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Recent posts here on Part15.org have touched on this subject without offering any conclusions about it.
Below is a NEC analysis showing one comparison for those setups, for those who may be interested.
The statements in the conclusion there might need some study to understand, accurately.
You can’t tell me that having clearance over nearby houses and other obstructions has no bearing on range!
With part 15AM, obstructions block the signal, there is no question about it! If the obstruction is not present then the signal is not hindered and will travel farther then if the obstruction was there. I’ve experienced such situations too many times.
The presence/effects of obstructions along a propagation path are much less significant to the field intensity received in the MW band than when transmitting in the bands located at~ 30 MHz and above.
Obstructions such as terrain and buildings _can_ affect MW signal strengths, but generally only within a small fraction of a wavelength from/in those obstructions.
The following graphic shows the signal strengths I measured using a Tecsun PL-310 receiver tuned to a local AM broadcast station, for the two paths shown there.
One path was blocked, and one path was clear — yet the signals had the same strength at the same distance from the transmit antenna.
This result may not be intuitive, but it is supported both by theory and measurement.
Let me throw in a few random observations. I suspect the signal blockage may be minimal when working with 1.4 kW as opposed to 100 mW. From a 1.4 kW signal, if the blockage stops 100 mW of the signal, that won’t even be measurable with even the finest field intensity meter and would be within the margin of error of the machine. But if that same obstruction was able to block 100 mW of a 100 mW signal, nothing is getting through.
Example. The property next to our house has a 70 foot long mobile home. It’s sided with aluminum siding. When I first received my Procaster I set it up on a picnic table in the backyard, just freestanding with it’s attached 10 foot antenna sticking straight up, and fed power and music into it and walked around the yard and neighborhood listening. Nothing scientific mind you, just confirming it worked before I mounted it permanently at the third floor attic window. When I walked around the mobile home next door and was around the far side my reception vanished. The signal was not able to penetrate two aluminum sided walls of a mobile home. I wasn’t more than 60 feet from the transmitter, but there was an aluminum clad house between it and me. Now, if this would have had as great of an effect had I moved away from the mobile home but still on the other side, I don’t know. But it was certainly blocking the signal.
I’m sure we can all site examples of where the signal vanishes on AM while driving our cars. Go under a bridge? Signal lost. But again, these are examples at the receiving end. When I pull into my garage the 5,000 watt commercial station I listen to all but vanishes. As a commercial broadcaster I often do “remote” broadcasts. We use a 50 watt FM transmitter to send broadcasts back to the studio, and we generally listen to a radio to pick up our cues off air. Our mall, the hockey arena, and the grocery store are all places where we can’t hear the off air signal on AM. Obviously the signal is being blocked. Again, on the receiving end, but nonetheless, signal is being blocked. So it’s my theory that signal can be blocked at the transmitting end, just when it involves thousands of watts with hundreds of feet of antenna tower, the result is minimal and very limited in size. Our FM transmitter for broadcasting gets out of these buildings just fine, but we have been at marginal locations where moving the transmit antenna next to a window was necessary to get noise free reception back at the studio, which demonstrates FM can easily be blocked by a nearby wall or building.
Further consideration: As part of my engineer duties for our AM station (one tower omnidirectional during the day and three towers directional pattern at night) I’m required to take the Potomac Field Intensity Meter to specified monitor points and measure the signal strength to insure we’re not over the limits for our directional pattern. We did this monthly for decades until the rules changed to “as often as necessary to show compliance” so now I do it quarterly plus whenever I suspect things might be unusual, either technically or because of conditions. I’ve been doing this at several stations for more than 40 years. There are an infinite number of things that happen on the planet than can change these measurements. One example is when management had let pine trees grow willy-nilly on the property where the towers are located. This is a large open field basically in the middle of a forest. If left alone pine trees start springing up inside the fenced area. We used to have a crew go out and remove them as soon as they started growing, maybe reaching a foot or two in height. Hundreds would be removed, piled, and burned. After that station owner passed away and the new owner who was cheap decided not to bother doing this trees worked their way to 6 – 8 feet or more over a few years. I had a fit and told them they had to go — mostly because their roots damage hundreds of ground radials running from the bases of the towers. But then an engineer friend of mine saw the site and went nuts about all the signal we were losing! He claimed that all those trees grabbed some signal and brought it to ground. Made some sense but I was skeptical. We convinced management to have the trees removed (mostly to protect the ground radials) and I went and took field intensity readings before the crew did their work, and the day after, and damned if they hadn’t gone up not only measurably but substantially. TREES at commercial transmitter sites for AM DO make a difference. Now, this engineer, who just retired after being in the industry for well over 50 years told me — when it comes to directional monitoring points for AM stations that were established many decades ago, you’re lucky to get 50% of what you did when the limits were established due to growth of a natural nature (trees, brush, etc) and growth of manmade nature, buildings, towers, utilities, etc. Our directional pattern and monitoring points were established in 1971. I pulled out the old logs from the beginning and checked them at 5 year intervals (all readings at the same points, on the same tower system, same output from the transmitter, same current going to the towers, etc) an they did in fact show a decrease at every 5 year interval. And present readings are about 60% of what they were in 1975. I’ve been doing the readings here since 1988, and it’s one of those gradual things you don’t notice — but when i pulled out my 30 year old readings the difference was amazing! This is a well known phenomenon that is well documented at directional AM stations. Now, how this applies to a 100 mW station with a 10 foot antenna may be nearly impossible to document. Other variables that I had been able to witness first hand include the construction of a metal building not far behind a monitor point but inline with the signal, reflecting signal and increasing the reading. And the same effect of a metal building being put up inline with the signal from the tower and me, causing a reduction in signal strength. This also happened with there was a new water tower built between the tower and the monitor point creating a signal shadow. All real things that I’ve experienced in real life. But that shadow was only measurable in a few feet — moving a few feet either way would move me out of the shadow and readings would go back up!
It is often said that the “elevated power and audio cables to an elevated Part 15 AM transmitter radiate signal….” create increased field strength. Maybe so. And I’ve often been told that that must be the case with my ungrounded, elevated Procaster installation.
My Procaster is mounted at a third floor attic window, mounted to a short section of gray PVC conduit, mounted to mast brackets screwed to the side of my wooden house. There is no ground connected to the rather substantial ground lug on the transmitter, and when I installed it I checked for, and noted no continuity between this ground lug and any of the power or audio cable terminals.
The studio is on the second floor. The power/audio cable (as provided with the transmitter) runs from desk height on the second floor, up through the ceiling into the attic and runs along the attic rafters at probably 5 foot height for about 25 feet, and out the window to the transmitter. Is this a radiator? I’ve never checked. But seeing as how the transmitter passed it’s certification with such a cable connected (It’s in the pictures at the FCC website with the certification paperwork) it would have been a radiator then too.
My one experiment when I was first set up, was to connect a wire from the ground lug and drop it to the ground and connect it to the house ground in the basement. Just to see what happened. I have a spot about 1/2 mile from the house where I take FS readings to keep tabs on things, and when I added this wire I got a substantial jump in field strength. Which showed me the effect of a long ground lead, and also made me believe that the power and audio lines were not providing a ground path, since if they were, adding an actual ground shouldn’t have made much difference. Anyway, I’ve always operated without this ground lead connected. Additionally, even if mine were a ground mounted transmitter, it would still need power and audio and since the studio is on the second floor the cable would be substantially LONGER to reach the transmitter at ground level. So if there was any additional radiation from this cable it would be even more so with a ground mounted installation. No matter where you put it, it’s still going to need power and audio. Unless you have your power supply and audio source buried in the yard and run the cables to the transmitter underground!
Just some real life experiences.
TIB
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<div class=”bbp-reply-content”>Hello, Tim (and all):
Below are some selected clips from your detailed post above, with some comments applying to them:
I suspect the signal blockage may be minimal when working with 1.4 kW as opposed to 100 mW. From a 1.4 kW signal, if the blockage stops 100 mW of the signal, that won’t even be measurable with even the finest field intensity meter and would be within the margin of error of the machine. But if that same obstruction was able to block 100 mW of a 100 mW signal, nothing is getting through.
</div>
The attenuation through/around a path blockage is not a fixed amount, such as “100 mW.” Rather, that attenuation is a fixed percentage of the original signal arriving at the blockage of that path. If the effect of the path blockage is not measurable or important for a 1.4 kW transmit system, that also will be true for transmit systems at every other power level (other things equal).
<div class=”bbp-reply-content”>I’m sure we can all cite examples of where the signal vanishes on AM while driving our cars. Go under a bridge? Signal lost. But again, these are examples at the receiving end. When I pull into my garage the 5,000 watt commercial station I listen to all but vanishes.
Such effects are common for MW reception, but they are localized very near the conductors/structures causing them. Once the receive antenna is moved sufficiently beyond those conductors, the received field increases to about the same value it would have if those conductors/structures were not there.
… Our directional pattern and monitoring points were established in 1971. I pulled out the old logs from the beginning and checked them at 5 year intervals (all readings at the same points, on the same tower system, same output from the transmitter, same current going to the towers, etc) an they did in fact show a decrease at every 5 year interval. And present readings are about 60% of what they were in 1975. I’ve been doing the readings here since 1988, and it’s one of those gradual things you don’t notice — but when i pulled out my 30 year old readings the difference was amazing! This is a well known phenomenon that is well documented at directional AM stations.
</div>
No dispute about that, but then the pattern nulls of a directional MW broadcast array are much more sensitive to re-radiated/blocked fields than those in azimuth directions well removed from those nulls. Some directional AM stations have had to re-locate/re-document monitoring points when re-radiating conductors have been installed close enough to the original monitoring points so that the array appeared to be non-compliant with the station license.
<div class=”bbp-reply-content”>…This also happened with there was a new water tower built between the tower and the monitor point creating a signal shadow. All real things that I’ve experienced in real life. But that shadow was only measurable in a few feet — moving a few feet either way would move me out of the shadow and readings would go back up!
</div>
Those effects really are the result of the net field at that exact receive location resulting from the relative r-f phases of the direct and reflected fields arriving at that location — more than the existence of one or more shadows.—-
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Other comments could be made concerning the Procaster installation, but maybe this is enough for now.Sorry for the garbled format of my post above, but I don’t find any way on this forum to edit it, once posted. Anyone know of a way to do that?
Sorry for the garbled format of my post above, but I don’t find any way on this forum to edit it, once posted. Anyone know of a way to do that?
For a few minutes after you post there will be a “modify” link at the top right of your posted comment window, you click that.
Correction: it doesn’t say “modify” it says “edit”
————————
I’m sure we can all cite examples of where the signal vanishes on AM while driving our cars. Go under a bridge? Signal lost. But again, these are examples at the receiving end. When I pull into my garage the 5,000 watt commercial station I listen to all but vanishes.
Such effects are common for MW reception, but they are localized very near the conductors/structures causing them. Once the receive antenna is moved sufficiently beyond those conductors, the received field increases to about the same value it would have if those conductors/structures were not there.
———————–
Ok, that’s understandable, but we’re not talking about your average MW signals, we’re talking about very weak part 15 MW signals. By the time the receiver is moved beyond that obstruction it’s very likely (and common) that your going to almost immediately run into another obstruction, IE: the building behind that.. the signal is not going to be returning in most cases unless your in a very sparsely populated area.. in which case there’s not going to be anyone close enough who could tune in anyway.
Height helps to avoid that problem.. If you can see the transmitters antenna then you’re certainly going to be able to tune it in. But if you’re at the same distance away and you can’t see the antenna due to structures in the way, then more often then not you will not be able to tune it in.
I’m not saying you have to be in visual range to pick up a part15AM station, but it does require a rather unobstructed path for the signal to be received.
@ Rich, If I try to edit a post to correct something for example I get an access denied window and have to fill out my email address and answer a math question and click on the allow icon and it comes back the unchanged so I just say to hell with it! Or if it really matters I delete it and do it again.
When the Obstacle and Antenna Are the Same
KDX AM 1680 radiates from a “Wintenna”, simply a metal-window-frame fed by a 3-foot wire at the inside-floor up to the window-frame and wire at the top of the window-frame to the porch roof, totaling 10-feet on the rear stucco wall of our building. By this method we are able to place a signal both indoors and the yard outside from a single antenna.
In previous discussions it has been estimated that the stucco-metal-webwork in the wall absorbs some of the RF energy, but an advantage is that the antenna is on the same vertical plane as the wall eliminating the rear of the building as a reflective surface; the antenna and wall are “in phase”.
What becomes significant in light of this thread is that the signal strength remains very usable around the sides and front of the entire building, most of which has brick walls.
Because of this “surface effect”, as I call it, I visualize the MW signal in this case as being “liquid”, because it “flows” around corners and fills in the opposite (front) of the building. I also estimate that this signal behavior is made possible by the “in-phase” nature of the antenna-in-the-wall.
Needless to say the other examples described in this thread are based on antennas located AWAY from objects, therefore out-of-phase reflections from objects plays a part in results at many points in their overall field.
I can’t comment on the effect of obstructions on licensed radio station signals.
But I can comment on that effect for Part 15 signals.
I also have observed that line of sight makes a huge difference in AM Part 15 range. I once conducted an experiment – I used the same transmitter (Talking House), antenna (wire) and power cord for each.
In both cases, I ran the wire antenna outside the house, but in one instance, elevated that wire antenna so that one end was above the roofline. In the other, it was about a foot lower.
I obtained substantially greater range with the higher antenna.
I don’t know how you would explain it otherwise.
If structures/buildings themselves always caused significant and irreversible losses to the signals radiated by Part 15 AM antenna systems, then that effect also would exist for these signals I measured on each side of a high-rise steel structure (graphic below).
Note that those two signals had identical values at the two locations shown on the graphic below after crossing the building structure along the same radial bearing from the transmit site.
If that transmit site radiated only 1/1,000th of the power it took to generate those two 71 dBµ signals near that hospital building, those signals would drop to 41 dBµ. but still be equal to each other.
This begs the questions:
What would that second reading be if it were measured standing 5 feet away from the building rather than out at the edge of the parking lot?
What would the effect be if that building were plopped down at the transmitter tower site, say 50 or 100 feet from the tower? Would there be no attenuation — readings would compare to those taken at other points around that tower assuming the same distance but with no building?
Is the thought here, then, that if I were to drop my Procaster from it’s 30 foot high mount, straight down to the ground with the same cable feeding power and audio, the same length, but still connected to no intentional ground — that the coverage would be the same? Even though at ground level it would be about 8 feet from a 4 foot high chain link fence, and between a stone and wood 3 story house and a 70 foot long aluminum sided mobile home, and be adjacent to a bunch of 30+ foot high trees on one side? Not to mention a cement block constructed garage? That any change in signal would be basically be too small to even measure in any direction?
Not something I could try, as 6 months out of the year the transmitter would be under 3+ feet of snow!
TIB
RE (from TIB): What would that second reading be if it were measured standing 5 feet away from the building rather than out at the edge of the parking lot?
Definitely it would be less than shown on the left side of that graphic, out in the street running along the east side of that structure — but I didn’t measure signals that close to the building.
The salient point here is that the signal measured on that radial further away from the structure matched the signal arriving via an “unblocked” path at the other side of the structure.
IOW, the affect of the structure on that MW signal does not extend more than a fraction of a wavelength from that structure.
What would the effect be if that building were plopped down at the transmitter tower site, say 50 or 100 feet from the tower? Would there be no attenuation — readings would compare to those taken at other points around that tower assuming the same distance but with no building? …
My earlier graphic (reposted below) shows the effects of a nearby structure on the radiation patterns of the same 3-m monopole when mounted nearby with its base at the surface of the earth, and when vertically elevated so that its base is 5 feet above the top of the structure.
Note that those far-field radiation patterns are practically identical.
Certainly the relative signal levels inside and immediately adjacent to that frame structure would not show that these two radiation patterns were as circular as they are when measured/received several hundred feet or more beyond that structure.
But at every horizontal distance and with other things equal, the relative fields/signals of those two 3-m monopoles for those conditions would be practically the same as each other, regardless of their installation heights next to that structure.
Not too intuitive, I know, but that is the reality for this scenario.
Building Upon the Conclusion
The conclusion offered up to this point is: “There is very little difference between the instrinsic radiation patterns of these two configurations ( ground-mounted vs. elevated MW monopole antennas).”
Accepting this general finding can be useful to part 15 operators faced with the choice of where to locate their transmitters.
Is there enough information within this presentment to extend our conclusion just a little bit further?
Can we say that there is very little difference between indoor transmitter/antenna location vs. outdoor?
Deduced
Enough raw facts and opinions have been written in this thread to make deductive thinking a useful tool for arriving at practical viewpoints.
We opened with engineered comparisons regarding two aspects of MW (Medium Wave) transmitting antennas:
1.) ground mounted; 2.) elevated
and
1.) full power licensed; 2.) 3-meter antenna at 100 mW scaled down based on the same physics.
While it was allowed that objects in the radiant field cast shadows, we learned that given the large territory of a full power signal those shadows were inconsequential.
Meanwhile, a 100 mW 3-meter antenna is also shadowed by objects, however objects remain fully sized and do not shrink in correspondence to the reduced power, and place shadows in a large portion of the small signal cast at part 15 strength, making objects of far greater significance at low power, therefore increasing the liklihood that a raised antenna might benefit from being above the terrain at the angle favorable to eliminating the shadows cast by objects.
As to my added question: whether an indoor antenna would perform on equal footing with an outdoor antenna, our deduction tells us that an indoor antenna is inside of a shadowing object and thus would be at least 50% shadowed as it passes through individual walls, further distorted by the reflections (standing-waves) within the object.
Our lesson tells us that simply scaling physics from full power to micro-power doesn’t faithfully predict results in an unshrinking world.
RE: …simply scaling physics from full power to micro-power doesn’t faithfully predict results…
On due research, one can discover that the factors/equations that determine the propagation loss to a radio wave in decibels or percentage when crossing through/around a lossy physical object such as a steel building or a tall hill do not include the magnitude (amount) of the radiated power producing that signal in the first place.
Over a given propagation path and for other things equal, the radiated signals of a “Part 15” AM station and a licensed, high power AM broadcast station _both_ have the same relative propagation loss in decibels and as a percentage.
<p style=”text-align: left;”>I also have noticed that trees can block out signal. Case in point when I try to get a good signal to the Deltaville Market by the time I get there my signal is about 19 to 20 dbuv which is barely listenable at about 1 and 1/4 Mile. Now on the other direction towards Taylor’s restaurant and out to the Citgo gas station I can get a slightly better signal at the restaurant and the signal seems to go out further in that direction. I don’t know if it’s because there’s less trees in that direction but it seems that there are. Towards the Deltaville Market there are several trees as you’re looking in that direction. I’m imagining if it were a clear line of sight I would have a much better signal. If I were to get the antenna way above the trees I’m sure the signal would be substantially greater.</p>
To reiterate what Artisan radio said about range indoors the building that I tried to do it in when I had a talking house 5.0 connected to its wire was made out of brick no aluminum siding and I had a big bay window. Well indoors I use the wire that came with the talking house and I attempted a range test. I could not transmit very far away from my complex. I didn’t even make it to the 7-Eleven which is only a half a mile or less than a half a mile away. But when I got the antenna Outdoors the range increased substantially. Now when I used a homemade ATU and connected that very same wire to it my range increased substantially and I could hear my signal at the 7-Eleven.
I used Station 8`s antenna connected to an ATU which was homemade and the range was greater yet. This antenna however it was only six foot tall and it was connected to the home brew ATU. And because the talking house transmitter uses the third prong as a ground I didn’t bother with connecting any sort of ground wire to it as it was pretty much irrelevant because it already has one.
We learned two things by this experiment number one the homemade tuner or ATU produced a better signal then the built-in antenna tuner inside the talking house transmitter. This makes me wonder if the R.A.T 1.0 s design will have a better tuning coil then one that you would see inside of an AM radio and A-Rod that simply moves up and down that tuner. The homemade ATU had a coil that was wound and it was very similar to ATU’s you would see in higher performance part 15 compliant transmitters this is why they do so much better.
My broadcast engineer friend built a homemade ATU that I am using now with a ASMAX2 C-Quam AM stereo transmitter with my antenna on a good 6 ft Pole and I do much better then with the antenna closer to the ground and with a 50 ohm transmitter using rg58u coax. This coax is well shielded so I’m not transmitting out my coax and most of the energy is going where it should be the antenna.
Your SWR makes a big difference having a good SWR is very important if you want range. I do believe that is why the range Master does so well because it’s tuning system was very well thought about and it was made to match up with that CB whip antenna quite nicely and to top it all off it can run without a ground as many folks have used it with no ground at all but in a higher location and have achieved ranges anywhere between three to five miles which is phenomenal. So the height as well as your tuning circuit makes a big difference I would concentrate on a well-made antenna tuning circuit and see what you get also get the antenna up there and you’ll find better results this is come from my own broadcast engineer friend. I’ve learned a lot from him as we discuss a lot of this kind of thing most of you don’t realize that SWR makes a big difference even on this low powered stuff you want to get as much energy as you can out the door and into the antenna. Elaborate ground radials won’t make much of a difference if you’re standing wave ratio is super high you’re just wasting all that energy. Concentrate on a good ATU circuit and use a good antenna analyzer when you’re done and a field strength meter and get that filled straight up there is high as you can get it because that will equal your range.
As far as I’m concerned I totally agree with Artisans post earlier that really says it all…
“I can only go by my experience, regardless of theory. When I raised my wire antenna so that it was above my roofline, range increased substantially.”
However, I wouldn’t exactly say the range increases because of height, but rather that the height substantially helps to overcome obstructions which otherwise would decrease the range.
RE: … the height substantially helps to overcome obstructions which otherwise would decrease the range.
However that belief is not supported by the two signal strength measurements shown in the graphic below.
The signals are essentially the same even though one path is totally blocked by terrain, and the other path is not.
“However that belief is not supported by the two signal strength measurements shown in the graphic below.”
Rich, maybe you should try that same experiment while taking measurements from a part15AM transmitter. I understand your point that it in theory, percentage wise – the reaction of the signal to obstructions should work out about the same as it does from a full power station.. but I – as ignorant as I am about such technical matters – can still accurately conclude from experience that obstructions (such as a two story house) can completely eliminate reception of a part 15 signal beyond that building.
Your charts simply can’t change the fact that a building will block a part15AM signal.
All Things Not Equal
The “equality claim”: “Over a given propagation path and for other things equal, the radiated signals of a “Part 15” AM station and a licensed, high power AM broadcast station _both_ have the same relative propagation loss in decibels and as a percentage.”
The antennas are not equal.
A full power station is mounted at the ground while ALSO reaching around 200′ into the sky, whereas ALL part 15 3-meter antennas are located at or near the ground.
The angles of incidence are not equal.
A part 15 signal hits a shadowing building or obstruction head-on, while a full power signal penetrates the obstruction from angles high, medium and low, giving it a disproportionate advantage.
RE: The antennas are not equal. A full power station is mounted at the ground while ALSO reaching around 200′ into the sky, whereas ALL part 15 3-meter antennas are located at or near the ground. The angles of incidence are not equal. … A part 15 signal hits a shadowing building or obstruction head-on, while a full power signal penetrates the obstruction from angles high, medium and low, giving it a disproportionate advantage.
Note that the _measured_ field shown at the end of a ~ 1-mile, obstructed path in the graphic linked below is the same as at the end of the 1-mile, unobstructed path shown there.
None of the tower was visible at the end of the obstructed path, yet the field there was the same as at the end of the unobstructed path.
This reality does not support the contention referenced above.
Carl states it best. The assumption that all other things are equal between a Part 15 installation and a licensed station is not correct. Otherwise, numerous Part 15 stations would not see the results they are seeing when elevating antennas (and with all other things being equal WITH THE TWO PART 15 TRANSMITTER installations).
I’m not even sure that the statement that the percentage loss in decibels would be identical is accurate when dealing with Part 15. I’d like to see experimental proof of that as well – there are many instances in science where general hypotheses do not hold true for boundary conditions (and Part 15 broadcasting is certainly a boundary condition for radio signals, compared with licensed stations).
RE: … numerous Part 15 stations would not see the results they are seeing when elevating antennas (and with all other things being equal WITH THE TWO PART 15 TRANSMITTER installations).
It is well-known (even by the FCC) that many elevated Part 15 AM system installations include conductors such as lightning grounds and other conductors that add to the radiating length of the ~ 3m vertical whip considered to be “the antenna.”
Other things equal, such systems have larger useful service areas than those without added conductors — but that is due to their greater radiated power, not to the height of the top of the whip above the earth.
Where We Stand
There is an iron-clad consistency in the Postulations of R. Fry:
Mr. Fry is inargueably correct at all times and in all claims, whereas those among us who have other conflicting opinions and experiences receive no recognition for ever being fully or partially correct with the implication that we are altogether misinformed.
Yet, despite how wrong he finds us, Fry always again demonstrates how wrong we are. Most pontificators would give up after a few fruitless years.
I am interested to know re: “…and Part 15 broadcasting is certainly a boundary condition for radio signals” what you mean by boundary condition?
In mathematics, boundary conditions are used in the solution of differential equations. I recall spending many days grinding out by hand the solution to temperature distribution in a metal plate and using boundary conditions in this solution. Is there another meaning which I have missed, especially how a boundary condition results from Part 15 radio as apparently opposed to high power broadcast radio?
This may be taken as a silly request but throughout this thread statements based on “science” and “experiment” have been made, few of which I can take seriously. SWR affects range? Really? By how much and why? When range observations were made, what confounding factors could have affected the observation? What repeatable measurements were made and how? When I make a range check on my station I get a certain subjective result. The next day, having changed nothing, I get a different result. Another day, another result. What I conclude is that I can’t conclude much at all with certainty since I am obviously not accounting for nor recognizing variables which affect my observations. Be careful when drawing general conclusions based on one observation.
I would suggest that TheLegacy invite his “engineer friend” to join this site and contribute to the discussions. Much could probably be learned.
Neil
“It is well-known (even by the FCC) that many elevated Part 15 AM system installations include conductors such as lightning grounds and other conductors that add to the radiating length… …that is due to their greater radiated power, not to the height of the top of the whip above the earth.”
That goes without saying. There’s no disagreement about that. But your response is simply avoiding the points being made. I think Tim already addressed that issue earlier in this thread while talking about his ungrounded elevated transmitter. I too operated ungrounded and elevated for about 5 years… and yes there’s also the matter of unintentional ground via power/audio cables, this too was address by Tim.
Although I have not actually tried it, I lay odds that if an AM part 15 transmitter/battery/MP3 player was elevated as a group on the roof of a house, it would outperform the exact same configuration placed on the ground.
If this assumption proved to be accurate, how then would you discount that?
RE: I lay odds that if an AM part 15 transmitter/battery/MP3 player was elevated as a group on the roof of a house, it would outperform the exact same configuration placed on the ground. If this assumption proved to be accurate, how then would you discount that?
I would expect proof that the two configurations WERE configured and operated exactly the same, and their performance was measured exactly the same in all respects before even considering that such a conclusion was valid. Theory shows that it is not.
Such a test and its evaluation would not be a trivial process, and would need a qualified and experienced r-f engineer and a controlled test site to be done accurately.
Artisan said “Carl states it best. The assumption that all other things are equal between a Part 15 installation and a licensed station is not correct. Otherwise, numerous Part 15 stations would not see the results they are seeing when elevating antennas (and with all other things being equal WITH THE TWO PART 15 TRANSMITTER installations)”
This makes sense. You can’t compare a part 15 set up with a commercial one on high ground on a 200? ft tower broadcasting down on the terrain with vast areas of line of site and getting to valleys and hills.
Yes, SWR affects range. SWR is a measure of the ratio between reflected power (back through the antenna, feedline, etc. due to mismatches) and forward power (what actually generates field strength). The lower the SWR, the higher the forward power and field strength, and the greater the range.
I suggest that it is not those who have actually conducted range tests that are required to provide proof. You cannot prove a hypothesis in science. You conduct experiments attempting to disprove the hypothesis, and even if you don’t succeed, that means that the hypothesis is correct, but only as far as we can tell (it still could be shown to be incorrect later). You can’t just sweep contrary results under the rug because they don’t fit a theory. You get rid of the theory, or at least enhance it, because of the contrary results.
When I first set up my Talking Sign, I was attempting to get my wire antenna over the roofline of my house. I mounted the transmitter on the ceiling, close to an outside wall, and ran the wire outside, up along a PVC pipe.
The first time I attempted this, range was OK, but not really what I expected (1/4 to 1/2 mile). Upon closer examination, it turned out that the end of the wire was about a foot or so below the roofline. Without changing anything else, and within a half hour of the first test, I raised the pipe that foot or so, and took another test. I could hear my signal clearly (subjectively, with the same quality as the first test) over a mile away.
Exactly the same configuration. The same conditions. The only difference was the height of the antenna, and the fact that it cleared the roofline.
If someone can come up with a reasonable explanation, I’m all ears. Until then, don’t cast aspersions on those who actually practice Part 15 broadcasting, and who take the time and energy and spend the money to conduct these sorts of tests.
As for considering Part 15 a boundary condition, I would venture to say that a radio signal that is generated by at most 1 milliwatt (0.001 watts) of output power (probably much less) would have the potential to behave somewhat differently than that generated by even the most underpowered licensed station of about a kilowatt (1000.0 watts) – you’re dealing with a change of 7 orders of magnitude.
Money Where the Mouth Is
Rich says: “Such a test and its evaluation would not be a trivial process, and would need a qualified and experienced r-f engineer and a controlled test site to be done accurately.”
Since you, sir, are the only qualified and experienced r-f engineer we have, can you pitch in and help us do it?
If we tried ourselves it would just be a trivial process, as you point out.
“As for considering Part 15 a boundary condition, I would venture to say that a radio signal that is generated by at most 1 milliwatt (0.001 watts) of output power (probably much less) would have the potential to behave somewhat differently than that generated by even the most underpowered licensed station of about a kilowatt (1000.0 watts) – you’re dealing with 7 orders of magnitude.”
Mathematically, boundary conditions apply where there is a physical boundary (or one of time) beyond which the equations are expected to no longer hold, such as if an RF signal impinges on a metal wall. Thus we need to be careful with the use of such terms.
Unless there is some non-linear effect as a function of power I suspect the equations governing both signals are the same. The only thing which would change is the calculated field strength at a specified distance. In the context of this discussion, the effect of a blocking object would be the same proportionally for each signal as was presented earlier by Rich Fry.
Regarding your experiment where you raised the antenna above the roof line, would the same range difference have been observed if you did the same raising out in the open? This would tell if the roof line had any influence on the signal (which it may well have but is this certain?)
It seems to me that it would be easier to attempt to duplicate the effects of obstructions on a Part 15 signal with a field strength meter, rather than attempt to explain away what seems to be a very real phenomenon that has been observed by many broadcasters.
It may indeed be that there are other factors at work. But in every reported case?
My contention is that the effects of buildings on powerful field strengths do not necessarily translate to the much smaller, indeed – micro, field strengths of Part 15 signals. It’s far more likely, based on my experiences, that there’s something else at play with these powerful signals, as well as transmitter installations with full quarter wave antennas and extensive ground radials.
Theory is all well and good, but you have to be able to explain observable results as well (and not just wave your hands and blame it on unknown factors).
As for the question posed to me directly regarding raising the wire antenna above the roofline. Since the amount of increased elevation was approximately a foot, it is highly unlikely that that factor alone would double the signal field strength (which is what a doubling of range would imply). I stopped testing when I achieved the range I wanted.
I do know that the only times I was able to get more than a mile range with a Part 15 compliant (with a certified transmitter) AM installation was 1) the one described and 2) a Rangemaster placed in an open yard, with no buildings nearby. In every other case, with Rangemaster, ProCaster, Talking House, Talking Sign, and probably a few other transmitters, installations typical range to a good car radio was 1/4 to 1/2 mile.
It was said that buildings and two story houses can block the signal in this thread!!
It makes sense because across the street from my antenna as your standing in front of this antenna there are a few two story houses. As you are looking across the street in a half circle there is several of these which could help figure my problem with range towards the market as well.
Looking at this I see that really my location is not all that great because I have houses and trees both a major factor in propagating my signal where I want it to go.
It was also said in this thread that one experienced differences in range from day to day.
I have seen dbuV differences when the ground is wet vs dry. When I walked to where my stepson use to live which is about 150-200 Ft some days I’d achieve a 60 dbuv signal on my Tecsun PL-380 receiver (city grade signal). and there are some days whereas the signal is 57-58 dbuv not 60. But when I walk to the end of the complex I still get 46-47 dbuv (unchanged). At the 7-eleven I get 27 dbuv as I stand right in front of it with my Tecsun PL-380 receiver. But when I had a sean Cuthbert transmitter with its ATU outside in a weatherproof box and did the same test as the temperature changed so did my range.
My engineer had to build a remote control so I could re tune my ATU TWICE A DAY to keep my dbuv the same. The capacitor inside the tuning circuit was greatly effected by temperature change because of the rating of the temperature on the capacitor that was used to tune. So this time when he came with the ASMAX2 transmitter and a separate ATU this one was rated to handle -40 degrees to 150 degrees. It was a better made capacitor therefore no change due to a temperature change. My dbuv stays almost the same only across the sidewalk 150 Ft has a 1 to 2 dbuv difference. I don’t really get to test at the market daily due to my eyesight and not being able to drive.
I’m curious how the RAT 1.0 will do will it too have the same defect I experienced when mounting a Sean Cuthbert transmitter inside a weatherproof box? It would take someone willing to do a dbuv test every day twice a day to find that out on a Talking House transmitter connected to that ATU. Does the Procaster do this too? If so you may need to build a remote control and have the servo motor connected to the pot and twice a day re tune. I’ll bet this is why some folks are having range issues as well. You will need a remote control from a toy car or model plane and you only need to worry about left and right. I’d go for the ones that don’t use 26-27 Mhz as some remotes do. This way you’ll always be getting 100% out of your transmitter. You will need a field strength meter for this and stand where you get a reading and use your remote control just like I did when my friend built it for me. Remember you need to tune with a DEAD CARRIER!!
RE: … Since the amount of increased elevation was approximately a foot, it is highly unlikely that that factor alone would double the signal field strength (which is what a doubling of range would imply). …
As a “heads up, ” doubling the radiated power of a transmit station does NOT double the radius of its useful coverage area — even for free space path conditions.
The field intensity present at a given distance from the transmit antenna changes with the square root of the _change_ in radiated power.
Examples (for other things equal):
- If radiated power doubles, the received field intensity present at a given location increases to √2 = 1.414 times its original value, not twice the original value
- If radiated power halves, the received field intensity present at a given location decreases to √0.5 = 0.707 times its original value, not half the original value
Conclusions about the performance of a transmit/receive system of ANY radiated power/frequency that are based on the quote referenced above will contain serious errors.
Note that this information was gained both by the study of radio theory, and by workplace experience. It did not require the purchase/operation of a Part 15 transmitter.
“Note that this information was gained both by the study of radio theory, and by workplace experience. It did not require the purchase/operation of a Part 15 transmitter.”
You are so missing the point… Theory does not trump real world observations. Theory is only deductive reasoning, it’s not fact.
RE: … Theory is only deductive reasoning, it’s not fact. …
However when the values calculated by theory and the “real-world” performance measured for that configuration are equal — as in this case — the results are indeed factual.
Added later – I have heard licensed, professional broadcast engineers (P.E.s) say that they can calculate expected values for/from an electronic system more accurately than they can measure them !
I cannot personally attest to either argument in the Part 15 world of AM radio. As all of you, I found different performance levels with different installations. Empirical? Probably not.
I can however attest to the accuracy of Longley-Rice type calculations with regard to the expected signal levels of our 85 watt E.R.P. LPFM.
Just my two cents and we know what that’s worth LOL!
However when the values calculated by theory and the “real-world” performance measured for that configuration are equal — as in this case — the results are indeed factual.
Understood, the theory corresponds to that configuration and ones like it in the real world, so it should be considered accurate. It has a lot of backing real world data to confirm it.
But that doesn’t necessarily equate to a part 15 configuration with it’s minuscule power that by comparison is entirely insignificant in strength to your example. You are making assumptions that the principles involved would apply the same percentage wise to a part 15 scenario… You are essentially seem to be saying that those who are actually experienced with part 15 (in the real world) are either imagining their observed results, or flat out lying about it to spite you.
You can’t know what you’ve never witnessed for yourself. I’ve witnessed it, and others have witnessed it, and line of sight with part 15 matters.
This is exactly what Carl pointed out previously but you choose to disregard it.
RE: You are essentially seem to be saying that those who are actually experienced with part 15 (in the real world) are either imagining their observed results, or flat out lying about it to spite you. … line of sight with part 15 matters. This is exactly what Carl pointed out previously but you choose to disregard it.
The reason I tend to disregard it is because both theory and measured results show that this belief is not valid for groundwave signals in the medium wave band for the fields received sufficiently distant from other (re-radiating) structures along the propagation paths, AND regardless of the power radiated by the transmit system.
I have posted measured results in several graphics in this thread to illustrate/prove this, but apparently some people either don’t comprehend them or choose to disregard what is shown by those graphics.
I don’t doubt that many Part 15 AM operators have formed an opinion about _why_ the performance of an installed Part 15 AM system changed, but suggest that it can be (and most likely is) related to factors other than those supposed.
All I can do to interject into this is to ask why do you think my broadcast engineer friend spent the extra time and money to mount my antenna so that the tip was above the houses and trees as possible?
On top of all of this he had to build a remote control so I could tune the ATU from ground level since I’m legally Blind and it is not safe for me to climb heights that surly would cause injury or even death if I were to fall. If line of sight did not matter I would think a broadcast engineer would want to go the cheapest way to get me on the air with Album Rock right? So knowing this alone he has experienced this too for he has the same exact transmitter as I do at his house.
We were even considering a 75-100 wooden pole to mount the antenna on top of with coax going to the ATU and then I’d get my signal to the Deltaville market without issue. I’ve been discussing this with him as I read this and he just laughs at all of this silly nonsense and otters the phrase “Its not the wattage in the cottage, but the power in the tower!” So I learned from him that I need to get this antenna up HIGH over all the houses and trees, metal objects so my signal will rain down on my little town of Deltaville, VA.
Doubtful Claims
Virtually all respondents to the opening claim in this thread, “There is very little difference between ground-mounted vs. elevated monopole antennas“, doubt the conclusion advanced by the claimant based on our own individual ACTUAL experience in the physical world.
We as a group say that THERE IS VERY MUCH DIFFERENCE between performance expected from full-power stations licensed by the FCC compared to the micro-signals of intentional radiators allowed under FCC part 15.
It would be prudent for our doubt to include the reliability of NEC Analysis, the principle mechanism cited by the claimant for his adamant conclusion.
Certainly the NEC software is formulated based on power levels in the range typically licensed by the FCC and is very likely not gradated to the microscopic hair-splitting RF power levels experienced with short-monopole part 15 systems.
Therefore it would be my recommendation to consider this entire discussion inconclusive and little more than a novelty.
Agreed, Carl.
Rich Fry is quite adept at ignoring arguments that don’t conform to his beliefs.
He has no experience in actual use of Part 15 AM and FM broadcasting systems, and the tiny signals that they generate.
When pushed, he doesn’t quite call people idiots (i.e., ad hominem attacks) for not believing what he’s saying, but he gets close, by hinting that they don’t understand and/or haven’t read what he wrote.
And finally, he sometimes deliberately ‘misunderstands’ what has been said and attempts to take the thread off on a tangent. Case in point – I stated that raising my antenna above the roofline (about a foot total) doubled the FIELD STRENGTH since the range doubled. He came back with “As a “heads up, ” doubling the radiated power of a transmit station does NOT double the radius of its useful coverage area — even for free space path conditions.” – I clearly did not state that I doubled the power.
RE: … Certainly the NEC software is formulated based on power levels in the range typically licensed by the FCC and is very likely not gradated to the microscopic hair-splitting RF power levels experienced with short-monopole part 15 systems.
Therefore it would be my recommendation to consider this entire discussion inconclusive and little more than a novelty. …
Think and do as you wish, however an accurate investigation of the capabilities of NEC software will show that its calculations of the _relative fields_ radiated by any given antenna system are independent of the transmitter power applied to that antenna system — as defined by the proven, measured principles of physics upon which NEC software is based.
RE: I stated that raising my antenna above the roofline (about a foot total) doubled the FIELD STRENGTH since the range doubled. He came back with “As a “heads up, ” doubling the radiated power of a transmit station does NOT double the radius of its useful coverage area — even for free space path conditions.” – I clearly did not state that I doubled the power.
I was/am pointing out that doubling the field strength at some distance does NOT double the radius of the useful coverage area, which is true.
Actually, you weren’t merely doing that. You attempted to bring power (which I never mentioned) into the equation to obfuscate the situation.
The NEC software has been proven to not work (or be inaccurate) in many situations. That conveniently has not been mentioned in the discussion.
We keep hearing about all these mysterious ‘other factors’ that could be influencing experimental results. No one has of yet talked about any of them.
The bottom line is that you can talk theory all you want. Real world results trump theory any time. I would welcome a test where a field strength meter is used to measure Part 15 installation field strengths at ground level and at height, as well as with obstructions. Measurements of a licensed radio station just don’t count, and that seems to be what you’re basing your real world results on.
I wonder if Bill DeFelice would be interested?
RE: … We keep hearing about all these mysterious ‘other factors’ that could be influencing experimental results. No one has of yet talked about any of them. …
Did you overlook (or reject) the info in my earlier post, linked below?
I wonder if Bill DeFelice would be interested?
He actually has commented something to the effect of taking measurements at both ground level and comparing to an elevated install under the conditions of battery power with MP3 player all with short leads to the transmitter to eliminate any possibility of additional radiation occurring (as I alluded to previously in this thread), but as of yet no such test have took place.
I think it would be a very interesting experiment.
Again, I do not see how an elevated install could possibly increase field strength under such conditions, but I feel certain it would substantially assist in overcoming any obstructions in the surrounding area that can block a signal, and thus in that respect would prove to result in an increased range.
If you were to transmit in a desert where there was no obstructions I’m sure your range would be equal rather or not your transmitter was elevated. The reason for height on the MW band is to avoid obstructions. 100 mW is 100 mW (even less with losses caused by long coax especially if its not high quality).
We even had a gentleman who put a Rangemaster inside a church steeple and achieved great range. Joe the Ham dude was called a Pirate when he demonstrated better Range when putting his Rangemastter on top of a wooden tower with no ground. All of these Real World experiments done by several different individuals came up with a conclusion that getting your transmitter away from obstructions does make a huge difference. In some areas you have no other choice but to elevate the transmitter in order to be FREE of such obstructions. Makes perfect sense to me and also may show me why I’m having so much trouble in one direction of my signal verses the other.
Until such time as someone can accurately measure the effect of height (and obstructions) on a Part 15-compliant system, this will obviously remain an open topic. The NEC software has been shown to deliver inaccurate results in many scenarios. And comparing a signal generated by a licensed kilowatt station to one generated by a Part 15 station is simply not logical. – particularly since the top of the antenna system of a licensed station is, by definition, well above any potential obstruction.
The reason that AM broadcast stations produce greater coverage areas than a legal Part 15 AM station for the same applied power is related to the superior gain of their antenna systems — not because their towers can “see over” nearby obstructions.
Note the 20+ dB advantage shown for the broadcast station antenna system gain in the graphic below.
Artisan,
I have been thinking a bit about your observed increase in range gained by elevating the end of your antenna above the roof line. One thing came to mind, namely, near field effects, which could be one of the mysterious other factors alluded to.
Did a bit of reading about this and in the near field much of the energy is contained in the magnetic and electric fields which are out of phase and hence reactive and which can cause induction effects which transfer energy back into the antenna and can influence the current in the radiating antenna. One effect is to change the impedance of the antenna system and another is to cause energy loss in the nearby material. You changed the spacing to a dielectric, presumably the roof materials or perhaps a gutter, which could have resulted in a change in the antenna current, impedance, and perhaps power delivered to the radiator and hence the radiated energy. I never doubted your observation but perhaps this is a technical explanation of what caused what you observed. If you are interested, search for a Wiki article using “antenna near field”. Long read with math but about two thirds down the author mentions these effects.
I have observed that while tuning my base coil that the measured impedance (antenna voltage, current, and phase angle) all change significantly when I am near (less than three feet from) the antenna. I have learned to move away at least twenty feet to check the readings after an adjustment. Once out this distance my movements seem to have little effect on the readings. The most sensitive to my proximity is the phase angle between the antenna feed point E and I, shifting as much as twenty degrees as I approach the radiator.
Neil
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…
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.
________________________
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
Accuracy Aside
Not really: “In my case, physical measurements have been posted several times in this thread.”
No. Your postings were based on fabricated measurements (NEC software generated), not physical ones.
Rich did indeed post some ‘relative’ measurements, but that’s not what is in question. The measurements were for a powerful, licensed station signal. The hypothesis here is that puny Part 15 signals may be affected more by obstructions than those he measured. This is derived from real world observations and measurements by real Part 15 practitioners. Rich’s contention is that that hypothesis is invalid, and he points to the NEC software as proof, which is known not to be perfect, and to have issues in certain situations. He cannot point to the real world, as he does not do Part 15 broadcasting.
I do not intend to enter into a pissing contest as to who is more credible – those who are out there measuring real effects, or those who are running software simulations in the comforts of their homes. I believe that the NEC software is accurate in the general case, but I’ll go back to my original statement. Part 15 signal strength levels may be a boundary condition or conditions for the mathematics behind the NEC simulations, and accurate (not relative) measurements need to be taken in the real world for the effect of obstructions on those signals.
Until such time as that happens, I agree that the discussion should be shelved. Since Rich doesn’t do Part 15 broadcasting, I don’t see why this is such an issue for him. Those of us that do, need to be aware of the potential effect of obstructions on Part 15 AM signals.
I knew I read a study having some relevance to this discussion, I just had to find it again, while this refers to TIS/HAR stations, it’s still low power AM.. Here’s a few choice excerpts from this 92 page document, it illustrates that lower power AM does not behave the same as high power stations, and that obstructions are detrimental to low power AM (I’ve quoted other things from this same study before). I tried to keep it short to avoid boring you off the page!. It’s not that long:
———————–
Improving Highway Advisory Radio Predictability and Performance
Requested by Ian Turnbull, Office of ITS Engineering and Support, Caltrans District 2
Revised August 5, 2011 FinalHighway Advisory Radio (HAR) stations, sometimes referred to as Travelers’ Information Stations (TIS)… Caltrans has deployed HAR stations across the state, but performance is often unpredictable…. This Preliminary Investigation is limited in scope to AM band HAR stations and is focused on design factors related to radio wave propagation; topography; environmental characteristics (geology, ground conductivity); relevant system components and configurations (antennae, grounding); and related factors affecting HAR performance.
Three different HAR Vendors shared relevant design considerations with us. Some common themes arose among these conversations. It was noted that considerations for HAR stations are often not the same as those for high-power commercial AM radio stations..
Interview subjects universally stressed the importance of system grounding…..
Interview subjects similarly addressed siting. Wide open spaces are ideal for AM radio wave transmission…In response to a request for information about practice at the regional level, Charles Price in District 4 put us in touch with Michael Lee, chief of electrical systems hardware support for that district. Lee discussed broadcasting challenges related to geography, such as hills throughout the region as well as low HAR signal strength compared with commercial stations operating at nearby frequencies…
AASHTO Special Committee on Wireless Technology
We spoke to Bill Brown, radio manager for Virginia DOT and chair of AASHTO’s Special Committee on Wireless Technology… Brown suggested that we speak with Information Station Specialists, an HAR provider based in Zeeland, MI…AASHTO’s Bill Brownlow, the association’s representative on the Special Committee on Wireless Technology, suggested that we contact Peter Moncure of HAR consultant RadioSoft, based in Toccoa, GA: “Peter Moncure is the vice president of RadioSoft, the firm AASHTO contracts with to perform our radio frequency coordination. Peter has more than 30 years experience in RF engineering and is recognized as an expert in radio propagation by the Federal Communications Commission. Peter also served as a member of the Telecommunications Industry Association (TIA) working group defining standards for the modeling of radio wave propagation and as AASHTO’s technical representative to the Land Mobile Communications Council’s Spectrum Committee.”
Information Station Specialists
We spoke with Information Station Specialists, a company based in Zeeland, MI, with 30-plus years of experience designing HAR stations and installing HAR equipment, including the design of some of Caltrans’ systems. Bill Baker provided information on the company’s approach to maximizing HAR performance through installation planning.
Baker said that for any HAR system, the first step is to define the geographic parameters… For best coverage, the immediate location should be free of objects that exceed 25 feet (about 2 stories.) This includes tall buildings, trees, terrain features, lighting, power and communication poles and towers, overpasses and highway signs. For example, Baker said that a critical factor for an AM radio siting is openness of location. Coverage in an open valley can be as good as a high location (unlike FM, where height of antenna installation is the primary concern). It is important to avoid crowding by structural and environmental features. It is possible, but not preferable, to install an HAR station near a structure, and performance will suffer.RadioSoft
RadioSoft’s Peter Moncure had the opportunity to review the AASHTO survey questions and responded via email: In a nutshell, low-power AM without a suitable counterpoise is so highly determined by very local ground conductivity that good prediction is impossible. There is considerable variation in specific antenna installations as well. We followed up with a telephone interview with Moncure. He described how generally the design guidelines and calculations associated with large commercial AM stations don’t apply to small-scale AM HAR stations. Moncure discussed with us some of the fundamental differences in approaching the design and deployment of HAR stations: The variation in the grounding systems and the small radius of operation for HAR stations result in propagation characteristics that can vary significantly, as much as ± 15 decibels, which makes performance hard to predict.Rich Powers thanks that sums it all up get your antenna away from obstructions and you’ll perform much better. For some this means Get It High As Possible.
Also if you have or know someone who has the Original Manual and ATU for the Talking House/iAM transmitters there is very interesting reading in the user manual which also states the higher you put the ATU/Antenna the further your signal will travel. It also talks about ground and proper location of the transmitter and time should be taken.
It is even suggested to do a temporary Install to find the best place for your transmitter as testing and comparisons need to be made before the permanent Install.
The Topping
Rich Powers totally relevant text from HAR/TIS studies and reports puts the perfect topper on this discussion as it wraps up: “The variation in the grounding systems and the small radius of operation for HAR stations result in propagation characteristics that can vary significantly, as much as ± 15 decibels, which makes performance hard to predict.”
It is also NOT trivial that our members all shared feelings, beliefs and intuitions that are the same as the HAR/TIS report.
Speaking as your resident “peer reviewer”, this conversation has been enlightening.
If only one point was to be made from the above quoted text in regard to this threads discussion it’s Peter Moncure of RadioSoft reputation and what he had said..
“…Peter has more than 30 years experience in RF engineering and is recognized as an expert in radio propagation by the Federal Communications Commission…. He described how generally the design guidelines and calculations associated with large commercial AM stations don’t apply to small-scale AM HAR stations…”
Talking House/iAM transmitters there is very interesting reading in the user manual which also states the higher you put the ATU/Antenna the further your signal will travel.
That is basically what any part 15 am transmitter manual will tell you… However, it is undeniable that in most cases the reason is simply because the antenna system is being extended in length..
Nevertheless, I still believe that height makes a difference with part 15 AM. Only real world test performed and compared while at the same time eliminating any possibilities of the length of the lead playing a part in it can confirm if height makes a difference or not – but theory, charts and graphs aren’t going to cut it alone.
Some only believe what they read and theorize, while others also factor in what they experience first hand. If the two don’t mesh, then they have to decide on believing the expected results of theory or their own real world experience… If they have no real world experience in the matter, nor wish to experiment to gain that experience, then they have no option but to believe in theory only.
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