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Author Topic: fiberglass antenna grounding  (Read 995 times)
KD5UYT
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Posts: 16




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« on: June 21, 2011, 04:58:10 PM »

I have been searching the site for a similar question because there is plenty of grounding info here but have not found what I was looking for. I have an older home that has no electrical grounds, just 2 prong outlets. I am using a mobile 10 meter radio with a power supply and have a solarcon fiberglass antenna mounted on a 10 foot mast clamped to a chain link fence post. The fence poles are in concrete on the patio entrance and I am unsure they are truly in the ground or not. The whole area around the antenna is concrete, either drive way or patio so I basically have nothing grounded it seems. I do have a ground rod way in the back but it must be 25 foot away from the antenna. What can I do to have a ground for the antenna to make it more effective and safer from lightning strikes. I was seeing some swr problems the other day when it was windy and had not rained for a month and seemed to have static electricity build up or something. The coax was giving me a tingly feeling when connecting my swr meter and the radio had been off for hours. It rained today and that has since gone away it seems. I am unsure what to try.
Terry KD5UYT
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M6GOM
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« Reply #1 on: June 22, 2011, 01:33:08 AM »

You need to put a RF Choke in the feedline to choke common mode on the co-ax. Ideally 8 turns of RG58 on a FT240-61 core would be the best but for a temporary measure, you can make one out of just a coil of co-ax of 5 turns of RG58 with a 4.25" internal diameter or RG213 with the same internal but that won't choke as well as the RG58.
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K5LXP
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« Reply #2 on: June 22, 2011, 06:46:28 AM »

Not sure why M6GOM is offering advice on common mode chokes when the symptoms point to a ground fault.  It would seem your antenna is at a different ground potential than your equipment.

The tingling you're getting is likely when you're holding on to the chassis with one hand and the coax connector with the other.  If you were to put a voltmeter across them, you will read some level of AC voltage.

In 2-wire AC power, neutral should be tied to ground at your service entrance.  You should at least have that.  I would physically verify that's the case.  If your house is old enough to have 2-wire AC, it's old enough the ground may have been compromised over time.

If you were to improve the grounds at your antenna you may actually be providing a better earth ground there than your home has.  Ideally you'd have a shack AC ground that's tied to your service entrance ground by adding a third wire ground to your AC service to the shack.  It's not hard to do, it was done in my home which originally had 2-wire AC.

A qualified electrician can review what you have and make specific recommendations how to best go about updating your wiring but I would also consider implementing a station single point ground for your antennas that's bonded to your service entrance ground.


Mark K5LXP
Albuquerque, NM
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M6GOM
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Posts: 875




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« Reply #3 on: June 22, 2011, 10:46:57 AM »

Not sure why M6GOM is offering advice on common mode chokes when the symptoms point to a ground fault.  It would seem your antenna is at a different ground potential than your equipment.


Because I've owned and used these antennas for years. They get static build up in dry windy dusty weather but not to the point where you need to do what you're suggesting.

You Americans sure have some funny outdated ideas about earthing systems in homes.
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K5LXP
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« Reply #4 on: June 22, 2011, 11:37:34 AM »

They get static build up in dry windy dusty weather

Assuming it's an A99 I don't see how radome static can make it to the feedline, the element is AC coupled and the feedline DC shorted through the matching coil.  In the event it were static, I don't see how a common mode choke as described would mitigate it.  Having had issues with disparate grounds on my own equipment, this is the first thing I thought of.  A voltmeter would reveal whether the issue is static or AC, but in either case a single point ground would mitigate it, as well as provide for the op's desire for improved surge suppression.

Quote
You Americans sure have some funny outdated ideas about earthing systems in homes.

It's an expensive proposition to bring the 2 wire systems in older homes to current standards, so you just gotta work around it.


Mark K5LXP
Albuquerque, NM
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KD5UYT
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Posts: 16




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« Reply #5 on: June 22, 2011, 12:24:46 PM »

I was getting the tingling from the swr meter and the radio had not been powered up for probably 18 hours, that was making me think about static electricity. The fence post the mast is mounted to is probably in the ground a foot maybe but after no rain for a month and 40 mph winds static could have been getting back inside I suppose. I am also going to replace the coax because it is the cheap stuff mini rg8 I think and about 10 years old. I wish there was some real dirt around there and not so much concrete. I guess could drill thru the concrete and drive some ground rods in close to the antenna.
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AD6KA
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« Reply #6 on: June 22, 2011, 02:36:55 PM »

Quote
I was getting the tingling from the swr meter and the radio had not been powered up for probably 18 hours, that was making me think about static electricity. The fence post the mast is mounted to is probably in the ground a foot maybe but after no rain for a month and 40 mph winds static could have been getting back inside I suppose

A static buildup, and IF (a big if) it were the case, would not cause "tingling",
just a one time arc discharge until it built up again to sufficient potential.

You have a ground fault methinks.
Doesn't matter if the rig was not "powered up".
Many radios have voltage flowing through them even while "off".

Was the power supply on during this "18 hour power down"?
It's also unclear as to whether the rig was on/off/receving/transmitting
when you felt the "tingling" in the meter. You just said "had not
been powered up for 18 hours".

This is a puzzler.
73, Ken AD6KA
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KD5UYT
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« Reply #7 on: June 22, 2011, 04:14:57 PM »

Power supply and radio both off.
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N4CR
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Posts: 1650




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« Reply #8 on: June 22, 2011, 04:27:24 PM »

I suspect that your mounting pole mounted in concrete is a better ground than you think. Concrete is a pretty good conductor. If you want to see how good, Google for the term UFER.

So what's probably happening is that your house wiring neutral is floating above ground and your coax shield is providing the best ground in the house, regardless of it not being a great ground.

The best place to start would be to drive a new rod at your meter box and reground the meter housing/input box. It's not ideal, but I suspect that you have little or no ground at your meter housing.

A good test would be to measure the voltage between your rig and the shield of your cox with your voltmeter set to measure AC. Won't surprise me a bit to see it's not anywhere near 0.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
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