Alpha Delta, Polyphaser, Cushcrafrt & I.C.E. [Modern Coaxial Lightning Protection Arrestors]

Control Lines – Modern Lightning Protection For Radio Facilities

Most communication facilities have a variety of unshielded control line wires used for antenna switching, sensor monitoring, antenna rotation, telephone service delivery, or other local functions. While these lines are a necessary part of the overall station design, they also complicate matters from a lightning perspective because they.

Offer multiple entry ports for large and potentially damaging EMP currents during storms. The same lines also couple into transmitted RF energy and often re-radiate the signal at ground level where interference is likely to occur.

Protection from both of these possible ailments is a necessity in modem facility design, and the best way to achieve such protection is in the station’s bulkhead grounding system. Both protective and bypass devices can be easily fitted into the scheme if the lead length from the connection point to earth ground is kept short.

The length of attached leads running to ground is far more important than the specific material used for the connections, but heavy copper wire in the size range of #12 or larger is recommended.

Here are a few reminders when feeding station equipment with control lines….

1) Make a map of the entire control line layout to assure that no lines are missed when designing protection schemes.

Include the estimated length of lines between destinations and include overvoltage protection and bypass devices for any lines exceeding about 25 feet. Make the map in pencil so changes can be made easily and date the map for future reference.

2) Try to keep control lines bundled together where possible but group them separately from RF transmitting coaxial lines.

Coupling of RF signals into control lines can be severe if they are bundled together and run considerable distance due to coax cable shield leakage. It’s best to run RF lines up one tower leg and attach control lines to another tower leg to help decouple the two.

3) The use of lumped inductance in control line leads is generally a good idea. An inductor should have the same wire size as is being used for the lead and a measured inductance of 100uh or greater should be used.

The effect from inductance in lightning protection is that it slows down the incoming wavefront from the reactance of the coil presented to the incoming wave risetime.

In RF interference it acts like an RF choke to help stop re-radiation of signals. Bypass both sides of the choke for additional RF decoupling with capacitors rated to 1,000V or greater.

4) Installing rotator/control line protection devices (such as our Models 348 or 349) provide an excellent method of shunting overvoltages to a grounding bulkhead termination.

Always try to shunt all lines to a single bulkhead point close to where the connected equipment is located.

If the station is elevated (2nd floor or higher) always bring lines to ground level first for the installation of protective and bypass devices, then route the cables upward to the equipment chassis in series with any incoming lightning currents, possibly causing both damage and injury if you’re hit.

5) If you’re able to install control line runs in conduit or buried plastic pipe it’s generally a good idea. Not only does the pipe protect cables from weather but they are also protected from small animals (who like to chew on them) and the appearance of the facility improves!

AC Power Lines – Modern Lightning Protection For Radio Facilities

Lightning damage to electronic equipment caused by induction or direct hit and traveling along AC power lines is the most frequent port of entry in modem telecommunication systems. It’s not uncommon to find facilities that have extensive lightning protective devices on RF transmission lines and telephone lines but have little or no AC line protection.

It is possibly because AC line service protection is less understood, but more likely because there are few products available. commercially that offer really sound protection.

The reason that AC power delivery is such a common entry source is easy to see. Power lines are heavily exposed, usually for many miles from the equipment site.

They are often strung overhead, sometimes hundreds of feet high. A single lightning blast to exposed power lines can travel for miles looking for distribution means to reach earth ground.

In its path the surge will divide among many low resistance points, usually damaging all of them. Virtually anything connected to AC power is subject to surge distribution, and delicate solid state electronics are normally the first items damaged.

Yet protecting AC lines is relatively easy compared to other types of entry ports. But the only truly effective method of achieving good protection is at the service entrance of AC power to the structure where electronic equipment is housed.

In modern applications popular plug-in type devices sold in hardware stores offer poor, if any, protection.

The reason is that they are located far from actual earth ground in most cases, and they often have voltage breakdowns so high that by the time the device begins to work the damage has already been done.

Structural type protectors offer unique advantages.

First, because they are located at the service entrance they protect nearly all AC operated items in the building. The units activate on incoming high voltage AC or DC wavefronts, stopping them in the line of travel before they enter the building’s AC wiring distribution system.

Second, service entrance panels are most often located in a place where local earth terminal ground connections are nearby, so short leads of heavy wire are both possible and frequently installed by electricians when the service box is mounted.

A structural protector is designed for large incoming voltage surges of very high power. The better units offer hybrid action, which means that they employ two different methods of voltage attack and power handling capability.

Normally the two internal systems employed are Metal Oxide Varistor (MOV) technology and Gas Discharge (GDU). MOVs are particularly useful because they feature fast attack to overvoltage surges, dual polarity operation, relatively high power handling capacity if paralleled and are inexpensive.

Gas discharge units offer even faster attack times, higher power handling capacity per unit and dual polarity operation but at somewhat higher cost.

The use of GDUs are also a bit sensitive in the design stage because they go short when activated, possibly rupturing or not extinguishing properly in AC line service. There use must be carefully figured.

A combination of the two types offer the best performance, and a unit can be tailored to slope the attack mechanism so that the device can safely handle both small wavefronts and the inevitable large ones.

MOV devices installed in equipment cabinets is also a good idea, especially if the equipment is located 100 feet or more from the service panel entrance.

Another feature of MOV devices, no matter where they are located, is that they have large distributed capacitance in the structure of the device, offering some RFI protection as well.

Don’t forget to connect the ac service neutral ground to the facility’s grounding bulkhead system for wider lightning current distribution.

RF Entry Ports – Modern Lightning Protection For Radio Facilities

Lightning is one of Nature’s most destructive forces. It has the power of a good-sized explosive and cannot be avoided if you’re connected to antennas that are high and in the clear.

And it’s not just lightning. On a recent evening, our 160 Meter dipole (260-foot wire span) strung between towers at 180′ here at the I.C.E.

Factory exhibited several hundred volts of charge from a light rain shower – enough to shock one of the technicians working with the cable outside. During an electrical storm with overhead discharges, many thousands of volts have been measured on this wire, respective to earth.

In installations using coaxial feedlines, the measures used to protect station equipment are simple but critically important. Here is a list of observations and our recommendations in the strongest possible terms

1) Always bring coaxial cables to the ground level before entering the equipment area. Never bring coaxial cables into the building at an elevated height directly. Lightning currents induced into the cables will be forced throughout the equipment chassis on their way to the ground, and that’s what causes extensive damage. Even if your equipment is on the second floor, always bring coax to ground level first and insert appropriate lightning protection, then route the cable to the station.

2) Absolutely, absolutely, positively, positively ground those shields with as short an earth terminal connection as possible. Use a commercial shield grounding block is possible, or fashion your own. In most cases, as much as 80% of an induced or direct lightning blast comes in on the shield.

This is because of the external exposed nature of the shield and its larger metallic mass. Always make sure that grounding the shields occurs BEFORE the cable enters the building. Multiple shield grounding (such as once at the tower base and again before building entry) is an excellent idea.

3) Use lightning arrestors on lines that feed sensitive electronics. But beware. Don’t use so-called lightning arrestors that employ nothing more than a gas-discharge device to ground.

These units are DC passive and only activate when the potential voltage between conductors reaches hundreds of volts. By that time in most cases, the radio has already been damaged before the arrestor kicks in, leaving you with an arrestor that did mostly nothing and a damaged rig.

Additionally, gas discharge tubes are very low power, typically only around 1-watt dissipation. They’re rated for 20,000 amps or more, but only if a lightning blasts starts and ends in a few billionths of a second. Few bolts ever do, and bolts that are slowed down coming through transmission lines almost never do.

That’s why gas discharge arrestors require repair and replacement so often. They’re overpriced and offer little if any, protection from induced voltages.

If lightning. arrestors are used always specify a blocking type arrestor – that is, a unit that has no DC continuity through from input port to output port.

And one that offers constant drain mechanism with no pre-determined turn-on voltage has enormous power handling capacity, far exceeding the units that rely solely on gas discharge tubes or varistor devices.

4) Establish a grounding. bulkhead near the radio equipment where the distance from the bulkhead to the soil entry is short – preferably less than a foot.

Use this bulkhead for lightning protection as well as RF neutral for interference filters and similar items. The bulkhead can be a bar, metal sheet, or just heavy wire.

Remember – the length of ground leads is far more significant to good grounding performance than the specific materials or even wire size used. Keep ’em short!

Alpha Delta Vs I.C.E.

This is a comparison report between coaxial lightning arrestor units manufactured by Alpha Delta Corp. and Industrial Communication Engineers, Ltd. Both companies make a variety of such protective devices and are sold worldwide.

The I.C.E. design described in this report is protected by a patent issued by the U.S. Bureau of Patents and Trademarks in Washington, D.C.,

Alpha Delta’s primary configuration is a one part system consisting of a gas discharge breakdown unit connected in a shielded enclosure between the coaxial center conductor and an insulated, external ground terminal fitting protruding through the case.

The gas discharge unit (GDU) has a rated breakdown voltage in the 400-1000 volt range to allow the transmission of an-RF waveform through the unit without creating a sufficient voltage potential referenced to ground to ignite the conductor referenced to ground the gas unit ignites, creating a temporary low resistance path to ground, thus neutralizing the potential.

While this arrangement may be suitable protection in a few cases it suffers from numerous limitations that we believe to be serious. Among them:

1) The case of the unit that is connected to the coaxial cable outer conductor passes throughout the unit and no provision is made for grounding the case directly to earth ground.

In lightning strike applications, both direct hits and indirectly (inductively) coupled events, measurement studies have shown that as much as 80% of the incoming surge flows down the exposed shield of the cable.

The unfortunate result is that a large amount of the strike simply passes across the arrestor chassis and reaches station equipment frames, dividing between many destructive paths seeking ground.

2) The unit uses a pass-through center conductor.

Although the gas discharge assembly will ignite when the breakdown potential is reached many hundreds of volts are presented to the input of the radio equipment before the arrestor action occurs.

In modem solid state terms it means that the radio will nearly always be damaged or destroyed before the arrestor activates to neutralize the income electromagnetic wavefront.

3) The use of a gas discharge unit as a sole-source mechanism for neutralizing lightning currents delivered by heavy coaxial cable line conductors is controversial.

Gas units have only a small dissipative power rating, seldom exceeding, I watt. While the devices can handle large jolts of thousands of amperes of current, they can perform that service only if the entire impact event lasts only a few microseconds.

Lightning currents, especially slowed down by time constants due to the inductance of transmission line conductors are much slower to rise, endure, and dissipate. The result is frequent rupture and failure of the GDU, requiring down time and parts replacement.

Additionally, it’s difficult to determine the condition of a GDU in service, notably after they have taken a few suspected “hits.” They don’t always go short circuit, but they sometimes fracture and separate.

4) No constant drain method is employed to leak static development from cables. A coaxial line often acts like a large capacitor, storing electrical charge which can only leak off the line through antenna joint connections or through the insulated dielectric region between the conductors. When this occurs it nearly always causes receiver “hash” noise during electrical activity.

The I.C.E. design, shown below on the right side, took these characteristics into account during development and testing.

Our arrangement uses a central high voltage rated blocking capacitor which allows the free flow of RF energy through the arrestor device but blocks DC voltage and low frequency AC voltage.

The heavy inductor on the antenna side of the unit is the primary neutralizing agent. Voltage development is quickly shunted to ground through the DC shorting nature of the inductor/RF choke.

If large currents of a fast-rising nature are presented to the arrestor in such a way that a back-EMF develops across the inductor then the companion paralleled gas discharge unit ignites, but its only workload is to collapse the short-lived magnetic field of the inductor.

The result is an arrestor that is constantly active, requires no predetermined voltage to activate, and whose GDU workload is so low that is will probably last forever.

To date not a single replacement gas unit has been sold by us. The added resistance on the equipment side of the arrestor was inserted to provide a similar drain function on the user side of the arrestor, shunting away tiny currents that may appear from capacitor dielectric leakage during an impact event.

Schematic diagrams of the two designs appear below:

Cushcrafrt VS I.C.E.

This is a comparison report between coaxial lightning arrestor units manufactured by Cushcraft Corp. and Industrial Communication Engineers, Ltd. Both companies make a variety of such protective devices and are sold worldwide.

The Cushcraft “Blitz Bug” design and the I.C.E. design are both protected by patents issued by the U.S. Bureau of Patents and Trademarks in Washington, D.C. Cushcraft manufactures two different arrestor units that are basically the same principle but utilize different methods.

The first and most basic is the “Blitz Bug” patented by Mr. Cushman around 1960. In this device both outer coaxial conductor (shield) and center conductor pass directly through the unit.

Three metal fastener screws are drilled and tapped into the outer metallic conductor and driven in to a close proximity to the center conductor.

With the outer conductor at ground connection potential a voltage spike exceeding about 1,500 volts that develops between the center conductor and ground arcs across the space between the center conductor and the tips of the embedded screws.

There are no other parts in the unit. The second and more modern unit uses nearly the same philosophy but uses a gas discharge assembly between the center conductor and an external insulated ground terminal fitting protruding through the case.

The gas discharge unit (GDU) has a rated breakdown voltage in the 400-1000 volt range to permit the transmission of an RF voltage waveform through the unit without creating a sufficient voltage potential referenced to ground to ignite the device.

When a voltage greater than the breakdown voltage of the GDU appears across the center conductor referenced to ground the gas unit ignites, creating a temporary low resistance path to ground, thus neutralizing the potential.

While these arrangements may offer suitable protection in a few cases they both suffer from numerous limitations that we believe to be serious.

Among them:

1. The case of the more modem unit that is connected to the coaxial cable outer conductor passes across the unit and m provision is made for grounding the case directly to earth neutral. In lightning strike applications of both direct hits and indirectly (inductively) coupled events various measurement studies have shown that as much as 80% of the incoming surge flows down the shield of the cable.

The unfortunate result is that a large amount of the strike simply passes across the arrestor chassis and reaches station equipment frames, dividing between many destructive paths seeking ground. ‘Me case of the earlier “Blitz Bug” design encourages connection of the shield conductor to ground, even providing a terminal to do so.

2. Both units use pass-through center conductors. Although the gas discharge assembly and the arc gap (Blitz Bug) both ignite when their respective breakdown voltages are reached many hundreds or thousands of volts are presented to the radio equipment before the arrestor action occurs.

In either case when used with solid state radio gear it means that the equipment will nearly always be damaged or destroyed before the arrestor activates to neutralize the incoming surge wavefront.

3. Use of gas discharge units or arc screws as a sole-source mechanism for neutralizing lightning currents delivered by heavy coaxial cable line conductors is controversial. Gas units have only a small dissipative power rating, seldom exceeding 1 watt. While the devices can handle large jolts of thousands of amperes of current, they can perform that service only if the entire impact event lasts only a few microseconds.

Lighting currents, especially slowed down by time constants due to the inductance of transmission line conductors are much slower to rise, endure, and dissipate. The result is frequent rupture and failure of the GDU, requiring down time and parts replacement.

In the case of arc screws each “hit” causes some of the screw tip to be burned away so that the next jolt must be even larger to start an arc. Additionally, it is difficult to determine in either case the actual condition of a GDU or the arc screws in actual field service after they have been used for a time.

GDUs often fracture and break apart while arc screws scar and often weld themselves to the case. In both cases it is assumed, of course, that the internal resistance of the radio equipment that can take input jolts of the magnitude and service without damage or destruction.

4. In both designs m constant drain method is employed to leak static development from cables. A coaxial line often acts like a large capacitor, storing an electrical charge that can only leak off the line through antenna joint connections or through the insulated dielectric region between the conductors.

When this occurs it nearly always causes receiver “hash” noise during electrical activity.

The I.C.E. design, shown below on the right side, took these characteristics into account during development and testing.

Our arrangement uses a central high voltage rated blocking capacitor which allows the free flow of RF energy through the arrestor device but blocks DC voltage and low frequency AC voltage.

The heavy inductor on the antenna side of the unit is the primary neutralizing agent. Voltage development is quickly shunted to ground through the DC shorting nature of the inductor/RF choke.

If large currents of a fast-rising nature are presented to the arrestor in such a way that a back- MF develops across the inductor then the companion paralleled gas discharge unit ignites, but its only workload is to collapse the short-lived magnetic field of the inductor.

The result is an arrestor that is constantly active, requires non pre- determined voltage to activate, and whose GDU workload is so low that it will probably last forever.

The added resistance on the equipment side of the arrestor was inserted to provide a similar drain function on the user side, shunting away tiny currents that may appear from capacitor dielectric leakage during an impact event. Schematics for all three are below:

Polyphaser Vs. I.C.E.

This is a comparison report between coaxial cable lightning arrestor units manufactured by Polyphaser Corp. and Industrial Communication Engineers, Ltd.

Both companies manufacture a wide variety of such protective devices and are sold worldwide. Each of the designs described in this report is protected. by patents issued by the U.S.- Bureau of Patents and Trademarks in Washington, D.C. Although – there, are.

some subtle variations. in, the product line, Polyphaser’s basic coaxial line layout is. basically a two-component system.

As shown in the schematic below, a high-voltage rated capacitor is used as a central blocking device to permit the unimpeded flow of RF currents through the arrestor while blocking DC voltages and low-frequency AC voltages from passing through the arrestor while blocking DC voltages and low-frequency AC voltages from passing through the device to reach station equipment.

A gas discharge assembly having a breakdown voltage rating in the 400-1,000 volt range is used for transmitting services so that when a difference of potential between the conductors reaches this amount on the antenna side of the polarized unit the gas discharge unit ignites, shunting the voltage surge to ground.

While this is certainly a workable arrangement and the Polyphaser units are well built, we concluded in our engineering studies that there were significant limitations to the design. Among them:

1) No constant drain mechanism is provided in the Polyphaser design. A coaxial line acts often as a large capacitor, storing electrical charge that can only leak off the line through antenna joint connections or through the dielectric, nearly always causing receiver “hash” noise during electrical activity.

2) The use of a gas discharge unit as a sole-source mechanism for neutralizing lightning currents delivered by heavy coaxial line conductors is controversial.

Gas units have only a small dissipative power rating, seldom exceeding 1 watt. While the devices can handle large jolts of thousands of amperes of current, they can perform that service only if the entire impact event lasts only a few microseconds.

Lightning currents especially slowed down by time constants due to the inductance of transmission lines are much slower to begin, endure, and end. The result is the rupture and failure of gas discharge units, requiring frequent replacement and downtime.

3) It is very difficult to determine the condition of a gas discharge unit, especially after it has taken a few “hits.” They don’t always go short circuit.

The I.C.E. design, also shown below, took these characteristics into account during development and testing. We also use a central high voltage blocking capacitor, but with a large discharge inductor on the antenna side as a primary neutralizing agent.

Any voltage development is quickly shunted to ground through the DC shorting nature of the inductor/RF choke.

If large currents of a fast-rising nature, are presented to the arrestor in such a way that a back-EMF develops across the inductor then the companion paralleled gas discharge unit ignites, but its only workload is to collapse the magnetic field of the inductor.

The result is an arrestor whose gas unit undertakes such a low workload that is will probably last forever. To date, no replacement gas units have been sold by us.

The added resistance on the equipment side of the arrestor was inserted to provide a similar drain function on the user side of the arrestor. I.C.E. uses a four-part system.