- Posts
Much is being made of some field strength ‘measurements’ (very coarse, and relative) made by Rich of a very powerful (compared to Part 15) licensed station signal.
I don’t think that you can use those measurements to prove anything about Part 15 signals.
Usually a city grade field strength measurement is pegged at 1mv. Most licensed stations, even those relatively underpowered at a kilowatt, will have that 1mv field strength (and much more) measurement over quite a wide area – certainly, a much larger area than the distance between the two points of Rich’s measurements. In fact, I suspect that Rich could have traveled quite a distance and found the same field strength measurement from that signal.
Contrast that to a Part 15 field strength, which is sometimes lucky to even equal 1mv. Certainly, a 1mv field strength degrades much more rapidly, even in line of sight situations, with Part 15.
So, if one takes one or two isolated field strength measurements, it means precisely nothing without the proper context. A 1mv field strength may mean that the signal won’t go much further (in the case of Part 15) or it may cover a large area (in the case of a powerful licensed station signal).
It’s possible that there may be factors other than obstructions that cause Part 15 signals to degrade, and elevated antennas for a clearer line of sight to be more effective. It’s also possible that there’s something else at work – we can see by my example that a 1mv field strength measurement doesn’t always mean the same thing in terms of range.
I will say it again. The ONLY way to resolve this is to conduct experiments with ground mounted and elevated antennas, along with an accurate field strength meter. I’d seen Bill DeFelice’s description of the testing that Rich Powers described, and that seems to meet the criteria. Hopefully he can find the time to get around to doing those tests.
We Are Not All Seeking the Same Thing
A good deal of attention on these forums goes to the part 15 stations that are seeking maximum range, and it would behoove them to experiment with several approaches until they find the most pleasing arrangement.
Others, like us here at KDX, have a specific target area which can be easily served without extraordinary effort, so for us we look for the most convenient place to set the transmitter with the antenna mounted within reach. A different arrangement would meet the same results so there’s no need for us to experiment with variations.
Our participation in these threads about “what is the best approach” are therefore to us an academic exercise while we would also like to be of assistance to stations so what we have to say is offered in hopes of aiding the inquiry based on what limited experience we’ve had.
Under the part 15 rules we have a liberty not enjoyed by licensed stations… we are not required to be “trained, studied, professional, experienced, or tremendously amazing RF engineers” nor are we expected to employ one.
Therefore we can “play” or “work” at running these stations while obeying the few simple rules. We can be as scientific or as fanciful as we like.
It seems intrusive, therefore, to have a character declare “the one and only truth of the matter”, entirely dismissing our “unschooled” thoughts and comments, promoting his own awesome credentials & remarkable command of the subject.
At the same time it challenges us to articulate what we know and believe like cats being offered a scratching post. We end up more confident in what we don’t know.
I read an amusing statement by a ‘scientist’ a few years ago, who claimed that we were close to knowing everything there is to know [in the universe], and would in fact know everything within 20 years.
Of course, soon after that came discoveries that threw everything that this scientist and science thought it knew into chaos.
The point is that arrogance is the undoing of any thinking individual. Those that claim they are smart and know everything aren’t by the very nature of the claim. One of the most intelligent people that I’ve ever met in my life would say that he was continuously humbled by how much he didn’t know, and that his life was spent trying to learn more.
That’s a pretty good philosophy to live by.
“We Are Not All Seeking the Same Thing
A good deal of attention on these forums goes to the part 15 stations that are seeking maximum range, and it would behoove them to experiment with several approaches until they find the most pleasing arrangement.
Others, like us here at KDX, have a specific target area which can be easily served without extraordinary effort, so for us we look for the most convenient place to set the transmitter…”
Myself, I’ve abandoned the quest for “maximum range”.. (as I’ve made known several times).. because I really think that kind of mindset is exactly what primes a station for trouble, and a potential NOUO. I feel a part15 stations best bet is to actually maintain it’s range to the well established accepted norm for such stations, and that is about a mile radius (per transmitter).
I don’t want to sound like a broken record, but the existence of 15.219 is a very convoluted thing. Other than having an installation a few inches from the ground (which is kind of ridiculous and impractical), the most prudent way is to install in a more reasonable method (for example a grounded pole mounted transmitter) and to abide by what has been “accepted methods” for the last half century, while being mindful of the range it achieves.
You can call this only an opinion, but it’s based on undeniable facts.
RE: Much is being made of some field strength ‘measurements’ (very coarse, and relative) made by Rich of a very powerful (compared to Part 15) licensed station signal. …If one takes one or two isolated field strength measurements, it means precisely nothing without the proper context.
So far in this thread I have posted two graphics including the _measured_ relative fields of an AM broadcast station. They show the effects of path obstructions on the received fields/signals near those obstructions. For each case, only two measuring points are needed to do this.
For all practical purposes, such effects were shown to be non-existent. Nothing more (or different) than that logically can be inferred from those graphics.
Those two graphics and their text are totally in context with exploring the claims made here by some that such obstacles cause serious and permanent losses to the propagation of groundwave signals in the AM broadcast band.
They don’t.
After I made my last post, I came across this article which illustrates what I was attempting to say far more eloquently:
RE: … I came across this article which illustrates what I was attempting to say far more eloquently: etc …
My observation: attempting to shift the focus of this thread from technical issues and technical responses to a belief/discussion about “personalities” does nothing that leads to a better understanding of those technical issues.
Who Said “Personalities?”
No one has “shifted to personalities”, which might be an interesting topic for another time.
Bertrand Russell, the intellect referenced in Artisan’s link, was one of the greatest thinkers of the 20th Century… for what it’s worth I have a large collection of his books within feet of one of my part 15 transmitters.
Those among our legitimate group of part 15 broadcasters have shown all the traits of high intelligence by maintaining skepticism and indecision about pat formulaic claims which run up against our experience.
Who is calling who stupid? Or, would it be, whom is calling who…
Rich proves the points of the article by continuing to post.
I could also use his own words from earlier in the thread, “but apparently some people either don’t comprehend […] or choose to disregard …”
Suggest that posts based on provable data such as shown in antenna engineering textbooks and other peer-reviewed publications, and/or by accurate physical measurement and accurate proof by their authors are more believable and useful than posts which are based on undocumented and unproven personal belief/opinion.
True But For
It is true to say “…posts based on provable data such as shown in antenna engineering textbooks and other peer-reviewed publications, and/or by accurate physical measurement and accurate proof by their authors are more believable and useful…”
Except that in this entire thread no cross-reference has been made to antenna engineering textbooks nor peer reviewed publications. No accurate physical measurements have been presented.
True, for posters other than radio8z and yours truly.
In my case, physical measurements have been posted several times in this thread (see the graphics/text links following the line below).
From my experience here, references/quotes from antenna engineering textbooks tend not to be well-received. Such can be supplied if specifically requested, but probably most readers wouldn’t have those books/documents to verify for themselves what was posted from them.
At this point I expect not to respond further to this thread. From a review of this entire thread, its readers can decide for themselves about the posters here that were most credible.
(Added) Obviously Mr Blare did not read the links I posted below, which show measured data, not NEC calculations.
________________________
It’s So Bad and Terrible
Parting words: “..but probably most readers wouldn’t have those books/documents to verify for themselves what was posted from them.”
I know. We’re just so dumb. We wouldn’t know what to ask for at the book store.
Mr. Fry commented: (excerpted) “From my experience here, references/quotes from antenna engineering textbooks tend not to be well-received.”
Mr. AMRadioLegend responded: I’m not sure I agree with your observation. It’s part of scientific exploration to compare and contrast theory against real-world experiences. (Science Fair Projects) That being said, a science fair project would consist of comparing theories of wave propagation at certain frequencies with regard to power levels. Would a signal operating at 1600 kHZ behave differently at 35 mW compared to 1KW with or without obstructions – natural or otherwise in the immediate vicinity of the antenna?
Also a gentle reminder, YOU started this unsolicited thread and to conclude it is certainly your choice. But to weasel out with the implication that the members do not have the mental capacity to comprehend your observations is somewhat of an insult.
With Kindest Regards, I am sincerely yours,
John
- You must be logged in to reply to this topic.
