RF Grounding

[shadow]

I've looked around the forum but i cant seem to find a good walkthrough on RF grounding my base antenna. I'm bleeding over my neighbors AM radios, i've installed a Drake low pass filter but it doesnt seem to cut out all the interference.

could someone with more advanced searching skills please point me to a post with some information about RF grounding or explain to me where on the antenna i should attach the grounding wire and what the wire should be made of?

thanks

[drdx]

Give us a little rundown of your setup. What kind of antenna, and height? How is is mounted, coax type? Radio, mic, and what's been done to the radio? Amplifier? Is the case of the drake grounded? Where do you have the filter placed? The low pass filter filters out, or tries to, above 30 mhz. AM radio frequencies are at 1 mhz, so the filter won't cover that. Maybe RF overload? Signal travelling through the AC lines? If so, a power line choke may be in order. -drdx

[Circuit Breaker]

RF grounding a base antenna is nearly impossible to achieve due to the conductivity of the soil, and would probably make little if any difference.

If a low pass filter didn't do anything to stop the interference to your neighbor's stereo, then you aren't coming in through the tuner. More than likely, you're coming in through the speakers. Try putting ferrite chokes on the speaker leads right at the speakers and maybe again at the stereo itself. Putting some on the AC cord wouldn't hurt either. Wrap as much wire through the choke as possible.

Of course, this requires your neighbor to be willing to have the chokes on his equipment. But truth be told (assuming you aren't running illegal equipment), the problem is more than likely with his equipment anyway. Part 15 of the FCC rules state that devices such as stereos may not CAUSE interference but must ACCEPT forms of interference. So, manufacturers don't bother putting in adequate shielding in their equipment in an effort to keep costs down.

[drdx]

Good mention on the speaker wire, as a speaker wire remotely close in length (8 ft, 17 ft, etc) to the wavelength of cb could turn into an unwanted antenna on the am radio's part.

He could still be coming in through the tuner. We're talking AM here, well with the range of where the filter does not attenuate RF.

On a base, RF ground is often reached by the ground plane, or radials, not to be confused with an electrical ground for lightning, which is also wise to have. You can also create an artificial RF ground via a wire counterpoise attached to the case of the filter, as an effective RF ground for the filter would have to be very close, as in a foot or two between the filter and the ground itself (the rod, or ground potential). There is much more to ground theory, and that is just a little, but lets hear about what you're running first. -drdx

[lonesome 500]

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to keep rf from radiating outside your coax....a cause of tvi/rfi

[Night Crawler]

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[DanzKat]

I've got a question about the whole balun / choke thing. Is it ok to make one say with RG-58x, and then put it between my antenna and my feedline of Jefatech 400, (LMR-400), Basically is it OK to mix coaxes like that a different on for feedline and than thinner one for the balun??
Thanx

[Night Crawler]

If it's the same impedance yes.

[shadow]

Give us a little rundown of your setup. What kind of antenna, and height? How is is mounted, coax type? Radio, mic, and what's been done to the radio? Amplifier? Is the case of the drake grounded? Where do you have the filter placed? The low pass filter filters out, or tries to, above 30 mhz. AM radio frequencies are at 1 mhz, so the filter won't cover that. Maybe RF overload? Signal travelling through the AC lines? If so, a power line choke may be in order. -drdx

The antenna is 3 piece, 16 foot (i think). got it from radio shack about 7 years ago. Its on 2 10 foot masts mounted on my chimney with water heater straps...
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the coax is from radio shack, RG-8/U. radio is a cobra 29 classic thats had a few mods done to it. i've tried turning down the modulation but that doesnt help. im also running a 150 watt tube linear.

what should the case of the drake be grounded to? the filter is after the linear, im thinking i should try putting it before.

My neighbor is willing to work with me to solve the problem. Heres what he's told me so far. The problem is with both of his AM radios and only when hes receiving in the AM band. FM is not a problem. When im not running the linear, the interference is significantly less but barely noticeable. I threw on my AM radio and had no interference in my house. He also said that when he unplugged the radio from the wall and put batteries in it, there was no interference. im thinking it a power line problem.

thanks for the replies.

[Choirboy]

First of all, you would need a high-pass filter, not low-pass, in this case. The AM broadcast band is 500-1700 kHz, below the CB band.

Secondly, Radio Shack RG-58/U coax bleeds RF like a stuck pig, especially with high SWR. Replacing it with good RG-8X would make a big difference. LMR-400 is overkill at 27 mHz, with only a 1 dB advantage over RG-8X in attenuation per 100', not even noticeable.

Finally, if the interference is significantly less without the amplifier, stop using it. It's illegal anyway, and this is one of the reasons why it is. Furthermore, if your radio has been modified, it probably is guilty of making spurious emmissions, which can also lead to RFI, TVI, etc.

[drdx]

That last hint kinda tells me you have a power line issue too. Two routes come to mind. Route #1 would be an RF choke or ferrite beads on the power line for his am radios. If that worked, it would only be working for him, and leave other potential victims of your signal. Route #2 would be to put and RF Choke, made of coiled power cord wrapped around a ferrite rod in between your gear and the wall outlet. This would, if it works for his issues, work on a more global scale as you're resolving it at the source vs. just his location. If you're interfering with him, who knows who else is getting interfered with and not telling you, but taking other action. I read in my book about the ferrite rod, and I don't know where to get one, but years ago I used a few pieces of rebar, wrapped the cord around it, and zip tied it and killed an ac radiation related problem I had, that was in the same house.

You mentioned that the radio has had some mods done to it, and we all love those, but the result of the modding may have resulted in a dirty signal, one then getting amplified making matters worse. My reason for that is the fact you mentioned that it still interfered a little with the amplifier off. Usually, a reasonably clean barefoot radio won't give you TVI trouble if you have the antenna decently high and so forth. Do you have a BONE STOCK radio to try? It may help in the diagnosis. I'd be leery running that box in the house if you are already hearing from one neighbor. -drdx

[DanzKat]

Does anyone have a good idea on how to drive an 8' grounding rod with out damaging the rod, bending or such, and also for someone with a rather bad back. and after that should I drive it below grade level or leave a "stub" sticking out of the ground? thanx

[preacherman]

First of all, grounding is very likely an issue because of the chimney mount.
Secondly, you may be overdriving the amplifier depending on the output of
your 29 after the modifications that have been done. Many tube amps need very little drive.
Thirdly...it is a LOW PASS filter that you need. You want higher frequencies
attenuated because it is harmonics that are getting into the if stages of their
AM radios and being amplied through their speakers.
Fourth, coax is an issue...not so much for db loss as for shielding. Good coax
will help in many situations.
Lastly, put the filter before the amplifier. The cleaner the signal going into the
amplifier (assuming it is not overdriven) the cleaner the signal will be coming
out of the amplifier.
Good luck...
preacherman

[Loudmouth]

Does anyone have a good idea on how to drive an 8' grounding rod with out damaging the rod, bending or such, and also for someone with a rather bad back. and after that should I drive it below grade level or leave a "stub" sticking out of the ground? thanx

I was surprised that I was able to drive the whole 8' ground rod by hand with a sledge hammer. I hit a rock about a foot down the first time I tried, but after I moved over a couple of feet it went right in. I was planning to rent an electric jack hammer from Taylor Rental, the 5/8" ground rod would fit (I was told) right in the chuck of the jack hammer. You might wanna try that. I plan to add several more rods and I will probably use the jack hammer idea.

LM

[drdx]

Dig a hole the size of a large bowl, and fill with water. Stick the rod in as far as you can and pull out. Let the water fill in the whole you just made. Repeat as many times as you can without the hammer. Keep that hole full of water too. Once you're past the point of doing it by hand, a ground rod driver is best for this job. They aren't overly expensive, but may be hard to find. I'm in tx, with rocky and clay soil, and it works here, but depending on your soil, it may be easier or harder. -drdx

[countryboy]

how much modulation is your radio puting out. if over 100% then you will splater.. ?

you might just try turning down your mic gain.

[DanzKat]

Does anyone have a good idea on how to drive an 8' grounding rod with out damaging the rod, bending or such, and also for someone with a rather bad back. and after that should I drive it below grade level or leave a "stub" sticking out of the ground? thanx

I was surprised that I was able to drive the whole 8' ground rod by hand with a sledge hammer. I hit a rock about a foot down the first time I tried, but after I moved over a couple of feet it went right in. I was planning to rent an electric jack hammer from Taylor Rental, the 5/8" ground rod would fit (I was told) right in the chuck of the jack hammer. You might wanna try that. I plan to add several more rods and I will probably use the jack hammer idea.

LM

Thank you for the info,, appreciate it.

[DanzKat]

Well, I got down half way and it's kind of stuck!! of course!! I guess I'll pull it out and start over about a foot and a half over or something. The first half was amazingly easy, even for me, but then BAM!!!
I'll keep trying,, I know some people don't agree with the whole grounding thing but I'm trying to do everything right!!!!

Thanx for all the advice, I'm going to try the water thing this time as long as it's not going below freezing tonight!!!

[lonesome 500]

post a pic when done :D

[shadow]

thanks for the suggestions, i'll give it a try with a stock radio ( i did once before but i dont remember the outcome)

as for the modulation, i turned it way down and it was still bleeding. I'll try a few of the suggestions and hopefully it will work out. thanks again!