Station Ground
Station Ground
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Related Pages: W8JI's new Contesting and Boatanchor Room Antenna System and my house station
If the antenna
system has common
mode current
problems, caused by
a faulty design or
installation, a
ground can help
reduce common mode
noise reaching the
antenna. This is
really from an
antenna flaw, and
not from the
"reflection of
signals". A ground will NOT.....
Unless you have a very tall tower or underground utilities, lightning most often strikes utility lines. Utility lines are a much wider area target. Power lines are much more likely to be struck than a tower twice their height. Lightning surges flow in the service drop and house entrance (D). A very small portion of the surge is diverted into the fairly high resistance entrance ground rod (C). The largest portion flows through the house wiring to the station equipment, and eventually out to the low impedance antenna system (A) and station ground (B). The station ground and electrical mass of the tower and amateur antennas look like a much better ground than the small rod at the service entrance. With the most common lightning hits and power line surges, good grounds installed at A and B actually increase current flowing through the house wiring and through radio equipment! Some people disconnect antennas. If A is disconnected and B remains connected, the radio is still in the lightning path from D to B. Disconnecting the antenna doesn't do much, unless the tower or antenna takes a direct hit or has induced charges from a nearby strike. Disconnecting the antenna, unless any possible path to ground is also removed, does not eliminate the most common cause of damage. Unplugging the radio equipment helps, but there is still a significant risk that lighting will flow though other paths from D or C to A, or from D or C to B. The best solution is to bond point C to point B with a much lower impedance path than any other path. B and C should always be bonded together. This is even spelled out in the National Electrical Code. "Common grounding is important to ensure an electrically continuous and uninterrupted path to properly dissipate lightning’s harmful electricity. Failure to make all of the required ground system interconnections is a common trouble spot cited in lightning protection system inspections." Many amateur radio installations have an independent ground rod outside the radio position. Ground rods that are not bonded to the power mains ground outside the house can, and often do, increase chances of equipment damage. Building and tower grounds and wiring methods provide virtually all equipment lightning protection. The building entrance ground must be tied to the power mains ground. The remaining work doesn't mean much one way or another so long as we don't do something wrong. Isolated Ground Leads and Grounds ( Avoiding Ground Loops)Never isolate equipment on the operating desk with feedline isolators. Our equipment is designed to be operated with the equipment tied together with low impedance cable shields. The only cables designed to and required to have ground isolation are shielded audio cables. While newer equipment is 12 volt operated, or has three wire grounded plugs, older gear often has internal HV supplies and two wire plugs. This equipment must be grounded to a good earth path for safety, otherwise the case of the equipment could rise to more than the highest voltage. For example a blocking capacitor failure in an old radio, with some antenna configurations, could elevate the s chassis to full high voltage. A line bypass capacitor could fail resulting in 120 VAC on the chassis, or a power transformer could short from primary to a grounded secondary winding, adding the secondary voltage to the power line voltage and applying it to the chassis by pushing against the power line. Older equipment also often has power line voltage, sometimes un-fused, on external relay lines. While more modern gear is generally safe, it is best to always bond all gear to a common heavy buss on the operating desk. This buss should be reliably bonded to a good earth path. Any claim you should run isolated grounds to the earth from each piece of gear is not only false, it is also dangerous. Such a silly wiring scheme actually encourages ground loops, as well as decreasing electrical safety for the operator. Some amateur gear is not grounded through a three wire plug. This equipment requires an external safety ground connection to the chassis. This means some stations actually require a station ground buss. This additional ground at the desk will never hurt, and it will never bring lightning in if properly done. It will only make things better, although it often is not necessary. More modern stations
sometimes do not require this
ground because all
of the gear has
three wire plugs or
is 12 volt operated.
If a station buss is
required, place it
at the desk. Every
piece of gear should
connect directly to
that buss as a
common point. That
common point should
run to the station
entrance panel on
one large flashing,
braid, or large
conductor wire. The
station entrance
panel ground must
ground all cable
grounds as they
enter, including
power mains and
telco grounds.
Everything has to be
at the same
potential entering
the room. Do NOT listen to fool's advice to run a separate wire from each piece of gear to the ground rod, or worse yet use separate ground rods, to avoid "ground loops". That would actually create undesired ground loops! This is true at your operating desk, at the entrance, or at the tower. Do NOT use isolators on coaxial lines at the operating position. That is not the place for them, it creates a harmful situation! My Station GroundingMy ground system works. My towers get hit at least once in every major lightning storm, and we have at least a dozen severe lightning storms a year. I never disconnect anything, not even consumer devices, and I have never even lost a sensitive computer modem or delicate VCR to lightning. Tower GroundsThe following is typical of my tower grounds:
Because this is the point where most lightning current passes, the grounds are wide flashing high temperature silver soldered to the ground rods. This ground does not reduce the chances of a hit. It prevents the cable shields and control wires leaving the tower from being the sole path for lightning currents. in other words, this ground reduces current on wires leaving the tower for the house in the event the tower gets a direct hit, or has substantial charge from a nearby strike.
Some people say you have to cad weld to have a good connection. That isn't true. We installed many commercial towers using silver solder, and those ground systems are still good after 35 years. The old green patina flashing in the picture was installed in 1998. The older tower and its grounding strap has been removed, but during its life the silver soldering survived what must have been hundreds of direct hits. This is high temperature hard silver solder, not plumbing solder. #14 AWG radials are also tightly wrapped and soldered with high temperature silver solder to a number 6 AWG solid buss wire. That buss wire follows the perimeter of the tower pad. I've never had a #16 or larger ground radial fail from lighting hits so long as there are at least ten of them to share current. I use copper pipe for ground rods. To make the connections to the pipe, we use a step bit and blocks of wood to drill a tight hole in the copper flashing. We force the flashing down over the rod. We fold it slightly upwards to cup the joint and fill the resulting depression with high temperature silver solder using a MAP gas torch. You must use high strength high temperature solder, not traditional plumbing solder.
All four corners are grounded to the tower legs. Most of the real work in the ground system is done by the buried radials, not the pipes. An interesting point, i measured the ground currents in my old insulated Rohn 45G 300-foot tower. During an approaching severe thunderstorm, the total corona current was a few hundred milliamperes maximum. unless there is a nearby or a direct strike, current is not that high. Also, the ground system does not "bleed off" and discharge clouds. That is a myth. There is no discharge path to the clouds other than lightning.
Workshop entrance and ground: Entrance grounds are critical.
This is the entrance ground point of my work shop. The copper pipe has no water, it is actually a ground. It is driven six feet deep, and connects to a buried #8 buss wire running around the outside of the building. Copper flashing ties it to an entrance bulkhead under the rain hood. A number six solid copper wire ties the telco and alarm ground to the feedline ground. The power mains (breaker box) is also located inside the building at this point, and it also grounds to this point. Receiving antenna, transmitting antenna, and control cable entrance at house:
Ground conductors and cable shields entering the house are grounded to wide copper flashing. The wide copper flashing connects from my station ground inside the house to the utility company and circuit breaker panel ground. The perimeter of my house has a #6 solid copper ground wire that bonds to the water line, propane tank, TV antenna tower, satellite cable, shack entrance ground, and telephone and electric service ground rod. The wide flashing you see also continues under the house directly to the power mains entrance ground about 30 feet away. This ensures everything in the house comes up at nearly the same rate during a lightning strike. Large lightning currents do not flow through the house wiring.
House station internal common point ground: My house station is being rebuilt. I'll update this over the next few weeks. Transmitting cables go to a single point where an 8-position relay cross-over antenna switch routes cables and harmonic suppression filters to various radios. This switch allows any tower's grouped feedline or single antenna feedline to be connected to any radio. Receiver cables are not wired yet, but will go to a common grounded switching matrix.
Station power comes from this point:
Every ground is bonded to the common point. That common point is bonded to the feedline entrance ground. The large relay transfers a 25 kva generator on line.
The power distribution to my desk follows:
That outlet distributes 120/240 volts continuous. The smaller metal outlet branches off to feed a battery backup supply for my computer, VHF/UHF radio, and scanner. Radios and low power equipment are powered from a master switched outlet:
This master outlet strip feeds a smaller strip for very low power devices:
Eventually these cables will be dressed up a little more.
My transmitting antenna layout. If I can protect this system and not have hardware failures during storms, other stations can be safe also. There is no reason for lightning damage to a 70-foot tower when I can have all my equipment connected in storms to a large system like this.
The receiving antenna layout (not shown) extends for almost one mile! Small dotted lines are buried feedlines. Solid black or gray lines are overhead spans. The transmitting antenna switch matrix is fairly complicated. Here is the basic switching matrix:
I have five primary towers; a 200-foot rotating tower with antennas for 160 meters through 70cm, a 220-foot tower that provides a 160 meter omni vertical and an eight direction four square, a 318-foot Rohn 65G tower with multiple antennas, a 300 foot Rohn 55G, and a 70-foot Rohn 25G for small Yagi antennas. Each tower has antenna switches at the base. The 318-ft Rohn 65G tower has an additional switch mounted 1/2 way up. Feedlines are sized to keep loss below 1dB to any antenna feedpoint in the system. Everything inside the radio room is grounded to the large copper flashing. This is additional assurance that everything in the radio room comes up at the same rate. Despite this system having miles of coaxial cables spread over an area covering many thousands of feet, and despite all of these cables being connected 24 hours a day, I have never even lost as much as a computer modem or TV set in a storm! I have had a super-bolt melt the shield of heliax at my 318-ft tower base. Radio, computer, and TV equipment in the house were not damaged during that hit. The worse damage I ever have are coaxial cable shields outside the house that melt from direct hits. Protection is really more about how things are connected than anything else. For more grounding look at my contesting barn's entrance.
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