Batboard

Vol FD has never had a base station. Spent DHS grant $ on "kit" speced by our normal vendor - an ICOM vehicle radio (same unit as in our trucks) w/115V power supply, tripod base, mast, antenna, coax, etc. This was spec by radio company we typically use and supposed to be all we need) I see no ground/earth materials which I assume is critical to proper function. Power supply will be plugged to a 115V PC style UPS.

Co Emerg Mgmt ran out of DHS$ before they could fund install so have to do so ourselves. Antenna install will be on the peak of roof of our metal (roof & walls) fire station. Station has 2' roof overhang all sides and interior walls are chipboard. Approx 50' of cable required from antenna location at peak of one end of the building to the "CP" desk.

I know diddly about this so I'm looking for advice/web links for proper install and routing of cables and associated equipment.

As you say you have no ground materials, I would assume grounding as in lightning protection. Yes, you should have this, especially if it is to be mounted on a metal building. I would recommend at least some nice thick copper wire from the tripod base to the ground, terminating into a 6-9' copper ground rod in the ground. As for the antenna cable (coax) make sure not to crimp it or bend it at too tight an angle weather it be in out out of the building. Also have someone come out and check SWR/Loss ratings on the install when it is done to make sure that all is well. Your comm. supplier could probably do this for you.

It's also not a bad idea to run a surge protector on the power supply of the base and anything elese running in association with it.

It is also a good idea to 'loop' the coax on the mast of the antenna, directly below the antenna an inch or two. This way, if in the unfortunate event it is hit, more of the hit it transfered to the mast rather than the antenna and feedline.

You may also want to invest in a lightning arrestor (clyndrical adapter put in-line in the coax that acts kinda as a 'fuse' for the coax when hit by lightning) near the rear of the radio where the feedline comes in (and ground the arrestor as well) that way the radio is at least isolated this much from a strike.


Now, althogh the setup should work fine without all of the above + grounding stuff, you should really have it grounded.

When mounting a tripod on a metal roof, you should take time to evaluate the internal roofing structure so the 3 leg brackets are fastened to 2 by 4 wood studs to insure a sturdy mount for the tripod, mast pipe and outside antenna during heavy winds. If you're using Schedule 80 water pipe as a vertical mast for the antenna, keep the lenght to 10 Feet or less, to prevent excessive wind loading from occuring between the antenna and mast pipe. Do not allow the mast pipe to rest on the metal roof otherwise the flexing could develop hole damage in the roof and allowing water to seep into the Fire Station.

Grounding the antenna, mast pipe and coaxial feedline is very important to prevent Lightning Damage from occuring. Use a number 6 or 8 A.W.G. securely fastened to the mast pipe and a 10 Foot Ground Rod driven into the Ground. Now this is very important, if your antenna Ground Rod is located near (within 50 Feet) of your Electrical building Ground, connect a Ground wire between the antenna's Ground Rod and the 110/220V AC Electrical System's Ground Rod. If you do not do this ... when the Lightning hits the antenna and travels down the heavy guage wire to Ground, the Antenna Ground appears as -Negative and the Primary Electrical Building's Power Ground appears as being more +Positive allowing the Lightning to come up on the 110/220V AC Primary Power Lines jumping over to the Telephone lines and damaging more electronic equipment.

Read about Antenna Surge / Lightning Protection at the following web pages:

http://www.polyphaser.com/kommerce_products.aspx

And:

http://www.harger.com/

Thanks for the help. Actual routing of the coax of importance? As coax I assume it shields itself. I think base at end of roof overhang (hopefully "feet" will land on purlins), coax falling over the gable end and running down along the bottom of the soffit then thru the metal wall. Drip loop outside of the at the wall penetration.

The UPS sufficient for surge protection or also a surge protector strip?

Will have to order a lightning arrestor.

The coax feedline should have a minimum of two grounding kits on it: at the first bend below the antenna and the last bend before entering the building. These kits should be cad-welded to your ground rods.

All the above information is pretty good except for the grounding.

I have been installing Motorola and others Fixed end equipment for the past 13 years. I have installed antennas on just about anything...from telephone poles to tower legs to roof tops to attics.

Just about every situation is different with respect to cable type, entry, termination and yes grounding.

You mentioned that you will be using a tri-pod type mount to secure the mast to and that the roof is made of metal, you will be wise to purchase large rubber mats to have under this tripod for a couple reasons. One is to give the tri-pod and more secure platform to rest on, meaning it wont move around as much if it was just sitting on the metal roof...sliding comes to mind in this case. These large rubber mats lay on the roof top and then you assemble your tri-pod to rest on top of them. Also, I'm not sure which tri-pod mount you got, but they do make very simple ones that allow you to place cinder blocks around it to keep it from moving. I'm familiar with all the various ones, I now the type you can get from radio shack and I hate those...LOL, you have to actually bolt those down into the roof for best stability, I've seen the use of railroad ties to keep them in place also. Second, the metal to metal contact becomes a major issue for lightning. The fact that you have a metal roof and you then place this metal tri-pod onto it, you have now in essence allowed the entire building structure to become energized if struck by lighting.

The statement above about putting a loop in your coax is a very bad idea, that can and will cause a ground loop and if the coax was ever hit by the lighting, it would not follow that path around the cable...it will jump off onto something with less resistance....proven fact that lightning always follows the lest path of resistance. It wants follow a straight line...it meets a curve or a bend or anything with resistance it will always look for a better path.

On towers with 200 feet or more, we put coax ground kits at the first vertical section of the coax under the antenna and then every 200 feet until we reach the Ice Bridge, we then place one just before it enters the building at the entry port, then just inside the building, we install a lightning arrestor to protect the center conductor.

The minimum size wire gauge you should use to ground your mast and the metal tri-pod is #2 AWG, either the green jacket stranded or the un-insulated solid...and unless you plan on grounding everything that your electrical system is connected to...do not tie your antenna ground into anything other than it own ground rod if possible, if you don’t have that luxury...then try grounding the #2 AWG to the building steel somehow, either with a beam clamp or nut and bolt it to the beams. Once you bond your antenna system into the electrical system without a single point ground ...you have just energized the whole building from a simple lightning strike from your antenna system.

So...this is what I would do if I was the guy coming out to install this base station antenna for you

1) Place rubber mats on roof top were your tri-pod will sit.
2) Assemble tri-pod and run a #2 ground wire from it to your dedicated ground rod or building steel.
3) Mount the mast into the tri-pod and run a short #2 ground wire from it to the first #2 ground with a split bolt.
4) Run your coax from the antenna to your radio location entry point into the building.
5) Place a coax grounding kit just below the antenna and attach the #6 AWG wire that’s part of the kit to the #2 ground wire that’s attached to the mast
6) Just inside the building were your coax has entered is where you should put the lighting arrestor.
7) Run a #6 green jacket ground wire from the lightning arrestor back out the wall you ran the coax thru and attach it directly to the #2 ground wire you ran to the ground rod or building steel.
From the other side of the lighting arrestor run another piece of coax to the radio itself.

This will give you the best protection...but its not full proof. I've grounded shelters using the Motorola R56 standard, and they still get hit by lighting and they still cause damage, but at least it’s minimal.

I sure hope this helps some.