Outdoor Grounding and Switching

Getting RF to the Antennas - and Giving Lightning an Easy Path to Ground

  

Shown here is an explanation of the grounding and control switching for the site.

The shack is permanent, but the antennas are not. When I moved to this QTH, the rush was on to get up a reasonable spread of antennas to take advantage of what solar conditions were (or were not!) - and to give me more time to figure out what I really wanted to put up for the long term. 

So all the antennas are temporary in nature. As are the runs of control wire and coax which lay on the ground for the moment.  Eventually these will be put underground once the "real" towers are put up.  A buddy of mine once told me that temporary often has a lot longer life that first planned - while I hope he's wrong, the system is built a bit better than "minimal" just in case he turns out to be right.  :)

  

  

 Shack Coax Termination

All wires passing into the shack from outside enter through the termination panel shown in the photo below. 

Coax feeds pass through Alpha-Delta units; control wires have MOV attached.  The MOV are on terminal blocks which make replacing them easy (MOV have a finite life and should be replaced periodically).

The copper back plate serves as the connection point for the grounding system detailed further down the page.

The inlet box was built by Chris K7FP and is powder coated with a very nice match to the house.  

  

  

  

  

  

Tower Switching Head

Except for the antennas on the short WARC/6m tower and beverage, all coax and control lines run about 250 feet out to the HF tower.  At the base the box shown below keeps things organized.

The box contains a set of Alpha-Delta arrestors and MOV similar to the shack inlet.  The silver box at the top half is a KK1L 2x6 So2r antenna switch.  Not shown here, a couple of smaller home-brew antenna switches and various coax stub trap filters set in plastic tubs at the base of the tower.

The box was given to me by a kindly gentlemen and was a nightmare to drill by hand.  But it's served well as an enclosure.  

  

  

Wildlife is (thus far) kept at bay with periodic pesticide treatments of the bottom and inside door.  Mouse "food" is left out in the tubs containing the coax stubs.  Eat up boys!  Yum yum!  So far, I have not had any problems with mice or other critters gnawing on wires laying on the ground.  Hope my luck remains good.

  

   

Grounding

Grounding is one of those things that you never can have "too much" of.  Unfortunately, I do believe that one can go bust

building the ultimate ground system so a risk assessment is required with prevention on one side, and insurance on the other.  An outline of the prevention here follows.

  

Outside Grounding System

  

As shown above, all the coax and control lines coming into the house pass through the shack termination box.  From this box #6 wire runs down to the ground screen, and up into the house and over to the AC breaker boxes.

10 ground rods (yellow ovals in photo below) are driven in the ground outside the shack inlet box location and tied together with the #6 wire.  

  

  

The base of the temporary tower has 16 4-feet spikes used to secure the base.  These are not otherwise bonded to the tower but I have complete confidence that a bit of corrosion would not impede lightning at all should it choose to touch the tower or it's antennas.

At the taller HF tower, the MOV/AD combination mentioned in the section above should help to brunt some of the lightnings effect.  And I believe that the series inductance and parasitic capacitance to ground of the 250 feet runs back to the shack would serve to take a bit more of the bite out of a strike.  Hopefully leaving nothing the shack side measures can't deal with.  Well, that's the plan and the hope!!!  Fortunately, it's not been tested as far as I know with the system up about a year now.  I'm crossing fingers and knocking on wood furiously as I write this...

  

Grounding Runs inside the Shack

There is no way to fully immunize against lightning damage.  About the best that can be done is to try to tie all the gear together well enough so that the voltage rise due to lighting is applied across all the attached gear evenly.  To this end, the shack side setup  is a rough single-point ground type.  Fortunately the layout of the shack, AC breaker boxs and the shack coax termination box are all pretty close together.

The shack coax termination and the house AC breaker boxes are connected with a direct #6 run as shown in the picture below (yellow).  From this jumper, a pair of #6 runs loop over to the back side of the shack wire closet wall (red arrow).

  

The two runs split off and connect to each end of a buss bar.

  

  

The buss bar is pulled from an old breaker box and is visible below, mounted on the edge of the shelf.

  

  

Short runs of strap connect the buss bars and the gear. The strap is made from RG-213 shielding.  Heat shrink on each end keeps things tidy.

  

  

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