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in another thread the hot topic was what TX performs better than the other but the topic of grounding kept coming up. what’s legal? what’s not? the opinions where everywhere, some of which didnt make any sense.
so here’s what i found… the fcc says we must not exceed 3m total length of antenna and ground connection. https://www.law.cornell.edu/cfr/text/47/15.219
so with that in mind we all know of at least one manufacturer using the lightning protection ground loophole yet others are afraid to use it? why?
i did a little research and radial lightning protection systems are industry (and goverment) accepted as can be seen by the following citations. the second being NOAA docs on protecting buildings from lightning.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwicx9Sw6oHUAhXC6CYKHWqmDHoQFgg2MAE&url=http%3A%2F%2Fwww.nws.noaa.gov%2Fdirectives%2Fsym%2Fpd03041006curr.pdf&usg=AFQjCNHIESZWUSLNLRhNrMni3Zdv6eZ2XA&cad=rja
the logic seems to be a capacitively coupled radial grounding system is more efficient than a ground rod at dispersing a strike. they also cite that its better to use thin wide copper ribbon than thick standard wire due to surface area. there is also mention of lightning protection radials in the NFPA code book.
so there’s no reason i cant put my TX in a box at the top of a mast, ground that mast for lightning protection and connect my equipment ground lead to my lightning protection “system”. being thourough in my fear of lightning i employ both rods and radials as does NOAA.
yep, its a fine line as we all know whats incidently happening. it is one that you can explain and show citations of it being a commonly accepted form of lightning protection until someone comes up with wireless lightning protection. it’s no different really than putting up your TX on the roof of a building and making use the ground lug on the power cord.
Total posts : 45366This topic became so contentious a few years ago that any mention of grounding was banned from this site. This illustrates that there are many opinions on this by many people all of whom insist that they are right.
You are going to have to gather information and form your own conclusion.
I have done so and my opinion is just that…my opinion. If one considers why the FCC would limit the total length of the antenna, transmission line, and ground lead then one can conclude that it is because these radiate a signal. The power radiated depends on the current amplitude and the length of the current carrying conductor. The current is essentially limited by the power limit and the length limit sets the maximum length of radiating conductors.
Any conductor connecting the transmitter circuit ground to the earth will have a RF current and will radiate, a fact that I have confirmed experimentally using a loop antenna as a pickup. If the FCC’s intent is to restrict the length of radiating conductors then any electrical connection from the transmitter circuit ground to the earth will be included in the 3 meter limit, be it a wire, a mast, a building girder, etc..
This is the information from which I have drawn my conclusion and it is offered here for consideration.
Neil
Total posts : 45366Radio8z’s conclusions make perfect sense in respect to the part15 rules. It is indeed an obviously correct interpretation by all accounts.
That said, it has also proved obvious that numerous inspectioning agents have noted installs not meeting the specific requirements and let it slide.. It’s a very flakey situation, ain’t it?
Total posts : 45366The comments made in this thread have so far centered on what has been called a “ground lead” which is any wire from the bottom of a transmitter to earth-ground.
My fuss is that I believe the term “ground lead” is not true… the correct description should be “negative leg of a medium wave dipole” with the antenna above the transmitter being the positive leg.
But it IS non-compliant regardless of the name because it radiates no matter what it’s called.
I’m thinking about buying time on national television to get the word out.
Total posts : 45366“But it IS non-compliant regardless of the name because it radiates no matter what it’s called.”
Carl, somehow you sound like Bill Clinton… But that depends on what your definition of “is” is.
Total posts : 45366What you say is interesting.
We all have an opinion about what a ground-lead is.
Is should probably be spelled “iz”.
Total posts : 45366Carl and I were discussing on TeamSpeak at the Alp be meeting that Carl and I were discussing on TeamSpeak at the Alp be meeting that if you took a piece of coax and you had a 10-foot piece of metal for the hot side and then you took the shield and connected it to a 10-foot piece of metal and had it on the lower side you would have a dipole. To make it legal you would have to cut those two sides in half so you would have 5 feet up and 5 feet down. It would equal 3 meters and it would be ian AM dipole.
so I wonder what the so I wonder what the effectiveness of an AM dipole would be? Just have a 5-foot piece of metal for the hot and a 5-foot piece hanging down your transmitter.
Now that range master transmitter we saw on YouTube if that thing was getting out as far as it did Sitting on the top of a roof that thing is pretty interesting.
it is it is only my opinion but if you’re near a radio Market that is huge I think they’re going to be stricter on you then if you’re out and about a little bit.
Total posts : 45366you know in reading this thread i just realized another item of abuse and user misrepresentation… the audio feeds to the tx.
going back to the TX on the pole. the small TX’s i have seen all have the audio input ground at same potential as the rest of the ground connections on the board. i need to get the audio from the “studio” to the TX dont i? ok. what’s the sheild on my audio feed doing? aha.. yep..
there’s so many loopholes i think your best bet is just be nice to the guy if he ever shows up, keep your antenna and TX legal, have plausible explanation for your lightning protection.
i’m in the process of relocating my part15 AM to the center of the yard and going with the lightning protection radials.
Total posts : 45366If, as is common in most transmitters, the power ground is common with the circuit ground then the audio and power ground lines can also radiate. This may or may not be a problem for an inspector but it is something to consider.
When I designed my transmitter I had a problem maximizing the output power to the antenna. Essentially, the maximum power happens with a 100 ohm load yet I knew my antenna impedance would be about 30 ohms. There are networks which can perform an impedance transformation but they also introduce loss. I decided the best and simplest way to transform the 30 ohm load up to 100 ohms at the transmitter output was to use a small toroid transformer. This maximized the power available to the antenna with only a few milliwatts of loss but it gave an additional benefit.
The transformer isolates the circuit ground from the RF output ground so RF does not appear on the audio/power ground lines.It also breaks the ground loop which results with a grounded transmitter and grounded power and audio source.
Though the transformer was not intended to stop unwanted radiation and ground loops it was a nice afterthought to realize that it did so. I don’t suggest that all transmitters be modified or built this way specifically to stop unwanted radiation but if someone wants to design their own then this is something to consider if for no other reason than to gain the highest power delivered to the antenna..
Neil
Total posts : 45366“..there’s so many loopholes i think your best bet is just to be nice to the guy if he ever shows up..”
That is so so true, and it makes it pratically impossible to have a 100% compliant 15.219 install. It’s also crazy that the most plentifully utilized and most established Part 15 certified transmitters in existence Talking Houses that have been around over 40 years have never actually conformed to 15.219 to begin with!
But that’s apparently the nature of part 15. It’s a crazy thing. But when I hear proclamations of acheiving in excess of five miles with an elivated ungrounded 100mw transmitter, and indicating it’s 100% legal — When even when our licenced 10watt TIS cousins can’t acheive that range.. Well, excuse me, but that’s total nonsense.
I really don’t care what someone is doing with their installs, but when it’s nonchalantly expressed that it these incredible ranges are being acheived, and it’s all kosher and legal with the rules of part 15 — That really bugs me, cause it’s not right, and it deceives potential newcomers into believing it’s true, and jeapordizes the part15 hobby.
Do you realize that it’s in the works for the FCC to recrute licensed broadcasters as members of the present formulation of “tiger teams” for combating the pirate problem?.. It’s not going to be a matter of the severly understaffed agents being unable to cover all these areas anymore. While the primary focus is for the FM, it’s reasonable to conclude some of the excessive range “part 15” AM broadcasters will be swept up in the net as well.
Expressing “legal install” with 5 and 6 mile range (with just a single transmitter) is just setting newcomers up for a fall. It’s deceitful.
Total posts : 45366Rich Powers said: “When I hear proclamations of acheiving in excess of five miles with an elevated ungrounded 100mw transmitter and indicating it’s 100% legal … Well, excuse me, but that’s total nonsense.”
I got to thinking about this and remember that many people have the easy habit of guessing distance. Some of these reports may be based on estimates out of left field with no real measurement.
Not long ago I had to look up how far a mile actually is… 5,280-feet.
With 2-radials my AMT5000 reaches about 1,000 feet, so I suppose that adding more radials could get up to a mile or slightly more.
If I hadn’t looked it up I might make a wild guess that 1,000 feet is “about a mile”.
Still, some of the reports of super-distance might be true! It’s kind of fun to wonder about it.
Total posts : 45366Also, as so frequently pointed out it depends just as much on the receiver.. I don’t know but it’s my understanding that most AM car and home radio reception don’t hold a candle to the ones of yesteryear – and then there’s the questions of whether the receiving radio is indoors or outside, the amount of powerlines, buildings, trees, and other signal interferences, and of course the ground conductivity.. humidity even, and any other number of other factors.
5 miles may be possible with all factors in perfection, but it certainly is not commonplace with a legal install.
Total posts : 45366I certainly agree about the “Radios of Yesteryear”. As a teen in the early 60’s and a AM BCB DX’er I would often go outside and fire up my Dad’s 1957 Chrysler, or 1947 Chevy convertible to DX. It was great back then and I logged AM BCB stations all over the country.Not so much nowadays.
Total posts : 45366Back then, there wasn’t the same level of background noise that there is today.
Never mind the fact that the electronics in modern day cars introduce far more background noise. You don’t even have to turn the car on – just insert the key (if you have one) and listen to the whines etc. that are introduced. It got so bad on some Fords that they did a recall to reduce some of the noise. Not on my car, unfortunately (stations that I can listen to with nary a crackle or whistle at home on cheap radios are virtually unlistenable on my Ford Flex).
So, I don’t think it’s entirely the fault of the radios.
Total posts : 45366seems the best suggestion so far is bake some cookies when the feds arrive and greet them with cold lemonade cookies and a smile because depending who’s on duty that day will depend on if you get cited for whatever violation they want to gift…
Play it safe and use a Mr microphone 😛
Joe the radio dood
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