps.
With an ohmmeter, I measured an open circuit from the ground wire to its grounding clamp! This was true for both the equipment ground outside my radio room and for the ground at the base of my beam antenna.
I do understand that contact points oxidize and their resistance increases. But the ohmmeter's needle didn't move even on the instrument's X 1000 range! I had no grounds that worked!
military handbook on grounding, bonding and shielding: A PDF download
any questions contact KB4GQN or KA1ULN