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.