[TowerTalk] PolyPhaser Inductance Calculations

[ROBERT A. WANDERER]

     Dan
     
     First off, it's a 150' tower in parallel with 135 feet of coax. 
     
     Insofar as #6 vs strap. There are three factors: surface area 
     [the grounding system's surface area must equal or, preferably, 
     exceed the circumference of ALL the cables and/or waveguides 
     attached thereto], skin effect, and inductance. Two 8'-long #6 
     wires will have half the inductance (and voltage drop) of one 
     wire alone, 3.4uH vs 1,7uH with Vd's of 8.2kV and 4.3kV 
     respectively, and be slightly better (0.1uH) to the value for the 
     one 6"-wide strap of equal length. In that respect you're 
     correct. However, those two #6's will suffer from the first two 
     issues and is akin to having a four-lane asphalt highway suddenly 
     become a one lane dirt road. Therefore, more surge energy could 
     get into your equipment. Remember that the PolyPhaser coax 
     protector is dumping the surge energy on the center conductor to 
     this ground system as well.
     
     The primary issue is inductance, but our bulkhead grounding 
     systems come with two 6"-wide straps, which of course is far 
     better than two #6's. I have been to many commercial sites where 
     they use but one #6 or #2 for the ground path. Our main point is 
     that the cables should come to the very bottom of the tower 
     before heading over to the building. In this respect, hams are 
     usually "better" than the commercial folks.
     
     Hope this helps!
     
     Sincerely and 73,
     Bob Wanderer AA0CY
     Senior Applications Engineer
     PolyPhaser Corp.

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