studio grounding

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grich
Posts: 311
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

studio grounding

Post by grich » Thu Feb 25, 2016 5:29 pm

When it's not practical to run strap between studios and the station ground, and you have a 1kw AM TX in the back room, what have you used for RF grounding? Slab floor, walls are finished, and 3/4" smurf tube is run to the attic, but the smurf has a couple of sharp bends, so getting 1/0 THHN through it ain't gonna happen.

Looking at MTW cable (with finer strands than THHN), flat tinned braid, even thought of cheap surplus RG-8 or triax, anything with a lot of surface area in the shield. I've been in other facilities where racks were bonded with 1/0. What say you?

TPT
Posts: 679
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: studio grounding

Post by TPT » Thu Feb 25, 2016 6:53 pm

Strap would be ideal--at least in each room--even if you then had to break it down to smaller wire to get outside.

Some basic questions: Own or lease building? What are the outside walls made of? Is the transmitter room on and outside wall? Studios? Interior walls?

We had to build a studio in a split level house--in two months (bought the station housed in a cluster & run under an LMA/LMA not renewed) but had the advantage of an unfinished garage beneath the bedrooms, err, studios. Ran strap up to each console, and to rack in rack room, electric panel, then out the garage window to a water well.

But back to your situation. I would tie transmitter, rack, & whatever else in that room together with strap--bond to any coaxes coming in from outside as well. If the panel is in the same room, run strap to that as well. Run the strap across that slab floor, then get some linoleum remnants or press & stick tiles (get the glue--they don't stick all that well on concrete) & cover the strap. Going up walls to cable entrances, breaker panel, etc. you can either just nail/screw to the wall or use the concrete inserts if the walls are block. For appearance sake, you can paint the strap if you like.

Now to get it outside.... My one transmitter building is a 40X60 former commercial garage, concrete block, transmitter room 25 X15. Some determined drilling (by a kid who needed money...) knocked a slit between two blocks near the floor. So the 3" strap runs from the sub-panel, down an interior block wall, across the floor to the transmitter and two 5' racks then over to this slit and outside. A second strap is bonded at this point inside the wall and runs up the wall to the cable entry port & is bonded to several cables (FM transmitter plant). Outside the strap is then bonded to another piece of strap that runs along the outside wall to the tower base and several ground rods (shallow burial to discover copper thieves).

At another, combined site, we simply knocked a hole in the block & ran a double ought cable outside to tower, leach bed and to electric ground. But then we had to knock a hole through the wall anyway to bring in the electric.

Interior walls? Well, if you own the place, I would knock a hole in the wall between studios, along the floor. I have a very simple studio plan at the combined site--former transmitter room (now rack room/studio)-control room--pro studio. All along the back wall of the building, interior walls typical stud/dry wall. I built a wooden trough that runs along the floor against the back wall of the studio and rack room. Now I use it for all the cabling--audio, CAT5, satellite coax, signaling (net cues of satellite)--the grounds go through the back wall to the OO cable. But the same approach could be used to hide strap. I just built the troughs using 1X3 boards that were then stained.

Finally--be sure and have grounds for such things as TV cable coming in from the outside. We lost an ethernet switch from lightning--TV cable to their modem was not grounded anywhere. After that, all these small cables go to a brass plate mounted on the back wall of the rack room, near the electric panel. They are grounded either by the typical RG6 ground devices, or polyphasors for the RG-8 RPU cables & a 1/2 inch translator cable; the plate is then grounded to station ground by some #10 copper,

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