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Ok, I know this the same old, same old.. But what is this saying? (specifically the last line which I emphasized in bold):
Avoiding a radiating ground
Ok, I know this the same old, same old.. But what is this saying? (specifically the last line which I emphasized in bold):
Avoiding a radiating ground
If you are connected to a ground that looks like an antenna , then you are going to get radiation from the system. Design the ground so that will not radiate, or does not function as an antenna. For example a pole grounded at the base with a short “ground lead” connected from the top of the pole to the transmitter has been shown to be a solution.
(http://www.am1000rangemaster.com/radiate.html)It sounds to me like it is saying exactly what it.. says.
How is this a solution?
I don’t get it, the entire page of the above link is devoted to emphasizing the importance of and providing tips to avoiding ground radiators, and even the paragraph which immediately followings the above statement says: Tower mounted and billboard mounted transmitters are notorious “ground radiators” .Am I misinterpreting something in the above solution statement?
I started to email Keith directly about it, but figure if I’m going to be asking a dumb question I may as well ask it here first, since you’re all already quite used to it!
Total posts : 45366Perhaps you should contact Keith directly.
I wonder if that’s an artifact of several updates to the section of his web site on grounding, perhaps one that didn’t get changed in edit.
There were instances where a certified transmitter is used for some purpose that licensees do not object to (like the famous Cadillac advertiser stations) where the radiating ground resulting from an elevated installation is not enforced against.
Part 15 transmitter sites on billboards, circa 1998 a saved copy from the internet archive, links go back to the archive.
This old web page is from the perspective of a broadcast engineer questioning some low power installations and being rebuffed by the FCC, so, like has been said so many times before – many layers to compliance, not the least of which is to not draw the wrath of licensees.
Another radio billboard advertiser is still live here http://radiobillboards.com – lots of really old info…
Total posts : 45366It is apparent that the once approved, then disapproved choke not only had no effect on preventing ground radiation, but obviously did not do anything as far as making the antenna system meet the 3 meter limit.
You want to provide a very low resistance path for lightning protection on elevated systems while at the same time choking off any RF emissions from that mounting pole or metal structure. Obviously this will affect range.
Wind too many turns on that toroid you end up creating a wire resistor thus resistance to the DC path. Wind too little and you do not choke off enough RF emission.
Now that an elevated system mounted to something metal and uses that metal structure as the DC ground path will also turn that metal structure into part of the resonant emitting system. This means that those single choke toroid forms will have to vary in their inductance value based on each site’s mounting structure length. The only way around this would be to design a very wide bandwidth choke effective for the entire range of the MW band as well as cover various lengths of mounting situations. However this may prove impractical since the more windings on a single choke form, or multiple choke forms to cover the variables, will no doubt increase DC resistance, thus the effectiveness of lowest resistance to ground becomes less, in turn doing nothing for lightning protection.
It is not going to be easy. Not every site is going to be perfectly exact from one to another.
Only one sure fire way to all of this in the meantime….mount the thing close to the ground where it should be and focus on a very well built ground radial system. If there is no room for such a setup, your choices are incredibly limited and at that point…you take your chances with hooking up to drain ducts or running ground wire down to the nearest point of ground.
RFB
Total posts : 45366I wonder if that’s an artifact of several updates to the section of his web site on grounding, perhaps one that didn’t get changed in edit.
Scwis, that would have been my initial impression had not everything above and below that statement been blatantly contradicting it! – so, that’s why I half questioned my own comprehension of what it said.. so at least now I know it’s not just me!
Oh, and I remember that link on the billboards from years back.. thanks for posting the archive of it.Only one sure fire way to all of this in the meantime….mount the thing close to the ground where it should be and focus on a very well built ground radial system. If there is no room for such a setup, your choices are incredibly limited and at that point…
RF, Ground mounting is not an option. I don’t know if you saw that video of where I was scanning the roof for an appropriate place to install, but in it, almost directly above the studio location is a steel pipe sticking out of the roof about 6″ – I’m reasonably sure that it belongs to the bathrooms of the restaurant of the same building my studio is attached (but fully separated).
Anyway, it is my intention to first try mounting to that pipe, since there is no way it could radiate with it being encased fully inside the building… it’s not as high as I would like (1 story), but it should prove legal, and that is something I’m really aiming for.
I already know it’s going to take additional transmitters to cover the 2 1/2 miles of the island — I hope a single transmitter will legally accomplish at least 3/4 of a mile with a good listenable signal in a car radio, and I don’t think accomplishing that in a legal manner should be a problem.I’m focusing on the car radio’s, to be more realistic about the whole thing, and will be promoting it as such. Of course I will also supply basic tips to the public on how to increase the possibility of hearing it in their home radios… and there’s always the internet streaming available – that is if this new bill that Ken pointed out doesn’t screw that up.
Total posts : 45366The comment “don’t attract the wrath of a licensee” would be especially interesting if the licensee of a silent station, as was discussed on a nearby thread, complained because a part 15er used the vacant frequency.
Total posts : 45366Wow Scwis! I just watched the 3 videos from ABC, NBC, and Entertainment Tonight on that second link you supplied ( http://radiobillboards.com ). I have never seen those before!… That’s all obsolete now huh?
How did something getting such a predominate nationwide media coverage simply fade into the shadows? – I’m surprised I never saw those clips.Here is a current newage of a talking billboard…
ABC 7: Animated Talking Billboard In D.C. Illustrating Google CEO’s Need To Answer To Congress
http://www.consumerwatchdog.org/node/10394Here’s a recent article from this year, which appears to be basically a just a Procaster ad, but worthy of comment..
http://universaldomainexchange.com/sjmsplash/broadcast-your-company/
Total posts : 45366The ability of a transmitter and antenna to radiate a signal includes a complicated combination of electric currents and fields. Below is an attempt to allow the reader to visualize what is happening in a transmitting system explained in physical terms and may not be useful to some who “already know this” but it is hoped that others can gain some insight from the presentation. As with most such simplified illustrations there are things left out and there are weaknesses in the explanation.
A transmitter radiates a signal by accelerating charged particles, usually electrons, into a conductor (the antenna). If there is no source of electrons other than in the conductors of the transmitter and antenna then a voltage will increase as the electrons move from the transmitter to the antenna which will eventually reach a potential where the transmitter cannot provide enough force to move more electrons. In the short time between moving the electrons out of the transmitter (leaving a deficit of electrons in the transmitter, a positive charge) and pulling them back when the signal polarity reverses this potential can be within the voltage capability of the transmitter but as the retarding potential increases the current decreases. This limits the amount of electrons (current) which can be pumped into the antenna with a given voltage and can be thought of as the impedance of the antenna. However, if the transmitter has a source for additional electrons to replace those moved to the antenna then the voltage due to the electron deficit is lowered because more electrons are available to move to the antenna.
What is the source of these additional electrons? If a path is provided to a conductor such as surrounding objects and the electrons in this conductor can be either pulled from this conductor into the transmitter and/or pushed into the conductor by capacitive coupling between the antenna and the objects then the transmitter will have a supply of electrons to push into the antenna with this source being the “ground” surrounding the transmitter. One such conductor is the earth surrounding the transmitting antenna, hence the use of the term “ground”. The capacitive coupling from the antenna provides a field which moves the electrons in the nearby conductive ground toward the transmitter allowing the transmitter to function as a “pump” and keeps the voltage required across the transmitter to move electrons into the antenna low enough that the transmitter can function. In other words a circuit is completed and the transmitter can now function as an electron pump with a low pressure (voltage) which does not exceed the transmitters capability to move the electrons.
These electrons are borrowed from the ground as they move toward the transmitter and a force (voltage) is created to pull them back to ground but at RF frequencies the polarity reverses fast enough that the electrons can move back into the ground before the voltage developed gets high enough to stop the movement.
The currents moving in the earth surrounding the transmitter are moving toward the transmitter from all horizontal directions and the radiation produced by these cancel. When these currents are collected and pass through the the “ground lead” in a single direction within the lead they produce radiation and this is why the length of the ground lead is limited for the purpose of limiting the radiation from all the conductors carrying the current in a single direction, both in the antenna and the ground lead, by limiting the combined length.
A simpler statement is that the electrons which are pushed into the antenna have to come from somewhere and this somewhere is the ground, including any power or signal leads connected to the transmitter. The use of a choke literally chokes off the electron path from the ground and thus limits the amount of electrons the transmitter can provide to the antenna.
Any conductor in which the RF current is moving in essentially a single direction will radiate a signal including water towers, billboards, and other structures already mentioned.
Neil
Total posts : 45366almost directly above the studio location is a steel pipe sticking out of the roof about 6″
This should be a good place to mount the antenna. Though not always, most setups like this using a pipe well embedded into a building structure are tagged as ok by an inspector. Again that is a 50/50 thing, but sounds like your best solution since there is no ground area to work with. I don’t know if that 10′ ground radial system being sold would do you any good on the roof! 😉
Without going into electron physics here considering this is Part 15 radio (roll eyes), I will spare the long winded formulas and blah blah.
As I noted in my previous post, not all sites are going to sport the same variables. A “one choke wonder” is not going to cut it, especially when no field testing with a range of variables are included in the design and prototyping. There is only so much that can be done in a controlled environment (lab) as well as on paper (theory).
We have all seen the result of attempting to apply a “one choke wonder” to a long metal mounting structure. There is no one choke wonder or one solution wonder to the endless varieties of installations. Each will have their own unique problems to solve. Take identical setups separated by only a mere city bock and there will be differences.
Some may come close to the same solutions, some will be drastic variants of one extreme to another. That is the neat thing about experimenting, trial and error, by guess by golly trait of the hobby. We have the basics to follow as the foundation, a starting point. But it goes MUCH further than that in the real world.
RFB
Total posts : 45366Without going into electron physics here considering this is Part 15 radio (roll eyes), I will spare the long winded formulas and blah blah.
Does this mean Part 15 hobbyists are neither interested in nor capable of understanding “electron physics” and “long winded formulas”? Is there not benefit from understanding some basics?
It is the reader’s choice to decide. If one does not like “blah blah” then one can choose to not read it.
Neil
Total posts : 45366Actually it was quite refreshing. Always good to have a review and introduction for beginners. 🙂
While we are on the subject of the physics of RF propagation, we also have to take into account elements other than the parts of the radiating system itself. Things like atmospheric conditions (not necessarily miles up) such as moisture and contaminants.
Ever been near a metal fabrication facility? Its surprising to some that in and around such a facility are tiny fibers of metal particles not captured by the filtering systems that fly around. These end up being released by simple means, such as that of the workers coming and going, open doors and windows of the facility. Stuff like this can affect a low power antenna system.
Even a saw mill can cause some issues with moist wood dust floating about.
During testing of my CC system, which covered weeks of different configurations and measurements, the one thing that never was constant was the environment variable. One day you can get a set of measurements, the very next day, totally different.
Finding that right balance is the challenge…for intentional radiator or a CC system, more so with a CC system as the power grid’s inductance is constantly changing from one minute to the next, then add all the other variables to boot!
I thought your review on the theory was quite good radio8z. Good post in my opinion. We should consider to not overload though, one small step for man, then one giant leap for mankind as it were.
RFB
Total posts : 45366The link to the 1998 billboard transmitter is interesting. Wonder if that would fly today?
I do find it really hard to believe that this installation would have been found to be compliant, even then, though…
Total posts : 45366I do find it really hard to believe that this installation would have been found to be compliant, even then, though…
You kidding? There are boat loads of silent and up and running stations getting away with things by simply throwing $$$ (corporate media) while the mom and pop/community outfits are swept to the gutter.
That billboard, and others, that are a part of a business are most likely to be tagged with an “A-OK” note simply because they can continue to contribute to the banksters and gangsters up in DC (District of Criminals). Can’t stop that cash cow flow don’t ya know!
RFB
Total posts : 45366You know, belief is a funny thing. Most of us approach most opinions and solutions with a certain amount of caution.
In his book, “Tribes”, Seth Godin points out how our beliefs are formed in this culture we live in.
“People don’t believe what you tell them.
They rarely believe what you show them.
They often believe what their friends tell them.
They always believe what they tell themselves.
What leaders do: they give people stories they can tell themselves. Stories about the future and about change.”It seems that the discussion involving “elevated” installations as opposed to “ground” installations is backward looking. We individually believe in one or the other because it is the story we tell ourselves. We receive a certain amount of comfort in our own story.
RFBurns is correct. What ever works, works. Get a life. Get over it. Next…
Total posts : 45366Comments like “banksters and gangsters up in DC (District of Criminals)” and “Get a life. Get over it. Next…” serve no purpose in advancing our discussions of low power radio and are not welcome.
Thank you for your cooperation
Total posts : 45366Thank you for your assessment of recent posts to this Forum.
PhilB knowingly threw fuel on the fire to inflame people who have had a reasonably cogent discussion for months on a variety of topics. He has, with purpose, gone after folks on the site, using reference to people and issues that have no business being interjected in the conversation (e.g – the R. Fry situation). RFBurns reacted without any previous knowledge or sense of history to references made by the manufacturer of the SSTran kits. Phil’s references were inappropriate in view of the guidelines.
My comment was to get contributors to use words appropriate to the thread at hand. Frankly, what we “believe” to be true in most cases doesn’t matter. I think we, who have been at this for awhile, would admit to the continuing contentious discussion about installation and grounding. The discussion has, for the last 5 years, gone around and around, like a dog chasing it’s tail. No one has made mention re: the differences between the application of each different device in its particular environment. RFBurns has attempted to steer the discussion in that direction, but with little success due to the rantings of PhilB (who in my opinion is trying to sell kits).
Also, consider that occasionally a bit of tongue in cheek humor is worth the time and effort just to keep a sense of community and brotherhood. My question: Where is the contribution of PhilB in this mix currently? I am satisfied that it is your, and other admin’s, call. Good luck herding (difficult task) the cat’s of Part15.us.
(Note: I would have sent this by personal email, but the “captcha”option is not working.)
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