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Author Topic: Grounding Question  (Read 1391 times)
N5XJT
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Posts: 33




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« on: January 13, 2019, 08:30:49 AM »

Running 100 watts to a vertical with a ground rod at the base via about 70 ft. of RG8X.  Also have a ground rod placed about 4 ft. from the station common buss to which 3 radios and two tuners are grounded with 1" strap.  The service entrance is about 65 ft. from the station, too far for an effective connection.  In it's place I have been advised to run a 14 or 12 awg stranded copper wire from the common buss to the nearest AC receptacle connecting it to the ground side.  Many local hams do this but it doesn't seem like such a great idea to me.  However I note that owners manual for one of my older rigs suggests doing this if a good ground is not available.  Thoughts on doing this connection would be greatly appreciated.
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AA4PB
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Posts: 15067




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« Reply #1 on: January 13, 2019, 10:20:21 AM »

Well, that connection does NOT meet the National Electric Code requirements. The NEC requires a minimum conductor size of #6 to be bonded (i.e. permanently connected) to all grounding systems in the building. You can attach to the ground rods, the grounding conductors, or the ground buss in the primary entrance panel. The primary purpose is to ensure that all grounding systems are maintained at a common potential (i.e. no significant voltage between them).
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Bob  AA4PB
Garrisonville, VA
K0ZN
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Posts: 1862




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« Reply #2 on: February 14, 2019, 09:37:52 PM »

Just "FYI"... if all you have is one ground rod for the "ground system" at the base of your vertical, you are losing about 50% of your transmitter power in ground losses.  i.e. of your 100 watts only about 50 is radiated. Dirt is NOT a good RF ground....it will ABSORB RF energy, but absorption is not going to help radiation. Install some radials if at all possible; 24 is about a rock bottom minimum number. 50+ is better. Ideally, they would be a 1/4 wave long on your lowest band. Length is NOT critical on ground mounted radials, neither is symmetry of the radial field. Many short ones are better than a few long ones. Just do the best you can based on your real estate/room situation. If your SWR is low and the SWR bandwidth is very wide, that is a classic sign of high ground loss. As you add radials the SWR will go UP....that is a GOOD sign. With an electrically "perfect" radial system the antenna feed point is 36 ohms vs. the 50 ohm coax impedance, thus about a 1.5 to 1 SWR. If your ground losses are high, you will have close to a 1:1 SWR.
Hopefully, the foregoing is a moot point, as you already have a radial system and just didn't mention it.

73,  K0ZN
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WX7Q
Member

Posts: 21




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« Reply #3 on: February 23, 2019, 01:00:50 PM »

Will be installing a vertical this spring. (Yes, I know antennas perform better when installed during blizzards, torrential downpours, hurricanes, etc., male ego and all...)
On the MOSLEY antenna site...they show radials with ground rods at the END OF EACH of the radials, in addition to one at the base of the vertical. (It's a vertical installation tips...PDF download)

http://mosley-electronics.com/verticals.html#

Thoughts? More the better? Six of one, half a dozen of the other?

Thanks in advance. The information put forth on this site by fellow hams is invaluable and greatly appreciated.

Jim
WX7Q
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K0ZN
Member

Posts: 1862




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« Reply #4 on: February 24, 2019, 10:19:33 PM »

Short version.  Factually: the radial system is literally the other HALF of your antenna !  On a ground mounted antenna with in or on the ground radials, the only thing the radials do is reduce resistance losses in the soil. Dirt is a TERRIBLE conductor of RF current. Conversely, metal (usually copper) is an excellent conductor....therefore, the more copper you have in your radial system the lower the losses will be and the more of your transmitter power will be radiated. With a poor radial ground system, you can easily lose HALF of your transmitter power to simply heating the dirt. Not good....

There are many books, the ARRL Antenna Book being the best, about verticals with graphs of loss vs. the number of radials. I don't know where Mosley is coming from; the only real function those ground rods would serve is lightning protection. Ground rods are nearly worthless for RF grounding purposes. What ground rods WILL do is absorb and dissipate your power! Many studies to confirm that. It has been known and documented since the mid 1930's that radials are a critical part of a vertical antenna system and more radials are better than a few. I would say, based on pragmatic experience that a minimum of 24 radials for "acceptable" operation; 50 is better and there is not too much to be gained by going over 75. There is no point in making them longer than 1/4 wave on the lowest band the antenna covers. Ideally, you want the radials to be a quarter wave on your lowest band, but length is NOT critical for in ground radials; in ground radials are NOT resonant. If you can't put in long ones, the next best thing is a lot of short ones. I would much rather have 40 30 ft. long radials than 20 that are 60 ft. You can install radials above and insulated from ground, but that is a much more complicated situation and you will need to do some research and study if you want to go that route.

If your SWR is very low and the SWR bandwidth is wide, that means you have a POOR ground....since half of your antenna is a resistor, essentially. As you add radials, the SWR will go up and the SWR bandwidth will get narrower. If your put in 75 to 100 quarter wave radials, the SWR will be about 1.5 to 1 at resonance because the feedpoint impedance will be about 36 ohms and the coax is 50, thus the 1.5 SWR. SWR does NOT cause loss of radiation...it is just a condition. (Very high SWR does cause loss in the transmission line/coax.) Again, respectfully, pick up a book on antennas to get a better handle on radial systems. Many hams put up a vertical, install a poor to minimal radial system, then say verticals don't work.... if you put in an extensive radial system a vertical is a very good antenna.

There is no free lunch with a vertical. Actually, a good vertical is a pretty labor intensive antenna!  Either you have a good radial ground system or you have a poor antenna.....that is not my opinion, that is just Ohm's law.

73,  K0ZN
« Last Edit: February 24, 2019, 10:25:07 PM by K0ZN » Logged
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