Space
 
In This Issue      
   
This issue of Extreme Currents is focused on exploring and answering some of the unique questions and requirements of protecting military equipment in whatever environment it is deployed. From the cold arctic to the scorching sands of the desert, military communications systems are subject to extreme environmental conditions, and a high probability of direct lightning strikes!
 
           
    On the Flight Deck...   Or in the Desert...  
    CVN-72 USS Abraham Lincoln in the Aranian Sea (Click for High Resolution jpg) C130 Hercules at Balad Air Base, Iraq (Click for High Resolution jpg)  
    (U.S. Navy Photo/Mate 2nd Class Aaron Ansarov) (U.S. Air Force photo/SRA James Croxon)  
   
At sea aboard the USS Abraham Lincoln (CVN 72) lightning strikes on the horizon light up the bow of the aircraft carrier during a storm in the Arabian Sea.
An incredible lightning strike near a C-130 Hercules at Balad Air Base, Iraq. Balad handles more than 750 cargo flights each month and is the DoD's busiest single runway.
 
       
    The Protection of Sensitive Communications Gear is Mission Critical  
       
   

Because communications gear includes an antenna, which works best unobstructed at a high elevation, odds are that the antenna is higher than anything else in the area. In addition, the unit may be deployed at sea or in the desert where there is nothing else around. Consequently, lightning or transient surges will strike the antenna. Without protection, the radio will fry probably causing an aborted mission, or worse a hole in the communications infrastructure.

Click to go to the Online Library of Lightning Resources  
    What can be done? How do we protect our gear from getting slammed?  
       
    The Direct Strike and it's Indirect Effects  
   
A direct lightning strike involves an enormous release of power -- millions of volts and 200,000+ amperes; nothing but extreme engineering designed devices can survive a surge of this magnitude. What's required is to provide the surge a direct path to ground, and provide secondary protection against the strike's cousin -- the transient surge. A transient surge is defined as the secondary effects of the lightning strike - the energized field surrounding the lightning bolt itself, or the ground potential rise.
 
     
     
     
       
    NexTek Case Study: A Sacrifice to Protect the Equipment  
       
   
The device below was developed specifically for a mobile launching vehicle with a 100' retractable antenna mast. Because of the deployment locations, there would be a high probability of a direct lightning strike.
 
         
    Direct Strike Protection (Click for Datasheet)

Even though a substantial grounding structure was developed for the vehicle, it was determined that a significant surge on the transmission line would be inevitable. The challenge was to protect the equipment regardless of the surge size - and to do it repeatedly!

The specifications called for a protector that could withstand multiple 150kA surges and survive at least one 200kA pulse - A tall order!

The antenna attaches directly to the large 7-16 connector on the exposed antenna end of the arrestor. In the event of a large direct strike the antenna and jumper cable is sacrificed to save the 100' cable and the subsequent equipment.

 
   
A spare antenna aerial, jumper cable, and, if necessary, a new arrestor can be on hand for a rapid replacement, with the overall system back on-line in minutes.
 
           
    Total Protection Design  
       
   

Although the system is protected from a direct strike to the antenna mast, the radios are still vulnerable to transient surges that can be coupled over from the grounding structure into the coaxial cables. The current of these transients can reach upwards of 40kA. To safely protect the overall system arrestors need to be installed at each end of vulnerable cables. The design on the right (click for a larger image) generically illustrates a complete coaxial protection design for the mobile vehicle.

With the exception of the upper antenna mast, each subcomponent is protected and will be operational after a direct strike to the upper most antennas. With the addition of the optional quarter wave stub units and the fine protector closest to the radio equipment, the transient surge has been reduced to about 30 volts peak going into the radio.

For more information on how NexTek can help you protect your system design please contact NexTek for a free consultation.

Multiple Radio Mast Design - Click for the large image  
     
     
     
     
     
           
   
A Layman's Guide to Choosing a Lightning Arrestor
 
           
   
Coaxial cables are often used for RF signal transmission in situations that significantly increase the risk of lightning energy and damage. Here we will touch on the most important parameters for the selection of a coaxial lightning protector, including Radio Frequency (RF) performance, Arrestor Device Type protection capability, and construction materials.
 
       
RF Performance
 
     
Coaxial protectors are intended to pass through a desired RF signal with minimum loss or disturbance. When RF energy enters a protector, the energy is, in some combination, passed through, reflected back, and dissipated within the device. The fundamental RF performance parameters of a coaxial connector are RF frequency and the corresponding insertion loss and VSWR (or return loss). The loss of signal level through the protector is called Insertion Loss and is measured in decibels (dB). The reflection of a signal back to the source is measured as VSWR (or return loss in dB).
 
           
   
Rule: To minimize the impact of inserting lightning protectors within the RF circuit, seek out products with the lowest Insertion Loss and lowest VSWR at the frequencies that you intend to operate.
 
           
   
Use only High Quality Arrestors
     
   
Protection devices are more than insurance against equipment damage. They keep the danger outside. Beware of the junk arrestor products that proliferate in the marketplace. Transient surges can have enormous power, and are extremely dangerous. Beware of the "it sounds too good to be true" marketing hype employed by some vendors. Only properly engineered designs, high quality materials, and certified manufacturing processes can produce products capable of withstanding the high surge currents which will not deteriorate over time (weather proofing and shock and vibration ruggedness are keys to protector longevity and RF performance).
  Got a Lightning Protection Question? ---Ask NexTek!  
           
   
Application Spotlight
 
   
Military
 
   
The Highest Performance Protection. Period.
 
   
 
    Custom Designs  

NexTek’s engineers are lightning protection experts who bring unsurpassed design experience and product knowledge to help you define the exact custom design to meet your specific application needs.

They will review your design requirements and work with you from project definition, through prototyping and final production to assure that you get the right product, on time and on schedule.

 
       
   
Our technical knowledge and library of custom designs combine to provide our customers with a tremendous resource that can expedite the development of highly specialized custom products. Whether you need a minor change to an existing product or a completely new design to meet specific requirements, call us today with your lightning protection challenge and experience the benefits of working with…Your Partner in Current Innovation.
 
           
    World Map of Lightning  
           
    Interesting Links...      
           
    Cool Lightning Facts      
           
    History and Mystery of Lightning      
           
    Lightning Discussion Group on Yahoo - Over 2400 members!    
         
    The most recent past issue of Extreme Currents The original Extreme Currents Newsletter!  
 
 
Visit us at nexteklightning.com Questions or comments? E-mail us at enews@nexteklightning.com or call 978-486-0582
©Nextek, Inc. 2 Park Drive Building #1 Westford, MA 01886