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Old 11-03-2014, 3:16 PM
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Question Grounding a balun longwire antenna

Hi,

Probably 10 years ago, I installed a longwire antenna on my house's detached garage. One end of the longwire is connected to a "magnetic balun" transformer. From there, a coax crosses over the driveway and enters in through the wall of the house. The antenna was grounded with two ground rods: one at the end of the wire and the other at the balun transformer. The antenna worked OK but I wasn't thrilled with its noise rejection qualities. I still seemed to pick up quite a bit of indoor RFI. Perhaps now at last I know why...

A few weeks ago, I discovered a ground loop issue with my broadband Internet connection. In an attempt to resolve the issue, I had an electrician install a new cold water pipe ground and bond it to the power company's ground rod outside. Even with this work done, I still had a bad ground loop whenever I connected the cable modem to a grounded AC outlet and the ISP's coax outlet. A ground loop isolator on the coax got rid of most of the hum but I was still left with high-intensity EMF radiation that caused me acute physical discomfort. I finally managed to hook up the cable modem to an ungrounded AC outlet and with a plain coax--no ground loop eliminator--with a blessed reduction in EMF radiation! Note that the cable Internet's ground is bounded to the house electric ground as is my landline phone.

So far so good, BUT I have observed with the help of an EMF meter that the new cold water ground is emitting high EMF radiation (>= 50 milligauss versus my house's overall 1.5 milligauss reading) even when the main breaker is turned off. Frankly, this has me a bit mystified, but it's gotten me to think about my longwire antenna. I now realize that I set it up wrong insofar as the grounding is concerned. I think what ought to be done is to bond the antenna's grounds to the house ground. The antenna being atop a detached garage, how to do this isn't obvious to me. The only thing I know for sure is that I ought to add a ground wire between the antenna's two grounds then somehow bond this ground to the house ground. Correct?

My questions:

1. What's the simplest way to bond the antenna's two grounds to the house ground: attach a ground wire around the existing coax, bond the antenna ground to the coax shield and add a ground block from the coax to the house ground, or what???

2. Is there any possible way that my antenna with its current independent grounds might be causing a differential (aka ground loop) with my house ground due to their being located 20-30' distant and not being bonded to house ground?

Many thanks!

Dave
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Old 11-03-2014, 3:36 PM
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Quote:
Originally Posted by d-ulrick View Post
Hi,

Probably 10 years ago, I installed a longwire antenna on my house's detached garage. One end of the longwire is connected to a "magnetic balun" transformer. From there, a coax crosses over the driveway and enters in through the wall of the house. The antenna was grounded with two ground rods: one at the end of the wire and the other at the balun transformer. The antenna worked OK but I wasn't thrilled with its noise rejection qualities. I still seemed to pick up quite a bit of indoor RFI. Perhaps now at last I know why...

A few weeks ago, I discovered a ground loop issue with my broadband Internet connection. In an attempt to resolve the issue, I had an electrician install a new cold water pipe ground and bond it to the power company's ground rod outside. Even with this work done, I still had a bad ground loop whenever I connected the cable modem to a grounded AC outlet and the ISP's coax outlet. A ground loop isolator on the coax got rid of most of the hum but I was still left with high-intensity EMF radiation that caused me acute physical discomfort. I finally managed to hook up the cable modem to an ungrounded AC outlet and with a plain coax--no ground loop eliminator--with a blessed reduction in EMF radiation! Note that the cable Internet's ground is bounded to the house electric ground as is my landline phone.

So far so good, BUT I have observed with the help of an EMF meter that the new cold water ground is emitting high EMF radiation (>= 50 milligauss versus my house's overall 1.5 milligauss reading) even when the main breaker is turned off. Frankly, this has me a bit mystified, but it's gotten me to think about my longwire antenna. I now realize that I set it up wrong insofar as the grounding is concerned. I think what ought to be done is to bond the antenna's grounds to the house ground. The antenna being atop a detached garage, how to do this isn't obvious to me. The only thing I know for sure is that I ought to add a ground wire between the antenna's two grounds then somehow bond this ground to the house ground. Correct?

My questions:

1. What's the simplest way to bond the antenna's two grounds to the house ground: attach a ground wire around the existing coax, bond the antenna ground to the coax shield and add a ground block from the coax to the house ground, or what???

2. Is there any possible way that my antenna with its current independent grounds might be causing a differential (aka ground loop) with my house ground due to their being located 20-30' distant and not being bonded to house ground?

Many thanks!

Dave

One of the first things I learned when I started working on cellular sites and grounding systems was to read and understand the NEC (National Electrical Code). There is one section in there that allows for a telecommunications site to have it's grounding system bonded to the electrical ground. This eliminates any possible difference of potential between the different grounds. Any time you have a difference in potential, you can cause noise and will have damage if the facility takes a lightning strike.

With that said, I have also run into electrical inspectors that won't allow common bonding to the electrical meter ground rod. The solution to that was to bond to the meter ground rod about 2 feet lower down on the ground rod. Have never seen an electrical inspector use a shovel to check for additional bonds to the ground rod.

What you might have to do is dig the yard up and run a #2 solid wire from your antenna ground over to the electric meter ground rod and bond the two of them together. This would then make sure both are at the same ground potential.

While on the subject of ground rods, if you don't already know it, you should not have two ground rods spaced less than double their length apart. This goes into the theory that you have a cone of influence around each rod. If you space closer that double their length, this cone overlaps and you loose some of the benefit both ground rods contribute to the low resistance of the ground system.
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Old 11-03-2014, 6:09 PM
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Not sure I understand the grounding "one at the end of the wire and the other at the balun transformer". Does this mean you grounded at the balun transformer and also at the far end of the antenna? If so that would make some kind of grounded loop antenna, which would normally be a quiet and inefficient antenna.

Anyway, in the US the National Electrical Code specifies any additional ground rods must be bonded to the main house electrical ground and by no less than #6 wire. If you don't the ground rod far away from the main house electrical ground will usually be at a different ground potential and the wire connecting the ground rod to the balun and your coax and the ground wire in the power cord of your radio will try to equalize the different potentials and current will flow on everything. This is probably what you are measuring with an EMF meter and hopefully not one of the dreadful Trifield 100EX meters.

I would recommend bonding your ground rods together as jim202 suggested and tell us more about the antenna and if the far end is just hanging in mid air or grounded.
prcguy
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