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I’m in the mood to pick some Brains.. :)~
Keeping within the Part-15 rules as for antenna restrictions, Is a 120 radial grounding system “Legal”? Or, Would this make the antenna system too efficient? (Beyond the allowed field strength)
I’m a nut when it comes to projects like this and I want to get the “Max” and remain legal. I have the area and the “Gumption” to install the ground system and I WILL if you guys think it’s worth it..
I’m in the mood to pick some Brains.. :)~
Keeping within the Part-15 rules as for antenna restrictions, Is a 120 radial grounding system “Legal”? Or, Would this make the antenna system too efficient? (Beyond the allowed field strength)
I’m a nut when it comes to projects like this and I want to get the “Max” and remain legal. I have the area and the “Gumption” to install the ground system and I WILL if you guys think it’s worth it..
From all of the readings I’ve done, not many have installed an “Almost Perfect” grounding system. Most are restricted by area. I understand it takes a lot of room and I’m lucky enough to have it. It’s not a prime area for listeners but I’ll know how to build one in a good area if this is ideal..
I’m also working on a design for an antenna that is center loaded, inductive tuned, (no more taps) And tuned at a distance so your body won’t detune things when at close range. (I think everyone knows all about this if they have tuned one) It’ll tune via field strength. I won’t get into any specifics untill the prototype is tested. That’s another incentive for the ground system..
Don’t send the guys in the white coats yet. Let me have some fun first..
Thanks in Advance..
Total posts : 45366[quote=12vman]Is a 120 radial grounding system “Legal”? Or, Would this make the antenna system too efficient? (Beyond the allowed field strength)[/quote]
Here is some background information from which people can make their own judgments.Part 15 AM does not define or limit the r-f ground itself — only that the length of the conductor(s) connecting the tx system to an r-f ground, together with the lengths of the actual “antenna,” and the wire connecting the antenna to the tx cannot exceed 3 meters.
By definition and the principles of physics, an r-f ground does not radiate. Anything that does radiate r-f is an antenna, or part of one.
A conductor leading from a buried r-f ground through space and connecting directly (or with a short “ground lead”) to a Part 15 AM tx chassis does radiate, because r-f current is flowing through it between the r-f ground and the tx chassis. The flow of r-f current through a conductor sets up radiation. In fact, that is the prime requisite of an antenna.
For a given r-f current through a conductor up to about 5/8-wave long, the longer that conductor, the greater the radiated field it produces. This is why the FCC limited the Part 15 AM radiator length in the first place.
And this also is why “elevated” Part 15 AM tx systems perform better than those installed at ground level, where the total length of the radiating conductors is 3 meters or less.
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Total posts : 45366Ok.. If the ground system is as good as it gets, will this make the 3M antenna more efficient? Would it help in the resonance?
Total posts : 45366[quote=12vman]Ok.. If the ground system is as good as it gets, will this make the 3M antenna more efficient? Would it help in the resonance?[/quote]
The more ground loss you remove from an antenna system, the higher its radiation efficiency. The “broadcast-type” radial ground system is about as good an r-f ground as possible.The inductive reactance needed to resonate the “3-meter” section of a Part 15 AM antenna system is almost totally a function of its electrical length and diameter, regardless of the r-f ground system. But if the r-f ground system is very lossy, not much of the tx power will radiate, even if the 3-meter section itself is resonant.
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Total posts : 45366If the ground system is as complete as possible, Would higher voltages be induced at the antenna? (Radiated Reactance)
Or, is there a % of ground that would make the legal antenna operate as efficiently as it possibly can due to it’s shortened state?
Total posts : 45366As I’ve posted several times now, anything that reduces losses in the antenna system will improve its radiation efficiency. Major losses include those in the r-f ground system, and in the loading coil.
So one goal is to use a loading coil with enough reactance to resonate the short radiator on the operating frequency, with low(est) r-f losses.
Likewise, lowering the r-f resistance in the buried ground system will improve Part 15 AM antenna system efficiency, for the reasons I’ve recently posted.
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Total posts : 45366Well, Guess I’d better get to the hardware store.. 🙂
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