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Grounding question

nealffischer

nealffischer

Hello everyone,
Quick question about grounding here. I am considering purchasing either a rangemaster or the less expensive procaster. I am thinking about installing it on my roof. I have a three story house, so the roof is about 35 feet up off the ground. Problem is there is not a real place to hook into a "massive ground" unless I violate the length rules. Being one who doesn't want a visit from the good folks at the FCC for rules violations, I was wondering if this sounded like a reasonable way to approach the problem? What I was considering was an artificial ground plain based on radials. Here is the picture of what I am thinking about. http://nealffischer.com/images/artificialground.jpg This uses two 8 foot radials, two 4 foot radials, two 2 foot radials, and 2 one foot radials. These radials would be something like a #8 or #6 ground wire placed under a rubber mat. The center would be essentially nut lugged together and that would allow for about a one foot ground lead from the transmitter to the ground plane. Please feel free to comment / critique away. If I am going to spend the money to really get into to this, I want it to work. I would at least like to cover four or five blocks with this up to 1/2 mile. The more the better. I had an internet radio station for some time unfortunately the rate hikes and the costs of streaming really hurt and I couldn't afford to do it all myself.

There is a Senior PGA event about a half mile from my home and it would be neat to be able to broadcast live from some of the festivities next summer.

Thanks for your time and assistance,
Neal
 
More radials and longer radials beats any other combination in "small lot" ground planes.
What you propose will work. If you can assemble it on the roof, and add radials all the way to the extremes, so much the better.
You may want to add an RF choke in the line from this radial ground plane to earth so the "worK" will be referenced against your
artificial ground as much as possible, rather than true earth. You may find that forgetting such a choke would be
be advantageous, if an inspecting agent doesn't mind it's abscence. And it may work referenced to true earth 35 feet away than any
radial system you devise for the roof. 180-odd meter wavelengths are not impressed by skimpy radial systems.
You'd do better to buy one of Carl's grounding systems and ground-mount the 3 m stick, if you have room.
How big is your lot?
 
Thank you for the quick reply! My front yard is a postage stamp. My back yard is ok sized but has two large trees and is kinda sunk down. It's kinda of the valley between two streets and several two / three story houses. I live on main street in my town and there are large power lines in front of my house. That is why I was thinking roof. RF Choke is something I will need explained a bit better - newbie here on the building of stations. No lack or respect intended and forgive my ignorance, but who is Carl?

Thanks again for the help.
Neal
 
My front and back yard are both postage stamps.

An RF choke would keep rf currents from flowing on the wire from the ground plane to earth proper, and keep that 35 feet of "earth wire" from radiating. It would "force" the currents to stay between the center radiator and the ground plane. This one of those issues there seems to be no end of discussion. If you run a search on ground and pt 15 antennas, you'll find the a knock-down drag-out
discussion form about a year or so ago.

Carl Van Orden, who frequently is in this forum, sells complete ready-to-go ground plane setups, probably cheaper that you can buy
the wire yourself. Look thorough some of the other threads here in the Community Radio board and you will find his notices
regarding the ground plane systems.
 
Why don't you mount the transmitter on the roof and use a choke in the ground lead? You would still get good range and there is a good chance that if you were inspected by the FCC (very unlikely), the installation would be acceptable. We could supply the choke with the Procaster at no charge.
 
Taking the risk of sounding like an advertisement, I know the RangeMaster has the perception of being a "$1000 transmitter" when really it is not, actually you can get one cheaper then the Procaster if you can qualify for the installer/dealer discount. Most folks don't seem to know that.
 
But also what folks may not realize is that the Procaster already includes all of the additional modules plus an audio processor plus real Hi-Fi sound for a reasonable price - the Rangemaster does not - it's all extra and some features are not available at all. (Sorry - also not wanting to sound like an advertisement - but facts are facts).
 
Gentlemen,
I didn't want to cause trouble. My comment was simply based on an apples to apples comparison of your websites. The more tested rangemaster was running about $250 more that the newer, less tested procaster with like options. My question was about grounding that is all. My situation is there is clear channel and citadel in town here and nothing else. No real independents. I wanted to give an option. That is all.

Peace,
Neal
 
I am not going to get into a shouting match about the two units either (whatever) People can do their own reseach. More choices can only be good for the hobby/industry.
 
On the subject, to be effective, any radial needs to be at least as long (radius) as the antenna is high. But not connecting your ground to the "dirt" can be dangerous with either tranmsitter (don't want to burn your house down). I would just run a wire down to a rod in good dirt (not sand or gravel). If the FCC says something explain about the lightning protection. Sure you could use a choke but it lessens the lightning protection. (However you can put a gas tube across the choke which will help)
 
Hamilton said:
On the subject, to be effective, any radial needs to be at least as long (radius) as the antenna is high. But not connecting your ground to the "dirt" can be dangerous with either tranmsitter (don't want to burn your house down). I would just run a wire down to a rod in good dirt (not sand or gravel). If the FCC says something explain about the lightning protection. Sure you could use a choke but it lessens the lightning protection. (However you can put a gas tube across the choke which will help)
Click to expand...

I really appreciate this. Thanks

Neal
 
Hamilton said:
But not connecting your ground to the "dirt" can be dangerous with either tranmsitter (don't want to burn your house down). I would just run a wire down to a rod in good dirt (not sand or gravel). If the FCC says something explain about the lightning protection. Sure you could use a choke but it lessens the lightning protection. (However you can put a gas tube across the choke which will help)
Click to expand...

There are means to r-f decouple the conductors leading away from an elevated Part 15 AM transmitter/whip, and still provide a low-resistance connection for DC and low-frequency a-c to a true ground buried in the earth.* This would keep the transmitter chassis (but not necessarily the 3-m whip) at ~earth potential for lightning protection. But it also may need a lot of explaining and proof to a knowledgeable FCC inspector who thought those decoupled conductors were radiating, and not in compliance with 15.219.

However with fully decoupled conductors then the radiation from that elevated system would be no better than if it was mounted with the transmitter chassis a few inches above the earth -- probably worse.

The reason that elevated, or whip & mast Part 15 AM systems are so often suggested and supported is because of the added coverage provided by radiation from those un-decoupled "massive ground," audio and power wires, which easily will radiate more r-f than the 3-meter whip attached to the transmitter.

Of course everybody is free to choose the installation details for whatever they install, but the information above might be useful in reaching that choice.

* the top of a "massive ground wire" is not "ground," even if the bottom of that wire connects to buried conductors such as ground rods or a buried radial system.

//
 
Some thoughts on grounding for lightning protection.

The first question is what are you trying to protect? My vote goes for people. We need also to be concerned about property which means keeping the energy from lightning outside. How does "grounding" help us achieve this? Two commonly understood things come to mind. First, a grounded object tends to discharge the static buildup before lightning strikes and it is theory that this discharge lessens the chance of a strike. The second is that if a direct or nearby strike occurs the energy must be dissipated to ground outside the building. Chances are whatever electonics are on the mast which is struck will be toasted regardless of discharge tubes or grounding but these methods can keep the energy outside the building.

Lightning contains energy at almost all radio frequencies as evidenced by the "static crashes" heard on AM radio during thunderstorm activity. Placing a choke coil in the transmitter ground lead essentially isolates the circuit ground from the protective ground at RF. So, the system is "floating" at these frequencies, but does this matter? A choke is still useful for draining off the static buildup mentioned earlier but what if there is a direct or nearby hit? If we depend on a good protective ground at the outdoor transmitter to steer the energy away from audio and power lines which enter buildings then by using a choke we have defeated this safety measure.

With or without a choke, the best practice is to provide lightning arresting protection at the point of entry of the building for all wires. Spark gaps and gas tube devices are available for this purpose and I urge all to use such devices on all lines at the point of entry to a building and to ground them to the electrical service ground stake. Electrical codes not only require this but are a source of guidance on how this should be done.

This is not a complete treatment of the subject, but I hope I have provided enough information so you can begin to appreciate the difficulties.

My message here, and I hope it is relevant to the topic of the thread, is always take measures to minimize the chance of lightning energy entering the building.

Neil
 
Neil,
So hard for me to spell it that way ;) - Thanks for this. I am trying to learn here. It would seem I have three knowledgeable people helping. Thanks!
 
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