newbie ?

[jwisecarver]

First I have a 30' aluminum flag pole that I am going to mount a rs discone antenna. My question is what size ground wire do you guys recommend for grounding? Want to do it right.

 

[Ed_Seedhouse]

A discone requires no ground. Shorting the coax shield to an RF ground probably won't hurt much if at all, but if you are worried about lightning you should use proper commercial lightning bypasses for that.

 

[WA0CBW]

NEC requires any antenna mast to be grounded, even it it looks like a flagpole. A #6 would be the minimum to use. Also remember that ALL external grounds need to be connected together with the main electrical ground. See NEC section 810.
BB

 

[LtDoc]

If that flag pole is metal and you have to 'ground' the antenna for some reason, why not use the pole as the conductor?
No, your discone doesn't need to be grounded for RF purposes. I can't remember seeing a commercially made/sold antenna that needed RF grounding. There's bound to be some around, but I haven't seen them. An end fed wire typically needs it's 'other half' to work so you could consider that an RF ground, I guess.
'Safety grounding' is completely different from 'RF' grounding.
- 'Doc

 

[WA0CBW]

Most antennas are "DC grounded" meaning there is continuity between the center conductor and the shield. If this type of antenna is mounted to a metal mast (flag pole) per NEC the metal mast has to be grounded. Physically this would take place at the base of the flag pole. A #6 jumper fastened to the flag pole and connected to a ground rod. This ground rod needs to be connected to the electrical ground. If the flag pole is 20 feet or less from the main electrical ground then a separate ground rod is not needed. In either case the ground still needs to be connected to the main electrical ground.
The other type of antenna is a non-grounded antenna (no continuity between the center conductor and the shield). When using a metal mast it needs to be grounded as described above. For masts that are only a few feet long that don't touch the ground a ground wire is still needed to ground the mast. When using an insulated mast (such as wood or plastic) a ground wire would be required from the antenna mounting bracket to ground as described above.
In addition to the grounding described it is a good idea to use a surge arrestor on the coax. NEC requires the shield of the coax entering the building to be grounded. A surge arrestor can satisfy both requirements if weatherproofed adequately.
BB

 

[DisasterGuy]

If you want to begin to understand proper installation practices, I would recommend spending some time reviewing the Harris Site Grounding and Lightning Protection standard as well as the Motorola R-56 standard. I have seen very few amateur installations that are actually done even close to professional site standards. Both are available online.

Here is a link to Harris' standard: http://www.repeater-builder.com/ge/lbi-library/t4618r3a.pdf

Here is a link to Motorola's: R56 Guidelines

 

[jwisecarver]

thanks for the link it is greatly appreciated. I didn't make my self clear, was wandering what size cable would be best to run from pole to ground rod.

 

[DisasterGuy]

There are several factors to consider but I would use no less than #2 in that application but remember that you also need to bond that ground rod to your building ground and the building ground to your station ground. The shield of the coax should also be bonded to ground at the base of the pole and prior to entering the house.


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