Batboard

cross-posting my ramblings from tower-pro and repeater-builder groups...



I have a unique site that I need some help figuring out exactly how to handle a unique site installation.

Reading through both volumes of the R56 site standards books… I have yet to find anything that talks about “abnormal” site installations.

Here’s the background.

One BIG bridge. Four concrete pillars. Roadway is approximately 200 feet above the water. Pillar height above the road is 460 feet ­ about 660 feet AMSL). Equipment access point is 100 feet below the top of the pillar (about 560 feet above the water). This is where the equipment MUST be installed. No option of placing it at the roadway due to some contractual limitations. Access to the site is pretty severely limited due to the traffic, coast guard, police, etc. This is truly one of the best sites still available at no cost ­ very high ­ great vantage of the city ­ free, and a minimal hardline run (<100ft) ­ did I mention free?

Besides the fact that the equipment has to be man-handled up to the access point (been there, done that before ­ cargo net and a bunch of fat guys can work wonders…) there is a problem with power and grounding.

The power in the access room is tapped from the bridge lighting system ­ it’s entirely adequate for our requirements (about 16 amps absolute max) but I am unsure of what the best way to protect the equipment from transients would be. In the past, and in my experience, a simple transtector (or similar MOV/SAD device) was entirely adequate for a site installation (think typical, properly outfitted radio site). However, there is NOTHING on the bridge AC system to my knowledge that provides even a little protection to the power circuits on the bridge.

Let me tell you that the equipment being installed is a Motorola Quantar repeater ­ not your run of the mill micor or MSF. Both of those (and other) legacy gear have massive ferro-resonant power supplies that can withstand a lot more abuse than the switching power supply in the Quantar. Since this Quantar is mine (and not some billion-dollar conglomerate) I would like to provide “well above average” power filtering for it. I am debating some kind of APC UPS or something for the repeater. I know I’ll hear volumes about that ­ but I definitely want something that will prevent “sags” in the AC power as well as the ability to clamp anything that gets past the old reliable Transtector. The idea here is to plug an APC/UPS into the transtector…. Hopefully providing a little better protection for the repeater. No, I am NOT hauling 4 deep cycle marine batteries up 460 feet to the access point.


Ok, on to question #2…. Grounding. Or lack thereof. The only grounding (besides the AC power system) is the lightning rods at the top of the pillar. Besides the fact that there is no way to ground the Quantar cabinet… The big question here is grounding the hardline. In all the installs I have been a part of in the last few years, the hardline outer shell was grounded at the TOP and BOTTOM of the tower ­ to the tower. I have no luxury of this at this bridge. Discussing this with a local Moto technician who installed a federal gov’t repeater on one of the other pillars at this site revealed that the tower crew grounded the hardline TO THE LIGHTNING RODS at the top of the pillar. Don’t think 10 foot rods here… more like “rooftop” 1-2 foot rods… With the antennas mounted to the railing (yes, it’s sturdy gavalized pipe sunk into the concrete). The hardline on the other repeater is also grounded at the bottom of the pillar near the government repeater (don’t know where though). I need some opinions here. Should I even ground the hardline at all? My concern is that the antenna (direct grounded) will need a proper ground path to shunt any (!) strikes to “ground” ­ no ground = nowhere for the energy to go (except blow apart the antenna)… trust me ­ I am NOT a big proponent of tying the hardline to the lightning rods.


Anyway, if anyone out there has “been there ­ done that” ­ I’d love to hear your thoughts and opinions.

If you made it this far - thanks for the read - i am also looking for what motorola calls a "modular rack" or "T-rack" - basically an open 19" rack that has a pedestal at the bottom. No way i am pulling a full size quantar cabinet up to the top of the pillars... not to mention - it probably wouldn't fit through the access door....if you have one of these and you're in the southeast (florida, georgia, alabama, carolinas, etc) - please contact me ASAP.

Doug

Is this massive pillar by chance steel?? If so, can't you just ground it to the pillar itself??

Power: one "Heart Interface" (Xantrex), 1 kW model, plus two G31 marine gel cels. Wire "AC In" to your bridge power system, "AC Out" to a duplex outlet, "DC" to the batteries in parallel.

Will cut in at VAC (rms) >135 or <95. Will provide at least 6 hours of stand-by power (at nominal duty cycle). Will transfer so fast that Quantar will not see the drop and re-boot.

Search on "Heart Interface" in the archives of this Board for more info.

My repeater antenna is at the 450 ft level of a 600 ft broadcast FM transmitter tower. I'm using the better part of 550 feet of 1-1/2 inch "hard" line. This is grounded where it enters the building. It's also grounded at the bottom of the tower where it heads down the cable tray to the building. I do not know if it's grounded up at the antenna or not, or at any other places along the route. Whatever method they used to attach it to the tower might be providing a ground connection. My equipment cabinet is also grounded to the building's ground, a four inch copper strap that runs around the perimeter inside, and to all the equipment cabinets in the room. This is then brazed to some ground system outside the building which is attached to steel girders that support the ice shield above the building. My repeater's antenna connection is through an Alpha Delta lightning arrestor.

I would agree with you that grounding to the lightning rod system is probably not a good thing, but you should provide grounding somehow. Certainly where it enters the building or equipment room, and optimally somewhere else as well.

The site has suffered nearby lightning discharges several times. Phone lines going to the transmitter's remote control have been disabled each time, usually at the main service panel at the side of the building. A few times there was also damage to the remote control unit, but I'm pretty sure that some protection equipment has been finally installed inside to deal with those transients.

My repeater is running through an APC SmartUPS 1000. It's entirely DC powered by an Astron RS-35M power supply. As the room I'm in is also on the station's stand-by generator, if the power should fail, my UPS only has to keep things running for perhaps 10 seconds before the generator picks up the load. I have no other connections to the outside world except the power line and coax. I've had absolutely no problems in the 2+ years I've been on the air.

This weekend (finally) my "MaxTrac" repeater will be replaced by an 80-watt MSF5000 station. Same duplexer, same lightning arrestor, same UPS. Hopefully it will run as good as its predecessor.

Bob M.

You have an interesting set of problems. Each with their own ramifications.

The power surge protection should have a top place in your efforts. You may want to go look at AC Data Systems web site http://www.surgeblox.com and take a look at the power protectors there. Have used their devices on cellular sites for a number of years now. They do an excellent job at protecting the equipment. The moduals that may fail due to a strike, are replaced free.

Next issue is grounding the equipment and power surge protector. There has to be some steel in that tower pillar. You just need to be more observant to locate a connection to it. There sould be a point where a ground point was made available. You just need to find it. They may have covered the steel with a fire proof covering.

Tieing to the lightning rods, may be your only choice up top. Again, look around and see just where the ground wire goes from the rods. It's going to go back to the main steel beams in the pillar some place. Just remember that most lightning protechtion people don't like their cables attached to. Some techs will tell you that doing so will viod the warranty on the system.

Just remember that you want everything to go up and down at the same potential at the same time. This means bonding everything together to prevent current flow.

Another problem that might show up on the bridge lighting circuit is if it has flashing red lights. These are high wattage lamps that cause the voltage to make several volts jump down when they go from off to on. If the normal towers have a voltage swing of several volts, it wouldn't be surprising to see maybe a 10 volts or more swing on the bridge.

Good luck. Keep us posted on the investigation and outcome.

Jim