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Author Topic: Builing the New QTH  (Read 971 times)
KG4PES
Member

Posts: 21




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« on: May 01, 2002, 01:42:08 PM »

Well I have a new QTH and have begun the construction of the shack and the supporing subsystems.  I would like to get some feedback on what I have done and what I am planning before I get to far.

I am working on the Ground system at the moment.  Here is what I have done so far.

1. Sunk 8' ground rod outside window of ground level shack.  The window is literally 2' off the ground.  6 AWG stranded wire to the internal ground distribution panel.  The run is less than 15'

2. Build ground distribution bus in shack.  All equipment has a 6 AWG stranded wire to the ground distribution point.


Questions:

1.  Any problems with the initial setup?
2.  I have seen references to an RF ground and an Electrical ground.  Do I need 2 different ground rods for this?
3.  The ground rod is not tied into any exisitng ground systems of my house. Is this needed?


Thanks for the help
Adam
KG4PES
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WB2WIK
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Posts: 20612




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« Reply #1 on: May 03, 2002, 11:57:52 AM »

I'm not a big believer in "grounds," as they don't do anything for me, and really never have.  I run legal limit power on 11 bands from my home station, using tower mounted beams and rooftop verticals and wires, and have no ground system of any kind -- and also have no problems of any kind.  The only "ground" anywhere in my station is the one supplied by the green wire in the power cords, to the third prong in the AC outlets.

However, grounds can be effective for some.  In general, a good rule of thumb is to make RF grounds broad, smooth conductors of very low impedance.  #6 AWG stranded doesn't quite fit that definition.  What most of the engineering texts recommend is 6" wide (or wider) copper flashing.  It's flat, smooth, broad and has much less inductance than #6 stranded wire.

Then, the "safety" ground is supposed to be a "single point ground" that is directly tied to your electric service panel ground.  Since it is only to prevent electric shock in the event of equipment malfunction, it needn't be the broad, smooth conductor recommended for an RF ground -- it just needs to have a low-resistance path back to your service ground, at 60 Hz.

Then, a "lightning" ground should _never_ be attached to station equipment in any way, and should never be paralleled with your RF station ground.  A "lightning" ground must be kept _outside_ the house, and have a shorter, lower-impedance path than any of your antenna feedlines.

I would think that #6 AWG stranded wire interconnecting equipment chassis is rather awkward, especially if you try connecting it to smaller appliances -- the cable could be heavier than the equipment it's attached to.

I'll admit I've seen hams use copper sheeting for the operating benchtop surface, with all sorts of elaborate grounds interconnecting everything -- although I never quite figured out why.  If you keep the RF "outside," by placing operating antennas sufficiently far from the station, and use matched antennas, and possibly ferrite line isolators installed outside the house, I can't see why "RF" would be a problem.  It isn't for me.

The only "RF" problems I've ever had are my primary signal (antenna radiation) interfering with telephones, stereos, Nintendo games, DVD players, VCRs, etc, etc.  All sorts of wonderful station grounds won't do a thing for that.  Those problems must be tackled at the appliance being interfered with, and I generally use clamp-on ferrite chokes to successfully deal with everything!

WB2WIK/6
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K9KJM
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Posts: 2415




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« Reply #2 on: May 17, 2002, 12:58:09 AM »

The ground system you describe is adequate for a "safety" electrical ground only. There are actually 3 ground "systems" for radio stations: Safety, Lightning, and R.F.     Each ground "system" has it's own requirements, but all three can be combined into one system. The wide copper flashing mentioned usually takes care of all 3 requirements. For lightning, the larger the conductor, attached to as many ground rods/radial ground wires, the better!      The way to do it is install a large copper sheet at the point where coax enters the "shack", this sheet should have all your lightning/surge suppressors, coax switches, etc attached to it. (Single Point ground) All wires coming into the shack should somehow be grounded at this point. A 6 inch wide copper strap from the single point sheet in the shack should go outside to the ground system. (All ground systems should be bonded together.)  The Further away from the tower/mast/ single point ground, the "lighter" your ground wire can be. (Look at this like the "roots" of a tree) Rule of thumb is to space ground rods twice the distance apart as the depth  (8 foot deep rods would be spaced 16 feet apart) Any ground "radial" wires installed need be no longer than 75 feet (unless you operate 160 meters!)  Check the POLYPHASER website under "tech tips" for a number of great articles on grounding. The safest thing to do during a lightning storm would be to "switch" your antennas to Ground. (I use Alpha-Delta switches, but there are other goods ones out there) DONT listen to anyone who tells you to "disconnect" during a storm.........  I have worked on & installed a number of commercial systems (Police, Ambulance, Fire, etc)  that MUST operate during severe weather. These tall towers usually take several "direct" lightning Hits most every large storm. Over the past 25 years, NO damage to equipment from lightning!  (But when lightning is involved, nothing is 100%)  Good Luck!
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