Examples of Work on Electronics
Amateur Radio Station -- K1TMA
|General Theory -
This little “dissertation” on grounding systems is not meant to be an exhaustive study of every aspect of the subject but has the intention to provide the amateur radio operator with an insight into the purpose and the way it works and the reason behind its existence.
* Grounding has several purposes. Most commonly it is used for “electrical ground” in our homes. From the “service panel” there is a grounding rod directly below meant to provide protection for the house and consumer of the electricity. It provides a “continuity” of electrical current flow from the “hot” wire to ground. Every circuit must have a continuity between positive (+) and negative (-). By definition, ground is “earth” or the “conductor serving as earth.” With a good low-resistant ground in the electrical circuit, the earth serves as one half of the electrical circuit. As long as we do not get in between the “hot” wire and ground (earth) we will not interfere with the continuity of electrical flow in the circuit; if, however, the resistance to earth is too great, then the electrical system will seek out a lower resistant path to earth. A grounding rod provides us with that low-resistant path.
* An RF ground, on the other hand, though technically precisely the same, from a system’s or circuit’s viewpoint, provides continuity to the other half of the antenna and RF circuit. As an example, if we were to erect a vertical antenna, or an end-fed long-wire, we will soon discover, without a proper grounding system, the Standing Wave Ratio (SWR) will be very high, or too high to operate with our equipment, and the relative effectiveness will ultimately prove bad. A proper ground provides continuity in the RF circuit and represents the other half of the antenna. We can quickly prove this statement with a simple experiment.
* Erect a vertical antenna starting off with a simple vertical pipe in the ground. Place the antenna, say a multi-band vertical, on the pipe and connect the center conductor of the coaxial cable to the center conductor of the antenna. Leave the ground braid on the coaxial cable alone and go into your radio shack to listen to any band. Notice the noise level and radio signals to be very low. Now go back out doors to place the ground braid on the ground conductor of the vertical antenna. This time the noise level and all radio signals will be much, much louder.
* Go back out of doors and place 4 ground radials, with each length to correspond with the quarter wavelength of the lowest frequency the vertical antenna was designed to resonant, on the antenna in a north, east, south and west configuration. One end you connect to the ground conductor of the vertical antenna and the other end to a 10-penny nail in the ground. Wrap the end of the wire around the nail two or three times before driving the nail into ground. Then go back into the house. This time you will notice a significant increase in both noise level and signal. As you continue to progress with an increase in the number of ground radials you will experience a corresponding increase in the signal + noise to noise ratio. At some point, when the system finds ground path efficient and proper, the SWR will level off to correspond with the design-limitations of the antenna, ground radials, feed-line, etc.; noise level will start to peter off and the signal strength continuing to increase until its maximum increase roughly corresponds to approximately 120 ground radials. If the SWR still proves to be too high, then it will be necessary to either increase or decrease the electrical or physical height of the antenna to correspond with the resonance of your operating frequency. Noise level will vary significantly each day through-out the year; most of the noise is solar radiation from our Sun and it varies in strength and polarization constantly. On one band one day the polarization may be vertical and then horizontal the next day. You will notice, as an example, on 80 meters, the polarization of the solar radiation (noise) will be vertical and, on 40 meters, horizontal; on 20 meters, however, as you switch from a horizontal antenna to a vertical antenna, there may be no appreciable difference in noise. About 1 1/2 years ago, on 80 meters between the hours of 10 o’clock in the morning and 2 o’clock in the afternoon, the horizontal antenna was absolutely useless; the diagonal antenna partially useless and partially useful and the vertical antenna completely silent. Noise level with the horizontal antenna would register a S-8 on the S-meter; a S-4 with the diagonal antenna and almost no registration of noise on the S-meter with the vertical antenna. Then recently, when the Sun changed its polar polarization -- the North pole went South and the South pole switched to North -- the order reversed itself and now the vertical antenna proved useless from between 10 o’clock in the morning and 2 o’clock in the afternoon; the diagonal antenna stayed the same and the horizontal antenna was silent with no registration of noise on the S-meter.
* Another way to register the effectiveness of a grounding system is to compare the “growing antenna” with another antenna already in place. I did just that about 2 years ago. I was building a 3-wire grounded folded-dipole vertical antenna about 50 feet from my house in the center of the backyard. It was designed to resonant on the top end of the 80-meter band, or 3948 KHz. It is 59 feet high and each wire 15 inches apart from each other fed with 300-ohm feed-line; from there, it would go under ground to an enclosure 25 feet away. Inside of the enclosure was a constant-drain DC- continuity to ground type lightning arrestor and, from there, a balun to take the 300-ohm impedance balanced feed-line and to drop it down to 50-ohm impedance unbalanced coaxial cable. From there, it went underground again but to another enclosure to a remote-control antenna switch and, then, back underground into the house and my radio shack. Almost immediately, even before I had started the project of installing the ground radials, with a “capture area” of nearly 700 percent greater than the multi-band vertical, the noise level and signal level were just slightly less than the multi-band vertical antenna.
The reference antenna for comparison was a Hustler multi-band vertical,
trap loaded, and designed to resonant on 80 to 10 meters, including the
WARC bands. It was mounted on the side of a 5-foot high steel fence
about 150 feet long part of the way around my property. It did very well
on most bands but particularly well on 30 meters CW. The fence
was commonly grounded to the “system ground.” As I continued
to place more ground radials on the 3-wire grounded folded-dipole vertical
antenna, its superiority became more and more obvious until there
was no comparison. On the nightly Century Net, 3904 KHz, from 10 o’clock
in the evening to about 2 o’clock in the morning, until I was getting far
too tired to function properly, when I had placed almost 60 ground radials
in the system, the Hustler could not even begin to compete with the other
antenna. There were instances of not even a hint of a signal on the
Hustler, such as in the instance of my listening for an Hawaiian station,
when it was a solid 5 x 5 on the 3-wire grounded folded-dipole vertical
antenna, an excellent example of the effectiveness of a grounding system
(and superior capture area).
Relationship of the Whole Grounding System to Each Other
Starting from the back of the rigs on the table we attach the “bus bar ground” which is basically a piece of metal plate, bar or angle iron of 24 to 40 inches long, made up of brass, aluminum, copper or steel. From the back of each rig we would then attach a small metal strap, of about 8 to 14 inches long, to the “bus bar.”
From the “bus bar” we attach a 4, 6 or 8-gauge copper wire to the “system ground” outside of the house. This “system ground” is the major grounding system for the whole radio station and may consist of a single grounding rod, a series of grounding rods or an elaborate grounding mesh.
From there we would go to the “foundation ground” for the tower. If the tower uses guy’s wires, we would ground each guy wire at the anchor point and bury a “common grounding cable” from the “guy wire ground” to the tower “foundation ground” and finally to the “system ground.” Lets not forget the “plumbing ground” and the “electrical ground.” Connect them to the “system ground” in between the “bus bar ground” and the “system ground” from inside of the house.