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This was answered off-line but for the group:
"Floyd Sense" wrote "Jack Painter" wrote in message snip The coax shields grounded at the tower (min. at the bottom, best top and bottom), and again at the basement entrance single point ground. Shields must be grounded before connection to an arrestor. Jack - regarding your comment on grounding the shields BEFORE connection to an arrestor: My arrestors are mounted on the common ground panel and the coax is grounded via the coax connector to those arrestors. What is the reason for a separate ground prior to that one. Maybe I misunderstood something, but it seems redundant to have a separate ground a few inches from that one. Coax shield grounding must be accomplished at the tower top, tower base (on ground level, not even 6" above!) and before the arrestor to comply with protector manufacturer requirements and to be in keeping with best engineering practices that are used nationwide in communication tower designs. The grounding just before the arrestor is for two purposes: 1. preventing unnecessary energy (whether capacitively or inductively coupled) from challenging the gas tube, MOV, coil (or all three) mechanisms of a protector, and 2: to help limit the differing potential available to reverse-path voltage from a nearby strike in ground potential rise conditions. A nearby strike can saturate the ground system, and a station ground can reference hundreds of thousands of volts 'up' from the ground, and 'out' via arrestors, phone, power cables to lower potential felt at some distant point. Grounding cable shield at the station single point ground thus helps maintain equipotential for both directions. Even if the station coax arrestors are mounted on the master ground the additional grounding is still helpful for voltage-division during saturated ground conditions. But in all cases that ground bus mount must never be the only place the coax shelding is grounded! In response to another's comments regarding protection of the SteppIR, rotor, and other control lines: I use MOVs and .01 bypass caps on all those lines in a box at the base of the tower and have another set of the same at the entry panel box. Those components are mounted via European-style screw terminal strips (12 positions per strip) obtained from Jameco via the Web. Much cheaper than the same from Radio Shack or other sources. MOVs came from Mouser. A lightning strike last year entered my shack via relay control lines which were unprotected at that time. Hopefully, the new arrangement will help. 73, Floyd - K8AC Several amateurs have reported successful use of private design MOV on control lines. While this could exceed commercially available equipment specs in some cases, for those less familiar with such designs, they are readily available in package-form to protect control lines. Jack |
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